2.8 MFI dyno
 

Here's a dyno baseline on my 2.8 twin plug motor. HP seems low based on build. Besides lean AFRs, dyno shop thought engine could be suffering from ignition break up at higher rpms.

Specs are DC80 cams, Mahle 2.8 pistons/cylinders (11-1 comp), 38/37 ports, 46 mag stacks/TB tapered to port, 1&5/8 European headers, twin plug XDI2 electromotive crankfire ignition maximum timing at 25.5 degrees, rev limit 7,800.

Thinking of richening up a bit at full throttle. Engine is already running rich at part-throttle. Any tips on how to extract more HP? Does it look like possible ignition issue at the higher rpms?

http://forums.pelicanparts.com/uploa...1593820174.jpg



https://youtu.be/rZPR6-U-FNY

Thanks for posting. Looks like a good build. Yes, I think there is some spark and lean issues at 5500rpm and above. What heat range plug are you running? 11:1 is pretty steep too. That all said, about 220-230 at the wheels is common for this kind of build, but yours has plenty on the table to give with some tuning. Work out the lean issue and that may calm the spark issue. Perhaps go down a heat range. I would start with NGK BPR7ES, 8 heat range may be too cold but perhaps 8s might work best at high rpm. You sort of give up a little plug cleanliness at lower rpm when running such cams. It's a trade-off with such hot cams.

The plug I’m running is a R5671-A7. The engine stays remarkably cool.

This is my second 2.8 and I was able to get close to 300 hp out of a very similar build except the cam was different. I ran an Elgin RSR sprint cam in that engine and first dyno got 279 at the crank but it was lean on top. Gus replaced the space cam and then it worked great.

I thought the DC80 cam would be stronger and it does seem to hit harder in the mid range but feels like less duration. I didn’t think the difference between the 2 builds would be 40 hp though.

Once the lean condition is sorted you may be able to throw a bit more timing at it as well. I'd say you're pretty close to the limit though. Your previous motor with 279 flywheel would likely put down about 230 or so at the wheels so you're there or thereabouts

I would have expected peak torque to be much closer to 6k rather than 5500 rpm. You have a continual torque curve fall off (and flat HP) above 5500. I would expect HP to continue to build.

Something is choking down your airflow at higher rpm. Just need to figure out what...

Are you getting WOT? What muffler?

yeah the muffler can't be understated with these as others have demonstrated in other threads. Looks like it could be a 2 in 2 out peashooter muffler? I would have gone 39-40mm intake port and 38mm exhaust port with that rev range in mind too. Doesn't make that much of a difference down low, but at high rpm with this build it could. What was your goal at the wheels? 230-235? It's still possible....

muffler question
 

Hey guys - I really appreciate your help trying to diagnose this so thanks. Jamie, I believe the car is at WOT and had two other local engine/tuner experts look at it, but I agree that there seems to be a restriction somewhere.

Below is a picture of the exhaust system. I bought the muffler from a company called Silent Power and the owner is Pete Weber who designed the Phase 9 muffler with Jerry Woods many years ago. As mentioned, I bought a set of European Headers (1.625 OD, 1.5 ID) and they came with street adapters that measured 1 and 7/8 inches ID.

Peter said that Jerry Woods found that 2 and 1/8 inch secondary tubes to muffler work best with my type of motor so I had him make me secondaries that went from the headers to the muffler. Peter said the muffler would flow well and also keep the DB down. Since Peter has expertise in this area, I just assumed the exhaust would work reasonably well. I'm open to other ideas though, so if you know of a better flowing muffler that I should try, please let me know.

Here's a pic of the exhaust when Peter put together a test fit:

http://forums.pelicanparts.com/uploa...1593943336.jpg

Thanks lvporschepilot for your help as well. Admittedly, I was hoping for better numbers. My goal was 300 horsepower like my last 2.8 that I had built many years ago. You asked about ports, and after consulting with many builders went with the 38/37. Also with standard 46/40 valves the port size is probably limited to 85% of that generally so probably 39 intake would be the largest size that would make a difference and I was already at 38.

Also, my first 2.8 generated nearly 300 hp and only had 36/35 ports and standard plastic 73 rs TB and stacks. It also had SSIs. It was an original 73 RS motor that I bought in 2001 for $5K from a local shop, and I had the owner rebuild it into a hot rod 2.8. Because those standard ports generated so much power I didn't think that I needed to go big. But that engine had big problems, too. I was blowing black clouds of smoke because it was way too rich at the low end, however, it was also way too lean at the high end.

So, the dyno below of that engine is before the AFR got right and it eventually got to 300 after it was fixed and after Gus reworked the pump. I remember that the dyno operator was coughing and the entire dyno room was filled with black smoke on this test. As previously mentioned that engine had an Elgin RSR sprint cam. The other difference is it had the MFI plenum and used a modified 019 pump and just standard rods with ARP bolts. It revved to 8,000 rpm with no problem.

Unfortunately, for me I sold the car several years ago so this is my effort to build another one. And the guy who built the first engine had some issues preventing him from building the current engine. One other difference I noticed between the two builds is that my current engine just doesn't get very hot, but my first 2.8 got much hotter.

In any event, here's the baseline dyno from my other 2.8 engine with standard RS ports/SSIs before it was tuned back in 2003.

http://forums.pelicanparts.com/uploa...1593944604.jpg

I see a possible problem with the dyno scales . The toque should equal hp at 5250 and they do not line up . Talk to the dyno man about this .
icarp

Weber makes a good exhaust. I doubt that's the bottleneck. Being lean on the top end will hurt power in addition to not being good for engine longevity. If it were my engine, I'd want to see 13:1 AFR or even a touch under at higher RPM and WOT. Also of note is a dip in the power curve a little earlier than I might expect with an engine with specs like yours.

I'm a little surprised that whoever dyno'd your engine didn't note the lean condition and adjust it for another run. Did you run out of adjustment on the MFI pump?

Can I ask for some basic information that seems to be missing here and in many threads similar to this one. The most basic and the most important information when doing any sort of camshaft change or engine build.

What are the flow numbers through the complete Intake system as used on the engine? Doing this work, building these engines is not cheap. It costs real hard earned money. Why take another engine builders suggestion without backing them up with real data? That just plain nuts!!! Typically you want the intake flow to be approx 25% greater than the exhaust flow. Choosing a cam requires this data to properly select what cam spec you need.

Heat range will not cause you to lose power unless you are having some detonation issues. The spark plug will tell you this if there is no warning devices used. So read them. I cannot see that you are having a gap issue either. An engine of this spec should be able to run a wide gap plug easy.

If you do have an ignition issue, I would suggest it could be a stronger. Weak ignition is the killer to any engine's performance. It needs to be strong and these engines need powerful ignition systems, CDI not Inductive. I cannot think you are trying to meet current emission standards or fuel mileage numbers. Remember, the ignition is the last event to happen before combustion.

But first, find out what the flow numbers are and then go from there. Work one problem at a time. Once you have the flow numbers, figure out if the cam choice is the right one. Then work on lowering the fiction numbers, coatings, spring pressures, ring tensions etc, then the fueling and Ignition an finally the dyno calibration.

mfi adjustments
 

Hey Stownsen, good question. The operator didn't know MFI well and I didn't bring the special MFI tools knowing that there would be 4 of us getting dyno tests at the end of the day. In fact, the 3.2ss dyno thread was another car that was tested just before mine. I was 3rd in line and the last guy put on a new exhaust so he last and needed more time for a tune.

With respect to your question on MFI adjustment, my pump is one click away on the main rack from being in the full lean position, so I can make it richer. The problem is that I also have a part load issue. While I'm a bit lean at WOT, I'm very rich at part-load (e.g., cruising down the freeway to the dyno shop) and at the lower rpms. I'm probably about a 10AFR to 3,000rpm and at part load, I'm in the low 11's. It idles about 12.

So, the issue that I may run into is if I adjust the main rack for WOT, it may make my part-load even richer. There are also the part-load screws but everything is tied together and it took a lot of effort to get to this point. I'm sort of leaning towards a recalibration and will be talking to Mark at mfi werks to see if that's something he can help. I may be able to get the MFI pump closer but I suspect that I may need to get the spacecam or pump adjusted.

Neil, I am glad you piped in and I really appreciate all the information you provide on the forum! This has been a long process for me and I've learned from you and others on this forum over the last 5 or 6 years while I was gathering engine parts for this build and building the car. I'm still learning and probably would make different choices knowing what I do now based on knowledge you've shared and others with more experience.

But the short answer to your basic question is no, I didn't get flow data for the TB/stacks/heads. I had Eurometrix do the boring of those stacks/TBs but I didn't have them flow test them. Nor, did I flow test with the heads later. One question I have on that is that even if I had the flow data numbers, then what would I do with them? Would I need to find engine design software that would process this information or hire services from you or someone else? If I got those numbers is there some place that provides the services? I think there are a lot of people on this forum in the same boat that could benefit from a service like that! Some builders don’t seem to do it either but just go with what generally worked in the past.

In my instance, I had a 2.8 engine that worked well and was mainly trying to replicate it with some small improvements, but those improvements may have backfired on me and I can understand the value of having that flow data to eliminate uncertainty which I have now.

I agree with you on the CDI ignition, and I plan to make that change in the future. I have programmable ignition with XDI2 but it's an inductive system and feel like I may have issues at the higher rpms. I may try the CDI+ with a distributor since I could adjust the timing with a system like that, just like the XDI2.

So, I need to determine how deep to go now to chase that extra horsepower. It seems there are two ways to go. One ways is to flow test heads, potentially re-port the heads, change cams, etc. Another possibility is to try to optimize what I have now until the next major rebuild. If I can get the AFRs closer and change to a stronger ignition system, perhaps that will get me closer to where I want to be performance wise Don't get me wrong, the car seems to run fine but just missing some extra performance that I had in the past. And if it has less HP but otherwise runs good around the rpm range,, I could live with that for now.

Thanks again for your help.

When starting out on an engine build, you make of one two decisions. Am I going to go with what I am told and have read about or am I going to engineer my own engine.

The results can be quite different. Either you miss the mark completely or you manage to get the performance you were told you would get.

Or you design the performance from the get-go.

As a business we must design the performance, not guess it. You are correct about how some shops approach this type of work. But to be fair, not all. Most do not have the time to do this type of work. Engine work is taken on just as brake work is or other car work. If a result can be had by doing the same as others, this works and the compromise on performance is accepted. Unfortunately, the customer is often unaware of the tradeoff.

The same can be said for many camshaft companies. Lobe profiles are often copied from other companies designs, most often bad copies and the final lobe is somewhat a copied and paste exercise. Horrible harmonics are built into the design where heavy spring pressures are required to dampen these vibrations.

When designing a lobe, the very first part is to flow test the cylinder head with the valve size that will be used along with the complete intake system as fitted to the engine when in the car. This includes filters etc. The exhaust side usually has a stubby pipe fitted which gives the flow out through the head. When designing a cam profile, this is all we need.

We do have flow numbers for stock cylinder heads and intake systems for the 2.5/2.7L engines fitted with the stock manifolds. As a business, we incur expenses in obtaining this data, so we would need to "sell" this data. How we would do this I am not sure. It was never obtained to sell but for our own needs to design camshafts for these engines.

My advice is for you to reverse “engineer” your engine on paper. Rethink what you did and what parts are included. Construct your engine from the ground up with all data. Figure out what the engines performance should be. This is not hard to do. But you do need the air flow numbers. These are key. From these you can calculate the engines performance potential and figure out the fuel requirements to obtain a decent AFR number. There is a simple equation that you can use to establish what the engine HP will be based on the max air flow numbers. This is a ballpark estimate, but it does help in putting you in the game. In your case, I think it is all you need. I am thinking the issue maybe not be air flow numbers.

Having another engine built the same with different performance will be a huge help in finding were the differences are. It could be in assembly or some parts are not what you thought they were. Do this first before you waste more money and time at the dyno. You should always go to the dyno knowing what to expect. Dyno time should be to perfect the fueling, ignition timing and possibly any camshaft adjustment to move the power up or down the RPM range.

From what you are telling, you are looking for a large amount of HP. So, focus on the major factors here. Compression ratio, camshafts, and cam timing. Look at the basics of throttle plate position, engine detonation possibilities, fuel delivery and any exhaust restrictions. Bearing clearances, ring tension and valve spring pressures are important, but these will add or subtract small amounts of power. Get the major contributors taken care of first, then work on the smaller ones.

When I get into the office, I will post what performance this engine "should" make with the air numbers we have recorded.

That would be fantastic Neil if you could ballpark performance for it.. Thank you for the good advice.

air filters
 

http://forums.pelicanparts.com/uploa...1594075536.jpg

I wanted to post a pic of the air cleaners. Could this be a restriction to flow or are there others that work better, like ITG.

I guess a very poor aircleaner could cause air flow restriction, but the fact that you are lean at the top would I think negate intake flow as a problem. Once you determine that the ignition is ok, Get a wide band and start trying a few things.
Multiple trips to the dyno are expensive and time consuming. Not being able to get some mixture balance between mid and top would indicate to me that the pump is out of calibration other than just mixture adjustment. Also would think that your exhaust primaries could be larger. Bob

Bob. Yes, I recently installed an AFR meter and it’s definitely a good tool for this. Yes I’ll be sending the pump for recalibration at some point this year. I am thinking of trying different exhaust options as well and agree with other comments that the muffler may be restricting flow.

Just to add this to the discussion, I think it's worth noting that a 2.7 RS MFI engine in very good shape makes high 180s on a dynojet, or 220-225 at the flywheel.

Just got back into the office today and as promised.

We flowed a full intake system off a 2.7L engine with stock manifolds, plenum and filter s used on the street. The Intake was stock. The front runner was the lowest, the middle on the best and the rear runner in the middle.

These are the max numbers at 25" (not 28") with the leakage removed. We flow all our tests at 25" as the bench is calibrated at 25". Most flow at 28" as it gives a bigger number but often the conversion factor is never applied to give what it would flow at 25". Numbers sell and this applies to head work too.

At 0.450" lift it was pretty much all over.


So based on the lowest max number of 155.6 CFM, the engine theoretically should make 223 BHP. This number is calculated on a algorithm we use when flowing a cylinder head. It puts us in the range of what we need to see for airflow to achieve a performance figure based on the head and manifold flow rate. This is based ONLY on the airflow. There are other major factors that can change this.

Hope this helps.

Neil, thank you for sharing the data but it is difficult for me to tell how relevant that 2.7 flow data is for my current build because I don't know the specs of what was tested and the comparative size of the manifolds. On my engine the magnesium stocks and TBs were significantly modified by Eurometrix for more flow. Specifically, they opened a set of the older 70-71 magnesium stacks to 46mm at the top which is about 4mm greater than a stock 73rs. Then the manifolds were tapered to the 38mm intake port.

The difference in a manifold between a stock MFI, CIS, or carbs for an S, E, T, or RS sub model can be significant. What might be interesting is what would the manifold on a 46 ITB or a 46 Weber Carb flow? Maybe that would be a closer comparison, but I agree that testing mine at some point would be ideal or maybe Eurometrix or Aaron might know the incremental flow value from these modifications above a stock RS since they have done this work quite frequently over many years.

However, to illustrate a situation where a stock manifold can yield close to 300HP, my previous stock 73RS engine that was modified 20 years ago did make such power. It had a few important modifications that made a big difference. While the manifold and the heads were not opened up, the second dyno chart on this thread shows that it was already generating 277 BHP even while running quite rough with poor AFRs.

Where did the other 67 HP come from above a stock RS? It had Elgin RSR sprint cams (instead of an S cam), it was twin plugged, and had high compression 2.8 Mahle RSR pistons/cylinders (about 11 to 1 instead of the lower 8.5 to 1 stock rs compression), aluminum flywheel, rsr injection pump, etc. Although my first engine was originally running quite rough it did seem to rev up much further and faster at the high rpms than my current engine and did generate about 17 more HP than this build (i.e., 277HP) in a similar untuned state. After the injection pump was fixed though, my old engine made 300hp and got better gas mileage, too.

As many know, a stock 73 RS engine was rated at 210 BHP from the factory and ran on normal 87 pump gas, but many say that HP was understated, so a stock 73 rs probably makes the power you indicate above. But then if one adds twin plug, more aggressive cams, head work, higher compression, a modified injection pump, the engine can generate a lot more power. If the power isn't coming from flow due to high valve lift, could the power be coming from higher flow velocity and longer cam duration? My previous engine also had a smaller SSI exhaust than what I'm using now (European headers that are about 1/8" wider). I don't know the answer to why the previous engine generated such high power with less performance modifications, but it did.

For this current engine, the stacks were opened to 46mm which is between what a 73 RS had (I think 42mm) and what a 73RSR had (50mm). It doesn’t seem that engine is reaching it's full potential yet based on my past experience and I don't think it's related to the ports being too small but perhaps I'm losing flow somewhere else along the line in the engine. The combination of everything just does not seem to be working together yet to generate the expected power.

Similar to the last build, this engine's AFR readings are also rich at the lower end and lean at the higher end. The oil also has strong smell of gas and it has been difficult to start when cold. When I pulled the plugs they don't look black, which surprised me due to the rich AFRs at part throttle and lower rpms. Here's are pictures of one of the plugs. What do you think? I did check that my throttle bodies are opening all the way, so I do have WOT. Thanks for your help. Keep it coming!!


http://forums.pelicanparts.com/uploa...1594691697.jpg


http://forums.pelicanparts.com/uploa...1594691737.jpg

I have a 2.7L MFI track engine with specs close to yours. I'm mostly DIY so have learned a bit about tuning the MFI, but am not an expert or anything. A few comments:
- Being so rich that you smell fuel in the oil is odd. I've never had that issue. I makes me wonder if you've got fuel dumping somewhere. Cold start or warmup circuit malfunctioning, or a leaky injector?
- I'm guessing your setup may have the cold start circuit disconnected. It's basically a set of tubes in the stock airbox that dumps raw fuel into the stacks for cold starts. If you do have this setup, maybe it's over-fueling?
- The warmup circuit is the bellows thing on the rear of the pump that normally attaches to a hose that is plumbed to the heater boxes. If you have headers, you need a way to tell the pump to operate in "warm" mode, or you'll be rich all the time. How is yours set up? Pumps converted for racing sometimes have this circuit blocked off and replaced with an adjustment screw.
- From a basic adjustment standpoint, if it's rich on the bottom, you should be able to lean it out using the so-called idle circuit adjustment. It's the little spring loaded adjuster screw on the rear of the pump. And it's counter-clockwise to adjust leaner (opposite of the main rack adjustment under the allen screw).

Scott

I can't say I've ever seen a non original RSR 2.8 motor make over 300bhp or even near 300bhp actually. The original 2.8 RSR used different heads, the valve angle was different so it could use 49mm intake valves, the intake ports were 43mm! Compression was very high too, higher than 11:1 I believe, Ti rods, it made 308bhp or so. That was the 'full bananas' race motor for Porsche then too. With modern cam profiles I'm sure a tiny bit more could be seen, but not much.

The wackiest build one could come up with and still have a streetable 2.8 engine with 46mm intake valves and 38-40mm ports would be hard pressed to see more than 280bhp on pump fuel.

I'll be going through this journey on the engine dyno in about a month on my build... I would be THRILLED with 300hp, but suspect 250~275 as this is a street engine and not bananas cam profile or race gas and a slightly lower compression ratio. Who knows :-)

Good luck to OP figuring it out. I love the look/noise of MFI, this is one of the reasons we chose Motec...

Every engine is different. The spec's are different as are the conditions when dyno'ed. But, before you lose sleep over missing HP, it would be good to understand the dyno sheet showing 277 BHP. Dyno's can be fudged and correction factors changed to show a different result. It all needs to be evaluated and understood. Maybe you are not off with this engine but the first engine could have been.

No that’s definitely not the case. Putting aside the dyno results, other engine was just incredible, and I felt like I was riding a super bike. My current car is 250 lbs lighter and it is fast but it doesn’t have that same high rev power.

I started thinking more about the cam difference. The GE80 cam is supposed to have more power than the RSR sprint cams according to a few cam manufacturers, which is probably based on the belief that the engine can take advantage of the higher intake and exhaust lift.

However, the Sprint cam seems to have more intake and exhaust duration than the GE80 cam which also can give rise to power at higher revs. I wonder if the power difference in the engines could be related to the fact that the modified 2.7 heads couldn’t take full advantage of the lift but did benefit from the longer duration of the sprint cams?

Here’s a comparison of the 2 cams from Anderson’s book:

Engine 1 cam specs (RSR sprint): intake lift- 11.79, intake duration 278, exhaust lift 11.43, exhaust duration 267

Engine 2 cam specs (GE80): intake lift 12.70, intake duration 274, exhaust lift 11.94, exhaust duration 256

It has already been said, but the magic that goes on between the cam lobes, the intake and exhaust flow, the compression, has to be a cohesive package. High compression, big cams for instance don't guarantee power. You have to find what works together, and that can take enormous time and effort. It isn't necessarily intuitive. To quote a north Ga drag motor builder who's engines were legendary, ''no we are not geniuses, we have for years just been willing to come to work and try different things, everyday.'' Trial and terror

Another point that I think it worth making is that this engine isn't tuned yet. Rich on the bottom, lean on top, oil smells of gas, etc. Definitely not making peak power. I'd want to tune it before comparing to another engine.

Yes, great points. I’ll tune first with this cam and report back later. I’m running the Supertec enrichment device so don’t have fuel squirters or any other things that would effect enrichment. The problem is that if I adjust the rack to make it richer on the top end then I will become too rich on the bottom. The good news is that Mark Jung said that he can help recalibrate pump so I’ll sending to him this winter.

1) Mixture & timing makes a big difference. ~12.6-13:1 AFR under full throttle from 4500-redline & solid ignition required to see max power and get apples-to-apples numbers.

1*) It is time-consuming/difficult to get proper AFRs across the board using MFI on "custom" combinations (different cams, ports, etc from a factory config). to give you an idea, you will have the MFI pump on/off the motor, and apart/back together multiple times to get it close for all conditions.

2) I built a 3.0SS (98x66) w/ Weber 46IDA for a street hotrod. We ran it w/ SSI & 1-5/8" headers on dyno (same day/conditions), and I recall it was 230hp/243hp, respectively, on pump fuel. The 1-5/8" headers moved the powerband up by ~400rpm. As it was a pump fuel, street car we decided on SSI. Slight trade on top end, much more usable and torquey for street.

If it's built well (reliable, good leakdown, good compression, no obvious issues) and tuned well (proper AFRs + timing), I would go deep on the cam timing. . . :
--your config sounds like a reasonably "cookbook" hot rod. Similar engines have been done many times.
--"super bike" top end power is the result of highly effective scavenging from the exhaust. This means having a good exhaust and high overlap of the intake & exhaust valves. Your intake is great, your headers look fine (the issue is more obvious when you are using a crap exhaust like SC/Carrera stock manifolds, cats etc.) but, I'd still recommend SSI/factory original heat exchangers for street use.
--RSR Sprint cams have "tight" lobe centers (my measurements ~97deg., vs. 102deg for DC80)/high overlap. This makes a surprising difference. I built a similar 2.8SS MFI w/ DC80 on a 104 and if I had to "fix it" knowing what I know now, I would have run a cam on a 97-100deg. lobe center instead. It didn't really improve low-end torque to have the 104, and it really hurt the top end.

Also, I am not too sure how your muffler works, but I know the factory muffler and sport muffler (based on factory banana) works quite well with MFI.

Porsche knew what they were doing and a '73RSR w/ 43mm ports, 11:1, race fuel, and headers making 308hp IS "top of the mountain" for a 2.8L 911 air-cooled engine.

So, takeaways if it were me, I'd go to smaller headers/HEs, try a stock or sport muffler (factory-style). You're not far away though; I suspect you are missing only about 10%. If you are looking for a super bike feel, I think RSR sprint cams would be next.

Best
Scott

Hey Scott, My muffler is a 2 in / 2 out sport muffler that I got from Pete Weber who’s shop was reasonably close. It’s quiet but I think it may be a bit restrictive at higher revs so I want to compare power on dyno with open exhaust and perhaps I can find a muffler that will gain a little.

I’m running a 100 LC on the DC 80 cam, and I was thinking that a 104 LC would move powerband up but for now I won’t change anything major. When it comes to rebuild time, I’ll probably rethink the type cams if the power isn’t there, maybe a custom grind?

I’m hoping with modified injection pump, less restrictive exhaust, and better ignition will get engine in a better state of tune regardless of the final numbers.

I can't comment on that muffler. I know Pete Weber (RIP) did nice Fab work. I also know MFI is kind of 'particular' on muffler choice. This is fundamentally because it has no method for sensing airflow (like carbs do, with vacuum) or mixture (EFI w/O2 sensor). It just sends a predetermined amount of fuel--so tuning has to be optimized for each specific exhaust (see my previous #1 point about mixture for max power).

Why do you say your current muffler is restrictive?

DC80-100 should be great if they are ground properly and timed properly. It should feel like a superbike in character.

FYI, a 104 LC would move the power band *down* and flatten the curve, theoretically. It improves vacuum response at low revs (good for street driving) and reduces the 'supercharging' effect of scavenge at high revs, due to less overlap of I/E valves.

ytnulkr
 

YOU are correct.The exhaust makes the difference.Fred

I don't have any real experience with these early mechanical injected engines. What work what doesn't. However, if we were to get involved with building one of these mechanical injected engines, I would want to know a few things about the pump. How many crank degrees is it on and how many off. I could calculate the start of the Injection, or the end or the middle. Then, I would look at the cam spec's the dome of the piston and consider if I needed to include a bowl in the piston dome then figuring out of the pistons are suitable without. Injection timing plays a huge role here too. I cannot see how you can consider a cam profile or its settings without first knowing the injection timing.

Do you know this?

Neil, yes the pump timing instructions were provided by the pump builder and times at 14 degrees before top dead center overlap cylinder 1. This is the same timing for both the 2.8 and 3.0 RSR motors since my pump had V94 space cam and was built to flow like a 2.8 RSR.

For most other models like T, E, S and RS, the pump timing is 40 degrees after overlap TDC 1. One thing to note is that sometimes small adjustments from the recommended settings can sometimes help. The MFI squirt is relatively short compared to time when valve is open though and it can retarded or too early. I feel that mine is just right, and pump is just about as good as I can get it.

As far as pistons, I have a set of 2.8 Mahle RSR pistons with same domes and pockets just like my last build and what the 2.8 RSR ran. They are fairly rare so wouldn’t want to modify except as last resort.

Scott, the posts I read from camgrinder says that using a higher lobe center spreads the rpm range and explained in another thread on this forum that if a customer is using a DC80-100 but wants more power on top he might recommend a DC80-104 because it will allow the engine to continue to make power at higher rpms, and this can be done in lieu of going to a more aggressive cam like a DC100, for example. He says the lobe center depends on induction and says for Webers lobe centers of 98-102 work better and not higher lobe center which is different from PMOs which seem to work well with both narrow and wider lobe centers and narrow lobe centers.

For the exhaust, I think a straight through muffler design may be less restrictive at higher flows than my current set up. Also, I think there are headers with better merge collectors, so I may be in the market for an exhaust upgrade at some point. On some performance builds, the exhaust can make a 15 hp difference along the entire curve.

The MFI squirt is relatively short compared to time when valve is open though and it can retarded or too early. I feel that mine is just right, and pump is just about as good as I can get it.

Even more reason why you would want to time the injection with the valve opening. If its short, I would think you would want the middle of the injection to be right when the intake flow is at its best.

Why accept that the two injection timing points that have been used, are what you need and with different cams and settings. Seems like a huge compromise going on. If you change the characteristics of the intake flow and not the injection, you may be leaving a lot of performance unseen.

How does the pump builder know how the airflow is working in your manifold? Seems to me its an historical injection timing of what worked in years past. You start changing the manifold, Valve timing and opening duration and not the injection timing, you could be way off the performance, the engine could make.

I'm not saying I know this to be factual, but its something I would look into if it was me, and not leave it to the pump guy. I would ask him the fuel flow numbers and the opening times in crank degrees. Then with air flow numbers, cam duration and piston shape I would figure out the best time to inject the fuel. It very well may be the times you suggest, but I would check this and not take it for granted. In an electronic engine the injection timing and the pulse width play a huge role in power production. In your case I figure you cannot change the opening time as much, but you certainly can change the time it opens, or closes or choose the middle of the event.

I would bet that a lot of the fuel is dumped on the backside of the valve waiting for the valve to open. You then get puddles of un atomized fuel and droplets of fuel on the cylinder wall that don't get atomized very well and end up out the exhaust. Then the efficiency goes down as the energy in the fuel is been wasted.

I could be completely wrong here, but I cannot get my head around cam changes and set injection timing.

All this timing stuff is pertinent and as in everything, synchronisity is everything. But with all of the thrashing, turbulence, crashing and revving up and revving down, how does everybody keep up especially when some players are slower than the other guys. Air/fuel charge cannot adjust at the same rate as the mechanical pieces, and it would seem that everything would start running into each other. But there is a sweetspot in there somewhere and some how it all works. Jack Atkinson, I think that was his name, Peter Gregg's crew chief, would stick his timing light into the #1 stack and watch the injector pulse and set his pump timing accordingly.

All this timing stuff is pertinent and as in everything, synchronisity is everything. But with all of the thrashing, turbulence, crashing and revving up and revving down, how does everybody keep up especially when some players are slower than the other guys. Air/fuel charge cannot adjust at the same rate as the mechanical pieces, and it would seem that everything would start running into each other. But there is a sweetspot in there somewhere and some how it all works. Jack Atkinson, I think that was his name, Peter Gregg's crew chief, would stick his timing light into the #1 stack and watch the injector pulse and set his pump timing accordingly.

The 2.8 RsR was the only racing pump with a good fuel curve at least from peak torque to max RPM
It is hell trying to make a good fuel curve from initial load 2,000+ all the way up with the counter weights working against you all the way.
Some people have gone to great lengths to cure this problem.
Electromechanical injection pump - MFI2ECI - VGS-Motorsport: Weber Carbs - BOSCH Motorsport - ECU

Good points everyone. Thanks. The MFI timing has been checked multiple times and there has been an adjustment made from standard setting to time it right but I’m sure that it will be revisited again. Just like I have checked cam timing, fuel pressure, linkages, throttle bodies air flow and synchronization, etc. this is part of the check, measure and adjust part of MFI tuning.