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MST0118 07-03-2020 04:53 PM

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?

lvporschepilot 07-03-2020 06:36 PM

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.

MST0118 07-03-2020 06:52 PM

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.

lvporschepilot 07-04-2020 07:45 AM

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

jpnovak 07-04-2020 09:10 AM

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?

lvporschepilot 07-04-2020 10:05 AM

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....

MST0118 07-05-2020 03:06 AM

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:

MST0118 07-05-2020 03:36 AM

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.

icarp 07-05-2020 06:50 AM

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 .

stownsen914 07-05-2020 09:03 AM

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?

Neil Harvey 07-05-2020 09:21 AM

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.

MST0118 07-05-2020 10:45 AM

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.

MST0118 07-05-2020 11:08 AM

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.

Neil Harvey 07-06-2020 09:10 AM

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.

MST0118 07-06-2020 10:41 AM

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

MST0118 07-06-2020 03:49 PM

air filters

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.

r lane 07-06-2020 04:05 PM

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

MST0118 07-06-2020 06:23 PM

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.

lvporschepilot 07-07-2020 01:21 PM

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.

Neil Harvey 07-13-2020 04:10 PM


Originally Posted by MST0118 (Post 10935543)
That would be fantastic Neil if you could ballpark performance for it.. Thank you for the good advice.

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.

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