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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!!







Last edited by MST0118; 07-14-2020 at 11:51 AM.. Reason: Typos
Old 07-13-2020, 07:57 PM
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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
Old 07-14-2020, 12:36 PM
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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.
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Old 07-14-2020, 01:29 PM
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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...

Last edited by spyerx; 07-14-2020 at 04:32 PM..
Old 07-14-2020, 04:28 PM
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Originally Posted by MST0118 View Post
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 doesnít 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!!





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.
Old 07-14-2020, 06:22 PM
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No thatís 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 doesnít 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 couldnít take full advantage of the lift but did benefit from the longer duration of the sprint cams?

Hereís a comparison of the 2 cams from Andersonís 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
Old 07-14-2020, 10:47 PM
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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
Old 07-15-2020, 06:33 AM
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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.

Last edited by stownsen914; 07-15-2020 at 08:39 AM..
Old 07-15-2020, 06:59 AM
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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.

Last edited by MST0118; 07-15-2020 at 03:14 PM..
Old 07-15-2020, 09:37 AM
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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
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Old 07-15-2020, 12:23 PM
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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.

Last edited by MST0118; 07-15-2020 at 03:33 PM..
Old 07-15-2020, 03:27 PM
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Quote:
Originally Posted by MST0118 View Post
Hey Scott, My muffler is a 2 in / 2 out sport muffler that I got from Pete Weber whoís shop was reasonably close. Itís 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.

Iím 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 wonít change anything major. When it comes to rebuild time, Iíll probably rethink the type cams if the power isnít there, maybe a custom grind?

Iím 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.
Old 07-15-2020, 03:57 PM
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YOU are correct.The exhaust makes the difference.Fred
Old 07-15-2020, 06:23 PM
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Yes, great points. Iíll tune first with this cam and report back later. Iím running the Supertec enrichment device so donít 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 Iíll sending to him this winter.
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?
Old 07-15-2020, 06:26 PM
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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.

Last edited by MST0118; 07-23-2020 at 09:43 AM..
Old 07-15-2020, 09:55 PM
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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.

Last edited by Neil Harvey; 07-15-2020 at 10:54 PM..
Old 07-15-2020, 10:51 PM
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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.
Old 07-16-2020, 06:41 AM
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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.
Old 07-16-2020, 06:47 AM
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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
Old 07-16-2020, 09:31 AM
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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.

Old 07-16-2020, 09:50 AM
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