Another RSR Clone Project - Dyno Day
 

Today we dyno'd the motor on my RSR Clone. Auto Associates has a chassis dyno that hooks up with the rear hubs for better repeatability in the measurements.
http://forums.pelicanparts.com/uploa...1129593189.jpg
As a reminder the motor is based on a a 3.0 SC case with the following:
Twin plug heads and dizzy
RSR spec twin plug heads
10.5:1 Mahle RSR pistons & Cylinders (CR verified by build measurements)
GE-60 style cams from Camgrinder
Turbo oil pump
46 mm PMO's
RSR headers
RSR style ralley muffler
Single MSD driving two coils
I built it my self using Wayne's book as my bible and the guys at Auto Associates as my consultants.
http://forums.pelicanparts.com/uploa...1129593421.jpg
We dyno'd the motor both with the ralley muffler caps off and then on.

HP results
http://forums.pelicanparts.com/uploa...1129593499.jpg

HP peaked at 250 at 7500 RPM's with the caps off. There are three runs clustered together showing about the same results with the caps off. Accounting for 15% driveline losses gives about 285 HP from the engine. The lower light blue curve is the one run we did with the muffler caps on showing about a 20 HP drop for the muffler.
Torque
http://forums.pelicanparts.com/uploa...1129593895.jpg
Torque is between 165 and 180 ft-lbs from 4000 to 7000 RPM. Accounting for driveline loss equates to 190-207 ft-lbs from the engine. The muffler causes a loss of 20 ft-lbs across the rev range consistent with the 20 HP loss.

A/F Ratio

http://forums.pelicanparts.com/uploa...1129594155.jpg

AFR runs at about 13-13.5 across the rev range. The muffler leans out the mixture and causes it to run between 11 and 12.

Overall I'm very satisfied with the results and would love to hear your comments. Scott at Auto Associates has built several motors to this spec and he predicted the HP dot-on.

The dirveability is great. It is very tractable from 1000 RPM idle up to 4000 RPM. At that point it begins to really kick in. I cant say thay I've really explored the upper limits just yet. Next up will be some acceleration trials and then a drivers ed at Lime Rock in Nov.

Congrats! Will you be driving this on the street? What octane level gasoline will you put in it?

You've done an amazing job! Congratulations! BTW - in this statement, "AFR runs at about 13-13.5 across the rev range. The muffler leans out the mixture and causes it to run between 11 and 12." I think between 11 and 12 is richer than 13 to 13.5. Am I missing something or maybe misunderstanding.

Which parts on your car are FG? How'd you get the weight down to 2140 lbs?

Doug

You're right. The muffler restricts the air flow causing the mixture to richen up no become lean. A little brain fade after a long but great day for me.

The car is set up to run on 93 octane pump gas and I will be hot rodding it on the street. At the track I'll be mixing in 110 octane race gas

The lower number is richer. Others more knowledgable should chime in, but ~14 at 7k may be too lean for track use ....

Wow. That's a 3-liter motor with a 993's power.

What's your rev limit? 7800?

I'd be a little concerned about the lean A/F numbers. But I'd check the motor out with something more accurate before I changed anything.

you are not too far from me, we should get together for a nice drive and photoshoot, should be fun!
yellow and orange RSRs:D

I will have to agree with Jack and Greg the A/F needs some tuning.
Way to lean from 3500 to 4500 and a little between 6800 up.
It must be really lean below 3500 RPMs.
Next time you get on a dyno start the runs at 2000 to 2500 RPM. That way you get to see the carbs do all its transions.
You don't to see it above 14 any were on the graph
13.5 is best to keep it alive for a long time. You gona lose about 5 HP but its better than 5000 bucks!
That is the set up on the engine. Like CR, Cams, what size carbs. What size ventures, jets, ACs and emulision tubes do you have installed?
We have a 248 in ground Dynojet. It was probely the best tool that I ever bought. Go find one close and tune on it.
You have a good start it's just gona need a little more dyno tuning.
Great job Man!
http://forums.pelicanparts.com/uploa...1129606361.jpg http://forums.pelicanparts.com/uploa...1129606378.jpg

This is fantastic. I would like to drive to Conn to see this asap. Week days, week nights, weekend days, weekend nights.. meaning I'm ready 24/7.. huh?

And this sister thread, http://forums.pelicanparts.com/porsche-911-technical-forum/246163-air-fuel-ratio.html is where this chart was first posted.


http://forums.pelicanparts.com/uploa...1129608611.jpg

I hope no one interprets my remarks as any kind of criticism....this engine is most excellent....but it makes about the same torque as my engine, which is mostly stock. I don't have my dyno sheets in front of me, but I recall it made about 205 lb/ft assuming a 15% drivetrain loss. If so, this illustrates the function of horsepower, which is simply a mathematical derivative of torque. I think it is (torque * rpm) / 5250. So, you can build an engine that makes the same torque as a wimpy engine like mine, but just coax it into making that torque at a higher rpm, and you've got a high-hp engine that makes no more actual power than the wimpy engine. Or am I missing something?

not at all. So about what rpm are you peaking out the torque.. It would be great comparison info w/your 20/21 cams.

btw.. notice that I use an E cam for lower rpm torque.

My torque curve looks like my kitchen table. It goes to about 90% power around 3000 or 3500, with good power below that, and peak power remains until about 500 rpm, where it begins to trail off, but not much. I think someone posted it once. Perhaps I'll search.

Nope, I didn't find an image of the graph, but I noticed that my stock 3-liter with 20/21 cams, '73 heat exchangers and Triad final exhaust made 174 lb/ft of torque at the rear wheels. That's less than the motor above, but not by that much.

Again, you can build a high-hp engine that never makes much more power than the stock version. Torque = power. It just makes that power at higher rpm's resulting in a higher hp calculation.

Fantastic Tom, one of the best looking cars around, great job.

Enjoy the drive.

Cars like this make "original" not quite as exciting...:)

Superman,
You are right to a certain extent, however, because of the big increase in available RPM over stock, (maybe 20% +) at a given speed, Tom can remain in a lower gear. Maybe at 50mph Tom's in first gear when you are in second, at least for a while. Since he can run a larger torque multiplier (lower gear),acceleration can be much stronger (if you wind it out). Torque does not equal power. Imagine the extreme case of two engines - a diesel which revs from only 1k to 2k where Tom's rev's 3X to 4X that engine, but both put out 200 ftlbs (really simplified model). He can use a lower gear multiplier of that same ratio for a given speed. If torque is equal between the two engines, and vehicle weights are the same, Tom's acceleration is 3X to 4X, assuming no wheel slip. Force applied to the ground is as much a function of gear ratio as torque.

An good demonstration of this is to look at the torque and horsepower curves of F1 or Indy motors. They rev to 20k rpm, have big horsepower but meager torque numbers. It is all about the gearing!

Tom, beautiful car! Can you make it to the NE fall run so we can all drool over it? (next weekend).

DW, well said.

Torque is very closely tied to displacement.

That is awesome, tom. I especially appreciate your posting the dyno info here because this is nearly 100% the engine I am looking to build. A couple of questions:

Did you have any trouble getting the Mahles to 10.5:1 during your build?

Is the muffler the type with two outlets that are in line with the inlets, and a factory type end outlet in addition? is there normally this big of a difference (say 17.5%) between megaphones and a good muffler?

what heads did you start with (78-79 SC)?

what size are the header primaries?

Thanks so much,

Nice job Tom! 95 hp/litre at the crank is great. Especially from unported cylinder heads.




Here is a very good explanation of HP and Torque:
Hp vs. Torque