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

Very similar to Chris Streit's engine. Maybe he'll chime in a bit. I've seen his car go. It GOES. And has kept going for 3 race seasons now. And he drives the snot out of it every time out. As evidenced by his success. GT-2 champ once again.

One difference that jumps out at me is Chris uses Electromotive crank-fire twin plug.

Fabulous work!

re Single MSD driving two coils - see comments from Steve Wiener re my setup like this -- you may want to buy another box...

nice one
 

Beautiful motor,

question, why stop at 7500rpm? what is the limit?

cheers
Brett

From the author 2x
"What this all boils down to is, as far as maximum automobile acceleration is concerned, all that really matters is the maximum torque imparted to the ground by the tires (assuming adequate traction)."
"It's the torque applied by the tires to the ground that actually accelerates a car, not the torque generated by the engine."

----- So if I understand all this correctly then if Tom's & Super's car both started in the same gear and speed at 3.5k, and pulled to 6k, then they should be about equal.

That means those carbs need tuning. We confirmed this based on A/F?

How much torque is left on the table? It's gotta be a noticable amount? Tom's running the GE-60 cams in a 3.0 which is more cam than the 3.0 RSR cam. It better be really noticable or Tom will have to work at beating Super's engine.

my little carb brain says Tom has some serious action still left on the table IF his carbs are really dialed in. And If 46-IDA aren't too big?
http://forums.pelicanparts.com/uploa...1129695375.jpg

i gotta hear this engine.. http://www.pelicanparts.com/support/smileys/wat6.gif

Ron, I know off topic, but where does the Carrera 3.2L 84 to 89 cam specs fit into this chart?

Toms car after 5k would pull away from supers. Super would have to shift and lower the multiplied torque to the rear wheels. That is if they both have the same gearing and tire sizes.
Toms engine is designed to be run from 4500 to 7500 rpms.
Supers engine is probably happy from 2500 to 6000. Hopefully both are geared correctly to take advantage of thier powerbands.

The DC60 (Ge60) has less duration than the 3.0 RSR cam and a much lower powerband.

The specs listed in BA's book for the L cams are incorrect. The L has the same cam specs as a E cam.

The 3.2 Carrera cams have the same specs as the 3.0 Sc , they are timed different in the engine.

Wayne didn't have lift #'s in his Engine book for the '84-89. Neither did Bentley. That's all I have.

Wow...I didn't think my dyno results would generate this much discussion.

I am running 46mm PMO's set up as follows:

AV's 4.5
Vens 4.0
Mains 160
Idles 55
Idle Airs 180
Tubes F16
FBCV's 50

Scott at Auto Associates and I discussed the AFR results and decided not to make any changes in the carbs, Here's why:

The dyno runs started at 3500 RPM so the data below 4000 rpm is not real. Most of the time I will be running the car with the muffler capped and the car running rich (between 11.5-13 AFR). This will be true on the street and at many of the racks I expect to run where noise is an issue. When I am able to run without caps, It will be on the track where the engine will be operating between 4500 and my 7500 RPM shift point (I have a short gear stack in the tranny). If we were to richen up the carbs, we would end up with an AFR at 11 or below with the muffler capped. This would give away too much power.

Someone asked about achieving the 10.5:1 CR with the Mahle RSR P&C's. I'm running early SC heads that have been machined for twin plug and to give 84 cc chamber volume. With that and a deck ht of 1.2 mm, I measured 10.5:1 CR. I'm told that this is a pretty standard set-up for a high performance 3.0 liter.

There was also a question about single vs dual MSD for twin plug application. Auto Associates recommended the single set-up. They build all of their twin plug motors that way and have spoken with MSD who concur with them. I'm told that Jerry Woods also uses the single MSD in his applications.

The muffler is really trick. It is a replica of a factory ralley silencer. There is a pic on page 138 of Bruce Anderson's 911 Perf Handbook vol 1. The discharge pipes line up with the megaphone inlets from the headers so when the caps are off it acts like open megaphones. With the caps on it dischages to a downward pointing exhaust hidden behind the rear valence. I'll post some pics when I get a chancce.

Another thing that might be a problem with a comparo of the two motors is the dynos that were used.

I am guessing that Superman used a Dynojet and we know Tom used a Dynapack. The Dynojet is much more optimistic with the #'s than the more conservitive Dynapack. So it is hard to compare different dynos.

Dean

Excellent job Tom!
I am anxious to get mine out to the dyno now, as we started with the same base engine but ended up making different choices along the way:
3.0 SC
11.5:1 JE Pistons
Carrera intake megasquirted
Heads ported and smoothed (but not polished)
Boat-tailed mains
Twin plugs EDIS
DR20 cams
Bursch headers
Flowmaster 2-into-2

If I knew now when I ordered them I probably would have gone with a more aggressive cam but lets see...

again, congrats

Just spent the weekend running DE at Watkins Glen. We were able to run caps off on the muffler. The car made great power and sounded outrageous.

Keep us [posted on your dyno results.

Hey Tom how about your engine temps? What did they run into?

Thanks!

I've noticed at the top of the graphs it states "Fly Wheel Horsepower". Is there some correction factor (15%?) already being used to give these numbers?

Tom,

Love the car. Sorry, longish question.

Why did you go with the 46mm PMO's rather then 40mm. I've heard that 40's are perfect for 3.0 & 3.2 liter set-ups, and 46mm are best suited for 3.4+ motors. The reason I ask is I just picked up a 3.0 litre SC with euro heads and 46mm webers. The motor seems a little sleepy below 4500 rpm but loves 5-6000. I guess you can always downsize by running smaller venturis but there must be some downside to this as well.

If he's running to 7800 RPM, that motor needs the 46mm carbs to get enough air into it.

The HP numbers on the dyno charts are rear wheel HP and torque. A 15% correction still needs to be applied.

My son and I ran the car in back to back sessions at the Glen last weekend. After 40 minutes of hard running the oil temps were still below 210 deg F.

The motor needs 46 mmm carbs. The GE 60 cams combined with the big port heads, 1 3/4" headers and the 7500 rpm rev limit require lots of air and fuel. We used almost 17 gallons of race gas in 6 20 minute lapping sessions.

What kind of lap times were you running?

Thanks for the info Tom.

We're still learning the car.

I was the 2nd fastest car in the yellow run group. I was turning around 2:28 minute laps. I was braking way too hard gong into each high speed corner and was not carrying enough momentum into the turns.

Still learning!!

Ok, thanks Tom. Was just curious, as my brother ran the HSR race there a few weeks ago.