Dyon'ed my SC last week

[GBStu]

For reference purposes I am posting the dyno data of my recent engine rebuild:

1979 SC
Re-ringed using Alusil cylinders
9.3:1 pistons (were orignally 8.5:1)
964 grind cam
M&K 2 in 2 out exhaust
Pre 73 headers

Other cars dyno'ed that day included a stock 944 S2 (177@wheels) and a 993 RSR (310@wheels).

[Buckterrier]

Very cool Stu. Doing the same May 3rd after a rebuild and other goddies. Are the numbers as expected? What was stock hp & torque?

[the]

Interesting.

I think stock was rated at 180 hp at the flywheel. Using a drivetrain loss of 12%, yours would come out to around 190 hp at the flywheel.

I'd have thought it would show more - I would think the approx. 10% increase in compression alone with have given more than 10 hp.

[911quest]

How many miles on the rebuild? I would suspect it to get better if the rings haven't yet broken in not that there too shabby now.

[GBStu]

Tony, I have about 2500 miles on the rebuild.

the, I was under the impression the 911 drivetrain loss was about 15-17%?

Thanks, Stu

[burgermeister]

the, (does anyone have the username "a" ?? )

A change in CR should not affect volumetric efficiency, so the only power gain to be had from a change in CR is from thermal efficiency.
From Taylor's Internal Combustion Engine in Theory and Practice, a chart of thermal efficiency for fuel-air cycles as a function of air-fuel ratio, with lines representing different compression ratios. The bump from 8.5 to 9.3 looks like it ought to yield a 2% power increase?

[tonythetarga]

Hi Stu,
I was wondering how it went. Glad you were able to finally get a baseline dyno done. Now...have you signed up for the Niagara PCA DE at Watkins Glen at the end of May??

[rjay]

I'm no expert, don't know my cam grinds from coffee grinds, but judging by your torque curve, it would seem that your cam profile isnt very aggressive, so its not that surprising that peak power isn't that numerically impressive. OTOH, the torque curve is very flat with the resultant linear power delivery. dont know how you use the car, but if its street and track, it seems like a good compromise.

[gestalt1]

are those a/f ratios normal? seems rich to me, but i really don't know what is the most efficiant vs best power.

[mb911]

Originally Posted by gestalt1

are those a/f ratios normal? seems rich to me, but i really don't know what is the most efficiant vs best power.

yeah those AFR's look great for a turbo engine but not for a NA engine

[GBStu]

I was thinking it was a bit rich, however, adjusting the Rube Goldberg (CIS) injection system may be more trouble than it"s worth. Is it really that far off?
Thanks, stu

[911st]

I am not an expert but I read once that going up on point in compression should add about 3-5% more power.

I think a good running 3.2 Carrer is pulling 200 to 220 rwhp so an SC should be 180 or more. With your cams you should get another 10hp or so. 200+ rwhp should be very doable.

Not all dynos are compairable. Some can read high, some low, sometimes the correction factor is used or not.

The A/F's do look a bit high so there is some power hiding there.

Yes, that is a very interesting torque curve. I would think the TQ peak should be close to where it is the factory C2. I would guess near 5200rpm.

The TQ peak is where a motor is running at it's most efficient level and making the most power with each power strock. You are loosing your effecency way to early.

You have big ports and a good exhaust so it should not be falling off.

I am not an expert but something looks to be up. Cam timing, total advance, or A/F ratio

Re adjust the A/F (12.7 --- 13/1 goal) and check ignition total advance at 4k.

There is a lot of drivability and some power hiding in the ignition side of many of these cars. A programmable ignition that is set up correctly could wake these cars up.

I understand that CIS is susceptible to weather change. What is a good A/F during a wet cold winter will be to lean during a dry warm summer.

Good luck.

[htron435]

Rjay-

You really need to update your website. Your 911 actually looks clean in the photos.

By the way, we're gonna miss you at Mid-Ohio in May. You're in for the Glen in June though, right?

[rjay]

Originally Posted by htron435

Rjay-

You really need to update your website. Your 911 actually looks clean in the photos.

By the way, we're gonna miss you at Mid-Ohio in May. You're in for the Glen in June though, right?

Yep. I'm intending on signing up to that one. Course if you think my car was dirty before, wait till you see it in June. Its going to look like a total turd. But it will be a little quicker. Put him on a 300# diet and got him some new shoes. RSR Tire Sizing

Not going to paint it until next year when we can do a total strip rotisserie job. So, for this year at least, Whitey has been renamed Blighty.

[JV911SYDNEY]

having mine dynoed in a few weeks

rebuilt '83 3.0 with quoted 204hp @ 5900rpm
9:8 compression
SSIs
Monty 2-1 muffler

will post results

will be interesting to see before and after i do PMOs & 964 cams

[rjay]

Originally Posted by htron435

You're in for the Glen in June though, right?

Just signed up. Truly looking forward to hanging with you again Jay!

[justinp71]

I think that the big port 79 heads hurt your power a little, if your not running a big cam and carbs.... Had this experience on another motor once.

[Paulporsche]

JV911Sidney,

Looking forward to seeing your results.

Just a word of advice: if you include the relative atmospheric and geographical date relevant to adjusting the hp calculations you will cut down on flaming.

[Rusty Heap]

So since facts and data is being present here, (which I love) here is my dyno chart from last year for comparison as we have very similar cars and mods.

Mine is going back to the dyno soon though, after having to FIX my ugly airfuel metering rod on the CIS. I don't know if it's going to gain more power, but you can see how rich it was and hunting all over for the right ratio. John Walker fixed it, and since this dyno chart have rebuilt my distributor for proper advance/retard.

I note we're both real close on horsepower, but with your high compression pistons you may be getting more torque than my stock 145K mile engine.

Mine:

1982 SC, 3.0L
Web 20/21 cams
SSI headers.
Monty 2 into 1 exhaust.
Black Wrinkle Paint Valve covers - 10% more torque and another 500 RPM right there. he heh.

[GBStu]

Dave, thanks for posting. I figured 170hp at the wheels equates to about 200hp at the flywheel and therefore a 20hp gain over stock (it was what I was expecting).

Since you like data.......I will be mounting a wide O2 sensor (LC-1) in the header this weekend which will connect to my G2X data acquisition system. I will have throttle position, A/F ratio and acceleration, almost as good as a dyno!!

All I need to figure out now is how to adjust the warm pressure on the WUR such that I can dial in the A/F ratio easily.

Thanks, Stu