On the dyno

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piezopaul

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Hi all,
Just had ny CSL in the shop for a little spring work and had it put on the dyno. With all the work in the 80's (3.5 l block, oversize valves, 304 cam, headers, triple webers, 10:1 pistons), it still only put out 190hp at the rear wheels. What do you all think drivetrain losses amount to (old question)? Any suggestions to improve? (It WAS a hot day.)-Paul
 
I'm not that surprised. There is always the obvious "something has to be wrong" check list to go through with the fuel and electrical systems.

I had my car (3.5l, 282 cam, twin 38/38 weber, mild porting) dyno'd last year while trying to get the jetting perfected. IT turned 165 at the rear wheels and was absolutely flat above 4200. Turns out the tech had set the max advance at 14 @2800 and 5 at idle. Started and ran well but no glory in the top end. Reset that and I'm hoping for 180 rhp but haven't taken it back in for a run. Also changed out the fluids but don't expect that to matter.

Mechanically, I just don't see how there could be so much loss on cars that should be relatively free turning through the whole drive line. Fuel is crappy 93 octane premium but that is a constant not a variable.
 
At a reasonable guess you could be loosing 10 - 15% of the output in the drive train so that would be giving you 210 - 230 BHP at the flywheel

Possible improvements (Open your wallet and say after me.... Help yourself :D )

1... 6 into 2 into 1 branched exhaust manifold - good for up to 5 BHP (Left hand drive only!!!)
2... 2 or 3 inch diameter exhaust pipe, straight through silencers - 2 maybe 3 BHP
3... Triple cut valve seats and valves and gas flowing - up may 10 - 15 BHP
4... Cool air ducting to intake - 1 - 2 BHP on a good day
5... 95 - 100 Octane (RON) fuel if you can get it or afford it - 5 BHP

To be honest unless your going motor racing in your E9 190BHP at the wheels is pretty reasonable, and the shed load of money you would have to spend to get the power up a lot probably isn't worth it IMHO
Malc
 
The drivetrain losses are closer to 25% as I have experienced things eg. My 3.5 block produced 150 at the wheels at a dyno renowned for giving true figures not optomistic ones. This equated to 197 at the flywheel after the dyno measured the drivetrain loss. My engine is standard so I was happy with that figure.
Doing a quick calculation on that basis your motor is producing 253 bhp or 72 BHP per litre which is a respectable figure considering that the compression ratio is a litte low for the cam duration that you have. Also have you had the distributor modified? If you haven't the advance curve will be wrong for your mods.
I would say that your C/R should be arround 11:1 or higher to get the best from your cam then you need to limit the ammount of overall ignition advance and play arround with the timing once the car is back on the dyno.
 
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Mechanically, I just don't see how there could be so much loss on cars that should be relatively free turning through the whole drive line[quote]

It might be free turning but it still weighs something...  

Its not worth getting hung up on what the horsepower "really" is, as the listed power output is always higher than the real-world measured output. A better approach would have been to dyno your car before putting in the cam, etc and then measuring it afterwards to see what % gain (or loss) it gave.[/quote]
 
Paul
just out of interest what was the lb/ft result , numbers are numbers how quick is it in real life?

PJ
 
Those hp numbers are pretty good, actually. Don't be so concerned with max hp -- you should really be looking at torque figures. My 3.5 was putting out 191 hp and 220 ft/lb of torque. The beautiful part is that the torque curve is incredibly flat from 2000 rpm all the way up to 5000 rpm. It is fast. :D

I think 25% hp estimated loss through the driveline is high -- Malc's 10-15% is more accurate. My dyno shop used a 13% figure. You also should have received a wide-band O2 readout. Take a close look at that and you'll be able to figure out where you're running rich or lean. I bet you can get another 10-15 hp out of it with some tuning. Every motor is different, but I tuned mine to be about 13:1 AFR at WOT and noticed a big difference in torque. It leans out to about 14:1 on the top end and then hp and torque drop off significantly at 5000 rpm. I've also added timing in small increments, but haven't noticed any real difference since it was pretty well timed to start with. Post up the dyno charts if you have them.
 
Hi all and thanks for the input. PJ the torque was 201 and peaked around 3500 rpms. The car actualy drives great, makes good noises and seems fast. Its faster than my son's e36 328is and obviously slower than my m3. About right given the numbers. Are torque losses similar to HP losses? ps we ran it to 6500 rpm and the torque had started a mild downward drift. If I can figure out how to upload the chart I'll do it.
 
Those hp numbers are pretty good, actually. Don't be so concerned with max hp -- you should really be looking at torque figures. My 3.5 was putting out 191 hp and 220 ft/lb of torque. The beautiful part is that the torque curve is incredibly flat from 2000 rpm all the way up to 5000 rpm. It is fast.
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I only quoted 25% from experience but having said that all cars are different and so are rolling roads e.g. I have a lsd fitted and staggered Alpinas so there could be more drag from the tyres and the diff, also the tyre pressures and the diameter of the rollers can have an effect. The last time my CS was on the rollers she showed 150 at the wheels which was corrected to 197 after losses, interestingly my torque curve was the same as yours :D .
 
I only quoted 25% from experience but having said that all cars are different and so are rolling roads e.g. I have a lsd fitted and staggered Alpinas so there could be more drag from the tyres and the diff, also the tyre pressures and the diameter of the rollers can have an effect. The last time my CS was on the rollers she showed 150 at the wheels which was corrected to 197 after losses, interestingly my torque curve was the same as yours :D.
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You are quite correct -- there are so many variables its pretty much comparing apples to oranges unless the cars are done on the same dyno. Not to mention the skill of the operator. . .which can vary dramatically in my experience. There's really no way to know how much is lost through the drivetrain without an engine dyno - but even then the calibration on the chassis and engine dynos will be different. :? I just use the numbers for comparison on my own car to see whether my tuning actually makes a difference.

Paul -- I saw your chart a few days ago, but the link doesn't seem to be working now. If I recall correctly, they curves started around 2k rpm and it came on cam around 3k. Both curves were somewhat peaky over the rpm range. I'm no expert, but I bet you can get the numbers up with some ignition and fuel tuning.

Did they use a wide-band O2 when they did the run? If not, find somewhere where you can get a printout with rpm, air:fuel ratio and map (vacuum). It will go a long way helping you figure out where its rich or lean to fine tune the mixture. Then, of course, you'll need to find someone who actually knows how to tune your car -- which may be hard to find these days. BTW, are you running carbs or D-Jet?

A timing light with adjustable advance will help you dial in the total advance. That 304 cam is going to want more advance at idle, but you need to avoid too much advance at high rpms. The distributor really needs to be recurved to take advantage of the cam. My spark is computer controlled, so I've been adding in total advance a degree or two at a time until I hear detonation, then back if off slightly. Adding timing in the mid-range made a huge improvement in torque. :wink:
 
Thanks all- I have little in the way of experience, but have a good mechanic-I think_ who should be able to help with the changes to tuning. I guess the link to the graphs was temporary (bastards!). I guess some more computer skills are in order. -Paul
 
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