in chassis torque tuning: accounting for drivetrain and other losses

[bigbreak_2000]

I want to get opinions on possible root causes for larger than average power losses that occur between the torque measured at crank and the torque at the wheels for a 280zx (s130). This is not about arguing this a good/bad dyno machine, not questioning the reputation of the engine builder or ECU tuner. I just want to get a general sense of what power losses others are seeing, kind of getting an idea of what % loss would be considered normal, or what would be exceptional high that justify further investigation, and ideas how one go about root cause analysis. I may be overlooking something very obvious in my car that cuases a 1/3 power loss between the crank and wheels. I want to put my mind at ease with the numbers, or go after something that would provide a noticable benefit. Don't ask me for names of the engine builder , the person who made the exhaust system, designed the intake system or who the tuner is, several are on east coast, other one west coast, and all of them have either international or national levels of experience working with race teams be that with Datsun/Nissan, Austin Martin, engaged in regional and or national scca as drivers or supporting cars, etc. There are some big names.

 

So here is my situation: iStarted as a bone stock 1981 280zx 2+2, NA, 5speed. Bought the car with extremely low orginal miles. The car is in Charlotte NC. Everything stock except for new tires and new OEM exedy clutch, on Mustang dyno we had 129whp. Factory rating was 145hp. Not too bad. Very low power loss IMO. This was kind of my benchmark.

 

Then I put a highly modified 3.2l NA motor in, pacesetter header, excedy stage 1 clutch good to 270whp, KN cone filter, 2.5 in mandrel bent ss exhaust with only 1 back muffler. Took car to same tuner shop, Engine builder dyno (with pacesetter header on, but without kn filter, and without my exhaust system) at 287 crank hp, on the chassis dyno best I ever saw was 215whp. Thats a 25% difference. I had it to various tuner shops, Dyno Jets, Mustang they were all pretty close, so I concluded its not a tuning (fuel/spark) issue. The engine was in best state of tune for where it is.

 

Recently I decided to modify the engine further. ITBs, new high com head, bottom and ECU still the same. The engine with the ECU and header was tuned again and on the chassic dyno turned out 340hp at 6700rpms and 297 torque at 5500rpms. That is much better than the single TB setup. Swopped the stock diff for a new quaife lsd and same gear ratio. Put the engine back in the car, add air filter, connect the same exhaust as before, and for comparison purposes now we're getting 240whp at 6500 rpms and 197 torque on the wheels at 5500 rpms. No signifcant changes were made on the street tune (from the tune/ECU settings provided by the engine builder). I'm not hung up on HP numbers, torque is what matters and I want to get the best bang for my buck, and this is a larger than 30% loss between crank and wheels that I need to understand what is going on. Ok I get it, more power equates to higher friction and temps and one can expect a higher loss ratio. But is 33% loss acceptable? I heard other Z car owners with a similar engine setup see 270whp, So my expectation to see higher numbers does not sound unreasonable, or is it?.

 

The gearbox shift good, no noise or anything weird, the clutch seems to held well, no burning/slipping, Car drives good, nothing strange with the differential. The entire drivetrain is just very smooth. I cant tell if there are any underlying issues with the u-joints, it just feels like a new car, no vibrations, clunks or anything. Engine sounds good, accelleration/pickup is excellent with the ITBs. However in the numbers someting does not seem to add up: is a loss of 100lbsft of torque between the crank and wheels acceptable or what could cause such a large difference? If one argue 20% loss is more of an average on these older rwd Z cars, then I shoudl be making closer to 230-240 torque at the wheels, and looking at explaining where am I loosing the other 20-30 lbsft of torque? I just cant think that an exhaust system backwards of the header , or an airflter can cause an engine to loose that much power. Could it, or is there a possible drivetrain issue I need to look into? I could upload pictures if someone thinks it is worth to see what the intake or collectors/exhaust system looks like. If one of you are in Charlotte NC I would also be happy to take the car to someone to have a look if they have experience solving these overall car setup issue. Im willing to change the exhuast system if someone convince me it would make that difference.

 

 

[Dans toy]

As you said yourself, I would not get hung up to much on the numbers. I'm sure you could get lots of suggestions as to why you seem to be getting unusual readings. It might be a little late for some before and after 1/4 mile track runs but Mile Per Hour change is a really good indicator for power change as long as your driving technique is consistent. 

[johnc]

The engine with the ECU and header was tuned again and on the chassic dyno turned out 340hp at 6700rpms and 297 torque at 5500rpms. T

 

This is a BS number.  Something was wrong with the dyno or the operator during that particular tuning session.

[m1ghtymaxXx]

Your main issue is that different dyno's can't be compared. It's a tool for measuring difference in performance over a session, but unless it's been SAE calibrated, not useful for determining outright power figures.

[Leon]

To elaborate further on dyno testing differences (and I assume you meant the 340hp figure came from an engine dyno)...

 

If the quoted max power from the engine dyno came from a steady-state test, then power figures (and torque, they're related) are not comparable to chassis dyno ramp runs. A steady-state test will show higher power figures than a ramp run.

[bigbreak_2000]

sorry I said it wrong, the 340hp was on the engine dyno.

[johnc]

Ok, engine dyno numbers are somewhat more believable. But, unless you're running a 13 to 1 CR and spinning the engine near 8,000 rpm I would be sceptic all of 340 hp.

[bigbreak_2000]

yes it is a high CR motor, 298/298 cam, I forgot the exact CR, running on TEL fuel and max power is at 6700rpms.