Dyno results and drop off

[D Hanson]

Finally got a dyno in today. Just curious if readings are normal or if I have an unsually quick drop-off that could be a back-pressure issue or A/F mixture issue. Dyno did not have an A/F reading. It was a Chassis dyno.

(HP 291 +/- fw): rwheel hp peaked at 245.9 at 5,800, but hit 240 at 4,800 rpms and went virtually flat, and dropped off to about 220 hp at 6,400 rpms where it remained until red line. Should my curve not have been going up here.

(Torque 284 +/- ft/lbs fw): rear wheel torgue peaked at 239.9 ft/lbs at about 4,800 rpms but was over 200 at 3,600 rpms and I had 215 ft/lbs by 3,900 rpms. Torque went to 235 + and stayed there for 1,000 rpms until it dropped below 200 lbs at about 5,800 rpms.

torque seemed great and was about 190 or so all the way down at 3,200 rpms or the lowest reading.

Lines were remarkable smooth according to dyno guys and have virtually no dips or jagged lines.

Did all 3 runs in 4th.

With hp peaking so quickly and remaining virtually flat from 4,800 rpms to 6,000 rpms and then droppoing a bit, is this possible a back pressure loss? SHOULD IT NO KEEP GOING UP.

Torque seemed very strong and I would hate losing torque by tweeking to get hp line to keep increasing, but it seems like I have an air flow, fuel flow, or back pressure issue keeping it from realizing max hp in the upper RPMS. Any ideas would be greatly appreacted.

[Jack Olsen]

What's been done to the motor? Those are great numbers, but they're also puzzling -- I have similar hp with my 3.6, but my torque numbers are significantly lower.

Do you have the ability to scan the dyno sheets? What model of dyno was it?

[D Hanson]

I have a scanner. I had to re-set my hard drive recently and need to find the software to reload. I will look this evening after dinner.

The Dyno was a Chassis Dyno and the print out says Dynojet Research, Inc. I guess that is the software.

Someone just mentioned that it looked like I was running out of sufficient air intake in the high revs. An A/F would be nice. Maybe my MAF and chip are not in sync.

Motor includes new rods, pistons, valves, valve springs, head work, porting, polishing, balancing, MAF, polished intake, throttle body, cat by-pass, GHL primary, no secondary, and Ruf chip.

[TimT]

Dyno pulls without a/f information are about as worthless as a fart in a high wind.

Knowing your torque and hp #'s is great... you need a/f and possibly EGT's this way you can check the graphs, and try and tune out the flat spots..

[Mike Feinstein]

With a stable like that, the boys in Stuttgart ought to come to your house and have a look-see.

Seriously, it could be anything...I'd expect to see peak hp at around 6200-6500 rpm. If it was starving for fuel, I think it would sputter and not produce such a smooth hp line. With an MAF, I doubt your running out of air. Was the chip tuned for your MAF? Your exhaust is pretty open, so I doubt it's the problem either. Will be interesting to follow this thread.

FYI...take a digital pic of your dyno sheet and upload it. Poor man's scanner.

[D Hanson]

I will try and get the guys to email it to me tomorrow or scan it at work tomorrow.

Chip is Ruf and what was installed when original rebuild was done back in the early 90s. After the most recent rebuild, shop had put a stock DME in for the break in and I was losing alot in the upper RPM range. Very noticeable and my G-Tech times were in the 5.2 to 5.3 range.

I put the Ruf DME back in and my times immediately dropped to 4.6 to 4.8 range. I did two runs last night heavy (with 60 +/- pound subwoofer box in and had 3/4 tank of gas) and hit 4.7 and 4.9 on 2 runs. Here are the last 4 G-Tech times on this car. The 4.6 was without the sub box and 1/4 tank of gas.

The first two are from last night. I am pretty happy with the performance considering this is a cab with 18 inch wheels, a heavy stereo system with three large amps and nothing has been done to reduce weight.

[jluetjen]

...(HP) peaked at 245.9 at 5,800, but hit 240 at 4,800 rpms and went virtually flat, and dropped off to about 220 hp at 6,400 rpms where it remained until red line. Should my curve not have been going up here.

rear wheel torgue peaked at 239.9 ft/lbs at about 4,800 rpms but was over 200 at 3,600 rpms and I had 215 ft/lbs by 3,900 rpms. Torque went to 235 + and stayed there for 1,000 rpms until it dropped below 200 lbs at about 5,800 rpms.

Before I worry about having a problem, I guess I'd start with the basics and see what -- and more importantly -- where your engine should be making torque (and by extension) HP.

The factory specs (per BA's book) says that your engine should develop peak torque of 228 ft/lbs at 4800. The dyno shows your torque peaking at the same point with roughly the same order of magnitude numbers. The reason that I'm not hung up on the actual ft/lbs is because I'm sure it will be different from dyno to dyno. The good news is that your engine is developing its torque where it is supposed to be.

The factory claims peak HP at 6100 RPM, and your dyno run shows the peak at 5800 RPM, so it sounds like your engine may not be doing all that it needs to be for the last 300 RPM. But either way, without some significant changes in your engine, I would still expect the HP to go flat and fall off after 6100 RPM. The first question is what have you changed on the motor?

RUF chip -- I saw that you have pretty clear proof that the engine runs stronger with the RUF chip versus the stock chip. Unfortunately you didn't do a run with the stock chip versus the RUF chip to see the difference beyond your "seat of the pants". What you might want to do with your G-Tech is do a run in 2nd or 3rd gear with a rolling start at 1500-2000 RPM and take it up to redline. Then repeat the process with the other chip on the same stretch of road. I'd then plug the first chip back and and repeat the process again as a control. This would replicate a dyno run as opposed to the acceleration run which you were doing.

Valves -- Stock sized I assume?

"Headwork", "Porting", "Polishing". "Polished intake" -- In my book these things could mean almost anything -- many of which may or may not help performance. What was changed on the ports? How smooth of a finish was applied to the other parts?

"cat by-pass, GHL primary, no secondary," I could picture that these things would change the accoustics of the exhaust system. Once again though, it is such a black art that there is no way to know if they made an improvement, made it worse or just changed the attributes of the exhaust.

Not to mention, when the engine was rebuilt (both times), how was the cam timing set? Was it advanced, retarded or spot on. This could make a significant change to the torque curve. By shifting the torque's shape by a little bit, you could easily gain or lose a couple of HP at the top end (and conversely at the bottom end of the rev range as well.)

As TimT pointed out, without A/F information as well as the other data which is easiest to collect on the dyno and the information I mentioned above, it's really hard to tell which part or parts of the system are not working well with the other. Using your G-Tech as a dyno, it might be possible though to untangle the problem some and come up with a strategy to solve it.

[Bill Verburg]

Besides a generally good post John made 2 very significant statements

I'm sure it will be different from dyno to dyno

how was the cam timing set? Was it advanced, retarded or spot on. This could make a significant change to the torque curve. By shifting the torque's shape by a little bit, you could easily gain or lose a couple of HP at the top end (and conversely at the bottom end of the rev range as well.)

and hinted at a third

"cat by-pass, GHL primary, no secondary," I could picture that these things would change the accoustics of the exhaust system. Once again though, it is such a black art that there is no way to know if they made an improvement, made it worse or just changed the attributes of the exhaust.

Unless cams w/ significantly more overlap than stock are used the exhaust only needs to flow freely, pipe tuning isn't an issue. In a 964 the primary exhaust constraint is the primary muffler follwed by the cat.

[D Hanson]

Originally posted by jluetjen
Before I worry about having a problem, I guess I'd start with the basics and see what -- and more importantly -- where your engine should be making torque (and by extension) HP.

The factory specs (per BA's book) says that your engine should develop peak torque of 228 ft/lbs at 4800. The dyno shows your torque peaking at the same point with roughly the same order of magnitude numbers.

I was wondering about torque. Do you not convert by dividing torgue by .85 for drive train loss like you do hp numbers. I was not sure about this. I think the car stock only does about 220 or so ft lbs which would be about 190 ft lbs at the rear wheels.

If you do convert, my engine is making about 70 more ft lbs of torque than stock which to me may be more desireable than hp if the conversion applies. The reason I am curious about this is because my plan were to go with the Lenz system if I was under 300 hp, but I would hate to drop another $ 5k to add hp, but to lose torque.

Incidentally, my 04 C2 does roughly the same G-Tech numbers (conistent 4.6 to 4.8) my 964 cabriolet does. The 04 C2 has 320 hp and weighs less than my 964 carbiolet.

For my heavier 964 cabriolet to be matching the 04 C2 Coupe's numbers with maybe 40 less hp, would the difference not have to be made up in torque. Someone on the Rennlist pointed out that the C2 has around 270 ft lbs of torque and that the similar performance is probably contributable to the roughly 284 ft lbs of torque being made by my 964.

[D Hanson]

Here is a G-Tech snap shot of the 964 v. 04 C2 coupe with 320 hp and roughly 270 torque.

You can see that the heavier 964 is nose to nose so to speak with 04 C2 until it hits upper RPMs than the 04 C2 lines go just a bit steeper and they come back together after shifts. The C2 then pulls away a bit at 75 or so miles per hour.

If I am not doing it with hp, it must be torque or I am wrong.

BTW, the first 2 runs are the 964 and the last 2 are the C2.

[jluetjen]

D;
I think that you are confusing torque and HP. If one car is pulling the other at high rev's, it's because it has more torque at the higher rev's (and thus more HP at higher revs).

As far as multiplying torque or HP by .85 to correct it -- I doubt it will give you the right answer. This is because the amount of frictional losses in the transaxle varies with the transaxle speed, so it will be different from gear to gear. Not to mention if took my 140 HP 2.0 and hooked it up to your exact transmission, would I also loose 15% of my 140HP??? Once again I doubt it since that would suggest that my engine is losing less energy through your transmission then your engine is. That doesn't make sense. I believe that the frictional losses will be some sort of torque or HP number which should be subtracted from the engine's output. Whatever it is, it won't be a flat percentage in all cases.

[D Hanson]

I read 15.5 percent or .845 for torque if 2 wheel in 4th gear and 23 percent if AWD in 4th gear from the dyno guys on the 996 TT Renlist site and .85 was mentioned in Adrian Streather's 964 book and by a couple of people on the 964 site. 4th gear is very close to 1:1 ratio.

The only other dynos I have seen posted on the 3.6 964 motor are Jacks with 211 at rear wheels and 217 at rear wheels when adding his NBD chip. I think his 211 was with his exhaust mods. Evos supercharger numbers I saw on the 996 were 271 ft lb. at the wheels.

It seems the guys here are also estimating torque losses at 15 percent on SCs, 3.2s and 3.6s.

Reseda Dyno Day - Results

I understand it is not an exact science, but I have to making some great torque to get my heavy cab with 18s to 60 in 4.6 or 4.7 seconds with only 290 hp. I bet I could see a 4.5 if I took the 60 pound sub box out and took the three amps out (McIntosh each weighing 28 to 35 pounds) and got a really great launch.

Prior to my recent rebuild I was only getting about 5.4 to 5.6 range 0 - 60. My shop guaranteed a performance increase with their head work which they are known for in RS America track cars around this part of the country. I don't think they increased the porting size as they said that would do nothing or hurt. Their work was focused on seating and flow issues. They also went titanium or light weight with with valves, springs and something else valve related (maybe guides). I am not a techie. The only other thing I did was replace a sport cat with a Fabspeed cat bypass. What ever they did worked pretty well as my 0 - 60 G-Tech readings dropped from 5.4/5.5 to 4.6/4.7s. I don't think I have had a single G-Tech run out of the 4s since I got it back and put the Ruf DME back in, although I do have pretty consistent launches.

The 964 is actually sneaking up on my 03 TT which only sees about 3.9 to 4.1 0 - 60 on the G-Tech. I also have not seen any other G-Tech readings on 964s in the 4s. One Rennlister sees about 5.2 and he has chip, air box mod, cat bypass, GHL and G-Pipe or secondary bypass and he also has a 964 coupe that is much lighter than my car.

[Jack Olsen]

15% drivetrain loss is an inaccurate way of determining crank horsepower, but it is better than trying to compare one motor to another when everyone's using their own scheme.

Rear wheel horsepower is the easiest comparison number, but even this figure will vary from one dyno pull to another, and different types (and models) of dynos will not compare in a straightforward way.

(My rear-wheel numbers were 243.2 hp and 216.3 for torque. With a 15% drivetrain loss, this would (roughly) translate to 286 crank hp and 254.5 foot pounds of crank torque.)

[AES]

If anyone believes that a relatively stock 964 chip or not headers or not is putting out 286/245 then I have a bridge I would like to sell to them

Good grief guys use your heads

[D Hanson]

I think my main concern got lost in the shuffle. I was curious if I have problem with the early drop-offs and mainly if I try and correct the hp issue with possibly a Lenz system, I might lose some torque which would be anti-productive in the big scheme of things. I am more concerned about 0 6- 60 or 0 - 100 performance than peak hp or peak torque.

[sammyg2]

My first thought was timing too retarded or throttle body not opening up all the way.