Mike Simard

Here's the dyno of what's in my sig.

Driving it is way different than what the torque curve looks like.
At 4500 rpms, if feels like something kicked in and it pulls strongly all the way over 7500. You would think the torque curve shown would have a big step instead of the 'gentle' curve. The in car feeling is surprising, it's like a booster rocket fires at 4500.
The intake tract is the reason, it's tuned for that rpm range at the expense of low end torque but who cares about big low end torque in honkin' V8 anyway, it's not like an old small engine car, it still has 3-400 ft lbs in it's 'un-tuned' range.

I agree about a broad usable torque output being king, a range of usable power to cover gear conditions.

It's not really 928 related but a small high revving engine may have an advantage although you wouldn't think so at first. If something like a sport bike is a dog below 10k but makes power to 15, you'd have 5k of usable power, a big low revving engine would have less range even though it seems like it because it's 'all torque'. Not that any of that applies to us

Louie928

Maybe a little clarification on the rear wheel power my 6.4L engine makes. I think Gregg is correct in that the 928 5 spd loss is likely about 10% and not the 15% - 17% that is the general consensus. I've found that RWHP varies quite a bit with tire pressure and the type tire you use. Shallow tread stiff sidewall track tires do better than street tires. High pressure of around 40 - 45 psi will get better results than 30 - 35 psi. You'll get more top end rwhp in 4th gear than 5th gear due to a lot of power being absorbed by the tires at above 130 mph. You'll get better low end torque in 5th gear than 4th gear due to the lower loss in the tranny in 5th gear, but that goes away as the wheel speed increases in 5th.

My engine seems to do quite well on any chassis dyno because I use 200 proof ethanol injection at WOT in addition to the normal gasoline. I cheat. The ethanol is fed through atomisers at the top of the intake horns. It is injected only at WOT and I reduce gasoline injection also at WOT to keep gasoline+alcohol AFR around 9:1. Otherwise it would be too rich with the alcohol on top of the gasoline. The addition of the alcohol not only cools the charge, adds some O2, and lets me increase ignition advance by around 4 degrees. This gets me about 50 - 60 rwhp more than with gasoline alone. The car will reliably make 545 RWHP with gasoline alone (estimate 600 crank hp if you will), and anywhere from 595 - 603 rwhp with the alcohol. My alcohol tank is about 2 qts and is good for maybe 2 minutes at WOT. Fortunately, I only need it for a few seconds at a time if I want to pass some cars or similar. I had hoped to better 600rwhp at Dallas, but didn't quite make it. I was tired, driven a long ways, and it was hot and I forgot to pump up the tire pressure from my usual comfy road trip pressure. That's my only excuse.

The throttle bodies are 50mm diameter and do strangle the engine a bit above 6600 RPM. The cams are Devek B1 and are not mild. The lobe separation is too narrow for street use, too much overlap, and the engine is not well behaved when trying to drive below about 35 mph although idle is good at 900 RPM. It does pull smoothly in 5th gear at 1200 rpm or above. Light throttle opening is rough running.

Mike Simard

Louie, it's great to see pics of your work. I always learn something!

IcemanG17

WOW great info....... I always knew Louis was a cheater :>)

Hmm so 545hp or 600 crank....thats a peak power BMEP of 191psi....much more "normal"....

GregBBRD

When I was more involved with racing 911 engines, I frequently had people bitching about my engines.

One of my "big time/big dollar" competitors once said: "If your engines are legal, you need to shut the doors in your shop and never let anyone know what you are doing."

They were legal.

So, I've kept the doors shut, when an engine gets built, ever since then.

Any pictures and things I do show are "edited" for content.

You, I would tell anything.

Louie928

Thanks MIke. I always appreciate nice words from a real artist.

mark kibort

Yes, dynos are all calibrated for SOME factors, but a dynojet 248e is a set of rollers that are a known weight. you accelerate them , and that's that the GOD witnessed HP, PERIOD. no fudging, no nothing.. If you want to increase air pressure in your tires, good for you . mess with the SAE adjustments, great, but actual HP is what the car is putting down. this is why I always get two sheets. actual and adjusted SAE.
Sure, you are measuring all the losses in the system as well. (transmission, wheel friction, and very little inertial factors if you use 3rd gear .

By the way brian, your buddy that owns the smaller roller (heavier weight) dyno said that you don't like to run 4th gear, he pulls you guys in 3rd gear! I convinced him of the speeds of my 4th, (which is more than yours) and he even let me drirve my own car on his dyno (no one drives my car to redline on a dyno!). so, your numbers will be much higher in 4th. already been there! so, what ever you did in 3rd gear, add about 10hp in 4th .
(to your point Greg) comparing dyno run to dyno run, is more difficult obviously, because there are some factors to think about and control.

Mk

mark kibort

on the dyno, you can actually measure the rolling or coasting friction.

it was 20hp at 150mph and dropped down to 10hp loss at 80mph (all in 4th gear) this right there proves that the "loss" is variable. this was on a 250rwhp dyno run. and, it doesn't measure the transmission loss, which I would suspect as being double, and also variable to a certain extent.

IcemanG17

MK
Kevin is correct....he used to pull the Estate in 3rd gear....since its a 140mph gear...and 4th gear is 1-1 in the auto but spins his dyno too fast....one pull got over 190mph....ya in a 198whp automatic estate....

I always use 4th in the 5 speeds....

mark kibort

He said he drives your car on the dyno, and always uses 3rd for you and sean. I know 4th in the auto is like the 5th in the stick's with a slightly higher numeric rear end.

So, it would be interesting to see If your dyno runs have been done in 3rd as he said. if so, maybe there is a little more power you didn't know about in the new racer. (like I said, dyno runs we did one time to just see the difference, was about 10hp in 3rd vs 4th)

Speedtoys

"no one drives my car to redline on a dyno!"
---
Don't ever race a spec series then, or one with HP/TQ rules.

A responsible RD would never let the competitor operate the car on the dyno.


We've caught more than a few cars in the last 12mo with illegal ECUs (modified fuel cut limit) and 'oops you forgot to hit the switch' tricks when the driver could not be IN the car at WOT.

IcemanG17

With modern ECU's it would be quite easy to have a switch somewhere in the car that changes the spark-fuel curve to the "dyno" curve....drop an easy 20hp-torque...I even heard some have bluetooth capabilty, so the owner could be standing there "texting" and change the tune!!!!!

Speedtoys

Spec classes are rarely modern ECUs. And sealing ECUs is becoming more common as well.

Generally trickery on tune at WOT being de-tuned compared to a tad above WOT.

No reason you cant have a 'hot' build 928 for example, where at WOT hitting what looks like a stock kickdown switch on the floor, changes the ECU map via the code plug.

Just saying, have -seen- this. Racers do not drive spec dyno runs in their cars.

danglerb

When you do these "spec" car dyno runs, are all the cars pretty close?

Speedtoys

We do them at the track, immediately off the scales.

Looking at four E30s and four Miatas on my desk here at Sears Pt now..

E30s:
159
160
156
145

Miatas:
118
124
123
122

Thats top four each class, in no specific order (just the order this stack is in)

But I'll say that the low HP E30 was I think 3rd Saturday, and won on Sunday by about 25seconds.