mark kibort

Here is where Colin and Greg brown might have a point. you start comparing hp peak values and Yes, that is in the hands of the noise at the end of the dyno run. dennis' run was 387 peak, but that was noise at the top rpm, just as Andersons was 485, and you didnt hear Greg Brown fighting those results after the CF intake was installed on his science project motor. (Greg, you know I love you ) anyway, so, you do have to use your heads a little, so, Dennis' motor was about 375 real , rwhp, (SAE i think too. dont know what the actual was and I dont even know if it was on a dynojet or a mustang). mine were all on the dynojet 248e.

Now, let me go out on a limb here. if you run on a 248e and you get 335rwhp, you DID make 335hp, because you spun up the drums fast enough, quickly enough, to make this power point at any point on the curve base on the rate of change of speed, which is the rate of change of kinetic energy, which is by definition, power. So, there is no way to fool the dyno. the sensors, optically tell you the speed in pretty high resolution. the software contains the simple information of the drum diameter and the weight . bearing friction is negligible, and wala, you have a power detector that is extremely accurate and repeatable. now, with tire pressures, strap down technique and the myriad of air intake issues like fans, close hood, open hood, fuel regulation, sensors for temp that can change the run results one after the other, all bets are off for mirror image control of hp measurement. there is always a variance. but, its nothing like greg and Colin are pointing too.

if you spin up the dyno rollers at a certain rate, at that rate, HP is calcuated. its a pretty simple formula and you cant fool it, unless you out and out, cheat the system (change the speed monitering sensors, play with drum weight, etc, you know, things that are just not done very often)

mk

point is, his baseline was with the special cams, or was the baseline for all the mods you did, and then just run it, 350 before the after tuned version was in the 380rwhp range?

in otherwords, what did he have as mods, vs bone stock like the holbert engine was, to get 335rwhp. and yes, the holbert engine was stock. i had stock pistons, a cam like a GT, but I was able to replicate it with a stock 85 cam , so call it an S4 engine with stock 85 cams or GT cams at best. and, coincidentally , it made the same power as a GT with a set of headers and fuel regulator.

Colin, now you are contradicting yourself. ive been using all of the 3 dynos in my area for 15 years now. infact, one that devek used, was in sacramento, and it has changed owners several times. I still use it on occasion. more for convienence than to prove anyone wrong. no, these dont need to be calibrated. there are speed sensing pickups that tell speed. they are pulse driven. you either have a pulse or you dont. the software incorporates the basic elements of the dyno rollers. if you could get into the code and change that, sure, but no one Ive ever heard of has done that, have you??? for what purpose, so your dyno reads high??? anyway, you contradict yourself, because you say my stroker, a proven formula by others before me, (ie devek, anderson, fan and others) runs the same hp , probably less than they did. remmeber, same dyno . So, you have to ask yourself, if it was high before, (335rwhp going down to 320rwhp over 10 years of brutal racing), why wouldnt it be high now?

Now, if its a rolling dyno, andyou make some hp number you made it! if you go back and it changes, something ELSE has changed and Ive seen 100s of things that can make this happen usualy 2-3% changes, but they can be traced back to something technical. not the dyno. Now, if you are talking calibration of the SAE correction factors, then YES, that can be off by a lot. but as was mentioned, do you want dead sea elevation and the air density and temp of NOS out of a bottle??? sure that would skew results.

Jim Morton

MK: Baseline was with mods as assembled, 24# injections, stock fuel maps, "GT" ingition maps, fuel pressure slightly above stock... as I recall around 55-ish psi at WOT... no value changes via Sharktuner.

Mods to the fuel maps to level out AFR yielded the "350"-ish tests. Mods to fuel, ignition and "other values" produced the best power. Lessons learned are that there is more to tune than simply the LH maps. Key to success is to understand that cam change affect the basic breathing of the engine.

sportscarclassics

So much time spent arguing about practical vs theoretical numbers. Can't we all get along and pay someone to perform several tests on different dynos? Assuming similar ambient temps, humity or use SAE #'s. How about a dyno day at the next octoberfest?

Jim M.

I'm ready, lets do it!

Chuck Schreiber

Brian, you are correct, it's all with what you're happy with. Especially with a lightweight racer, I bet it's an absolute blast!!

I'm usually a fan of the #s, but not sure they tell the truth in real world driving. ???

I've driven several S4s and GTs as comparison.

Compared to my GTS w X-pipe, high flow cats, and an RMB.

NO comparison.

My GTS will SMOKE the tires with less than full throttle out of 1st gear and 2nd will get squirley on some roads. I would say it pulls pretty hard to redline as well!!

The S4's and Gt's I've driven, not even close.

Jim's and Roger's cars are SUBSTANTIALLY stronger than mine with their cams and Sharktuning.

Even Jarrod Wise (Velvet Hammer) from Tusla drove my car and said the torque is VERY apparent vs his well sorted GT.

So before everyone goes off the deep end saying that there is NOT that much difference between the 928 breeds, go drive one and decide.

The Assometer tells a much different story. My own oppinion.

I'm just sayin........

I think Doc Brown may have said it somewhere in a previous rennlist thread. (forgive me if I misquote him) He mentioned that it's not the absolute power that the motor makes, (dyno #s can be BS) but how usable that power is. (or something like that)

I've ridden in The Texas Stroker. I'm not sure if that car is the most powerfull 928 on the planet based on dyno #s (probably not). But the usable "everyday" power on that car is un Friggen real!!! So What if it has 50 less HP than someone elses, Joe can thrash that mother F###er all day long and have fun. The car launches like crazy, pulls like a freight train, and has an unreal top speed!! I'm sure there are some that may have more "top end" power", but can't hook up, will eventually granade, and barely idle in traffic.

I'm still convinced that (I think Dennis said it?) it's the DELTA we are looking at.
(Difference in now vs what the baseline was) rather than just a dyno in DFW vs one half way across the country.

Assometer/real world driveability of the car is the fun part!!

Iwanna928

GTS, cam's, exhaust, sharktuning, 5 spd

Sounds like pure heaven!

mark kibort

dont confuse driveability with how fast a car willl run in a race or on the track. the driveability has to do with a broad HP curve, that strokers and GTS's bring to the table. but dont discount the dyno runs, ESPECIALLY if it is a dynojet 248e. it will match reality, trust me. In all the years of racing, all the cars Ive race toe to toe with , the dynos, vs their weight and then driving style tell the entire story (with factors like tires, set up,and other things too) . You do this long enough and you get a real good feel of what it takes to go fast. this is why Dennis' car, with near the same HP has no chance. its a peaky hp curve vs a 6.4 liter stroker with a flat HP curve (i.e., or AKA known as more torque in the mid range)



dynos, especially a dynojet 248e is not theoretical. its real life, because it take into account rolling losses, and drive train losses.
However, ive already done this , as I have mentioned near same days, different dynos and and different types of dynos. results were not that different. remember, Ive been dynoing the same cars , with mods incrementing from 178rwhp all the way to 272hp in 20-50hp increments!
(lots of repitition, and a moderate amount of control with each session)


Key point for Colin to understand. the basline of 335 before your mods to the fuel maps, brought you up to 350rwhp, and then up another 30hp with timing mods? All this was not with stock S4 or GT cams, they were the modded cams, correct? I know the car had a 298rwhp dyno when I was looking at it, but dont know if any other mods had been done to it while dennis was driving it. (before your cam, engine work, tuning mods )

RKD in OKC

Oh man, now I am going to have to see if I can get my GTS on the dyno THIS WEEK.

Dennis K

I wanted high rpm torque. I hated the way stock S4 and GT torque curves fall off the table after 4000 rpm. If you look at the torque curve on my engine, Jim & Bill made my wishes come true. I also specifically chose to base the cams on S3 cores in order to have a wide LSA and late intake valve closing.

Anyway that's all old news. Screamer Motor v2.0 has been built & installed (thank you Jim & Bill AGAIN) and it incorporates all the old stuff plus:

• Morton Engineering Stage 2.5 intake manifold porting
• 928 R US intake manifold spacer
• Morton Engineering Stage 3 valve seat modification
• Porsche 968 intake valves (39 mm)
• Kao Racing Stage 2.5 cylinder head porting

All of this needs to be re-tuned. It'll take some time before we'll have any results as Jim has a bunch of fun projects in his hobby queue and I'm suffering under a ridiculous workload (I'm writing this from the office at 10pm on a Sunday).

Keep the debate & info flowing. I find these threads a whole lot more interesting than the "look at this POS 928 on ebay" or "will these 11x19 ET63 wheels fit on the front of my 928" threads.

mark kibort

high torque at high rpm= greater HP.
interesting that you were able to get the hp I got with the 6.4 liter, with only a greater lift cam, and some tuning!

Lizard928

I think the only way for you to see what I am talking about MK is to go to two of these different dynos in my area on the same day and get print outs from them showing their variances.
And if you think because they have sensors etc and dont need calibration, you are dead wrong.
Hell alignment machines need calibration, exhaust gas analyzers need calibration. I have a wheel alignment machine and without calibration it was OK, but after calibration the numbers were easier to obtain, and the person who came and did the calibration even noted that it had an error that caused it to read too much camber.

Also regarding your last statement that "high torque at high rpm= greater HP", this is simply not true.
I made my cams with the 114 LSA to raise the peak torque curve, and give good drive-ability, and work better for boost. But the fact of the matter is that with a lower LSA say around 110-108 deg is where a lot of race cars run because more overlap means a slightly greater peak power. The downside to this is that drive-ability suffers greatly, mainly in the lower RPM part load area. When you start adding boost a little overlap can help, but not nearly as much as in a NA setup.

So MK, maybe you would like to explain to everyone as to what you do to get 335rwhp from a stock S4 motor with GT or S3 cams? Headers? Dual 2.5" race exhaust? Single 3 or 3.5"? Seeing as how you dont seem to believe in sharktuning, how does turning up your base fuel pressure affect your top end AFR when the S4 map is notorious for being too rich to begin with?

mark kibort

Colin, ive gone to multipe dynos. Ive seen no substantia variance, actual wise on a similar day. (again, when im not tuning, i go twice a year. once on a summer day and one on a winter day, to see the calibration differences. The actual on the same day on two different 248e dyno jets will be identical. we are NOT talking about sensors that are calibrated, we are talking about halleffect or equiv sensors which never need calibration because they are binary. just like your calculator in the computer never needs to be calibrated to calcuate 4 + 4. its always 8.

Now, if you read my post, you would clearly see that I was not taking about O2, and other outputs and readings which certainly do need calibration. thats the SAE corrected stuff. Im talking ONLY about actual. you spin the rollers, in the US or Australia, if the acceleration rate is the same, the HP will be the same at any change of speed.

Please explain to me how "High toruqe at high rpm ", is not high HP. seriuosly, you cant discuss this stuff, and make a comeback like that. its just silly. If you have a point, make it. your LSA, cam description tells us nothing of your point. High torque at high rpm will certainly mean more hp. more torque anywhere is more hp at that point, but high torque at high rpm does result in more HP , even if it is before or after peak HP. this is undeniable, and I would like to hear what you are talking about for this statement and description to be "Wrong"

Now, you want to know how my car and one just like it, almost Identical, were able to make 320 to 335rwhp? (actual and SAE by the way)?? If it spun the rolllers at this power level, then it made this power. unless the software had the wrong drum weights and the clock output showed an Increase of pulse timing outputs to create faster rpm than the drums were going, then it would be physically impossible for this HP number to be wrong.

How I did it?? How Ron did it?? how Sean and Brian both got 300rwhp out of a stock S4. how Dennis' baseline was 298rwhp before he started messing with his stock S4??? think about it. the Holbet and Ron GT, were 320rwhp. the Sean and Dennis machines were near 300rwhp.

I had only GT equiv cams, and no cat. 290rwhp. when I pulled off the exhaust manifolds, put on equal length headers, opened up the air box, added a RRFR, and used a 3.5" single straight pipe with merge collector from devek, i got , first try, 335rwhp. fuel was cranked up to near 70psi, because stock, the fuel was ok at the start and went lean at the top. 13 to near 14 at redline.
after a fuel pressure change, it went from 12.6 all the way to 13 at redline and was runnning safe. no HP changes were found by this adjustment. we only cared about WOT, from 4500rpm to 6500rpm. Also, you might have remember all my flappy tests too. with and without.

the fuel regulator was added to beef up fuel in the mid range. Yes, the mixture was fairy rich up at the top rpm. (opposite what we found with the Ljet cars) in fact, 70psi is what I ended up with, and most have seen my dyno runs. by the way, i used a bone stock ezk brain from 928intl, that came on the holbert car when I got it. even using the 928intl used wirng harness.

So, colin, you find an s4 making 298 with the stock cams and headers. put on equal length headers, open the air box, put on a 3.5" open exhaust, and then a GT cam or 85 cam, you too will make all the power that my car made, that Rons car made and what Dennis' car made before his high end tuning. I dont count the 25lb lighter clutch assemby, because the dyno acceleration rates are slow enough, for that not to be a factor over a 7 second dyno run from 3000rpm to 6500rpm.

Mark

ps, as a side note. I bet if you showed me your "different dyno shops" accross your town and their methods of testing, i would find no less than 10 things that were different between the two operators. from strapping the car down, to fan orientation, engine warm up and ECU stabilization, to operation temps to how the driver applied the power, to time lapse between runs. these are relevant factors that I control, best I can on each and every dyno run. the operators look at me like Im from Mars, but they dont get the fact that some of these elements in the tests can give a 10hp diffference. they are easy to control and I always control all I can.

by the way, in comparing the holbert car to my previous 84 5 liter part euro, with 290rwhp (same as scots) the 60-100mph tests confirm the hp increases. 7 seconds, 60-100mph was the standard, and when i did this test with the holbert car before changes, it did this. and on the dyno was 290rwhp. no surprise there. with all the mods and the car being lightened, this number went to 5.7 seconds at 335rwhp. currently, the stroker at 372rwhp (all same dynos) is 4.7 seconds (60 to 100mph)


Here are some common dynos.
the 6.4 liter stroker
5 liter part euro 2 valve
and Holbert motor where we were holding flappy open and closed.

and of course Dennis' 380rwhp 5 liter screamer (380rwhp , because the 387 number was in the noise area)


compare Dennis' dyno with the 6.5 liter stroker. what would you rather have at the track. more torque up top, or the same torque up top, and more torque in the mid range (i.e. the stroker) ?

anonymousagain

...enjoying the debating, but in an effort to steer back to the OP...

Seems feasible that carbon build-up could be elevating the compression to detonate too soon, preventing appropriate timing. --> getting checked.

Seems feasible to expect that <300whp is "normal" for a stock GTS, just that the power delivery is more muscular than a <not too far behind whp> GT or S4.

Seems feasible to expect that the cam swap should yield more than 15-ish hp, especially with an experienced tuner.

Seems feasible that tuning for cams is a bit more involved than a typical ST session, as Jim points out, so maybe there's some addt'l dyno time required to find the sweet-spot ?? Any other thoughts for where the hp is hiding? Fortunately it's in Dave's skilled hands, but with such an unexpected output (even for him), a second set of eyes and experiences can only help suggest where to ID the culprit faster

mark kibort

stock air filter? air box stock? 314 just seems a little low, but for all the street stuff still attached, it certainly is not that far off. Plus, that is not a dynojet 248e inertial dyno with the big rollers. its another brand with tiny rolers, and certainly it could be a concervative number for the output. be interesting to run the car on the dynojet 248e if you had a chance.

anonymousagain

Mark, yes stock air filter and box. Upgrades are: X pipe, RMB, elgin grind cams, titanium lifters, r&r intake.