FlyingDog

I'm trying to decide which engine to drop into my new GTS Challenge 928. I have a few drop in (minor work needed) options: 84 EuroS, 83-84 US, 81 US, 79 US. Whichever engine it is, it will end up with electronic injection and ignition (probably LH 2.2/EZF to start). Also, it will hopefully be dry sumped before seeing the track, but that may come later.

For those that don't know, GTS Challenge is basically power to weight with no other restrictions (AWD and non-DOT slicks have mildly different pwr/wt charts). Power is HP unless torque is higher. If torque is higher, it's the average of HP and TQ in ftlb.

Anybody have some dyno charts from these engines so I can decide:
A) whether I want to run in GTS3, GTS4, or GTS5.
B) how I can take advantage of the pwr/wt rules with my engine choices.

IcemanG17

Matt
Since GTS is a pure power-weight class...it really doesn't matter...you will be classed with comparable cars no matter if your race 928 is 600whp or 200whp....

Pretty much the lowest dynoing 928 engine out there is a 4.5L & even those are around 200whp with slightly more torque....

Get a euro 4.7L and now your 260+ whp with 250 or so torque...more with the 5.0L and cams
Get an S3 or S4 and your easily into 260+ whp with 280-90 torque to as much HP as your wallet can afford

For example my track shark is a stock 89 S4 internal motor, with 928intl headers, custom 2.5" mandrel bent dual exhaust (no cats) and it puts down 304whp-291torque in a very rich state of tune... add some cams and your could be 387whp.....

FlyingDog

Brian, it absolutely matters. Not peak, but the area under the curve (hence the request for dyno charts). Tweaking the power to weight is how to win. I've gone through the rough math for each of these and they could all work based on peaks, but it's the area under the curve that matters.

My problem is that GTS3 is the best class to compete in... but my current euro (I don'tneed to get one I have one) motor needs to be detuned (or I need to add a pile of weight) to fit in. The way I want to build the car fits GTS4, but not well. I'd end up on the weak end of the performance range.

ShawnSmith

If it's a power/weight thing, I'd purposely aim toward the lower-power end of the 928 spectrum, since you're less likely to be traction limited there, and the unusually fat torque curve of the 928's v8 can pay more dividends.

IcemanG17

Matt
I see your point....since you are looking for the widest, flattest power curve you want a 32V.....they make most torque by a wide margin, which in turn offers the widest powerband.....This is how Kibort with "only" 372whp can keep up with 300lb lighter cars with over 400whp...since the S2000 makes 400whp at 8k...but maybe only 150 at 4k...... where the 400ftlbs of the 6.5L makes at least 300whp even at the same RPM....so his average powerband is 300-372whp.....and why he can run with "higher" hp cars

mark kibort

You want to run in GTS4, otherwise you are going to get your lunch handed to you . The reason, is that with the HP to weight classification, the heavier cars are at an extreme disadvantage. (Rememember, race performance has 2/3s more to do with handling and braking than just power performance)

The sweetspot is going to be around 10:1 hp to weight to have a car that will perform well. 260rwhp and 2600lbs would be a target.

I actually helped with the rules earlier when GTS was formed. We had a very competitive class out west called the porsche BMW challenge, and it later morphed into the PRC porsche racing club and BMW went their own way with following the BMWCCA.

GTS5 would be fine, and thats where I would fit now, but GTS3 would be a waste of time and be very difficult to compete in with a 928.

use the 84 euro engine and put a 5 liter under the top end ! remember, you have a pretty wide range to compete in for GTS4. 8.9 to 11:1 or so. (off the top of my head)

I was thinking of doing some races this season, but the turnout has been real low for the NASA events where they hold these races.
mk

FlyingDog

Shawn,that's what I'm thinking. As a bonus, replacement parts are cheap.

Brian, 32V is a waste of money for a GTS3 car. I will need to detune as much as my Euro. Plus, US 83-84 probably has the best area under the curve relative to peaks (peak TQ over peak HP usually ends up that way).

Mark, 260/2600 is impossible in a 928. This is race weight, not empty weight...

IcemanG17

Doesn't the faster cars fun in the higher #'s...meaning GTS1 is the slowest....GTS5 is the fastest?

mark kibort

If you are racing a car properly, its not going to matter that much. Sure, there is some advantage of a flat hp curve, but generally, if it is significant, it will be averaged out due to the generally higher peak torque . For example, if you look at the BMW e36, which would be your top competition as well as the much lower hp e30s, they have gearing and power bands that are not too different than the 928. What does matter is your weight class!

A little touch of reality here. Laguna seca, some of the e30 BMWs that weight 2500lbs and have a tad over 200hp, run near 1:43. (GTS3). good luck running this with a 3000lbs 240rwhp US 928. However, bump up the HP to 290ish, get the weight down to 2700lbd and suddenly you have a 1:40 car that can hang with most any GTS4 type car. Push the limits and you will be at the limit of that class. push the limit of GTS3 and I dont think you have very much with a 928 limited to around 2700lbs competitng against similar HP/weight cars that weight 500lbs less!
mk

mark kibort

IM talking in general terms. actually, you will get the same weight as any of us have got to, and thats 2700lbs as you come off the track. with driver, right around 2900lbs. (I built scots car, same as my old 84 and guess what, they wiegh exactly the same. nothing special) anway, the point is you can get in that 10:1 range pretty easily. heck, i hacked together a 243rwp on a 170,000mile low compression bottom end with only euro stuff up top, less the heads! Im sure a real euro can get around 275rwhp and with the 5 liter, near 300rwhp. what's nice about the euro and US S models is that the chassis and engine have about a 50lbs advantage. Heck, scot still can cut 40lbs out of his car, lightweight starter ,and 20lbs out of that cage (1.75x1.2" DOM).

Forget about the torque peak/hp peaks. you get what you get and its not that much of an advantage. Sure, its a little, but its the same for any class you run with, until you put in a stroker where you can get averaged up for higher peak torque, to fight an unusual flat HP curve.

if you were able to push the absolute limits in a GTS3 car, you might have a fighting chance, but remembrer, you would be fighting weight that none of the other cars would have.

mk

FlyingDog

Mark, I think you need a bit of reality... My competition is E36 and detuned E46 M3s, highly tweaked 993s, 964s, and 911s. The M3s win due to having fat power bands relative to the 911s. They're 240-250whp and run 245 wide (most R6s) to reduce drag. I'm setting up to run 285/30-18 R6s.

I currently run in a class where 5hp can be seen on the track, 5 ftlb can be seen in the race results. To win, you need to be in the penalty weight range for HP and TQ. BTW we run junk tires... Toyos. They're useless overpriced crap.

Again, your numbers are completely unrealistic. There isn't any 928 I know of under 2800lbs race weight and you're talking about 2600 and 2700 lbs. John V's car is 2780 wet empty. IIRC, Mark A's is in the high 2600 range. That's 2900-3000lbs with driver at race weight. My goal is 2900-2950, with a max of 3000.

mark kibort

How many years have I been doing this now? Those cars you mention are ALL Ive been competiting with for many of those years!

Name your car, ill provide you a dyno run of a well built top euro make competitor.

Reality. you should be able to get any 928 to 2900lbs as it comes off the track with driver. ( My cars have always been 2700lbs empty, and scot's "S" body could be 50lbs lighter without even trying.) Get in the 10:1 range and you will be very competitve in GTS4. In GTS3, you are going to race more racey e30s with 220rwhp and 2650 as they come off the track. 911s at near the same. You will have your work cut out for you . In GTS4, you need be near 290rwhp and that is not that hard to do, and you need to keep the weight in the same range. This is the sweet spot, and it is a sweet spot for the 928 and its weight. The weight and handling is the main issue.

I have a lot of data to support this. we have more dry races at laguna with more BMW and porsche laps than anywhere in the country. I can rattle off hp, weights and times till the cows come home. I ran in the BMW porsche challenge for a few years and have a good feel of our competitiveness with the 928. trust me, the little e30s are going to be a HUGE problem for you in GTS3. better to step up the hp and run with the e36s and e46s at a more comparable weight.

and by the way, the "junk" toyos is all ive used in the last 7 full seasons ive raced the Holbert car. my competitors, even Randy Pobst in a Grand Am GS BMW M3 e46, with 315rwhp on brand new hoosiers was only 1 second faster than my ill handling car at the time. (not tire related, wing related).

Do yourself a favor and run the 305s in the rear and 275s in the front as i dont think there is a tire size limit, is there?

Mk

mark kibort

dyno curves? this should keep you busy.

2 valve 928 vs 4 valve 928
m3e46 compared to S4
an 81 dyno
scots 5 liter euro vs his 4.7 part euro top end
e36 vs e30 BMW
Stock 84 porsche 911
part US 4.7 with euro intake

edit: as a note, you can see there is not a real difference in the shape of the torque curves where you race them. in fact, if you go to a 84 or earlier model, you actually get pentalized for the much higher torque, even though its not in the operational racing range. a 200rwhp 928 can have 250rwhp and that would average UP your competiting GTS numbers to 225 , kind of unfairly! but , those are the rules. The change I made with GTS , was to eliminate torque averaging for lower torque cars, which would unfairly reduce the GTS rated HP for the calulation for nothing more than the car can rev higher! think how unfair a cup car rating would be if that rule was still there, that I helped remove for basic common sense reasons.

IcemanG17

Matt
GTS class out here is pretty small..... Its either PCA-POC or SCCA.....everyone runs spec miata or spec E30...those are the big touring car based classes....

A properly running 928 can run with M3's short of highly modded E46-E92's....Mark competes with E36-46 in SCCA all the time....and beats them.....

Andersons race stroker is 2600lbs + driver....so 2800 tops..... Kiborts off track weight is probably in the 2950lb range (200lb driver)..... He can compete with and beat GT3 cups or GT3 RSR's....

My new race shark is at 2830lbs (about 40lbs of gas), with a bunch more stuff to take out...& thats with MONDO tires.....which brings up the next point....928's can fit HUGE tire pretty easily...I run 295's in front with near stock fenders and only a double rack stop.....335 rears, but with GTS style fenders....still pretty easy to do... Do the rules limit your tire sizes?

mark kibort

check out that dyno. " fat power band of the m3 "?? I have several m3s and a 911 for comparison. Now, where is that advantage that the M3 has over the porsche 911??
The only car that didnt accelerate predictably to its HP to weight ratio has been the S2000 with a blower. It has a much peakier hp curve and that kills the average HP. all other cars, you are splitting hairs if the driver knows what he is doing.

mk