Help me unlock the parts combination to a great LS2!

I'm in the final planning stages for a new project.
Think Ultima GTR and you're close enough.

Sub-2000 lb curb weight, Carbon fiber skin over steel unibody
5 speed G50 Porsche transaxle:
3.500 1st, 2.059 2nd, 1.409 3rd, 1.125 4th, 0.892 5th (falls 1300-2000 rpm ea)
3.444 Ring & Pinion (Geared to 160mph in 5th at 6500rpm with 25.44" 315/30-18 tires)
No emissions concerns
No accessories to drive (no A/C, no P/S, no air pump, just alternator)
Cooling requirements ARE a concern, cool running = good
Room for shorty headers or stock Vette manifolds

Needs to be Cost Effective of course
It must be streetable, but IS NOT an everyday car (only summer & sunny)
Will see the dragstrip and the racetrack only a few times a year
Looking for a combo that peaks at 6000-6500 rpm but can briefly take 7000 rpms
Would like to see min 500rwhp @ 6200rpm for that magic '4 lbs per horsepower'

Project doesn't have to be done until Sept/Oct 2005

I'm used to 3200 pound LS1's, so something that light may not 'need' the same motor,
so I'm asking the community for ideas and advice.

Here's what I was thinking:

Stock LS2 block 4.00" bore
Eagle 4.00" forged crank
Howards or Eagle rods w/ ARP
Mahle forged pistons around 11.0:1
ARP block/head/rod hardware
AFR 225 heads
Z06/LS6 lightweight valves
Titanium retainers
Beehive valvesprings
Stock rocker arms
Hydraulic roller cam around 240*
LS2 intake
TPIS 90mm TB
SVO 30lb injectors
LS1 computer / LS1EDIT tune

With SLP and APE getting 580-590hp from similar iron 6.0L's,
And Rapid doing 553 to the rear wheels with a similar LS2 set-up,
I thought the goals were realistic

Detailed responses are VERY appreciated, as I am clearly no expert
I will be buying these parts or partial/complete motor from our sponsors
It would be great to buy a complete 'turn-key' set up if $$ makes sense

Should I forget the stroke since I don't 'need' the torque?
The $1000 LS2 block is more attractive than sleeved LS1/LS2 at $3000+
I'd love a LS7 block and/or crank but can't wait that long (Nov/Dec?)
Could I get by with different heads?

What would you do if it were your money??

Thanks,

E

 

I find myself in a similar position... I am REALLY looking into getting a factory 5 GTM here within the next year or two, and would like to start collecting parts now, as it will make the cash outlay at build time seem a lot less expensive.

First of all, something to consider is that I recently read that the Porsche G50 transaxle has an input torque limit of something like 650 ft/lb (read: somewhere in the neighborhood of 550 RWTQ, assuming 15% driveline loss). The torque from the 4" stroke would be nice to have in the name of off idle/low speed drivability, but with the short gearing (12.054:1 effective 1st gear ratio... would be similar to a T56 (2.66 first) car with 4.56 rear gears) and the close ratio transmission, I really don't think it's necessary; especially in something that light. It should be noted that I haven't been able to confirm the 650 ft/lb limit on the transaxle, and I don't know what vehicle weight was assumed when that rating (if it's accurate) was assigned; logically, if the transaxle were rated to 650 ft/lb in a 3000 pound car, it would make sense that it could take more in a lighter car since it doesn't have as much mass "pushing back" against it as the vehicle tries to accelerate.

If it was me, I think that I'd be tempted to save my money from the crank and put it towards a sleeved block and go with a stock crank (all bore 382). The cost of the crank wouldn't make up the difference in price between a stock LS2 block and a sleeved unit, but it'd make up a big chunk of it. Anyhoo, to really take advantage of that setup, you may want to run a larger cam, maybe even think about going solid roller. Kind of a pain in the ***, but for the same basic specs (read: at .050 duration), the solid roller will make 15-20 more HP because they can get REALLY aggressive with the lobes at that point. You'd still have enough stroke to allow for (at least) 450 RWTQ, but you'd really open up the big end.

Whichever way you go, I have some parts that you may be interested in (a 4" steel crank if you decide to go stroker, some Jesel MoHawk rockers if you decide to go solid roller)... PM me if interested.

 

I am building a very similar engine now. Engine is being built for Z06 that I use at track days(20 minutes of hard driving per session. Eagle crank and rods with Mahle pistons. Comp with 64 cc aprox 10.8. Patriot heads just because of the money. Engine will be at 3500 to 6000 most of the time. The cam is what I can't decide on. I want about 250 dur and .620 lift but am torn between hydralic and solid. Crane says they have a "street roller" that doesn't need super high spring pressures but I don"t know if that is good advice. I am going to try the ls2 intake cause I have used the Fast and was unhappy with workmanship compared to OEM. With such a light car you will have incredible performance with whatever combo you come up with.

 

Chuck- the other day I spent some time speaking with someone who has been playing with the LS2 intake, and he greatly prefers the LS6 intake, even with the smaller TB. Just thought I'd pass the info along.

 

Why would you want to use ls6 valves on afr 225's? They're designed for 2.1 valves I think, and you'd be killing the flow.

 

Fast intake and TB.
For the price the AFR's are awsome.
The stroke isn't that important especially if your running something other than a full slick as hooking is gonna be a issue.

 

BurnOut:

The 901 transmissions were rated at 148 ft/lb input
The 915 transmissions were rated at 181 ft/lb input
The G50 transmissions were rated at 221 ft/lb input
The 930 transmissions were rated at 326 ft/lb input

There were some special versions, like the G50/50 from the '89 930 that were stronger, but nothing that can handle 400+ ft/lb without mods (billet diff side covers to minimize deflection, cryo or hardened gearsets, external fluid pumps and coolers with 'spray bars', etc.)

I've often wondered about just inverting a C5 Corvette T56 and using the 'dry-sump' external set up (like you'd have to do for a G50 anyway).
Anyone do this?

Also, I've heard the same about the LS6 intake, but can't imagine that a 400+ cu in LS wouldn't appreciate the extra flow and 90mm TB??

PMack:

I meant hollow stem intake / sodium filled exhaust...not the exact LS6 pieces.
Do you think the AFR's are the way to go, with 'as-spec'd' valves?

E

 

Have you seen this?

https://ls1tech.com/forums/dynamometer-results-comparisons/277037-rapid-dominator-402-ci-ls2-553rwhp.html

Give me a call with any questions.

 

YES! Of course I saw the thread....GREAT JOB! I did note you guys in my original post if you look close

Mikey, what would you change or suggest for my lighter needs..... to lessen the torque?

Again, great results

E

 

Stock stroke LS2. Callies Crank, Callies rods, CP or Diamond pistons...etc. They'll do it

 

Why not stock crank / rods? Wouldn't they last at 500 hp if you used ARP hardware and machined them properly?

What kind of numbers would that make? Would you need the extra flow/runner of the AFR heads with the smaller displacement?

Thanks,

E

 

If your goal is 500+rwhp, do yourself a favor and spend a few more $$ up front to get an engine that will last forever with a good rotating assembly. Given your application you are going to be spinning it regularly past 5k rpms. Will stock work? You bet, for a little while. Road racing is MUCH harder on parts than drag racing is. Down shifting will stress the rods past any kind of HP a drag car will throw at them. We see it every day on SCCA T1 and T2 LS6's with broken rods. Trust me on this one.

 

Mike: Thanks for the advice. Easy to believe the rods, I trust you there.

I'm all for spending money where it counts. All too often people have opinions founded in marketing hype about what is necessary versus what would be cool. I'd rather hear it from guys who have actually tried it and have experiences (including failures) to share.

Stupid people pay for things twice, as the saying goes.

If I'm going to upgrade to stronger crank / rods / pistons anyway, don't you think I should just buy a 4" combo?

Is there a big enough difference between Callies and Eagle to justify the $2000+/- for my use?

Anyone have experience with the Mahle LSx piston set?

E

 

The difference in a stock stroke Callies crank vs a 4" is very small but I thought you were trying to limit the torque. I personally think you would have a real blast with the LS2 combo I just built. It's a well designed, very well built plant that will last a long time.

As far as Eagle cranks, I'm not a huge fan of them. I've never seen or had a failure but then again I don't use all that many of them. I just tend to over-build my engines.

I've not used Mahle pistons but my impression of them is that they are a little on the heavy side. Good stuff for N2o or FI.

 

kaisen- what do you mean, "invert" a C5 T56?? I have thought about using a C5 trans/rear, but it's just so much longer than the Porsche transaxles, so I would think that making it work in an application desgined for the Porsche piece would just be too much work (read: stretching the frame/body).

As for the torque ratings on the transaxles, are you sure?? Those Porsche turbo motors can crank out some torque, and if those ratings are accurate none of those gearboxes would stand a chance. Also, I don't recall reading anything (take that for what it's worth, though) about the Ultima using highly modified transaxles (or the Factory Five GTM, for that matter).

 

Quaife has a variety of transaxles, and gearsets for the G50. Their G50 gear set is 1st
2.692 2.000 1.526 1.182 0.920, which sounds much better.

However, where do you get a G50 and how much are they? Quaife sells a new 6-speed sequential transaxle with LSD and 700hp capacity...for $20k.

What does this box cost?

 

On the motor side, I would think a 4.2" bore x 3.000-3.335 stroke with an Ultralight crank and crower maxilte rods. 1.78" rod journals and the smallest crank journal you can get. Jesel rockers. Morel or Schubeck lifters. AFR 225 heads with Ti valves and 1.550 x 1.9 springs. Twin/Triple carbon disc clutch (Tilton or Exedy).

This puppy will rev to 8000+, probably put down over 500hp to the rear wheels. I guess it would need an aftermarket ECU, however it won't break the transaxle. Less than 400 lbf-ft torque peak.

 

And while we are getting exotic (we are using a $20k gearbox after all), we can use the "HARROP HURRICANE" LS1 8 Butterfly Inlet Manifold and the Kostecki three stage internal dry sump.

Umm...is belt cam drive available?

David

 

And if the ECU is a Motec or EFI (we are probably talking close to $10k hear with CDI and sensors) we would also have traction control, launch control, and if using the correct Quaife gearbox, clutchless sequential shifting (up and down).

Unfortunately, we may also have a $100+k car...$20k gearbox, $30k motor, $10k electronics, $20k chassis/body, $20k for exterior/interior finishing, $10k misc.

 

Oh, while we are here, the Motec can drive low impedance injectors in peak and hold mode for more accurate fuel timing. The value is debatable.