moespeeds

Hey guys. Last year I built an LS6 for my C5 roadracing car off a Thompson Short Block. This winter I'm looking to completely rebuild from the bottom up for my new to me GTA Stock Car. I have an LS1 block sitting here that I will use for the build. I have a couple of noob questions since I've never done a bottom end.

-The GTA class rules are very specific about what I can put in the engine. So my options are a GM crank, or an Eagle Forged crank. Is the forged crank worth the extra coin? This is a road-racing car, it sees high RPMs and lots of heat for 30 min at a time. HP should be around 420-450.

-When I buy a rotating assembly, what machine work should I have done to the block? I see Texas Speed sells balanced assemblies. Is this what I want? If I buy the crank and bearings separately, would it then have to goto the machine shop for some type of work to match the crank to the bearings?

-valves and springs are open, so any suggestions there? Rev limiter must be 6800 RPM and I must use unmodified 243 heads, and an LS6 manifold/TB/MAF.

Reliable horsepower is paramount, and not much can be done since I must use the GM ASA cam, and a PCM that is sealed and tested by the SCCA.

Thanks in advance guys, you all were very helpful my last go around.

svede1212

iTrader: (3)

The stock crank is a good one and I see no need to "upgrade". I would take the block and parts to a machine shop and have all the journals checked for roundness and clearances as well as getting balanced and line honed. If you're going to do cam bearings having them do it makes life a lot easier.

VandykeT/A

The stock crank would be fine as far as power limit. I don't know if forged offers anything as far as a maintained high rpm. I would talk to a sponsor about what the ideal clearances would be for sustained high rpm use ( my 408 is set up at .0025 on the rods and mains). Otherwise for the power you plan to make you could probably get away with stock everything and just replace the rod bolts and have the mains and rods set to whats ideal. That would save a ton of money anyway. Another thing is if you do have a machine shop do the cam bearings make sure you can actually get the cam in and it spin free before putting the bottom end together. The machine shop screwed mine up and I had to order the tool and bearings and do it myself along with taking the rotating assembly back out.

JAH

I was only able to find the GTA class rules proposal.

It looks like you are planning on racing engine Appendix D combination.

In the proposal rules: there is not a connecting rod length or weight, or a piston weight. Ultra light weight rods and pistons, and a long rod might be needed. I have been looking for some light weight pistons, without any luck, to get light weight pistons they would need to be custom. As good as the factory cast crankshaft is, I wouldn't want to risk high dollar rods and pistons connected to a cast crankshaft.

Another point is crankshaft weight, the factory vs the eagle forged crankshaft.

moespeeds

JAH thank you, crank weight is something to consider for sure. Check appendix C and they specify pistons and rods. The complete rule set is below. Also, I'm allowed to use an LS2 manifold/TB. They seem to be easier to find than the LS6 manifold. Is there a performance difference?

Appendix C: “ASA Tour” LS-1 engine.
1. Must meet all requirements listed in Appendix A.
2. This is the LS-1 Corvette engine as used by the 2005 ASA series. This includes but
is not limited to the following:
a. ASA-spec filter box
b. ASA-spec air meter ducting (bellows)
c. Stock Mass Air Flow (MAF) sensor
d. Unmodified LS-1 intake manifold, part number 12560894
e. Unmodified LS-1 cylinder heads, part numbers 241 or 853
f. Camshaft part number 12480110 (“LS” V8 ASA cam) with 1.7:1 rockers
1. max lift measured at the intake and exhaust valves is .525”
2. duration at .050” lift: intake = 226, exhaust = 236
3. lobe separation is 110
g. Maximum compression ratio is 10.1:1
3. The 75mm throttle body must remain in place.
4. The stock stroke must be maintained. Cylinders may be honed as part of the normal
freshening procedure, but the engine displacement can be a maximum of 350 cubic
inches.
5. Crankshaft may be replaced with Eagle # 434636226100.
6. Rods may be replaced with Eagle # 612503D2000, Callies Compstar # 6125LS1, or
Engine Pro # 10-1108-8.
7. Pistons may be replaced with Mahle # LS1314-898-F04, LS1314-905-F04, or
LS1314-908-F04 (depending on the overbore needed).
5. Maximum engine RPM as controlled by the ECU is 6500 rpm.
6. All ECU’s must have either the ASA Tour or Schwanke-certified logos intact.
7. Cars using this engine may reduce their minimum weight by fifty (50) pounds.

Appendix D: “Upgraded” LS-1 engine.
ASA Tour LS-1 based engines (Appendix C) may be modified only as follows:
1. Must meet all requirements listed in Appendix A.
2. The base LS-1 heads may be replaced with unmodified cylinder heads, part numbers
243 or 799.
3. An ECU re-flash to raise the maximum RPM limit to 6800 is allowed.
3. Optional upgraded intake systems:
 Option 1: Any 90mm throttle body may be installed. One example is GM part
#12589181. A stock, unmodified LS-2 intake manifold to fit the larger throttle
body must be installed.
 Option 2: An LS-6 intake manifold (part # 12573572 or 88894339) may be
installed, but the stock 75mm throttle body must remain in place.
 Option 3: The fuel injection system may be completely replaced with a Holley
650 carburetor as specified in Appendix B, item 16. This conversion also requires
GM intake manifold part #88958675 and an MSD 6010 timing module.
4. The ASA-spec filter box and air meter ducting (bellows) may be replaced by
aftermarket parts, but the stock Mass Air Flow (MAF) sensor must remain in place.
5. New valve springs, Isky #165A or GM part #12586484, should be installed to handle
the higher RPM limit.
6. New ARP rod bolts, part #134-6006, should be installed to handle to higher RPM
limit.

JAH

Thanks for the additional details.

I can't help you with the fuel injection manifold question.

It sounds like a fun class.

DREAMZ28

iTrader: (1)

I remember reading that the LS2 intake is a step down from the LS6, can't remember where it stands vs the LS1. But don't quote me on that.

I'm trying to figure out whether that carb intake would offer more power for you, someone more knowledgeable on those should chime in.

moespeeds

Thanks guys. I don't want to go to a carb anyway, even if I can get more power, just not worth the fiddling when the race car already demands every minute of my free time as it is.

moespeeds

One more thing, I'm kicking around the idea of using 799 heads. I'll probably replace the valves. Can you guys recommend a valve for me? Again, high rpms for extended periods of time, and heat is always an issue.

A.R. Shale Targa

iTrader: (2)

Z06 heads would be my choice as the 243 castings have the lighter/hollow stem valves. A quality valve job can be worth a few cfms of flow as well.
Lastly, check with Kip Fabre about getting a legal lift and duration camshaft that has smoother/stable lobes for more power @ sustained rpms.
The stock crank should be fine when balanced for some aftermarket rods and pistons. Just be certain to run a quality balancer.

moespeeds

I'm keeping my eye out for 243 heads as they are my first choice for sure, but the few I saw on eBay did not have the stock valves. No cam mods or substitutions are allowed, it must be the "asa" cam.

KCS

iTrader: (20)

If the Appendix C engine allows you to remove 50lbs, I'd be tempted to go that route rather than the Appendix D engine. If you go with the Appendix D, go all or nothing.