geerookie

As far as I can tell all '99 and later motors had the improved rod bolts good for at least 450hp.
This came about as a result of the ASA engine program in which the motors were tuned for 430hp and 6800rpm operation for a full season without tear down.

And yes, from '01 on all C5's shared the "LS6" block casting# 125691168

ScaryFast

This is awesome information.

How much better are the 243 heads really? If I'm going to re-stuff the valvetrain on the LS1 head (what is it, 241?), is there a big issue? Do the 243's really flow that much better? As we all know, at 8.7:1 I'm not really looking for much power...

Can I get ~350 RWHP from an LS1 with a valvejob and a cam?

geerookie

some were 843 castings.

The 243 head flows much better and the SPM cast are worth another 7 - 10hp and torque in the mid-range - high rpm over the sand cast. I decided it was worth the investment. Mainly for the lighter valves and dependability with constant 6800rpm capability.
I only need 355 rwhp but the 243 head and proper cam will give you a wider power band.

Getting the power for ST2 from a 241 or 843 head shouldn't be a problem with the correct cam but it probably won't be as wide a power band and the lighter valves were the deciding factor for me because of the 6800 rev limit.

I forgot about the re-stuffing part...... I found the SPM cast '04 heads for $400 and it was cheaper than buying all the parts and labor to port my 843's. If you can get the labor for next to nothing and a good discount on the valves and springs it "may" be worth it. You probably won't give up much on the power side if you get a port job and cam designed for mid and high end power.

geerookie

843 and 241 heads have a larger combustion chamber 66.67cc vs. 64.45cc for the 243 heads which results in a lower compression ratio but this can be fudged with milling the head and/or a thinner head gasket. But you will sacrifice some efficiency by doing this unless you mill a pretty big chunk.

Also the intake and exhaust runner volume is bigger on the 243's 200/70 vs. 210/75.

Here's the numbers
For 853 & 241 Heads in the Corvette
Combustion Chamber Volume: 66.67cc
Compression Ratio: 10.1:1
Intake Port Volume: 200cc
Exhaust Port Volume: 70cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 66.67 cc------0.100--0.200---0.300---0.400---0.500---0.550--0.600
Intake 200 cc------------67----122-----178-----215-----219-----223---227
Exhaust 70 cc------------52-----97-----133-----156-----170-----76----180

And for the 243 in the Corvette
Combustion Chamber Volume: 64.45cc
Compression Ratio: 10.5:1
Intake Port Volume: 210cc
Exhaust Port Volume: 75cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 64.45 cc-------0.100---0.200--0.300--0.400---0.500---0.550---0.600
Intake 210 cc------------62------126----184----224-----251----256----257
Exhaust 75 cc------------57------108----143----163-----176----180----183

travisnd

1. I thought the 241 heads were "better" than the older castings? Your data implies they're the same?

2. Are you saying the 2004 243 castings are better than the 2001-2003 castings? I never heard there was any difference.

3. Refresh me on the valves. The exhaust valve is sodium filled and the intake valve has a hollow stem right ('02-'04 cars)?

4. The '02-'04 cam has a smaller base circle so the '02-'04 valves have longer stems to maintain correct lifter preload since they use the same length pushrods and same rocker arms from year to year. That accurate?

5. You may be right that 99+ have the better bolts. I heard the same thing about ASA racing failures. I had always heard it was 2001+ and the only real difference is that the bolt heads were sleeved in some manner.

geerookie

I got that flow data from GM so it may be skewed to make you think they are the same but I doubt it.

No not just '04 243 castings but the Semi-Permanent Mold (SPM) heads vs. the sand cast heads. GM has 3 plants they made heads at and one of them did sand cast and the other two SPM. This applies to any '01 - '04 243 head. You can tell the SPM heads by the chill marks left below the spark plug hole.

As I understand it all your info on valves, base circle and push rods is correct.
The valve stems are .6mm longer and the valves in the '02 - '04 heads are about 30% lighter than the valves in the 853, 241 and '01 243 heads.

travisnd

So the SPM heads are better? Any pics of the "chill marks" on the sand cast heads? This is the first I've heard of this. Curious what to look for.

sperkins

Hmmm. You sure?
I sure hope so, but it goes against what I've read in the past.

geerookie

Here you go....Google is your friend And it is the SPM heads with chill marks NOT the sand cast.

geerookie

I hate it when you doubt.....It means I'm probably wrong or at a minimum I need to double check!

You're right, they didn't go into production motors until MY01.

The issue was found and fixed in the ASA motors in '99.

Slight error but makes a big difference for those of us with production '99 motors

travisnd

Looks like I have SPM heads

ukrbmw

Something must be in the water - just picked this up today:

ScaryFast

Rod bolts...can't I just buy some from ARP and not care? I may put new pistons and rods in, anyway.

I'm looking at a 1999 and a 2001 LS1 longblock. Is the 2001 really "better" enough to be worth the extra dough?

travisnd

AFAIK yes you can put in ARPs or Katech rod bolts and be done with it.

geerookie

RE: rod bolts..I agree with Travis get some ARP's and be done with it.
If you get the '01 block and the bottom end is clean then don't mess with it.

As far as if the differences between a '99 and an '01 block is "worth it"?

Depends on what you want to do and how much power you need and how much of a premium you have to pay.
Scott and I have been beating the crap out of our '99's for many years and have far more hours than I can count and they are still going.

Kubs

With Jon's luck he is going to get the one out of the thousands produced that will pop its first time out....

ScaryFast

Ha, that's the point of going to the LS, don't jinx it!

I know you're kidding around, but all of my LTx problems can be traced to one thing: ignition. Never had a single issue with the motor except last august, which was 100% my fault.

Whichever LS I buy I'll be doing rings and bearings. No sense not to while the motor is out of the car. Geerookie I saw in your earlier post you were using an LS2 timing chain, what's the reason for that?

travisnd

It's cheap but way beefier than the stock LS1 chain. It supersedes the old LS1/6 chain and us the only one you can get.

ScaryFast

What about casting 12562174? Looks like a 1998. Which means no windows and old style oil passages? Seems like I'd want better oil flow for a RR car. Any insight on this? I was about to go buy the block until I found this out...

geerookie

Late '98 early '99. If you have choices I would look for a newer block.

Another option is to get a 327 aluminum motor out of a truck and bore to 346. This is a very popular option for guys who build race motors because the block is much cheaper and they are doing the machine work anyway. Other than bore the block is the exact same.