Well as it says, Im rebuilding an LT1(out of a Roadmaster with cast iron heads). Now I have the LT4 HC kit and Ive read mix answers, when the springs, locks, retainers and cam is being changed, do the lifters need to be changed also(assuming they are all in working order) or does it not matter unless it is with a much more wild cam?

On to the cylinder heads, since the heads are off while I'm swapping the HC kit pieces on, will a port job make much of a difference with the LT4 HC. IE will more cylinder head flow always be an upgrade, up to a certain limit, even with a factory option cam or again does it not matter unless it is a bigger cam that needs more flow?


And the last one. The cast iron headed LT1s IIRC have a 10:1 CR (unlike the F-body counterpart of 10.5:1) will .030 over raise the CR past its limit? I tried using a calculator to get the exact numbers but every time I found the Piston in the Hole numbers on another forum it was always different from the post I read before.(I just bought a few more informative books on LT1s so if I find the answer before a reply I will edit the post)

Thanks for any help

 

1. You can use your existing lifters.

2. Porting is always good; however, be real careful what you do. "Hogging em out" like Cletus and Billy Bob do to their sand rail will probably make it go slower.

3. You don't get reliable deck clearance numbers in posts on forums. You find them in motors using a straight-edge and a feeler gauge. The reason they're all different, is because they're all different. You need to know what YOURS are, not what somebody else hallucinates that THEIRS is.

 

Excellent, Ill go check it out.
Thank you

 

*Deep in the ozark mountains, in a shed with a dirt floor....... a grinder roars*

WOOOOOoooooooooo, HOG EM OUT BILLY!!!!! MORE!!!!!! MORE!!!!!

 

.030" over will raise your static CR by about 0.1. Not significant. Your pistons, head gasket, and deck height will have more of an effect. So would polishing the chambers.

 

thanks five7, just saved me a trip out in the cold. It just started snowing

 

I only addressed the .030"-over part as insignificant. You still need to know deck height.

 

I've already checked it, im leaving the deck height the way it is and using the stock gasket .029 gasket. Thanks

 

Keep those iron LT1 heads - they are better than the aluminum F/Y-car heads.

 

yeah, ive heard they flow 20% more, I have a graph of all the flow numbers for LT1/LT4s but I may swap to ported Al heads next year. Im just using the iron heads to finish off my project this year until I'm ready to commit to a power adder that fits my application.

 

Ive done all my homework/math and just want to make sure Im not missing anything. (btw this will be bored .030)

Stock
Compression Distance - 1.570
Deck Height - 0.15
Crushed Gasket Thickness - 0.28
Combustion Chamber - 64cc
CR - 10:1

Parts Added
KB Pistons - UEM-KB120030-8 (for reference)
Compression Distance - 1.561
Deck Height - 0.24
Same Head Gasket - 0.28

If the Deck Height is brought down to .012
CR - 10.11
Quench - .040

(I dont think the .11 will push the iron heads past there limit but just for my notes incase I hear otherwise before the next clear day)

If the Deck Height was just brought down to .013
CR - 10.08
Quench - .041

Any suggestions or does this look good? Thanks again

 

With the LT4 Hotcam in a reverse cooled LT1 engine, I'd be shooting for AT LEAST 10.5:1 CR with iron heads. Shoot for 11.0:1 if you'll be running premium fuel. That cam has slow ramps, so the IVC point is later almost any other 218 dur @ .050 cams you'll find. It's a roadracing grind with lots of overlap; more than the .050 numbers indicate.

 

I definitely want to get the CR to around 10.8:1 (like the LT4s had). so if the cast iron LT1 heads can hit 11:1 with premium fuel, do you mean 93 or 94 octance or more like sunoco's 102 octane? I want to stay on pump but would love to get the CR closer to 11:1. I appreciate this info, a few weeks ago I was looking through every post I could find to try and find someone that had a higher CR with these heads but had no luck.

 

http://www.h-body.org/people/project...t1%20info.html

http://www.chevyhiperformance.com/te.../photo_15.html

http://www.customclassictrucks.com/t...fications.html

 

those are good reads but the first one had a bit of mis-information, it said all 350 LT1s came as 10.5:1 CR but the iron heads were 10:1 and didnt say much about how far the iron ones can go. The second one was an LT1 383 build with AL heads and the 3rd mentions the LT1s in caprices and that the AL heads can be brought up to 11.5:1(unless I missed something, Ill read them again at work) but unfortunately I got the iron heads because the motor came with them and they were cheap. I know about reverse flow cooling but Im not sure how much CR can be pushed on the iron heads before they get heat soaked and cause detonation even with reverse flow cooling. Again I may have missed it in there and ill read it again at work, thanks for the links though

 

With the Hotcam, the iron headed LT1 will not only tolerate 11.0 CR, it will like it. The baby stock cam in those motors closed the intake much earlier, trapping more cylinder pressure. With the later closing on the Hotcam, it will want more CR and more spark advance.
Are you rebuilding the shortblock? If so, I'd deck it to get the pistons anywhere from .010" in the hole to zero. Then you pick the gasket, Felpro .026, GM .029, GM .038,...... to give .035 to .040 quench. If you're not decking the block, you'll have a hard time getting to 11.0 CR with just milling the heads and using the .026 gasket.
A tip on the LT4 Hotcam: advance it 2 extra degrees so the ICL installs at 107 versus the standard 109 for that cam. That will eliminate a lot of its sluggishness below 3500 rpm.

Edit: by "premium", I meant 93 octane.

 

Yeah Im rebuilding the short block with new pistons, rings and complete gasket set. Ill definitely be decking the block to get the optimum quench. Thanks for the all the info, especially on the CR and timing that really could have saved me from a motor I didnt like.



-Russ