Hi,

This winter I am doing a heads/cam swap on my LT1 T/A and I have some questions reguarding using larger valves and milling the heads. I bought a set of used heads that I will be having a friends machine shop do all the work on. I have been talking with that guy about putting 2.055/1.60 valves in the heads but he wanted me to talk to someone that had done this with LT1 heads allready. We are also planning on milling the heads to get the compression to around 11.0 to 1, or somewhere close. The cam that I am tentatively going with right now is the Comp cams Extreme 236/242 on a 112. I also plan on using the .039 thick gasket. So here are my questions.

1. How much do we need to mill off of the heads to reach our desired compression ratio of 11.0 to 1??
2. Will the LT1 heads work well with the 2.055/1.60 valve while being fully ported, or should I stay with 2.00/1.57
3. What is the biggest valve that will fit in the stock type seat??
4. Will I have clearance problems with the larger valves, milled heads, .039 gasket, and the cam I have chosen??
5. What will the lift be of that cam with the 1.6 roller rockers??
6. Do the stock pistons have valve reliefs and what size valves will fit with them??

I am sorry for all the questions but I am trying to get this all done with one post. I would really appreciate if I hear back from you guys.

Brian Black

 

1) assuming a stock deck height of .02, you'd need a 3.2 cc reduction in chamber volume. 1cc = .006 on a 23º head, which accounts for a .019-.020 cut.
Really need to know the deck height volume though... are you having the block decked?
I also assumed stock pistons, is that correct??

2 & 3) stick to 2.0/1.57 if you want to keep the stock seats. Shouldn't pose as a problem for a stock rebuild.

4) Don't know, but you shouldn't have a problem either way (more on this in question 6)

5) lobe lift x 1.6 or
advertised lift/1.5 = a
a x 1.6 = lift with 1.6 rocker

6) You have to check. Mock up the engine and check the clearances.

Take care,
Chuck

 

Chuck,

I am not having the block decked as I am keeping the shortblock in the car. I am also using the stock pistons. So you dont recomend going with the 2.055/1.60 valves?? ABout the clearances, I know you have to mock the engine up to check the clearances, but what happens if I dont have the right amount of clearance?? I have heard the pistons can be cut in the car but I dont know how well this would work. What would be a safe amount of max lift that I could go with?? I would kinda like that Exteme 236/242 cam with a little bit more lift, say .575/.600. Is this possible?? So the stock deck height is .020?? Well thanks for the help so far.

Brian

 

Try using Comp lobe 3196 for the intake to get .585 with 1.5 rockers.
For the exhaust, you could use 3115 (244@.050) with 1.5 or 3370 (246@.050) or 3318 (248@.050) with 1.6 rockers to get ~.600 lift.
You're gonna need some bad *** springs and probably a rev kit to avoid valve float though.

 

Valves that big are overkill on a stock bottom car, and will probably hurt more than help.

 

So the 2.055/1.60 valves are too big for the stock bottom end huh?? I kinda thought they would be, but it seems like everyone is telling me different things and I dont know what to believe anymore. Could I get some more opinions on the valve situation??

AdioSS,

What lobes would you go with if I was using 1.6 rockers, as this is probably what I will go with.

Would anyone else recomend going with different lobes or should I just stick with the ones that come on the 236/242 Extreme?? Thanks again

Brian

 

If you want my opinion... a pro can get over 330cfm through a 2.02 valve... you're talking bout a head that'll peak at no more than 50cfm lower than that generally. IMO, no sense in increasing valvetrain mass & having to remove more material to unshroud. The venturi is your last chance to pick up any velocity... why make it big enough to put your fist in

 

TTT for a buddy.