Rx7TyreBurna

iTrader: (1)

I have a LM4, long tube headers with dual 3" exhaust + x-pipe, LS6 intake, 52# injectors.
My goal is a moderate NA engine.

I'm thinking about PRC 2.5 heads. I am undecided on 5.3L heads, or the LS6 heads by PRC. I've looked at multiple threads around a similar subject and still don't fully understand what the better choice for my setup is. Does the bore size difference on the heads make a large difference in sealing?

I'm shooting for 11:1 or 11.5:1 compression ratio static, 8:1 dynamic.

I currently have the TSP 228R 112 LSA cam, but lost the cam card for it a while back. Anyone know the advertised duration and ICL? Trying to get DCR calculated, and I only have the @.050 lift numbers.

For the heads, I was thinking 59cc chamber.
Pistons, I was considering the Summit Pro LS pistons with valve reliefs cut +2cc dome.
Aftermarket 6.125 rods w/ floating pin.

I'm trying to figure out, how do I determine if the valves will hit? Summit has the catalog showing that +2cc dome would push compression to 10.9:1 with a 61cc chamber. With the valve reliefs cut, is P2V not as much of a concern?

Lots of numbers and things I'm trying to sort out. I plan on 92 octane, but trying to build the engine closer to the 91 octane rating. The car is a fun summer car, not daily driven. Long tube headers, and full flowing exhaust.

Any input is greatly appreciated!

theunderlord

Give Texas Speed a call, I'm sure they can help you on that cam card. You have E85 in your area?

Rx7TyreBurna

iTrader: (1)

They're on my list of people to call. Haha.

I'd prefer not to run E85. 91 ish octane will be what I'm shooting for. We have 92 mostly, but some 93 here and there.

theunderlord

No worries, I don't have it out here either, but I know many guys absolutely love it. It's usually cheaper too!

just some food for thought;

Regarding a "moderate NA engine". (depending on your definition of moderate) You really don't need to mess with internals at all. I get the higher compression idea, but opening it all up just to toss in some pistons, eh, I'd put the heads/cam (intake if you wanna spend some more money on the FAST) and then see how she rolls.

Engine disassembly just throws in a ton more variables and **** you gotta buy to put it all back together.

Rx7TyreBurna

iTrader: (1)

It's completely apart as is due to the bearings getting toasted.
I had dished pistons before (-8cc) with the milled 862 heads, and it felt okay. But, i wanted to get the dished pistons out of there. And, figured I'd throw the heads on while I'm at it, because the PRC 2.5 flows significantly better than stock.
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My biggest concern was the 2cc dome on the summit piston. I'm guessing they did 2cc dome to compensate for the 2cc valve reliefs. I don't think there would be issues, but mostly wanted to get other views and opinions.

I appreciate the input! I've considered just throwing it together. But, also don't want to take it apart again for a while.

Moderate engine for me would be 400-450 RWHP. But, peak power isn't my main concern. I want a nice torque curve and okay peak.

theunderlord

Ahh, well, in that case man, let's go all out torque monster! Full stroker, Texas Speed has you covered in that department too.

I'm assuming you dinked around with the summit compression ratio calculator? The head gasket gives you a little margin too, but without knowing the full cam specs its all kinda moot.

Rx7TyreBurna

iTrader: (1)

HAHAH, I mean, I wouldn't be opposed to it. But, it could cause domestic issues. HAHA

I used summit compression calc, and attempted cam timing calculator to get some cam specs, but, need better cam specs. Using .050" lift numbers gives me insane DCR. 10.17:1. But, DCR calculator wants advertised duration (that's the larger number, right?).

Overall, kind of stuck on TSP website not showing all specs and not being able to find them anywhere. Once I get that, I should be able to calc more.

Also unsure of LS6 heads milled, vs 5.3L heads. If I find a 6.0 block later, wouldn't the LS6 heads be better? Does the bigger bore from the LS6 effect the head circle? How's that play into 5.3L bore, etc.

LS6 vs 5.3L isn't a huge deal. I think I saw 3 cfm better flow on the LS6... So, maybe not even worth going after.

theunderlord

Yeah, I think the cam game has gotten a little more secretive, can't really blame people for that, but they should still be able to help you out.

I'd try to get everything optimized for your current build, and should you decide to up the displacement with a 6.0, then you can sell off the 5.3 parts, or the engine as a whole to pay for 6 liter stuff.

Darth_V8r

iTrader: (4)

Most ramp rates are 49-54 degrees you could just add 52 degrees to your 050 duration and you are with a degree