How can I best achieve 11:1 compression and have enough PTV clearance to run a BTR STAGE III cam, or similar, on a '02 LS 1? What head will allow me to achieve this?

I think the first question is, what cc combustion chamber do I need? 243 heads? 5.3 heads? Trick Flow Fast As Cast? How much do each need milled to achieve that size? I'd prefer to keep cost down with 243s if possible.

Or, just mill 243s as required and get a custom ground cam? Whatever cam I go with, it must have a nasty idle like the BTR Stage III or IV.

I talked to BTR and he said he wouldn't recommend taking any more than .020" off 243s with a Stage III cam. No more than a cleanup with a Stage IV cam. We're back to, how much do I need to take off 243s for 11:1?

 

Short answers: use a .041" head gasket and mill the heads 0.007, and you are at 11:1. 243 heads have 64cc. 63cc will do the job coupled with the thinner head gasket. A cheaper alternate plan may be to run 706 heads at 61cc, run the .041 head gasket, and rock an 11.3 compression ratio

Long answer: 11:1 is not enough for that cam in my opinion. If you run 706 heads and mill them 010 and run that .041 head gasket you are at 11.5, which will do far better on that cam. I do wonder if that cam is a mistake though. I seriously wonder if it wouldn't be better to run a BTR stage 2 cam and then set up the corrective spark int he tune to be superaggressive, which will help it to thump really hard but not be a pain in the *** to drive. If most of your driving is midrange, the BTR2 will outrun the BTR3. if you only plan on 11:1 and have no intention of going higher in compression, the BTR2 will outrun the BTR3.

I'm sort of at a loss, and I'm trying to help, even if it doesn't seem that way. On one hand you're a ten year member, but on the other hand, those are some basic questions, so I'm not really sure how much you've driven a larger cam like that. Please do not be offended by what I wrote. If you know what you're getting into and I'm off the mark, then that is fine and no hard feelings.

 

BTR stage 2 has an awesome street torque curve. I'd do the stage 3 for a drag car.

 

One thing to keep in mind with your LS1 is that at 346 cubic inches it has torque. As you mod your LS1 as long as you gear your car correctly you should have insta torque. Ask me how I know

 

Darth, lots of people are running a BTR stage 3 with stock or slightly milled heads. Does higher compression tame the cam?

 

No offense at all! I might be a ten year member but I haven't been active much in nine years, lol. Ten years ago I built the LQ4 that's in my truck and haven't done anything with an LS since then.

I know that a choppy idle is the LAST reason you should choose a cam. However, to me, a hotrod is just a life support system for a nasty sounding engine, lol.

I have a friend with an otherwise stock '02 WS6 running the BTR Stage IV, and made 426 HP on the dyno with 3:42 gears behind a M6. That's with stock heads and intake. He has a great tuner and it hardly surges at all even in a parking lot.

With that said, I don't want to go any smaller than a Stage 3. In my mind, that's already a compromise coming down from my friends Stage 4, lol.

I've done a lot of reading and have not been able to come up with concrete info on the questions in my original post. I've seen comments that I need everywhere from 60cc heads to 63cc to achieve 11:1 compression. Similarly, I've seen significantly varying info on how much I need to mill to achieve said compression. I just want to run a BTR Stage 3 cam with 11:1 compression, but am not 100% sure what is required to get there.

Stock 243s have 64.45cc combustion chambers. Every .007" milled reduces that by approximately 1cc. I can either mill less and use .041" gaskets, or I can mill more and use .052" MLS gaskets. @Darth V8r , you said mill .007" and use .041 gaskets. That would be 63.4cc chambers If using MLS gaskets, that would mean milling .018". That would be 62cc cambers. Is that correct? 706 heads have 61.5cc heads, so should be able to bolt right on with MLS gaskets to get 11:1. Correct?

I appreciate any an all input!

 

Maybe a little, but the main thing is to both help get all the power out of the cam and counter some of the lower rpm torque losses that are natural with a larger cam.

 

Do you think that would be too much compression on 93 pump gas?

 

Not at all. 11.5 will run on 91

Also in reply to your last post, use the thinner head gaskets. Quench around .035 is best. Sbe, pistons are .006 out of the hole. You will have less issues with detonation that way.

And on the 243 heads I rounded down to 64cc. What I should have said was mill to 63cc to be more correct. Hope that makes sense.

 

If you mill to 63.45cc and use a .041 gasket which is still 1 cc off your heads you will get 11.08-1 compression. Like Darth said though, compression is your friend with a bigger cam. If you are starting from scratch with heads and cam, there is a few ways to go about it.
if you get heads from advanced induction, he has what's called the high compression 241 castings.
or start with ported 706 heads which already start with smaller chamber.
if you get after market heads like trickflow or prc,they have 13deg angle for trickflow and 12 deg I believe for PRC and can mill a little more and maintain ptv clearance.
either way even 11 to 1 will feel strong but I'd listen to Darth and use the compression to your advantage. Especially on getting thinner head gaskets. Tighter quench will help keep detonation to a minimum

 

I ran the btr4 and a set of TEA tfs220s that were 62cc. That put me at 11:1 give or take a bit. It was a very potent combination in my opinion. It didn't feel lazy anywhere to me. Ran a best of 10.82 in the quarter

 

Are there any concerns running the Cometic gasket vs the GM? 3 layers vs 5 layers, correct? I want to do this ONCE! Do guys still use copper spray? I used it on my LQ4 with GM MLS gaskets and haven't had a single issue. The engine hasn't been opened since I built it.

 

you don't have to use copper spray . I didn't this time but prefer it

 

But would be considered good insurance? Might as well then. No concerns with the Cometic gaskets?

 

Cometic is the preferred head gasket in the LS world. The one exception is the older Ls1 heads that had a notch near the center cylinders. Cometic will not seal those. If you have 243 you do not have the notch

 

Fixed for you

 

Lol. NA is yay

 

I'm all ears if anyone has a set of clean 243/799 or stage 2.5 5.3 heads?

 

Curious as to why flycutting is not an option?

 

Isn't that rather difficult under the cowl of an F-body?