06X6spdGTO

iTrader: (6)

I'm looking into doing an budget Lq9 for my full time drag car. Im debating between hand porting and milling the stock 317's down to 66cc Chambers and running a .040 cometic head gaskets but would like to run an MS4/Polluter/Thunder Racing TRex/SNL Red Letter/EPS Single Plane (236/248/or EPS 234/236).

So what cams are possible to run with a 66cc Chamber .040 head gasket on stock pistons?? I would be will to flycut as well. Have never done the flycutting thing tho.

soundengineer

iTrader: (16)

If I remember correctly..317s already have Clearance issues...
you will be at about anybodies lower 23x cam at the max already...

I wanna say that a buddy of mine did a set of milled 317's and had to go with a 230/232 cam to fit without fly-cutting

then you want to mill it.. so you are taking away even more...
and use a .040 gasket which is even less again...(GM MLS is around .055 I believe)


you will need to be using a smaller cam and fly-cutting...

JPH

iTrader: (2)

Been there done that. You will have to mill the head down alot and go tight on the quench to get max scr. Big cams will require flycutting no matter what. A better suggestion is to run a set of wiseco +4cc dome pistons, which will net you the compression you will want to be at and at the same time giving you plenty of ptv clearance with whatever cam choice you desire.

06X6spdGTO

iTrader: (6)

how do Ls2 GTO's/c6's get away with soo much larger cam's is my next question?? Correct me if im wrong be isnt the Ls2 10.9:1 SCR??? There are many ppl running the HPE mega death cams without issues.

soundengineer

iTrader: (16)

stock LS2 head is a 243...not a 317/L92 style

06X6spdGTO

iTrader: (6)

317's are cathedral heads. L92/Ls3 are rectangle heads. The 317 design is almost identical to the 243's with the exception of the combustion chamber size. 243's are 65cc 317 are 72cc

JPH

iTrader: (2)

Yes. A LS6#243/#799 is a 65cc head and a LQ9#317 is a 71cc. It's the larger chamber that kills your compression, and after milling them alot, then it kills your PTV.

06X6spdGTO

iTrader: (6)

Okay I understand what your getting @ there but then how are the LS2 cam cars able to run cams like the MS3/MS4/Polluter/MegaDeath without the issues on stock 243 65cc heads??

soundengineer

iTrader: (16)

they are pushing the limits of what can be done...
Duration #'s dont mean anything unless you look at it in valve events...
with a 243, a trex size cam is about all you can get...and thats cutting it close.. a little valve float or valve bounce and you have dents in your pistons and bent valves...
yet still people just blindly put them in...
they are right at and even below acceptable limits for PTV clearance for most people.

now...mill a head .03 to get compression.. and realize just how much you have lost

minimums in general 0.080 intake, and 0.100 exhaust...
all those cams are right at or below that value on most cars.

now lets do math..
take off .03 for the mill work, and .15 for the gasket change
so now you are in the .035 intake and .065 exhaust clearance.... WAY TOO CLOSE

and if you want a visual on how close that is... check it out on a micrometer..
2 pennies stacked is roughly .100
a Nickel is Just under .080


Oh.. and that is only if your Valvetrain Geometry is right

soundengineer

iTrader: (16)

Also.. Chamber cc.. has nothing to do with Shape of the Chamber itself...the position of the valves can be closer to the piston or further away from the piston based on how the chamber is shaped.

06X6spdGTO

iTrader: (6)

okay so essentially the 317's and 243's are not the same head design so I would be able to hand port a set of 5.3 heads and put them on with the same valve clearance as the 243 since they have they have never been milled??? Your theory statement isnt making much sense to me sound enginneer

soundengineer

iTrader: (16)

you would be best with a good set of Ported stock heads and not have to worry about a small amount of compression that will net less power than a good port job will.

Consider the many options for heads that exist....

JPH

iTrader: (2)

Most people don't check or know how to check ptv. it's a guess and run type of deal with them. Soundengineer is correct on what he is saying to you. You have many options here, but milling a head .036+ and using BIG camshafts are going to cause you MORE work and headaches.

Damian

iTrader: (89)

317's are a 72cc chamber. Every .006 cut is 1cc, so to get down to 66cc you'd have to cut nearly ~.048-.050 off those heads. With a .040 gasket, you'd be lucky to fit a 220 duration cam in there.

You're better off running a different head and not flycutting.

hammertime

iTrader: (1)

Sell your 317's and pickup some used 243 or ls6 heads. Then check your actual PTV clearance with one of those cams and a .040 head gasket. Then you will see why you are getting these suggestions.

Don't forget to degree the cam - a must if you are going to push the limits on PTV clearance.

06X6spdGTO

iTrader: (6)

Thanks for the input. Looks like ill be looking for a set of stock 243s to have hand ported and selling my 317s

JPH

iTrader: (2)

Very smart choice.

06X6spdGTO

iTrader: (6)

thinking of going with a set of edelbrocks RPM Performer heads w/ 65cc chambers

http://www.summitracing.com/parts/EDL-61949/