will be running a 406 sbc, with true flat tops (SRP's)
got the heads, which are the 195 afr's. the chamnber is 65cc. I would have prefered the 72 cc (or larger one, i beleive they have differnet size than that), but this good deal came by on these heads that i couldnt refuse. i will be running pump gas. 92-94 octane. I'm wondering what thickness of head gasket you recomend I use, and also what brand if any over the others.


I remember reading that the quench is the vital role in detonation, and that too many people use too thin of gaskets.

cheers

blake

What's your deck height?
I think your CR is going to be sky-high....

yep i am bettin mid to high 11s
well for quench you should assemble the bottom end and measure how far in the hole the pistons sit then pick your head gasket to come out around .040 when you add the distance from the deck to top of the piston... that is why they give your the compressed gasket thickness with each gasket

sky high....... i'm going to say this would be about 11.3 :1 with a thin gasket. use a thicker one and probalby 10.8 :1

but that might be worse for detonation then the higher CR in order to get that low of a CR you would need something in the .049 compressed thickness range probably more which will kill your quench .069 if your pistons sit .025 in the hole... i would swap out your pistons to something with a dish or valve reliefs if you really want to use those heads to get it down into the mid 9s

falt top piston with 4 valve reliefs with stock deck height what would u say for me and i want around 11 to 1 cr
----------
with 62 cc heads

just looked up for an example. perhaps I shouldnt be using this as a reference.

but the new corvette has a compression of 10.9:1 and requires 93 octane.

the Z06 has an 11:1



perhaps I could use a differnet type of camshaft which woudl eliviat the high compression with valve timing.

cheers

blake

well i dont doubt the corvettes are running those compressions... but that takes millions of dollars of research and tuning to get a production car to run those numbers reliably and still not blowup if some house wife of OC runs desiel through it...

but yes you could use a cam to drop your DCR but then you are losing power that you might have had if you just lowered you SCR
----------
Need more info
well on what CID? 355?

Yea, thats exactly it. High efficiency tuning, good cooling, etc etc etc. You can't compare that to a 400cid carbed motor.

This is on a 400cid, that's why I said the CR would skyrocket. 11.5 assuming basic stuff (.025 in the hole pistons, etc).

What CR do you want to have? What cam are you going to run?

I think right now you're unfortunately stuck between a rock and a hard place. Either the pistons, or the heads need to change - a gasket won't save you.

motor will have fuel hsr set up. going witht he megasquirt for a computer to tune it. i would like to achieve 10.5-11:1 compression. with 94 octane availble i find this would adaqute for that CR. also they are increasing ethonal in gasoline, which is directly proportional to its capabilities of helping a high compression motor.

being that i'm in school, have the pistons already in the holes, perhaps i could get them machined out into a dish format. i dont believe it takes much to lower the compression. and would probably be my best bet $$$ wise.

, i'd just have to disasemble my short block and start all over again

here is the cam specs i was looking at the comp cam XFI 292
duration in/ex 292 300
duration @ .050" 242 248
lift in/exh.584 .579
lobe sep. 113

Ok, with that in mind - you having FI, AL heads, and a pretty big cam - I can agree, 10.5 is probably where you want to be.

Don't hold your breathe on more ethanol in our fuel, I have yet to see E85 in Canada... And so far it's just the 10% mohawk puts in, and whatever we get for our winter blend.

Not sure how thick the piston tops are, so do the math on how many cc's you need to remove, and where you want to remove it from, and if that leaves enough material left. That'll throw off the balance a lot, so you'll need to rebalance the rotating assembly eh?

Assuming it all comes together as mentioned - it'll be a rocket.

regreatably, i never had the system balanced. so i guess this might make me do the right thing, as this is going to hopefuly be my daily driver.

these are pretty nice pistons. i'll see if anyone would want to trade for some dish ones of SRP, ross etc.

then i'll get it balanced.

cheers

blake

i'm putting these heads which i just bought up for sale, hopefully i can sell them and buy replacements without loosing much money, if any. will be going with a 75cc head

this will bring the compression to 11:1 with .21 gasket
10.71:1 with a .31
and 10.5 : 1 with a .41 gasket





with a the depth of piston and thickness of gasket beign .040" it works otu to be 10.91 :1 comrpession

more or less what i need to achieve compared to what iam at now

what do you think

cheers

blake

You still haven't said what your measured deck height is (or did I miss it?)
Go out and measure it with a feeler gauge and ruler.

My numbers are coming out a bit lower than yours. Confirm what the pistons dish volume is (i'm saying 0, since you said true flat top, but confirm that, usually they have some valve reliefs.)

I still think 10.5 with perfect quench is as high as you want to be, if you want it to last.

sorry I dont go out to my shop too often right now. i will probably in the next couple days. i just looked up SRP's site, and realized they arnt 'true flat tops'

i appologize

they have a -5cc dish. i'm thinking this will be just perfect if i'm able to get a set of the 75cc heads