v6 crossflow racing questions

[dzalj1]

ok guys need some omc guru help. i have a big bore 235 block. it is bored 30 thou over size with after market pistons. now, i have heard that it is possible to bolt on the small bore 150-200hp heads? i have read that the piston has to be notched out on top and bottom is this correct? if so can someone either mark one up on a piston to show me please or if any one has any pictures. and if this was to work, what head gaskets will i use then? either the 3.5inch bore or the 3.625 one. does the timing have to be changed? my block is a ported tripple c spec'd block, with a custom made 6 dual throat carbie manifold, similar to the origional tripple c's. would the piston deflectors and scavaging side hit the chamber surfaces in the head or would it just clear it. please guys i am in need of you help. it is nearly summer back hear now, and i need this thing running , any help would be aprreciated

dzalj1:confused:

[Forkin' Crazy]

I was going to buy a set of CCC heads for a big bore and he had machined the heads for clearance. I guess you have an ample supply of race gas. :)

[chynewalkr]

http://forums.screamandfly.com/forums/showthread.php?threadid=12574


does this link help any?

[Forkin' Crazy]

http://forums.screamandfly.com/forums/showthread.php?threadid=12574


does this link help any?


Oh the memories!!! :cool:

[dzalj1]

i also heard to bump up the commpression on a crosslfow, that you can cut the top of the piston surfaces, so when you shave or deck the heads the piston wont hit, so if you deck your heads say arounde 20-30 thou, you cut that off the piston tops also. is this true? but i figured out in my last post and i answered my own question, but yes you do have to use the big bore head gaskets anyway, or else the pistons will not pass through the small borte gaskets. but still i need help on the notching out the pistons to use on a small bore 150 head. can someone please draw me up a diadram, or get some pictures please. i am stuck on this for a while now.
thanks again dzalj1

[dzalj1]

those nine pages are the best, all my port work and those racing requirments all got added up to or as close i can get to those nine pages. very interesting though.

[racer]

Do not cut the top of the piston the deflector is needed for flow direction, you cut the head for clearance

[dzalj1]

what about just cutting off the tips, just so the large bore piston will fit in the small bore heads. i will not cut the tops off, nor i will cut the intake or exhaust sides for it to fit. i just wanted to cut the tips off enough for the piston to fit in. like a square cutaway out off the corners.

[BarryStrawn]

If you cut back the ears on the piston I believe some air/fuel charge will short circuit out the exhaust instead of up over the deflector. But I've never tried it so I don't know for certain.

Why not just modify the heads for clearance?

[racer]

The heads need to be cut the entire way around on the intake side from the radius down to the squish or they will drag the edge of the piston up to the dome. You need to clearance more than just the tips.

[dzalj1]

ok, but then the easiest way around this problem is just to get a set of high commpression heads, the 638/9's. and then i will deck the heads 30 thou. then hopefully that will be it then. and then i wont really worry about the 2.4-2.6litre set up. ok, but if i was to make all the pistons to fit in the 2.4 head, and everything clears, will the commpression get bumped higher, is this kinda work for endurace, or quick sprints? and the reliabilty?

thanks guys so far with your inputs, heaps more will be great.
dzalj1

[Forkin' Crazy]

Get a hold of neveredge. He had a set of special heads that Alan (racer) modified for sale. I think they were heavily modified 638-9 heads.

[racer]

Those heads are for sprint type racing and will require 100 plus octane fuel. They will give you a very noticable gain in power, max timing at 24 degrees with those heads.

cutting the pistons for clearance is the WRONG approach,compression with poor flow will not gain power.

You also need to run the 2.6 gasket no matter what heads are on the engine.

[dzalj1]

ok, point taken, for my big 3.625 block, i will find a good set of 638/9 heads and deck them 30 thou, and for my 3.5inch bore 235, i will try to find a good set of 1976 200 heads and deck them 30thou.

thanks for all your input guys so far, and keep em comin if anyone else wants to add anything
dzalj1

[racer]

On your small bore the 78/9 235 heads are better than the 76/7 200

[dzalj1]

does the 78/9 235 heads have higher commpression? i always thought the 200 76 heads were the best. if the 78/9 heads are better then i am lucky, cause i have a set.

[Riverman]

Do not cut the top of the piston the deflector is needed for flow direction, you cut the head for clearanceAlan, is this the same for cutting V4 heads?