can you swap a lean burn cylinder head for a hemi type without changing the pistons etc?

 

indeed you can but no-ones saying what it will run like, massive difference to the compression ratio...

 

what would you need to do to sort it?

 

that unfortunately i do not know the answer to i havent messed around with carb engines that much. Just out of interest what engine is this on, i see you have a S2 cabby turbo?????

 

my cabby isnt a turbo. its the carb model. with a lean burn head and ive got a hemi type stage 2 head i want 2 put on. i thought my head was the hemi type but i got it wrong.

 

ahhh right yeah i saw the turbo bit on the wrong side lol

yeah all the later carb CVH's have leanburn, im not too sure what the pistons in the earlier type are like?

on the other hand if you want to go up to a better engine ive got an XR3i engine, coming out of an orion some old boy has owned, just done a bit of a service on it and its running as good as they get, no smoking or anything, and does 120 with ease and plenty more throttle to go, if your interested?

not much u can do to the carb models

what size is yours aswell 1.6 or 1.4?

 

its the 1.6. and i have the stage 2 head with kent cam in it(though it is the hemi type) and i also have a pair of twin 40s to go on so couple all that with the freeflow exhaust and piperx airfilter i should have a good 135-140bhp. trouble is tryin to make that head work lol

 

forgot to mention its the later 88 hemi type head that i have, made for carbs but pretty rare apparently, serial code starts with D88SM6090

 

why the hemi heads are the better ones. better flow rates aswell. u got any local scrap yards near u? if i were u i would rip the head off one n hav a peak at what pistons they have.

yeah the 88 head allegedly is a rare find, although there is no difference between that and a 81 hemi off an injection, the only difference they are thought to have if any is the valve seats. where did u get the head from as thats the head that was fitted to carb models that didnt go leanburn

 

i know hemi heads are better. that was cos i thought mine was a hemi but its a lean burn. so obviously i wanna use the new hemi head cos its ported and polished with good cam. just wanna know how 2 make it work on my engine

 

bttt

 

any1 know?

 

A simple answer:
Yes, you need to replace the pistons aswell.

 

is it just the pistons i need to change? will everything else work ok then?

 

It's only the pistons and the head.

 

A Hemi head will fit AND RUN on a lean burn block, I've done it (XR2i head)!
The pistons are different in the way that a lean burn only has 1 high spot per piston, a hemi has 2 theoretically losing compression (how much I don't know) but this can be sorted by a: replacing the pistons or b: skimming the head.
You say you have a high lift cam, when the head is fitted and the cam belt is on, turn the engine by hand to make sure you don't have any valve contact before starting.

 

thanks marc. most positive news I've heard in a while. the head is a ford one thats been ported and polished etc so i reckon its probably been skimmed. so as long as there is no valve contact you reckon it should run fine?

 

Yup, no probs mate, I don't even have any trouble with hot starting!!!!

 

did you change your pistons? or are they the lean burn ones?

 

I kept the original lean burn pistons which theoretically loses a little bit of compression BUT for a standard engine it is still very fast and won a championship 1st time out

 

cool. im just gonna slap it on then, cos should make up for loss of compression with the bigger ports and cam and twin 40s

 

Go for it.
Time to start a new gearbox thread now

 

ive got a lean burn engine in mine. I’ve took the head off and put a rs turbo hemi head on. That’s been ported and polished. Sodium filled valves. I’ve put a piper 285c cam in running on twin 40s and a xr3i exhaust.
Was a bit shocked at the outcome as only made 104bhp was expecting a lot more. Not sure if it’s the head or not. Tempted to get the standard lean burn head ported and put that on and try it.

 

Might be the exhaust? A 4-branch & straight-thru makes loads of difference, or even just the 4-branch (or 4-2-1)