3 posts • Page 1 of 1
Currently I have dropped a 16V bigport with ST ITBs run by an aftermarket ECU into my car. Now before I take it to get mapped, there is a possibility of some 260/252 cams & Smallport Pistons I could get hold of. Is this going to see some gains and worth the trouble?
You would definitely see some gains with the new cams. Are the smallport pistons any different than the bigport ones? You might as well wait to get it tuned until you figure out what mods you want to do. Tuning isn't cheap.
Max2503 wrote: Is this going to see some gains and worth the trouble?
To change to smallport pistons you would need to have con rods that take a 20mm
piston pin. Early 3-rib bigport engines have 19mm piston pins so that will be your
first problem. Smallport cranks have a larger bigend journal, so it is not just a
question of installing smallport pistons and rods.
Second issue is the wisdom of installing secondhand pistons (I'm guessing that you
are talking about used pistons and not new pistons) into a used engine. The problem
with fitting used parts is that unless you measure everything very carefully, the result
may not be good, as you can end up well over the factory wear tolerances. You can't
tighten up bore tolerances to suit worn pistons. So when rebuilding an engine the
usual procedure is to bore the block to the first oversize and fit oversize pistons.
Never the less, more compression is always good and the smallport engine has a
nominal compression ratio of 10.3:1 which is a nice step up from the stock bigport.
If you do figure out a way to raise the compression then those cams will give you
a modest improvement across the rev range. You will need to check valve clearances
and re-shim where necessary. If you stay with the factory bigport the engine will run
a little better with those cams, but the result will be barely noticable on the street.
I'd suggest that you think seriously about where you want to finish up with your build,
and decide if you want to try making random parts work, or if you want to get your
car driving with what you've got, and put the money towards a full rebuild with new
parts a bit further down the track. With an aftermarket ECU I'd recommend cams
with at least 272 duration and some decent lift, but again, I don't know if you have
to meet smog requirements.
Maybe some of the above will help you to decide if it is worth it
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