Probably a stupid question

[thelynx]

Have plans for engine.. Worked valver head with larger valves, ported, cams so on. F7r Bottom end rebuild with forged rods and poss high compression pistons. My question being about high compression forged pistons.

Is there a sizable gain to be had by raising the compression?

[Chris H]

depends on what you class as a sizeable gain tbh.

It will respond better and will make more torque, but it has to be fueled properly to make the most of it and to prevent failure.

You only need better rods etc if your going for a higher rev limit.

I see it all to often, peopel throw 5k at an engien then retain the stock limiter and then moan that the cars not actually making any more power.

Don't fit it if your not going to use it.

[Scougar]

You only need better rods etc if your going for a higher rev limit.

I see it all to often, peopel throw 5k at an engien then retain the stock limiter and then moan that the cars not actually making any more power.

Don't fit it if your not going to use it.

You ever seen Initial D (the manga version)? Think that is perfect and simple example for the uninitiated in rev limits :D

Matthew

[thelynx]

Ok, what would you say the standard bottoms end limit is having been rebuilt? Im only looking for 200bhp so not crazy. Like you said no need fitting parts that arnt needed. Just dont want the bottom goin pop

Cheers the replys :D

[northy]

for 200bhp u need, head and inlet work (standard not bigger valves) cams and remap.

[stew]

depending how strong the engine is northy.

should be nocking on the 200bhp door anyway...

ive heard forged pistons can be "fun" for a non-race car. different thermal expansion rates can cause the engine to sound shit and run pretty rubbish until its hot, and the extra compression can cause fueling/nock problems. (just from what ive read)

forged rods and uprated bolts, std pistons, and a balanced and lightened crank would be the way id do it. possibly some tastey piston rings as well. maybe grind the cylinder head so its true and this way increasing compression ratio a little.

a well gasflowed head will give amazing gains, same with a well matched inlet and exhaust manifold, and exhaust system diameters.

some quite agressive cams 270 deg, well timed in to provide power through most the rev range, and a good remap, will see some very good power gains.

as always if the job is done shit then there aint much gains to be had. it seems like the quality of the cam setup, headwork and remapping has a huge amount to do with power ouput at the end of the day.

im sure benR or stan* could shed some more light, and correct me if im wrong.

[MAXIBOY]

i think forged pistons and rods only if increasing the revs above 7500rpm. otherwise standard rods and new bolts maybe apr,s and new cast pistons will be fine

[stan]

pretty spot on there stew really.

the problem with forged pistons on a road car, is that because they are rarely at full load(and therefore power) conditions, for prolonged periods...the bore/piston clearnace isnt very constant. this will lead to power less and extra wear...to what to degree for either I cant say in quantifiable terms really.

The main limit is going to be the OE managment system. To see any decent power you need fairly wild cams, and more agressive timing figures. the more overlap you run, the less stable fuellihng becomes at lower throttle angles. Its always a pay off.

If you fitted after market managment, even on the stock plenum set-up, if it was well prepared, you would get past 200bhp with ease I would say.

[thelynx]

So many choices... Dont know what to do. May even sell the thing yet.

[Andy P]

So many choices... Dont know what to do. May even sell the thing yet.

You know value for money that Hybrid Clio cant be beaten. IMO it cant be anyway.

Fairly reliable, non of this turbo and not boosting right bullshit. Just jump in and away you go.

Shed some weight headwork and cams with it mapped spot on and I think you would be satisfied with that for a while mate.