compression/stroke

Ok so been doing some reading but not really finding answers. so sorry for all the question in one feed.

Tuning the SR20DET:

To change the compression is done by head gasket and pistons correct?

lower compression = less torque but more boost
higher compression = more low torque less boost

So what is best for what?
If you wanted to up the rev limit would lower compression be better with high lift cams and a bigger turbo?
More low-mid torque a higher compression and smaller turbo?

What works best on a Fast Road R?

Where does changing the stroke come into it? say a 2.2 rather that the 2.0. Would the 2.2 give more power at same boost compaired to a 2.0?
What difference does a larger diameter piston do say 87mm over standard 86mm? or doesnt it matter just depends on how much you have to take out the block to reuse it? would the larger pistons weeken the block at all?

Getting a bit confused....

thank you

From what ive learnt so far, if you want good torque then go for a stroker kit 2.2 etc By having this you limit top rpm due to the rod angles being greater due to the stroker crank, so i dont think you would run a big turbo, as that would still be making power high up in the rpm range. I believe you would gain a bit more mid-range torque with the displacement increase but probably not that noticeable.
You can also change compression with different rods, but not sure if that if something done with our engines?

Dont take this for gospel as im sure someone with far more knowledge will be along shortly

lot of questions lol

first off i would forget the stroker kit if i were you

secondly stick to as smaller piston as possible...the larger you go the greater the heat and the thinner the cylinder wall thickness to waterways

if you want a torquey fast road car then use a stock flywheel which will give you more torque over a lightweight jobby.

compression ratio you want to run is dependant on many things such as size of turbo and boost level
wether your looking at low down to medium grunt or chuck back in the seat topend power but sacrificial to low down off boost losses

in a nutshell i think the 8:5.1 compression ratio works very well

Yeah i know as i was writing it more questions kept popping into my head!! sorry lol

I dont really know what i'm doing at the moment but quite fancy building an engine. so i was doing some home work and got lost.
i have a complete head and a crank shaft, not had the machine shop look at them yet mind and thought maybe i'll get the rest of the stuff and build myself an engine.
Cheers for the info tho always keep to learn.

How about having using longer rods with thinner pistons with either a stroker crank or std , this would reduce the angle of the rods ?
Should help adding cc but reduce additional wear?

Kate&tim wrote:How about having using longer rods with thinner pistons with either a stroker crank or std , this would reduce the angle of the rods ?
Should help adding cc but reduce additional wear?

When you say thinner pistons, do you mean using a crown with the gudgeon pin hole mounted slightly higher?

If you did the above: longer rods with thinner pistons, this wouldnt add cc's, only a slightly larger crank throw would...or have i got something wrong here?

pulsarmoley wrote:

Kate&tim wrote:How about having using longer rods with thinner pistons with either a stroker crank or std , this would reduce the angle of the rods ?
Should help adding cc but reduce additional wear?

When you say thinner pistons, do you mean using a crown with the gudgeon pin hole mounted slightly higher?

If you did the above: longer rods with thinner pistons, this wouldnt add cc's, only a slightly larger crank throw would...or have i got something wrong here?

No sorry didn't read what i typed only the stroker crank would increase cc , yeah Having the pin mounted higher would give less angle on the rod .

Disclaimer - its Tim not Kate

Was only thinking out loud as I'm thinking of having a project engine .
All thinking from evo engines but its pretty similar .

Also if heat is a issue a longer rod would give less side load on the bore so decreasing temperature no idea really !

sorry to jump in but i would never use a stroker kit, the reason being good old british leyland used to bore out there tractor engines and every few years you would get crackes forming between pistons.

BEBB GTIR wrote:sorry to jump in but i would never use a stroker kit, the reason being good old british leyland used to bore out there tractor engines and every few years you would get crackes forming between pistons.

Not quite sure what your saying exactly, I understand the cracking issue as i guess thats from weak walls? But why not a stroker kit?

standard cc of pulsar is 1998cc so you bore out your cylinder to 2200cc ie making cylinders wider, thus making cylinder walls closer to each other, this then results over time to cracks betwen the cylinders so water and oil are mixing?

BEBB GTIR wrote:standard cc of pulsar is 1998cc so you bore out your cylinder to 2200cc ie making cylinders wider, thus making cylinder walls closer to each other, this then results over time to cracks betwen the cylinders so water and oil are mixing?

Yeah i get that bit but whats the problem with stroking it? You can stroke it to 2.2 with little or no boring out.

I thought that for the tomei stoker kit to be fitted you had to bore out the cylinders, which may cause problems explained above, but is that not the case.

does the stroker kit extend the capacity of the cylinder via conrod size making the piston a longer strok and not bore width? if so forget what Ive posted then

BEBB GTIR wrote: I thought that for the tomei stoker kit to be fitted you had to bore out the cylinders, which may cause problems explained above, but is that not the case.

does the stroker kit extend the capacity of the cylinder via conrod size making the piston a longer strok and not bore width? if so forget what Ive posted then

A Tomei stroker kit you do but not much; it consists of boring out to 87mm(86mm standard)which takes it to 2048cc(like my engine) then the rest(approx 152cc) is achieved through a larger throw crank; possibly 90mm?

If you were to change only the conrod length all you would achieve is higher/lower compression as you are only altering where the piston travels in the bore but it will still only move 86mm.

I believe its when you start going for 2.3/2.4 then you have to get it bored out by a fair bit 90/91mm...

Hopefully if anything i have said is incorrect, someone with more knowledge will set us all straight

so stroker kits not to bad then if its only bored out a mm i was thinking more of several mm which would defo give problems

Mines using a BC stroker kit. Been bored to 89mm and running a 90mm crank. Had the block sleeved using the darton SR20 specific liners. Not got it back from Norris yet, but should only be a few weeks now (he says), so have to wait and see!

BEBB GTIR wrote:so stroker kits not to bad then if its only bored out a mm i was thinking more of several mm which would defo give problems

Another thing i left out is the more you stroke it you limit yourself more on top end revs due to the increased rod angle during use; but i dont know by how much.