Raising the compression?

A

Anonymous

Guest
Does anyone know how or has anyone raised the compression on the Pulsar?

I've been exploring ways in which you can get the engine to cope with a higher compression safely. I think I may have possibly found a way. :roll:

It seems clear to me that the World Rally cars with 300bhp and stupid amounts torque of anywhere up to 500lbft; would be a good way way to follow! :D
 
S

Sirnixalot

Guest
the easiest way to get a noticable chance in compression ratio is to change out to custom pistons.

If you plan on running a higher compression ratio keep in mind you will have to run lower boost on optimax to compensate.

As for the rally engine bit...they get rebuilt far more often that yours so keep that in mind
 
A

Anonymous

Guest
I think it may be possible to get a much higher compression ratio and keep running the same boost; all the while keeping with standard internals.

I'd just like to know how the compression ratio can be raised and to try and keep as much standard as possible. Would it be possible to fit pistons from the NA version?
 
A

Anonymous

Guest
I've been discussing this with a mate from the SXOC, and we reckon the use of some parts from the N/A engine (CA18DE in my case and SR20DE in your case) will yield a higher comp. ratio - provided they're strong enough.

We've just got to work out what is different between the two engines! I think the logical thing is either different shape/thickness pistons or longer conrods in the N/A version :)
 
A

ashills

Active Member
would the compression not be from either domed or dished pistons
as teh pistons from the Z32 na are domed but when machined to a dish are a straight fit into the sr20 and give low comp
 
A

Anonymous

Guest
ashills said:
would the compression not be from either domed or dished pistons
as teh pistons from the Z32 na are domed but when machined to a dish are a straight fit into the sr20 and give low comp
Click to expand...
Not sure - but I intend to find out :)
 
A

Anonymous

Guest
Well hello Pete, didn't know you were on here! :D

You'll have more posts than me soon!

Anyway, how much can the head be taken down safely (not sure of the clearances on a standard engine) ?
 
A

Anonymous

Guest
goats_breath said:
Well hello Pete, didn't know you were on here! :D
Click to expand...
I wasn't until today! Just thought I'd drop in and say hi, then I got a bit carried away :D

Anyways, get back to writing your CV you layabout! :p ;) :D :D
 
A

Anonymous

Guest
I know, it's just my own concious! :roll:

Off to the courtyard, reefer in hand, start work! :D
 
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Sirnixalot

Guest
becareful with the pistons.

Im not saying this will happen with the NA pistons (which if i was going through the trouble of swapping pistons i would never use, high cr + boost...piston killer), You have to watchout for the piston to valve clearance. Depending on the compression ratio increase you may need to have the pistons notched for valve clearance.

You have to take into account the cam specs as well because this will affect how far the valves protrude into the combustion chamber (obviously)

Your best bet would be to get a set of custom pistons made specifically for the GTi-R SR20DET.

The FWD NA SR20DE pistons come in either 9.5:1 or if you can find the JDM or UK spec 10:1 pistons. These will not yeild their respective compression ratios in the GTi-R SR20DET vbecause our combustion chamber is larger.

I do not remember both combustion chamber sizes at the moment but i will research it. I am confident that the FWD 9.5:1 cr pistons will yeild at least 0.2cr points lower when used in the GTi-R SR20DET.

You will not beable to run 1 bar on optimax (and no water/methanol injection) on a compression ratio any higher than 8.8:1 (you MIGHT be able to run 1 bar on 9.0:1 but for saftey i would limit 1bar every day usage to an 8.8:1 motor)

If you are talking fairly high compression ratios (10:1 and up) then you will be severly limited with your boost on optimax. With a 10:1 cr i wouldnt DREAM of running more than 10psi on optimax.

11.5:1 is the limit on pump gas (still being able to get to redline, sure you might get away with 12:1 but i garuntee you wont be able to rag it)

11.5:1 and i wouldnt dare run past 6psi on optimax.

This all changes on race fuel though. Rally cars can run stupidly high compression and boost because they run race fuel and water/methanol injection?? (not sure about the water/methanol injection but it seems likely).

Another thing to take into consideration is the head bolts. You WILL NEED UPRATED ONES!!! The stock bolts WILL NOT handle high compression and boost....no exceptions
 
A

Anonymous

Guest
We weren't thinking of using Optimax or even race fuel - but it does have a much higher RON than any fuel you can normally buy on a UK forecourt ;)
 
A

Anonymous

Guest
Right I'm going to let this little cat out of the bag because I'd love to see it done and many heads!? :D

It was an idea we got from Practical Performance Car on a feature about using LPG as the 'peoples' race fuel. With a Octane of 114 RON it may mean that set up correctly you could advance it hell and raise the compression with less fear of detonation.

It's an idea that was suggested for turbocharging NA cars so they could run standard internals with a fairly high boost. In principal if it should work for that then it could certainly help us? :roll:
 
Fast Guy

Fast Guy

Moderators
Staff member
Are you talking Avgas or methanol or something else :?

If you use methonal as the main fuel I think you have to purpose build the engine to run it.
If you use Avgas, you'll probably need to run the engine without an O2 sensor as the lead in the petrol will kill it quickly.

Where did the second page just come from :? :oops:

I wouldn't try it on standard internals as we all know they break. Try it on forged pistons if you realy want to try and let us know how you get on. :wink:
 
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Sirnixalot

Guest
methanol corrodes aluminum quite easily. I used ot have a car that could run on methanol and it said for every tank of methanol i used i should run 1.5-2 tanks of regular petrol through it.

Methanol injection isnt as devastating as its usually a 50/50 mix with water and fuel is washing it away as well.

If you guys are talking about a race only motor...build what ever you want. But remember what Carl (Fastguy) said...leaded fuel kills O2 sensors.
 
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MarkTurbo

Well-Known Member
He's already mentioned its LPG that he's thinking of hasn't he :?:

Would be nice if you could get good performance from LPG :D 40p a litre 8)

Thats if it works :?
 
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