Adam

The prob being that pistons are not round and the none thrust side of the piston is the smallest part, also the ring land part of the
piston (as a norm) is a good .015-.020 smaller than the skirt as this is in contact with the flame front and a good deal of heat is past to the cyl wall through the ring its self, so my point being
that there is room for the ring to move, as we know the rings turn
in the bore in operation so there is a chance the scraper part of the oil control ring could get cault up in the hole. Not saying it will hapen but if does and it could the result will be expensive.
The ring land arrangment on a 2.5 is ok as std but i meant there is no room to move them up further as the compression hieght is about 3mm less due to the extra stroke.
As a safty factor i will leave one half of the block with no holes
and fit the pistons fitted to the rod, and mess about with smaller
pin fitting holes on the other two holes so fitment will be a pain.
Steve.


[Edited by SMG - 11/6/2002 8:35:39 PM]

 

So what is the best engine size for a quick but RELIABLE scoob,is a 2.0 rebuilt from the crank up with bigger turbos etc the way to go or will a 2.2 or 2.5 give the extra performance with more reliability.
I am just looking for general thoughts, no need to get too technical as I realise there is more to do than just the basic engine, that bit will come later & I will post on drivetrain for that. Those who have already replied to me either directly or on other forums thanks & I will be in touch again, just posting here to see if their are any others with constructive thoughts & experiences

Thanks

Stuart

 

Would have to be 2.5. Jun have made a 2.5 show car on GC8 chassis. It was mental. Something like 470bhp@wheels. It has covered a lot of mileage and its still going strong. You can bolt some serious turbo charger on a properly prepared 2.5 engine. Something like a Greddy T78 which is absolutely huge and guarantees to transform your car into a rocket. Lag is not too bad either.

Cheers

Gez

 

OK, Ignorance time, who is Jun

 

Jun are one of the biggest jap tuning companies in todays market like HKS, Apexi etc. Only difference is that they usually make part for the engine rahter than electronics etc. They ahve come up with some of the most powerfull cars to date. 1000bhp skyline and Supra. They basically take an engine and run it to destruction, look at the weak points, make them stronger, then they look at the strong points and make them even more strong.

Cheers

Gez

 

its interesting that the opinion of jun and subaru in japan, is not to touch ej series engines. They describe them as being like glass.

Great!

2.5 is great for capacity.

As I said on your same thread on 22B.com, my current preference if I could do it all again would probably be a destroked 2.5, giving 2.33, but allowing it to rev to 8000 rpm, which I would not be happy with doing on the 2.5 stroke.

 

I agree with adam on that one i am going to do my screamer with a 100mm bore and a 75mm stroke, but i am also doing a 97mm/75mm 2.2 along with the other combinations so a lot will be learnt here. My main concern with stroker engines is that the oil control ring passes into the hole that is for the pin fittment. There is not anough material in the crown of the piston to move the rings up to compensate, this will leave the ring lands to thin and the heat from the compresion rings will melt the ring lands, which is a shame. On the ones i will do i will only machine one hole for pin fittment which reduces failer by 50% but still not ideal.
Steve

 

steve,

all the jap 2.5s seem to manage ok still.

Also the standard ej25 still manages a normal life despite suffering what you have described. Admittedly the heat in a 2.5 turbo will be different.

 

Would the rings passing over the pin hole matter really??? Im not too familiar with 2 strokes, but dont the pistons on a 2 stroke pass over the inlet and exhaust ports all the time?? The rings must be doing pretty much the same thing then??
Or am I completely wrong?

 

Stevie
You are indeed right, but on a two stroke the rings are held in place by a pin in the ring groove to stop them spinning. The result in that being rapid and excessive wear. 9 times out of ten the pin will be positioned so that the ring gap travals down the bore where there is no ports.
Steve

 

10 times out of 10!

Interesting point about the longer strock I hadn't considered. Although I wouldn't otherwise worry about the stroke, even with 92x79 it's still well oversquare.

To get 97mm bores, would an ej20 closed deck block require relinering?

Paul

 

Paul

Yes it will need relining, the std liners are cast into the block
and boring to 97mm leaves very little cast iron. The 2.2 blocks
are of a thicker wall thickness and there is more iron cast into the bore.
Steve.

 

Be warned that the experience from the yanks turbo'ing the 2.5 litre engine is that the torque produced tends to eat clutches until you uprate them, then they break gearboxes.

 

That's true in the USA, but they are turboing there 165bhp normally aspirated engines, and the clutches, and gearboxs aren't designed to cope in the first place.

However, even the Sti clutch, and gearbox won't cope with a well tuned 2.0lt, let alone a well built, and tuned 2.5lt.

Mark.

 

bttt