how do the yanks run high comp zetec turbo engine (9.1) and get away with it and get big power out of them
but all the tuners here dont like high comp?????

 

Dont believe evrything you read in magazines mate...

If they run high comp on normal fuel then the must run retarted as fuck or special fuel...no getting round it...

 

They typically don't run much boost when on pump fuel so are no way near the power you often see quoted which is normally the fiqure for when running on 100+octane fuel.

Over here fuel at the pumps is in octane which is (ron+mon)/2. 100+ octane fuel is pretty potent as 93 octane fuel is about the same as 98ron super unleaded.

That is of course if your state is lucky enough to get 93 octane, the highest grade you can normally find in california is 91 octane which is the same as 95ron unleaded and 91 is the expensive stuff most cars are set up to run on cheaper 87 octane . There is a simple reason fuel is cheap over here, its rubbish.

 

On the East Coast side of things, we get 93 octane no problem in fact it's the norm. Some places even carry 100 at the pump.

 

It's called a) low boost, big engines, b) low dynamic compression ratio due to silly cams and b) typically only used on the 1/4 drag strip where you don't get enough heat into the engine to drop pistons (unless it's really bad).

 

Physics is the same there as it is here, they arent doing anything that wouldnt work here too.

All down to what you want from it though, if its out and out power in a quick burst for the quarter then fair enough, if its being reliable in top gear when you plant it in the midrange up a big hill and hold it WOT with loads of ignition retard, then not so good.

 

You have to realise that the geometry (bore and stroke) of different engines means that some will take an increase in compression no problem and there will be good gains to have by this (Eg. Evos), where as others, all this causes is major heat related issues requiring severly retarded ignition (Cossies).

So saying high compression is good or bad is a misnomer, as it is TOTALLY reliant to it's particular engine configuration application.

 

Cue Phil and the high v low comp discussion again

 

We have an Evo 6 that we mapped that is running over 9:1 and it made 730bhp.

Between that and Gary's (715bhp @ around 8.5:1 I think), it looks like they are the 2 most powerful GT35 equipped Evo's in the UK.

 

Yes, but what fuel was it running? How much advance on the top line? What were the pre-turbo EGT's?

 

OK, granted it was on high-octane fuel, but both cars make 650bhp on pump fuel.

 

Mike, the OP was referring to zetec motors in the states and over here.

 

What about the other two questions?

 

That makes it even worse, as they rate their fuel differently to us as well, so you have to be careful making direct comparisons to the Yanks.

Without checking, I don't know the bore and stroke of the Zetecs, so couldn't comment on whether these engines (like the Evos) lend themselves to high compression?

 

As Mike has said chamber design and particularly bore diameter has a large part to play in det resistance.

I have dealt with bike engines that can take a bar of boost with a static CR of nearly 11:1.

There are other factors that allow this eg cam timing but it does have a lot to do with their relativly small bore when compared to something like a cossie engine.

 

Zetec 85 x 88

 

This is and will be an interesting thread

 

iv been thinking about this latley to want to see tho outcome

 

is it a well matched bore/stroke that lends itself to high compression motors??
just wondering which way round as a general rule and how well the cvh would fair??

 

Its not just bore and stroke, its also a lot to do with rod angle, as this dictates the piston speed nearer to TDC where Det is most of an issue, for some reason though, that NEVER gets mentioned on PF

 

Chip, hardly anything of relevance gets talked about in these kind of threads, you should be used to it!

 

People keep harping on about high compression DESPITE posts CONSTANTLY mentioning different engine architecture being a defining factor of the compression ratio, and this still gets TOTALLY ignored, so it seems pointless adding another engine design variable, as it will get ignored anyway .