Club G40 Forum
Technical => Turbochargers => Topic started by: Oily Fingers on June 28, 2009, 05:34:14 pm
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Hello, well i knwo i havent posted much on here but i do hide in the shadows alot.
Anyway, i have a 94 reg mk3 GT and i have just scrapped one, keeping the enigne for a little project i want to do.
My idea is to use the spare GT cylinder head, get the ported and polished, and maybe use a g40 bottom end and Turbo it.
Now my question is, from speaking to a mate of mine who is Ford turbo made, he said how about using a turbo off a Ford Fiesta RS Turbo.
Now this seemed a good question to ask all you g40 turboers!! what are your thoughts????
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They are a T2 turbo on fiestas as standard. A lot of people fit the T3 off the Escort RS turbo.
Best way is K03 as you can get the manifold and downpipe off the shelf.
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no reason it wouldn't work but like Dan said since the parts required to fit a k03 (which are cheap and plentiful at scrapyards) it makes more sense to use that turbo. It's well matched to the engine too, no lag at all really and can get you to 200bhp if you wanted.
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GT bottom end will be too high CR but on a 55bhp bottom end im running 0.9 bar boost with no det. No real need for the G40 bottom end if you want to keep it on a budget.
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the reason i thought to use a g40 bottom end, is because i am lead to belive, that the g40 bottom has a combustiopn chamber to cope with the turbo/supercharger??? corect me if i am wrong.
got loads of reading up to do yet so, whatever advice you have, lay it out.
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Yeah the G40 pistons are different giving a much lower compression ratio. I was just stating that its not totally neccessary if you are only after standard G40 power, plus a little more perhaps.
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yea budget 2 head gaskets and retard the timing lol ;D.
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Mine is still on the standard HG.
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so is mine and going to be prob just below 200bhp.
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erm its not the pistons bein differnt that make the change i did lot of measuring the other day and comparing to see which bits out of my gt engine i could use in the py block and its the con rods that are shorter thus lowering the compression why not try a garret t25 or t28 turbo they are plenty full and cheap and as for those off the shelf manifolds they are quite expensive when ya on the dole and arnt perfect costed it up and is guna work out alot cheaper to make my own with equal length pipes which will fit around the oil filter so when im done i will send you a few piks so you can get an idea.
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Ah, how interesting. But Im sure I read somewhere that all engines from 1.0 to G40 use the same rods?
Ive got a T25 on my polo, you have to be careful not to get anything with too bigger turbine housing otherwise you probably wont see full boost until the wrong side of 4500rpm. I fitted a turbine wheel and turbine housing off a nissan terrano, which is a .49, as opposed to the .64 that it had as standard (turbo was off a 200sx S13)
To be fair its not really worth the hassle making your manifold with equal length pipes, there is next to nothing to gain because there is no scavenge effect with a turbo car. Mine is just 4-2-1 with the turbo on the number 4 end.
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conrods for all these engine codes are the same:
HZ,2G,NZ,3F, AAU,PY,AAV, ACM
only the 1W diesel engine has different rods. It's the pistons that give the g40 it's compression ratio. Con rods aren't g40 specific.
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Con-rod length does not affect compression ratio.
I know what you are thinking, that shorter rods increase the total compressed volume (combustion chamber), but also increase the maximum total volume of the cylinder. And as the CR is the maximum total volume over the total compressed volume the two differences you make by having shorter rods cancel each other out.
But, if this were true, then no pistons you ever fitted would alter the compression ratio. The truth is that the volume of the combustion chamber is a far more sensitive factor in an engines CR than the total volume of the cylinder, so altering each value by the same amount does give a change in CR.
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Needs different crank throw.
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Hmm, Im wondering if I misunderstand what you are saying. What I have written seems to make sence to me. I can only think that you misunderstand the meaning of the CR, neglecting the combustion chamber.
So, shorter conrods than stock = Same compression ratio?
Lets work it out for a G40.
so: (((3.14xbore squared)/4)x stroke) + combustion chamber volume
CR: ---------------------------------------------------------
Combustion chamber
I have no idea on the size of the combustion chamber for the G40, it can be derived from the formula but I cant be arsed.
For the purpose of this I will just say it is 50000mm3, bore 75.00 mm and stroke 72.00 mm
Bang the numbers in and we end up with somthing that starts to look a bit like this...
(4416 x 72) + 50000
CR: ----------------------
50000
CR: 7.3585 (:1)
So now lets say we have shorter con rods. Same swept volume (because the stroke remains the same) but the piston does notrise as high at TDC, and at BDC it sits lower. Lets say we use con rods that are 2mm shorter. So now we have more volume in our combustion chamber, 2mm multiplied by the cross sectional area of the bore is 8832 mm3
So back into the same eqn
(4416 x 72) + (50000 + 8832)
CR: ---------------------------
(50000 +8832)
CR: 6.404 (:1)
Which is lower.
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What you're saying is that you've got more volume in the combustion chamber (correct) but the same swept volume (incorrect) this is impossible with a fixed length con-rod/crankshaft, You cannot gain in one area and remain constant in another.
Swept volume always remains the same unless you alter either the stroke or the bore. By swept volume I mean the cubic capacity of the engine, ie the CSA of the bore multiplied by the stroke. So yes you surely can gain in one area and remain constant in the other?
You appear to have neglected the combustion chamber volume increase in your calculations, in your second calculation your combustion chamber volume remains at 50,000mm3. But how can it remain the same if your con rod has changed length?
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Your total chamber volume at BDC also increases, but this figure is not as sensative as the figure for the volume at TDC, the two figures both increase by the same amount.
A 2mm shorter conrod has the exact same effect on CR as skimming 2mm off the top of the piston crown would (assuming a flat top piston). Thats why dished pistons reduce compression ratio.
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Yeah, fully agree :) have removed the crap I previously posted ;)
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No worries.