As my dreaming is turning into an actual desire (to supercharge my M20 rebuild), theres a few things I need to know still.
One of them is about forged pistons.
My knowledge is that forged pistons are custom made pistons which you would use in certain situations. Namely, boosting a 325i (especially the earlier engine) should entail getting pistons that have a lower compression ratio. Am I right?
This takes me to forged pistons, which to my assumption are slightly modified pistons.
Now,
1. Am I correct? Where can I find more info about forged pistons, and who does them?
2. Compression ratios. What actually affects the compression ratio and where can I find a good read about it?
Anything else I should be thinking/learning about?
Forged Pistons and compression ratios
Moderator: martauto
Ah, does Mr. Ant do forged pistons?
I suppose I should have a speak to him one day, as it would be used with the supercharger kit he sells me thinks!
I'm basically trying to find out about unearthing more potential out of the S/C with the M20 motor without going too close to blowing it up!
From what I've heard/read, the rotex charger is good for more boost than the internals of the M20 are capable of.
Oh, and Jason, cheers mate, but is that book aimed at turboing? As I'm trying to go S/C root and would rather read something as good, but aimed at S/C.
I suppose I should have a speak to him one day, as it would be used with the supercharger kit he sells me thinks!
I'm basically trying to find out about unearthing more potential out of the S/C with the M20 motor without going too close to blowing it up!
From what I've heard/read, the rotex charger is good for more boost than the internals of the M20 are capable of.
Oh, and Jason, cheers mate, but is that book aimed at turboing? As I'm trying to go S/C root and would rather read something as good, but aimed at S/C.
Uni is killing the project.
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ross_jsy
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from what ive read, on stock internals you can get a nice 280hp out of a 325i.
thats way more than you will need for an e30 on jerseys poor roads imo. mines lively enough stripped and stock on r888's....
and a forged piston refers to the metal its made of, or rather how that metal is tempered, making them stronger.
thats way more than you will need for an e30 on jerseys poor roads imo. mines lively enough stripped and stock on r888's....
and a forged piston refers to the metal its made of, or rather how that metal is tempered, making them stronger.
Cheers Ross!ross_jsy wrote:from what ive read, on stock internals you can get a nice 280hp out of a 325i.
thats way more than you will need for an e30 on jerseys poor roads imo. mines lively enough stripped and stock on r888's....
and a forged piston refers to the metal its made of, or rather how that metal is tempered, making them stronger.
My dangerous brain was thinking about the fact that if you use a rotex charger, there is a lot more boost available from them, so if your spending ludicrous money anyway, why not over do it?
Ant's info and dyno graph showing a 325i kicking out 280bhp on stock internals was using around 10psi. These little blowers are capable of 20/21psi. Not intending to go all out, but if sorting the engine out with a lower CR, and allowing it to rev beyond 7k (without nackering the rockers, so stronger rockers) along with other parts and a good cam, then pushing that up further could be done.
Haha, and an explaination agian. This is a toy/project car. It will have to be on specialist insurance (roughly 24 days a year aloud, limited milage!). It will get a nice run in jersey once/twice a month, late evenings etc, but still not stupid speeds.
It'll be for taking to the UK, shows, meets, santa pod drag strip?, maybe a few track days and hopefully, the plan is to run it round the nurburgring.
Uni is killing the project.
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m_jermyn
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Ok Nay, forged pistons are exactly that, forged as opposed to cast. We all no anything forged is stronger then cast, thats why they are good for high stressed motors.
Compression ratio is measured by the gap between the top of the piston at Top Dead Center TDC and the bottom of the cylinder head. The tighter or closer the gap the higher compression. Bigger gap gives lower compression. High compression motors generate more heat and are prone to pinging or knocking hence higher octane fuel. Turbos naturally make more heat so they need a lower compression ratio to compensate.
Thats not saying though you cant have a high comp turbo motor as you can. Add some methanol which burns much colder then petrol and you can run silly compression ratios 14.1 and higher.
Maybe Gunni the turbo king can explain better.
Mike
Compression ratio is measured by the gap between the top of the piston at Top Dead Center TDC and the bottom of the cylinder head. The tighter or closer the gap the higher compression. Bigger gap gives lower compression. High compression motors generate more heat and are prone to pinging or knocking hence higher octane fuel. Turbos naturally make more heat so they need a lower compression ratio to compensate.
Thats not saying though you cant have a high comp turbo motor as you can. Add some methanol which burns much colder then petrol and you can run silly compression ratios 14.1 and higher.
Maybe Gunni the turbo king can explain better.
Mike
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m_jermyn
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P.S diesels work with no spark plug. The compression ratio in a diesel is so high (like 20.1) that the heat and the compression alone the the motor make is enough to explode the air/fuel. No sparks plugs needed.
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SteSE
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Interesting thread, I'm looking into force induction. Claims on the internet suggest that the internals on the m20b25 can withstand circa 400 brake, the only thing changed were the rods for b20 items. The pistons were the later, lower compression type.
High revs seem to be the killer, as long as you limit the revs to 6800rpm you can achieve high bhp, reliably.
http://www.e30tech.com/forum/showthread.php?t=3473
High revs seem to be the killer, as long as you limit the revs to 6800rpm you can achieve high bhp, reliably.
http://www.e30tech.com/forum/showthread.php?t=3473
My understanding of the compression ratio was the difference between the volume in the cylinder when the piston is at top dead centre and when it is at bottom dead centre, and dividing these volumes will give you the ratio. You could have a small gap between the piston and the head at tdc and still have a high compression ratio?
Also I thought that people turbo lower compression engines becausee when the turbo kicks in the compression ratio increases, and so the lower compression to begin with the more boost can be used.
That was my understanding anyway...
Also I thought that people turbo lower compression engines becausee when the turbo kicks in the compression ratio increases, and so the lower compression to begin with the more boost can be used.
That was my understanding anyway...
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ross_jsy
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from memory from college, compression ratio is swept volume/total volume.
its just the ratio of how big the gap is at tdc compared to bdc. so say you have a 1cm gap at tdc, and at bdc there is 10 cm, the CR is 10:1.
and with regards to:
"You could have a small gap between the piston and the head at tdc and still have a high compression ratio? "
there will always be a small gap, otherwise your fecked. the piston will never touch the cylinder head in any engine no matter how high comp it is
its just the ratio of how big the gap is at tdc compared to bdc. so say you have a 1cm gap at tdc, and at bdc there is 10 cm, the CR is 10:1.
and with regards to:
"You could have a small gap between the piston and the head at tdc and still have a high compression ratio? "
there will always be a small gap, otherwise your fecked. the piston will never touch the cylinder head in any engine no matter how high comp it is
Cheers lads..
So is Ross right about the compression ratios? If so that makes things easy to understand!
Eventually I'll probably end up using the car a lot, but the point is to make a car that only people who put the time, money and effort into will have.
Ross, remember that kit car? Well theres a boat outside that my dad's trying to get his brother to move. When that goes, the kit car will take its place and then I'm allowed to shove my E30 into there.
When that happens, are you up for a bit of dismantling over a weekend?
So is Ross right about the compression ratios? If so that makes things easy to understand!
Eventually I'll probably end up using the car a lot, but the point is to make a car that only people who put the time, money and effort into will have.
Ross, remember that kit car? Well theres a boat outside that my dad's trying to get his brother to move. When that goes, the kit car will take its place and then I'm allowed to shove my E30 into there.
When that happens, are you up for a bit of dismantling over a weekend?
Uni is killing the project.