Compression ratios (come and add to my piston spec list too)

[Turbo-Brown]

The time has come!

I'm going to call up Ireland Engineering next week to get a quote for and discuss this stroker kit they sell.

Seeing as I can have any compression ratio I want, what do we reckon I should go for?

I reckon that about 20psi will see a 2.9litre engine make about 450bhp but I'm undecided on the CR.

My feeling is that 8:1 would be safe for use with regular unleaded fuel but I'm very much open to persuasion on this!

Cheers!

Alex

[march109]

Are you going to be running the engine on F.I?

I was looking at this, current exchange rate puts the 2.9 kit at under £1000 and comes with lightened and forged parts which has to be a bonus. I emailed them a day or two a go about postage and import tax but no reply as yet.

[Turbo-Brown]

I sure am going FI

God bless the strong pound!

[Ant]

20 psi should see well over 450 Alex !

[march109]

wanna see if theres a cheeky discount for buying two? Depending on what they come back with I might be in, otherwise its back to looking for a m52 crankshaft.

I'd go for 9:1 or 8:1, I was thinking of building the 2.9 and then (when finances allow strapping on an ant special super charger kit). That would require me to run a decomp heas gasket any way I think so the lower the compression the better. Apparently the 3.0 M20 kit though makes the e30 power to weight comparable to a e36 m3. That can't be that bad .

[Turbo-Brown]

Hmm, thought on the E30tech is that the IE kit is overpriced and that you can get forged pistons custom made over there for about $500, then just use the crank and rods from an M52.

Going to probe a bit deeper into that because if it turns out to be that easy....

How much would an M52 cost? Apparently the rods are forged and about 100g lighter than the M20 ones (not that the M20 rods aren't forged, but the weight saving is worth having)

I'm basing my veeeeeeery rough assumption that I'll need 20psi on the following (feel free to laugh)

171bhp/2.5Litres=68.4bhp/L

68.4bhp/L*2.9L=198.36bhp

PR @ 20psi = 2.36

2.36*198.36bhp=468.1296bhp

I know it's nowhere near that simple to work out what you'll get but it's a vague idea.

Will be more than happy if I can get to 450bhp on less than 20psi though!

[DanThe]

Got a set of rods here if your interested Alex

[Turbo-Brown]

From an M52 Dan?

Now, where can I get a crank and the spacer for the nose from?!

[Gunni]

Hmm, thought on the E30tech is that the IE kit is overpriced and that you can get forged pistons custom made over there for about $500, then just use the crank and rods from an M52.

Going to probe a bit deeper into that because if it turns out to be that easy....

How much would an M52 cost? Apparently the rods are forged and about 100g lighter than the M20 ones (not that the M20 rods aren't forged, but the weight saving is worth having)

I'm basing my veeeeeeery rough assumption that I'll need 20psi on the following (feel free to laugh)

171bhp/2.5Litres=68.4bhp/L

68.4bhp/L*2.9L=198.36bhp

PR @ 20psi = 2.36

2.36*198.36bhp=468.1296bhp

I know it's nowhere near that simple to work out what you'll get but it's a vague idea.

Will be more than happy if I can get to 450bhp on less than 20psi though!

Math is fun and all
but there is a aspect that is beeing missed and that is the new VE of the engine assuming 170hp is made at about 83% VE (just a rough estimate)
with your efficient turbo system exhaust scavenging will have a great effect on the VE of the "N/A" aspect of the engine.

I´d assume the engine to get more efficient , well alot actually as now wasted exhaust energy is put into mechanical again. soo even at 100kpa the engine is stronger.
Anyway. Assuming 95% VE after the turbo conversion at a pressure ratio of 2.36 you´ll be getting 466whp, again just a rough estimate.

[Turbo-Brown]

If I can make my 450bhp on less boost, then so much the better

[Gunni]

exactly

On my T4 setup I think I´ll need to see the other side of 20psi.

Again to compression ratios.
Select something like 8.2-8.5:1 or there abouts.
The M20 head is alright in turbulence and thus resist fairly to detonation. But since your building a massive turbo boost low down , turbulence tumble and swirl are less and knock is WAY more likely. Even straight 8:1 I think would be a good bet.
As your not going to have ANY lag and you will have 2.9L anyway.
There are no benefits in higher compression in your setup.

[maggspower]

hi there @ Turbo-Brown ive gotta say i'm loving your work your other thread has got my mind well and truely boggled!!! hats off to ya dude.

anyway just picked up the m52 bottom end i bought off ebay tonight and saw you talking about the rods.

so i whiped one out and weighed it against an m20 one.

m52 135mm rod 590g

m20 130mm rod 620g

these figures are very aproximate as i was using a kitchen scales, i would say +- 5g but you get the idea

if you are going for custom pistons i would say the m52 rods are the ones to go for. they could no doubt take a few more ponys to

they have a completely different section as well more like H than an I but at 90deg to a normal H beam. I'll put a pic up if you want

keep up the good work

[Turbo-Brown]

Hey Maggspower, welcome to the Zone dude!

And that's a fair old weight saving there! Guess the 135mm M20 rods would be heavier yet!

Be great if you could post a pic

Gunni, I've been talking to JE about 8:1 pistons so I'm glad you've suggested that CR too

Going to ring the company this evening to finanise the details and then order them tomorrow hopefully!

Guess if I ask for pistons to suit an 85mm bore, I can just have the block bored out to 85mm and the pistons will slot straight in?

[reggid]

Hey Maggspower, welcome to the Zone dude!

And that's a fair old weight saving there! Guess the 135mm M20 rods would be heavier yet!

Be great if you could post a pic

Gunni, I've been talking to JE about 8:1 pistons so I'm glad you've suggested that CR too

Going to ring the company this evening to finanise the details and then order them tomorrow hopefully!

Guess if I ask for pistons to suit an 85mm bore, I can just have the block bored out to 85mm and the pistons will slot straight in?

i would wait and let the machinist achieve the proper clearances once you receive the pistons.......

[Turbo-Brown]

That's a fair point, guess if I say to suit the 85mm bore and then give the pistons to the machine shop all will be well.

So, guess I need the following spec (if anyone can think of anything else then please feel free to add to the list!)


Pistons to suit:
1990 BMW M20B25 block
135mm M52B28 rods
84mm M52B28 crank
85mm cylinder bore
Turbocharged engine

8:1 compression ratio

Ceramic coated crowns and moly coated skirts
High strength gudgeon pins

Think that's about it?!

I've convinced myself that standard rings are more than up to the task, especially in light of the problems people have had getting a good seal with "total seal" gapless rings.

[maggspower]

forget what i said last night, the scales i was using are the equivilent of an elastic ruler!! i have also got a 135mm m20 rod for a direct comparison.

finished work early so went to the post office to weigh the rods with a decent set of scales (was going to go to Dai Escobar Evans but he didnt want oil contaminating his product )

any way m20 135mm rod 680g

m52 135mm rod 610g





i recon most of the weight saving is on the big end cap, its much smaller.

Where are you getting your pistons from, Top End Performance Hollywood?

What are your issues with total seal piston rings, i was going to use them for my build. Going to think twice now as yours is not the first bad report i've heard

cheers Maggs

[Turbo-Brown]

Top end performance indeed! I sent JE and e-mail and they put me straight onto TEP.

Sent TEP a few e-mails and they got straight back to me and answered all my questions which is always encouraging.

Think total seal rings are fine if you can get masses of pressure behind them straight away after first starting the engine. However to do that, you need full throttle and when my setup is so hazy on the management side I can't do that.

Ideally you'd load normal rings like that too, but they don't seem to react as badly if you can't whereas total seal rings seem to leave you with a smoky engine if they're not run in absolutely perfectly.

Probably 99% of the problems come from people being unwilling or (in my case) unable to full throttle their brand new engine.

So is the M52 rod the narrower one? Hope that is stronger than the M20 one!

[maggspower]

yes they are thiner but they are much wider almost as wide as the small end bearing


the other thing is those pistons are going to be lighter, less mass to change direction at TDC. Although thats not gonna make much difference when you have 450bhp!!!!

TEP is a good site they seem realy clued up on the m20 motor too. I just wish it was still economicaly viable to have stuff like that made in this country, i havent looked in to it but there is no way tou are going to get a set of 6 custom slugs for £450 in this country

total seal rings
that does sound a bit scary WOT on a newly built engine, ones i've built i try to run at fast tick over as it's not so stressful on the cam, then an on and off the throttle 20 miles, but i know what you mean, force them in to the cylinder walls, stop them glazing over must be the key.

looking forward to the next installment

[Ant]

bedding the rings in N/A is the best method, total seal are nice but not really a must have item TBH

perhaps a group buy on the IE kits for a month would be a good bet, see how the land lies and whack a large order in for extra discount ??

Me Like !

[Turbo-Brown]

It would have to be a very hefty discount!

A set of forgies from JE (via TEP) comes to $895 which is bloomin' cheap with the exchange rate being as it is!

For the spec I want, I'm looking at about $1250 which will hopefully translate to about £750 once the import tax is paid, including delivery.