Considerations for running boost

[Appletree IS supercharged]

Hi, i'am looking to take my car to the next stage of tune and am looking at building an engine for the job!

My current engine is a bog standard lump running a eaton m45 supercharger off a mini cooper s with charge cooling making 205bhp.

This time i'am looking to start the build properly as last time was a bit of first as no one from the Uk had supercharged an IS as far the info i could find suggested.

Anyway the goal BHP for this build is 280-300bhp any more would be awsome!

I will be using a Rotrex supercharger running through a large front mounted intercooler and possibly water injection.

The engine on this will obviously need to be uprated to cope with the extra BHP so what do those who run the big bhp suggest?

What CR for 20-25PSI i was thinking 8.5:1

Do i need to change the Sodium cooled inlet valves for solid steel ones?

Is there any point using MLS head gasket? i read alot of people on here and some with m20's on other sites have gone back to the standard BM ones?

What do i need to think about when specing pistons? i see MM ones have no valve cut out and a thicker crown on the turbo spec ones is this nessasery or can i just get some made the same as standard but forged and lower comp?

Any advise would be much appreiceted especaly from people like rob who have been there and done it at the extreames of M42 tuning.

Cheers Matt

[Appletree IS supercharged]

Also when i get my block board out is there any point in trying to get a few  more cc's and going to 86mm or just go for the minimum overbore to keep the block as strong as possible??

Is there much work to do with the head for the FI side of things or does it flow pritty well or is it a case of it flowing ok but to make it flow much better you have to spend alot more money???

Tim_S has suggested i get some non stretch head studs and also big end bolts.

Is there anything else that needs to be NON strech??

Is there anything else that i should pay attention to when building the bottom end??

Cheers Matt

[GrindCulture]

Hey Matt have you concidered LPG? Much more resistant to detontation than even superunleaded. With this in mind you many only need to get a thicker headgasket in order to decompress just enough for it to see 300bhp. However, it's a lot of number crunching needed in order to get the flow rates right, and you'd have to get it on LPG only. I was thinking of doing a similar thing with a turbo once I've sorted the niggles on the touring, better off boost throttle response too, but you wouldn't need to worry about that

[Appletree IS supercharged]

Y i read the artical in PPC to on the R5, intresting but not when you find yourself on the motorway with only petrol avalible.

Its all the hastle of messing around with tanks and running new lines in to. i'd rather build it right in the first place as as far as i could see the only real benifits to using LPG in FI is to help off boost performance and reduce lag which hopefully with the rotrex design there wont be much of:)

Good idea though

[nuvolarossa]

why don't you switch to a M90? a M62 at 16psi on these stock engines is near 250rwhp there is a guy on bimmerforums that has a DASC(m62) pushed to 16,7 psi on a stock M44 engine
You know that rotrex doesn't have that low revs torque that your eaton was giving you, right?
I know that rotrex are smaller and it's easier to intercooler them because there is a lot of space, but rotrex aren't cheap, plus there aren't rebuilts kit for cheap as for eatons and I wouldn't go that way;)
 
[hijack mode ON]
are you sure that you don't want a turbo and save the assle of do brackets for the s/c and align it? with the garrett GT series the lag is low because is a dual ball bearing, and over 3000 revs boost is simply istantaneous...
(we know that under 3000 revs we are only saving fuel, but going over 3000 is easy on these cars and it's their nature)
 
sorry to hijack but in case you want to investigate the turbo route, their spool time, boost threshold here there is a good thread for mazda miatas, look at turbo models, engine displacement and boost vs.revs and you'll see what I mean: http://www.miataturbo.net/forum/showthread.php?t=26641
You'll ask: "WTF miatas if we are in a bmw forum?" => because they have very similar engine to M4x as displacement and revs, so basically you can have a pretty good comparison data. If you was able to align the s/c you'll be more than able to do a turbo conversion (mechanical side), then there is the knowledge side....
[hijack mode off]
 
making specs for custom pistons for a given CR is not simple... you need to keep in mind valve size, valve distance from the piston(valve lift), headgasket thickness, head chamber volume and a lot more... but pistons for your supercharger build will not be differents for the one made for M42 turbo engine, so search a bit in older posts of this section and you'll see that a lot of pistons makers have done them, so they have the specs for these engines...
 
P.S: I had a custom made (by me ) M62 intercooler setup and I know what eaton are on these engine, the good part (whine, torque) and the bad part (assle to fit them)
now I'm near ready to fit all parts of my custom turbo setup to see how is my T3 S60 turbo on my M44 engine;)

[Appletree IS supercharged]

Thanks for the reply
 

i do acctualy have aM62 charger i bought with the idea of up gradeing from the M45 which is running at max revs and making 8PSI, But the problem i have with the Eaton style chargers is the mounting of them to make it easy to intercool or charge cool them, before mine was charge cooled at motorway speeds the inlet charge was 70 degree C!!!! with the charge cooling it went down to 45C which is still very high.

Although there will still be some heating of the charge with the rotrex theres less than a turbo set up and a lot cooler than a eaton.

the rotrex chargers are designd to run 100kmiles with out a rebuild depending on the streign on them, which i would guess i'd never get my car to 100k running boosted as its only a weekend car and for trips to the nurburgring.

As for the power delivery difference between the two types of chargers i do relise that the eaton has alot lower low down torque but thats what i dont like about my car, this my sound odd but its too smooth and drivable like a big lazy v6/8  thers no excitment!!! there is obviously "power bands" and sweet spots but i want a kick in the arse  like a turbo but the anti lag of my supercharger.

Theres also the issue of mounting a big supercharge like the  M90 there maybe a bit of space but i think it would be tight! this is why the M62 is for sale and the moneys going towards a rotrex.

Hers my current dyno run

peak BHP- 205.5 (Red)
peak torque- 176.8  (blue)



My car











Cheers matt