Thread: is 9.3:1 compresion too high for turbo?

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I've got an m90/euro 3.5 high compression engine in my 79/635.
I've just gotten a 81/745ia donor car for my next motor.I'd like to use the m90 bottom end as it is larger 3.5 vs 3.2, but I'm not sure if comp ratio is too high. the 3.2 is lame off the bottom, vs. my 3.5 will burn out nicely, also the 3.5 has great midrange torque for around town,so I'm thinking just a little turbo boost on topend would make the 3.5 very streetable & fast.anyone have experience with high comp ratio & turbo?
thanks
marc

you had a lower comp engine. We've run 12+psi on an 8.8:1 M20 non-intercooled... though, running 9psi with less timing retard on this engine performs better.
The problem you face MAY be that the k27 will not be suited to the application.

I also have a 79 euro 635 with 5 speed. It needs new bearings in the bottom end and probably gaskets and oil pump. I'd like to turbo it while the motor is out of the car. I think I know turbos pretty well and would probably use a Powerstroke Ford turbo which is .84 A/R turbine 1.10 A/R compressor. I know it's slightly large and I won't see much boost until 3000rpm or a bit higher, but that's fine with me. It flows 615cfm and is good to 570 flywheel hp. My questions are:

1) I have LJet injection and don't know what mods need to be done. I know I'll need bigger injectors. Can I use standard Bosch style injectors with my motor if I make a custom fuel rail? Do I need low or high impedance injectors? Would 40lb/hr be a good starting size?

2) Can I swap my block with an american 3.5L to lower my compession? Meaning, is it the piston dish or chamber volume that makes the euro motor higher compression? If I do this swap, should I go ahead and take the pistons out to open the ring gaps a bit?

3) Back the the EFI stuff, what do I need to do as far as AFM and fuel pressure regulation? Can I cheaply and easily switch it over to MAF? I would think a MAF would work better than the swinging door AFM with boost... correct?

I have a customer with a '96 318ti that wants a turbo kit. I would like to work with you guys for this and other BMW's that come into my shop looking for turbo setups.

I have a full service facility in McLean,VA with over 10 lifts and 7 techs, etc. I look forward to hearing from you.

Thanks,
John

john@revhighmotorsports.com

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I use in my 635 Csi 10:1 compresion with 3 turbos IHI at one presure maximal of 15 psi without problems

I have the 3 turbos Intercooler air to air and 3 airfilters of motorbike (very small filters) we have in wheels 501hp

Note : The only internal in engine change is forgered pistons

Of course I change L-Jectronic by 1996 Motronic Control Engine and use Mass Air sensor

You can see photos of my 635Csi in : http://www.elecauto.com/635i.htm

This photos is old when the car not have installed the 3 turbo

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Jorge Priotti

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