Shaving P90 head ?

[corolla turbo]

i am at restoration at my L28E from 1983. is hat P90 head and flat top pistons. Now iam thinking about shavin the head to raise the CR. but if i shae 0,02" (0,5mm) i got much timing problems??? does i also have timing problems if i only shave litte 0,1mm to the the head 100% plan. I know i can put spacers under the cam towers, but du i need these also with little shaving or only i shave 0,5mm

[stprasinz]

.007" maximum , .015" shims under towers, and shave .020"? I've shaved something like .070 off? or something I forget now, but added a set of shims someone offered, and increased the compression, but that was a turbo motor, with dish pistons.. eitherway, good luck...

[Tony D]

Performance gained versus money expended and potential problems says 'don't do it!'

 

All you will do is shorten the lifespan of a head that is no longer in production.

Once you shave it off, it's a bugger to put back on!

[corolla turbo]

i found spacers fpr the cam towers, witch are needed after cylinderhead RESURFACING. but 0,02 Seams very much?

 

i only plan to shave a little, dont know whats the minimum the engine builder can shave

[NewZed]

I believe that you can get essentially the same effect for less money (in the States anyway, not sure about Europe) and effort by using an N42 or N47 head. I haven't done it myself so can't speak to degree of difficulty but I think that the heads are interchangeable, as long as you get the right head gasket (match the block seems to be the right way) and make sure the oiling system is right (spray vs. through-the-cam). Search "N42 head on F54 block" and you'll find lots to read, and you should be able to confirm how hard it would be.

 

If you decide that you really need the higher CR. You said that you were cutting the head to achieve a higher CR but now you say you only plan to shave a little. Don't you have a target CR in mind? The discussion (argument) on the benefits of running a high CR in the L motor using pump gas has, from what I've seen, been going on since gas quality dropped when they took the lead out (you'll see it if you use the search term above). Maybe German gas is of higher octane rating than US and you'll be okay.

[corolla turbo]

I have an N42 head at my actual engine. this is L28E from 1981, OEM dished pistons and N42 head. I think can take these head, with my 1983 flat top pistons but i think this will make to much compression. Because OEM ECU doesnt have an knock sensor.

 

i have no planed CR, think oem is 8,8:1 ?

this is ok but little more doesnt kill the engine. but shving a lot, makes timing problem. because of this, i asked what i can shave without have problems with knocking an timing

 

we have 95 octan an 98 octan. best is 102 octan but very expensive. so i only use 98oct

Edited September 15, 2011 by corolla turbo

[NewZed]

This calculator might give you some ideas - http://www.ozdat.com/ozdatonline/enginedesign/

 

Flat tops are shown as "Late L28" in the Pistons category. You can use negative numbers for head gasket thickness to simulate a shaved head (subtract amount shaved from head gasket thickness planned). You'll get a warning message about piston height if you "shave" off more than HG thickness but it will still give you a CR.

 

An N42 head on a stock F54 block with flat tops and stock thickness HG would give 9.75:1 CR. Your 1983 engine should be at 8.8. The N42 head with dished pistons is at 8.3.

 

I'm only writing from what I've read. People who've actually done this kind of modification will probably have more valuable comments. Also, I'm not sure if Europe uses the same octane numbering system as the States so that needs to be considered.

 

Considering Tony D's remark, and what's been written out there on the internet and on this forum, it seems like it might be a lot of effort and money for a small increase in performance, with an increase in the potential for future problems.

 

Good luck.