fortee9er

I recently purchased a complete 5.0L engine out of 1986 928. I wanted the bigger bore of the 5.0 but not the complication of an interference engine. My thought was to keep the stock heads from my 1983 928 (not a Euro). I have read about the Euro Hybrids but what gains can I achieve using my proposed combo. I realize that the heads will need work to unshroud the valves and take advantage of the larger bore. What compression ratio will result from this combo.
There is a lot of experience on this forum and I will like to hear their advice and/or comments.
TIA

slate blue

Well there is a lot to do right if you want big results, less so if you are prepared for more average results. I have done this a couple of times with more optimisation every time.

I have a thread which details what you can do and expect at least 400 HP at the crank. It is a package and you need a great exhaust. Don't go too small. I run a dual 3" low restriction system which there is also a thread. The intake can do with some work and I ported the plenum. You will need to properly retune the engine as basically nothing will be close enough to maximise your return on investment.

https://rennlist.com/forums/928-foru...fold-test.html

There is a link in the first post worth reading. Good luck and where are you based?

John Veninger

I built a CIS based 5.0L hybrid years ago using EuroS heads, EuroS intake and EuroS cams. Heads were mildly ported and connected to headers and a 3" free flowing exhaust. This setup put down just over 300hp to the ground.
Using stock 83 components is going to give you a bump being 5.0L, but and real gains are going to take a bunch of work and $$.

fortee9er

I am overwhelmed by the amount of information on this site. You people are incredible and WAY ahead of me.
My 5.0L has about 107k miles, assuming the bores are ok and there is no thrust bearing damage what should I do to the block besides the obvious of new bearing and rings? My only experience is with SBF Windsor engines where I had the machine shop zero deck the block, align hone the crank case, balance the rotating assembly, blue print...etc. Does the 928 block require the same level of preparation: more? less?

James Bailey

the increase in displacement will gain something like 15 HP.....not even noticeable when driving the car...Your 4.7 already runs out of go around 5,000 RPM simply makes noise not horsepower the extra displacement will just hit the limit of the cams and intake sooner !!! plus unless you cut very deep valve reliefs it becomes an interference motor. . The magic happens with the Euro S intake and bigger camshafts but even then 300 RWHP is about as far as most ever get.

James Bailey

think of it like you have a Chevy 305 two barrel carb engine and you slide a 350 under it using the same camshaft, heads, intake and carb....not much good is going to happen. and that is 45 cubic inches not 20 . You need a better plan.

mark kibort

having built a few of these engines sucessfully, and have documented the gains, i think you would be best served by getting some euro heads and intake to match to the 5 liter bottomend. if the 5 liter is in good known shape, just pull the pistons and re ring. (best to cut some 2 valve reliefs too ) yes, it will be an interference engine, but so are the 1983 euros too! )
if you do want to get something together, just do the block and heads and do the intake later as that is pretty easy to bolt on.

the gains we saw just for a 300cc increase was 250 rwhp to 290rwhp. that was on pure euro stuff. Jim has a thought that without the cams and the valves, (and intake) that the gains willl be less. 40hp might only be 20hp, but no one knows for sure. thats a guess, but probably a decent one.

Mark

fortee9er

I have no objection to the Euro top end as long as I can find it. I searched eBay tonight and did not find any labeled as Euro cylinder heads. If anyone here has a complete Euro top end please contact me.
Thanks

mark kibort

you can always just modified yours, but the compression ratio is not as good, and you have to port it and put in larger vavles and seats. (this usually is not cheap)

i can say though, the cam is probably more important.

my stock 4.7 84 motor was 240rwhp with euro cams and all the intake stuff.

with the 5 liter and the heads, we got 285rwhp. .

when i built scots, we only did a bottom end change. litterally, in days we went from 250rwhp to 290rwhp with only displacement. the heads seem to not be worth as much as the other components.

they are out there. even if you have to trash the rest of the motor, buy an entire euro motor and use all the bits. you should be able to find some euro heads. mark anderson?

V2Rocket

FORTEE9ER:
I might be able to help your project by buying the stock 4-valve 1986 "S3" cylinder heads off your engine. Maybe that could start your "Euro heads/cams" fund

Please send me a PM.

fortee9er

Thanks but I think I will hang on to them for a while. There is a '86 928 with blown head gaskets that could be a new home for my motor. If that works out I'll still have a 5.L short block to play with.