Iwanna928

I have been looking at a lot of options for my 79 US CIS model. It is time to put things into perspective and put away my fantasy's.

I am looking at two options to start. They both concern changing my shortblock and keeping the rest stock for now.

The shortblock's I am looking at are a euro 4.7 shortblock( Does it need to be a certain yr?) and a 85/86 5.0L shortblock. How many ponies would this take my 928 to. It is currently at 203rwhp.

Is one swap easir than the other. I would have to fly cut the pistons on the 5.0L.

Concerns are CR's and ease of swap.

Also if one refreshed there heads and put in larger valve would this be money well spent. They should flow a little better and I understand that other things would need to be added to maximize flow, like all the euro top end stuff that I could add later.

End result I am shooting for is a hybid of sorts and make around 275rwhp.

Stephen

dprantl

4.7 Euro short block with EuroS top end will be around 270-280rwhp. 5.0 liter hybrid with EuroS top end will put you to 290-300rwhp. Almost the same output, except the 5.0 will have more torque at lower RPM.

Dan
'91 928GT S/C 475hp/460lb.ft

Iwanna928

What can I expect with a 4.7 or 85/86 shortblock with my top end to start.

I will be doing this in stages and was wondering what to expect performance wise with just the change in shortblocks and which stortblock would be the better option.

Stephen

dprantl

It's hard to say because no one has done such things. I will take a shot in the dark and say the restriction caused by the old Euro stuff will cost you about 40-50rwhp in either configuration.

Dan
'91 928GT S/C 475hp/460lb.ft

GregBBRD

If this was easy/cheap, there would be a line of early cars around the block, waiting to have it done.

Why not find a Euro S model and transplant the whole thing? Got to be the easiest/cheapest way to get close to your goals.

When you get rich and famous, prepare a 5.0 lower end and put the Euro S pieces on that.

danglerb

I really doubt your car is putting out 203 rwhp, 180 is a better guess for a 4.5L in stock condition. Power comes from how well the engine pumps air through, yours is restricted by the heads, cam, and intake, so changing the short block will make very little change, much less than exhaust work.

Iwanna928

Danglerb

She dyno'd at 202.6rwhp to be exact! The first thing I did was dyno her so that as I moved along I could see the improvements.

In my post when I bought the car I posted a link to my photobucket page that had a video of the dyno run.

The car isn't stock it came with headers and a custom duel exhaust w/ rmb, so that is what got her to 203rwhp(I round her off) otherwise I would agree that she would have been around 180. The exhaust is restrictive in the OB'S

Stephen

Iwanna928

I have a member that has a Euro 4.7 that lives locally to me. The cost of the shortblock would be 700 bucks. Let say I have a budget of 1k to refresh it then I would have 1700 into the bottomend. Then I would switch the shortblocks and that would be the first step into my project.

A complete Euro transplant I believe makes more sense but I would have to find a CIS Euro in good shape still have to freshen every thing up and switch them out.

So the shortblock could be a 1st step and would be within my budget.

Stephen

GlenL

What's a "short block?" I ask because it means different things in different parts of the country.

To me, that's $600 more than it's worth. The plum parts of the Euro engine are the heads, cams and intake. WUR, too. Without those it's just 2mm wider pistons with notches you don't need.

Iwanna928

Block,pistos etc. The compression is higher than my 8.5.it is 10 something, can't remember. So I quess from your statement thatyou think it would be better to start w/ a 5.0L and go from there.

Stephen

GlenL

The higher compression is due to the heads having smaller chambers. There's numbers for all of the volumes out there.

Iwanna928

Thanks, I thought it had to do with the pistons.

Stephen