Tazzieman

Stuart tells me it is...Armin will know

stuartbrs

The compression was definitely played with a bit according to the guy that built the engine. Tazziemans car certainly feels like the most powerful 928 Ive been in/owned, compared to a normal 81S, S4 and GTS. Of course, the S4 and GTS must be a bit heavier? The motor was reliable for the 11 years I owned it, apart from having the head gaskets replaced in 2011. The gaskets got a bit second hand as the car sat for two years with old coolant.
It was never dyno`ed when I owned it, so this is all seat of the pants stuff, but the motor in that car is a bit special.

Mark Anderson

To be totally clear, has anyone built a 5.0 with euro heads and cams and not cut the Pistons?

mark kibort

Youre out of your element here.
building stock stuff, puts down 290rwhp Ljet and 310 to 320, repeatable and these same results were held on more than 4 differnet dynos... and why wouldn't they be identical... accelerating rollers is accelerating rollers... there is not much that can vary to make much of any different at all and are very accurate.

Greg, also remember we used your trick of optimizing the piston offset for which you said might be worth near 10-15hp.

the 3 cars we did this to , were all 250 ish when starting, and did gain 40hp by adding 300ccs.. Scot's was a great example. no other changes at all were made.
its reasonable to think that the USljet version of a 4.7 liter might not make more than 250rwhp, as it had better cams than the euro 82 stuff on the US 4.7 that had made 232hp before other subtle mods.

the 4 cars I worked with before , the best 4.7 made 237-243 rwhp on 10 to 12 dyno runs. bolting on the heads and 5 liter, made 280rwhp with the equal length headers bringing it up to 290rwhp. Keep in mind, that was heads and 5 liter block. so, the net gains might have been going from 255 if that US Ljet 4.7 made 255hp it went to 280rwhp , so that's only 25hp.

scots was full euro at 250rwhp and with the 5 liter bottom, went to 290rwhp as well.

pettys euro with the 5 liter bottom end , made 310rwhp, but it was CIS. this is your "stock euro" in the 275 range to measure against) by any measure , that's your 35hp.

I have , nor has anyone else seen a euro that made more than 275rwhp .
that seems like about 35hp by any measure

the US versions Ljet, are restricted to about 20-30 less.

its the way it is.... to question the dynojet is just plain silly, its as actual as a dyno can be.

mark kibort

the flycuts are very subtle... even with the late model euro S cuts , its an interference motor. the earlier flycuts were much more deep and were non-interference. the shallow cuts still allow the valves to hit at .3".... (lift is near .45"). without the valve cuts, the engine will still run without hitting, but makes that interference a little more non-tolerant!

the compression without the flycuts is not much different. I think they both are about 2cc. maybe it goes from 10.5 to 10.7:1

123quattro

I didn't cut my US 4.7 pistons when I put Euro heads on. It's interference either way so I don't care. Runs just fine. I would assume you could do the same on a 5L bottom end.

Mark Anderson

That's a dangerous assumption. Your 4.7 already had some valve relief. The 5.0 piston has nothing in the location needed.

mark kibort

you don't understand the differences.. all the cars will probably run. the valves chase the pistons down the bore on intake (max lift is mid stroke) and the piston chases the valve on exhaust. (max lift is mid stroke ).

there are valve reliefs on the US pistons that are in the correct position and have some clearance built in to fit the extra 1mm wider valve at the edge. the 5 liter piston is a 4 valve set up and the valve reliefs are no where near the same position... so if you put a 5 liter piston using a Euro 4.7 liter head, its like using a perfectly flat piston. it might work, but it will or could be impossible to rotate the engine around without the cams in perfect position. the 45 degree trick might work on the crank, but there is no guarantees. I think the shallow cuts were .2" and even with that, there is contact at TDC at .3" this means witht he cuts, the pistons contact the valves at TDC with only .1"

123quattro

I'm pretty sure I understand how it works...

mark kibort

If so , then why would you say that you put on euro heads on a US 4.7 and thought that meant that it might be ok to do that with a 5 liter bottom end and piston?

the cuts are totally different... in other words... if you need the cuts, in the positions they are, then bolting on a Euro 2 valve head onto the 4 valve bottom end would not work, right?

also you say, runs fine.... sure, most engines dont need cut outs to "run fine", but some might want to be able to turn the cam without hitting the piston top during servicing. (cam belt change) OR, if there is a situation where you slip a tooth or two (or three). a flat top piston might make it so you cant ever move the the cams without them connected in perfect position to the cambelt and crank.

here is what we know.

the euro 4.7 heads can work with US 4.7 pistons because there is a 1mm of safety margin with the US pistons to accommodate the 1mm larger radiused valves.

the 5 liter pistons have cuts in totally different places., so if you dont flycut the pistons, the pistons look totally flat top with nothing on them.

the euro 85 pistons have .3" clearance to hit the cut outs and cam lift is about .45". on the euro 80-83 pistons, those valve reliefs are much deeper and allow for a non interference engine.

some information about valve cuts and piston position:

summary: if you remember about setting cams in the S4, you know that with 20degree crank movement, the valves get depressed about 2mm max. never is the piston at TDC, and the valve fully depressed (12mm). but the total clearance between piston and valve at TDC if the valve was fully depressed is .3", and cam max lift is .45". so that is the problem. its also why you put the engine at 45 degrees so that there is not a piston at TDC and the valves cant hit the pistons.

https://rennlist.com/forums/928-foru...need-help.html

terry gt

I am planning on putting a 85 5L bottom end under all the performance 16V stuff I have . And am looking for advice on preparing the short block . Its a 85 with 50 K on it , bores look perfect .
top end list
heads are fully ported ,intake flows 280 , 944 bigger valves /sodium cooled exhaust valves
titanium spring retainers
HP springs
billet cams 110 lobe centers .515 lift on the intake
euro runners
85 32v throttle body
no air flow meter
3 inch velocity stack
32 #injectors
haltech engine management
MSDS ceramic coated headers
Y pipe into a single 3.5 SS system

mark kibort

dup

mark kibort

I would just re-ring the pistons and notch them. those injectors might be a little large. 24lbers might be the best suited.

terry gt

Thanks Mark for the response . how deep are the notches ? did you rebalance the rotating components ? Do the bores need to be re polished to seat the rings ? The injectors are very controllable with the laptop , fully sequential / cam sensors / tps / map / air temp / water temp . with a 5.8 L bottom end was getting 300 rwhp at 4000 rpm and running out of fuel with 24# injectors

Ducman82

when i did my motor, the short block came from a 40k car that had run nothing by synthetic oil, super clean. bores were in excellent shape, so all i did was rings, rod bearings, and notch the pistons.