mark kibort

Got the block and pistons back from the machine shop. all balanced with the crank to .25 gram! (i guess that's good???) 4.7 block bored to 100mm, and there aint much cylinder wall left what is the thickness that the cylinder wall has to be? we went to 100mm from a 97mm bore, got to imagine when a 5 liter is punched out to a 6.5 liter, that its about as thin. i measure near 5mm, but its not even. (that also worries me)

Anyway, we are going to put the crank in this week, along with the pistons and then start pulling Scots blown headgasket brand new 4.7 euro motor out of the car! ( at least we hope it is a blown head gasket, i think its warped heads so we will need a hair cut and an shave for those!)

This is a true basdard engine. 84ish crank, 82 rods, with 2 unknown year, 85 pistons, and an 82 euro block bored out to 100mm. What is nicer, i think, is the larger rod bearing oiling holes of the later crank for this engine build up.
Even timing belt Tensioner adjuster componets are made from 3 different year 928s. porsche 928, a car that would make Eli Whitney proud!

Mk

danglerb

Johnny Cash had a song about a Cadillac you might want to listen while putting it together.

IcemanG17

MK
5.0L 16V hybrid.....euro cams and intake? what do you expect it to dyno at... 300whp?

Bus

I need more details!!!

Do you plan on doing anything to the bores after the bore/hone?? (like coat the block?)

What pistons? Custom, off the shelf aftermarket, 100mm from something else?

mark kibort

Since we have done this exact same thing before, i think i have a reasonable expectation. actually, there are some subtle differences.
1. devek B1 cams vs my old 5 liter euro had the 82 euro cams
2. pistons valve cut outs, oriented for the pistons' offsets. (only done on the S4, not on any other model. good for possibly 10hp)
3. block was shaved slightly, so there is a .020 piston rise over the block surface.
4. heads will be shaved (i think, if they are warped like we expect)

since my part euro 5 liter was dynoed at 293rwhp, (but devek equal length headers), I would expect this engine to be near the same, maybe closer to 300)

mk

mark kibort

No, the shop knows how to do the 928 block process. we will be doing nothing but installing the 2 valve cut , but stock 1985 5 liter pistons (100mm, thats how we get the 5 liter)

Ill take some pictures of what we have so far.

Mk

danglerb

Mark you mentioned 85 in a few posts, Brendenc's block/pistons that I am thinking about are 86 IIRC, are those the same?

Shaving the block and heads, whats that going to do to the quench zone and compression?

mark kibort

"IIRC"? 85 and 86 US 928s have this same 4 valve 100mm piston that you use for this kind of conversion.

Im a little worried about the shaved block, that only raised compression slightly. as was said, i think it was only about .010-.020". i dont know what it will take to fix the heads, hoping its just a blown head gasket. Scots car is FINE for street driving and street racing. No issues. HOWEVER, on the track, he pushes out water and drains the system in 7 laps. Big difference street punishment vs track. so, i be the issue is going to be slight, and this will make it hard to find too!
mk

danglerb

I was thinking the other day that track use is almost as tough on a motor as marine use. I never gave it much thought until I went out on a friends boat and as soon as we cleared the harbor it was full throttle for a couple hours.

mark kibort

full throttle, but no blips and no WOT at high rpms. WOT is not that big of a deal, especially at cruise with a big block that is putting out only 50hp/liter!

Its the rpms, change of rpms, g forces, and heat that usually is the killer

mk

danglerb

Most of the big deal is not being able to coast to the side of the track and walk back to the pits. We blew a water hose about a mile from a rocky coast, and got back home on a 5 hp outboard.

Both have lots of stress, just not the same ones. You worry about your shark, in the boat we worry about all the sharks.

I have had bad thoughts going through my head lately, like gee I wonder how fast I can safely spin a 928 motor. Chances are I will stay below 6300 rpm and behave myself, but Mark A says its fun with a 7200 rpm redline. I need to stay away from that crank scraper web site.

mark kibort

see if you can notice what is unique with these pistons. #2 and #6 shown.
Also, I wonder if scot trusts these automotive engineers working on his main bearing tollerance values.

GUMBALL

There have been problems with boring those blocks, and not using sleeves. Part of the problem is from the block casting not being of consistent thickness, another problem is the grain structure and silicon content of the metal. Have you checked the bores to be sure they are neither tapered nor oval? Not trying to be negative, but trying to prevent a future problem.

SharkSkin

The reliefs are not cut consistently -- a minuscule issue in the scheme of things, but it's odd... usually machinists like things to all line up symmetrically as they stack the finished parts. The walls look thin to me, but that's pure armchair quarterbacking... I don't really know what the lower limit is on wall thickness, but I've heard others express concern at 6mm.

Vilhuer

5mm is too little in my opinion. Reynolds says 6.35mm minimum IIRR. Good think is that towers get wider lower down. If you want to be sure how wide they are its possible to measure them fairly accurately with home made special tool for example.

https://rennlist.com/forums/928-forum/211311-how-to-recognize-perfect-block-for-stroker.html