I've been thinking about boring an 85/86 block to use 104mm pistons. Purpose is to increase power just enough to hit what I think is a sweet spot for an early 928 between 350 and 400 rwhp that a 100mm bore motor might be just shy of, and to do so at minimum cost.

Intake and heads will be Euro S2 with very minor port match and cleanup. Cams are from a US 80, ground and welded by WebCams to a basic hot rod 244 @ 0.050 duration .506 lift profile. US LH 2.2 brains sharktuned with stock injectors to start with. Crank also stock, likely Chevy drilled.

Custom pistons, or new or used 944 S2 pistons?
Custom pistons are the slippery slope, since they require custom rods and Nikasil bores, might as well get the stroker crank, and that is NOT what I have in mind. I want a low cost high revving motor, so making the 944 S2 pistons work may be the key go/no go issue.

Bore and lap block, or Nikasil?
Despite the cost, I am thinking hard on the Nikasil for flexibility in piston selection, reduced friction, and proven nature of the process.

Custom or modify a common stock rod?
This will depend on piston used, but some likely candidates turned up if I would be using the 944 S2 pistons.

Valve springs and lifters?
I have two sets of used 944T valve springs, more than a few sets of used stock lifters, and have been told not to use the light weight VW lifters with a WebCam. If any doubt remains I will get new parts, but I don't want to spend $500 if I don't need to.

 

Just for old times sake......


AHH NOW WHAT THE HELL WOULD YOU WANNA GO DOING ANY OF THAT FOR!







welcome back

 

I have a full matched set of 968 pistons and a GTS crank ... as well as 85/6 cams For sale, as always.

 

Sterling, does the 85/6 block that Dangler proposes, not a thicker one than the stock S4, and therefore perfet for overbore?

 

Mike - Speak to Chris white about the pistons. He may have some ideas for you. Forged pistons, but not JEs - and they are coated properly as I understand. That would allow alusil being left, and no need for nikasil. Pop! I just took 2k off your cost.

 

Why not the stroker crank?

Stock pistons with new rods and a stroker crank. Might not cost much more and will net 6.0L, and should also net the numbers you want or even a little more.

This way the stock cylinder bores will allow more power adder later like Boost or Nitrous. I'm a little scared of taking 2mm away from the cylinder walls all the way around.

 

Sorry to make such a long post, drives me nuts to read them. The reason for me being so fussy is that I want to make more than just a motor for myself, I want to come up a recipe for a motor with power greater than a normal hybrid, but costs MUCH less than a stroker.

Before pestering anybody directly I'll be doing more reading and searching. People don't like being asked a bunch of detailed questions, then not having the advice followed.

I've been following the thread with Bud Hart in it, very tasty stuff for the 16v inclined.

Chris White and Calico coatings I recognize from the 944 groups. 944's seem to be where a lot new stuff is happening.

Coatings are fascinating, very tempting, but very hard to find out what really works until they have been used a fairly long time. What I have read shows mixed results with Alusil.

Stroker plus custom rods = $$$$, and a more torque than top end power curve. I want a strong top end, and the direction of improvement won't be boost or nitrous, it will be breathing, bigger valves, which I think are already limited by the 100mm bore even stock.

If all the lower cost 104mm bits actually work, used 944 pistons, no Nikasil, finding a common rod within resizing range of fitting, the added cost to a base hybrid is VERY modest, maybe as little as $1500.

Some advice so far is against used pistons for a serious motor, something about ring lands. OTOH used Porsche pistons are known to work without issue in a bare Alusil block, and going to new pistons starts a slide to a lot more expense. Piston choice seems the key, once decided the rest falls into place.

***********

I've been thinking about this motor for a LONG time, and making some progress. I'm confident it will be done, but also confident that I will want a working motor before I am sure about how to start this one, so logical thing is to build two motors. A normal hybrid now to learn on, and the second one as each issue is resolved.

 

Very cool. Cheap, reliable, more power!

 

I have built one, a 5.4l 16v using an 85' euro top end, base ground cams and 89' 2.7l pistons with an 85/6 block. It has been converted to late style injectors and has a clean-up port match done. I believe it will be in the area of 390/400 fwhp when I finally get around to firing it up. It was built for a long term project so it is still sitting on a stand waiting. Everything was either polished, powdercoated or cad plated and it uses 85/6 exhaust headers also. I will post a pic or two on Monday when I get back to the shop.

 

Please send few my way. After searching for over three years all I managed to find was same thickness or only slighly better than best S4 blocks. I'm still looking for that magical super thick 32V block. Could use one. Especially if its cheap. Can have up to 2mm deep problems in cylinder walls.

Cheap 104mm setup do not exist and probably never will. There are many reasons and all of them must go away for really cheap setup to exist.
1. Finding thick block, gets expensive fast if one has to buy many complete S3 engines to find thick block
2. Machining block to 104mm costs $1000+
3. Alusil pistons are not cheap, not even good used 944 S2's
4. All used pistons available will require custom rods as 3L setup compression height isn't same as any 928 engine, another $1000+ even if cheapest possible Chevy small block rods are correct size for maching them

All together, above means short block is coing to cost $4k+ no matter what. Basically doing 6.5L stroker costs only stroker crank and difference between 944 S2 and 968 pistons above any feasable 104mm bore setup. There really isn't point in making 5.4L using 104mm pistons as same displacement can be achieved more cheaply by simply using GTS parts in any 32V block as long as tolerance group is correct.

 

Dave, I am looking forward to hearing more about that 5.4L. Does that estimate include using a Y merge? How hot is the base ground cam, vs my 244 duration .506 lift?

When I hear expensive, I always ask do you mean expensive or PORSCHE expensive. I suppose the converse is cheap and PORSCHE cheap.

The base hybrid motor is about $5k depending on sourcing of parts, work done yourself, local machine shop costs etc. with expected results in the area of 285 rwhp.

Brendan, what does the guy down in SD charge to bore to 104mm and lap?

OTOH if 285 rwhp doesn't ring the fun bell, and the bell must ring, it costs what it costs. 350 to 400 rwhp I think is the sweet spot of the funzone for an early 928. I am open on how to get there cheapest, with the caveat that my personal preference is a high revving motor, not a low end torque motor.

Either stroking or boring should reach the target rwhp, but I don't think doing both is required. Its more power to do both, but I think edging toward a less fun car. A basic tenet of fun car to me is that the wheels spin SOME of the time, but not ALL of the time.

Not finished with my thoughts, but lunch is calling, more later ...

 

With your current cams, your hybrid could hit 300RWHP easily with a more open exhaust. Add a little head work, headers, X and better springs to hit 7000rpms and you'll be real close to the fun zone right now. You could also get a 75RWHP shot of giggle gas for the straight aways.

 

The SD guy may not do it anymore. I would just use whatever machine shop Greg uses if you are boring it out.

 

I wouldn't bore out a good block. Part of the idea is finding a very cheap block with bad cylinders so the machine cost and block cost even out. Thats also part of the reason for building the "normal" hybrid now, I have a nice block and I know it may take some time to find a boring candidate.

Ricers, I agree, the first motor could be very close to the funzone target. How are the cams working out in your motor? Any hard numbers on power yet?

Maybe a big part of my reluctance to go to a stroker is that I think I would end up doing exactly what Greg does for a short block. Its a proven reliable design, and despite the cost that makes it hard to argue for a cheaper part to be substituted, and that is a very slippery slope to spending.

That's actually how I started thinking about a 5.4L, its a suppose I take Greg's stroker design and skip the Nikasil, and Moldex crank, substitute S2 pistons, some kind of off the shelf rods, etc., and build with a Euro S top end. First round was using 85/86 heads with some bigger valves since I have a couple sets with bent valves, but with only slight drop in power going to the Euro S provides a LOT of simplicity and cost savings.

What I am looking for here is the cheapest reliable serious power bump over a Euro hybrid. I need to look as some costs and read Greg Gray's thread, to get a better picture of how stroking and boring compare in practice.

 

I checked the cylinder thickness at the top of 2 spare 85 blocks I have. Both were just under 4mm. Increasing bore 4mm would take away 2mm, leaving a little less than 2mm. Half the original thickness. Is this really safe long term?