Humboldtgrin

Looks like I'm using turbo Pistons with 4v reliefs cut out then. I was looking back on racerboys posts and that's what he did, although he used a 944S head and was around 9.0 cr. I thought he used 944S pistons with 1mm shaved off but I may have mistook that info from a 928 owner "tony" who shaved down his S4 pistons and was ceramic coating the tops, but I don't know what the outcome was. That will bring CR down. It's going to a super laggy beotch! But when the turbo kicks in hold the .... on! This is a fun project.

V2Rocket

Raceboy did use 1mm shaved 944S pistons under a 944S head
which put him at 9.6:1 or so.

stock 944S pistons under your 928S3 head would be around 9:1.
shaving 944S pistons under the 928S3 head would be about 8.3.

Humboldtgrin

Well heck then I'll still use the 944S Pistons and cut the valve reliefs deeper. Maybe shave the top to bring it down to the 8.0cr range. And rennlister racerboy uses Vems as his ECU and has the maps for the 16v 2.5l turbo. That's if I can't get chips for made for the DME and KLR for this setup. What is the weight of a 944S piston vs the turbo piston? I'm trying to go light weight as well. I have a knife edge crankshaft that I'll be using because I got a great deal on it. And aluminum flywheel. Yes I know already everyone about the side effects. I took that class too. And seen the broken 944 flywheel YouTube video. But I did notice a difference with the aluminum flywheel when turning, the centrifugal force on the stock flywheel wants to go strait. I might even spend the extra $ to get some better rods too. But this is after I get all the other items I would like, such as aluminum radiator and expansion tank. I definitely getting a crank scraper with a screan, pick up tube support and baffle the oil pan.
Also what is your idea about not drilling the coolent passage? You said it will keep the head cooler? And relocated the t-stat? I'm all down for not having to mess with the t-stat where it's at now! Is there a aftermarket t-stat housing that can be used inline with the radiator hose?

V2Rocket

look about halfway down this page

https://rennlist.com/forums/944-turb...or-fans-4.html

Humboldtgrin

That is a very cool mod! Still need to drill an 1/8" hole in that coolant passage. More parts went on the list...

V2Rocket

I'm not going to bother - just going to route an external bypass hose instead.
I'm taking my S3 heads home today so I can take some more pictures for the Rennlist world.

Raceboy

At first I used 951 pistons but upon assembly discovered damage on one of the pistons (had a dent in the skirt reaching the oil ring land) and just went on to use 944S pistons. Both options would work apparently

Humboldtgrin

Spencer which are you going with? Turbo or 944S Pistons? I'm going for the S Pistons and shaving them down 1mm and the valve reliefs. I think lighter and 8.0 will work. I can maybe use a thicker head gasket to bring the cr down a little more. It nice that the 944S cam gear is adjustible unlike the 8v cam gear. And using the CR calculator I can up with 8.47 CR without shaving the 944S piston top. 8.13 CR with .5mm shaved off the top and 7.81 CR with 1mm shaved off the top. Under a 928 S3 head.

V2Rocket

Going to cut reliefs in 951 pistons like Raceboy did.
Staying with 8:1 compression is good for my purposes.

Humboldtgrin

Turbo Pistons under that head are 7.53 CR without reliefs cut.

V2Rocket

How?
928S3 head has same chamber size (~56cc) as 944T.
So since pistons, head gasket, etc are the same, compression should stay the same too.
Valve reliefs will add some CC but not enough to make a big difference like that.
So it should be 8:1 like 944T, or slightly under (7.9 maybe).

Humboldtgrin

Because the calculator I used spit that number out. Just talked with Mike Lindsey and he said the same as you. With turbo Pistons it's 7.94:1 CR and 944S Pistons are 9:1. The 8v head has three differant cc's from what he has messured. 62cc is super rare, 60cc and 58cc and if you shave the head then 56cc is possible. And Mike said I should just run the turbo Pistons because they are forged. So I guess it's back to using the turbo piston. I used .027 as my piston to deck hight which dropped the CR down on the calculator. If the piston is flush with the deck then almost 8:1 is right with the turbo piston.

V2Rocket

I intend to use these guys' valve cutter tool, I think you send them a valve and they give you a tool, or maybe just knowing diameter is good enough for them.

Would you be interested in splitting the cost with me? We both need to cut identical reliefs.

(since we'd need one for intake and one for exhaust valves....or maybe just cut all 4 reliefs to intake-valve size so the exhaust valves would have a ton of clearance?)

http://www.lindytools.com/#!ihpc/c1yc1

Humboldtgrin

That's cheap! Great find! I can get both sizes and loan them to you. And I was thinking about you not drilling that 1/8" hole in the 928 water port for the water pump mod. What are you going to do about the DME coolant temp sensor if it isn't reading the flowing coolant? And that may creat an air pocket that you don't want. I'm going to drill an 1/8" hole at the outside edge so when the block sets at an angle the air will still excape that pocket. And I don't want any miss readings from the temp sensor. I'll call lindytools tomarrow.

V2Rocket

You think 2 sizes is worthwhile, or just get one sized for the intake valve and cut the exhaust reliefs with the same tool, they'd just be oversize?

Was thinking I'd just move the sensor, but I guess an air hole would be a good idea. Easy enough to do.
But that passageway lets water go down from the head back to the front of the pump to be run through again. Above it is the upper rad hose, where the air gets out anyways...