Voith

0,8 bar at what CR? Do you think 8:1 CR @ 1bar would not be too sustainable?

Thom

Well, boost affects the dynamic compression ratio which affects peak cylinder pressure thus peak torque. From what I have experienced so far, the 16V engine will have a wider torque spread than the 8V thanks to the higher VE allowed by the extra flow of the head, but not necessarily a higher peak torque. It's only really thanks to the extra 1000 usable rpm that the 16V makes more power, simply because power = torque x engine speed.

If things start moving in the short block then it's neither the head's nor the boost level's fault, so to speak, and this happens as well on 8V engines making more cylinder pressure than the short block can handle. I believe a deck plate is no luxury and solves many strength issues at the top of the cylinders.

The latest king of the 8V hill in my book is "someone's" 3L 8V making 615 hp and 647 lbs.ft at 23 psi of boost, 100-200 km/h in 5.8s... it is deck plated. With this level of torque the next weak link is probably the girdle.

Voith

What spark plugs do you people with 16v turbos usually choose?

Thom

NGK BPRE9EIX, but with proper coils.

Voith

I have gm d514a coils. 9eix it is.

Not sure where I got the idea that iridium plugs are not good for these engines.

Thom

Bump. Any update on the front of big engine builds?

Dutch944

Well.. My 944 burned down but i now have a 968 Turbo CS..
basically a 968CS with turbo.

My old 944 engine is going back in next year, ready to turn up the boost!

ealoken

My 3.1 is up for sale.
Going the 07k path

EliteThink

Great to hear, I'm looking at 07k as well, would really appreciate updates. ;-)

Thom

Some little bird had sent me photos of your burned car. Sorry for your loss after all the effort you had put into it.
Good to hear that you keep the faith and haven't defected to some other car and/or engine. Please post about the progress with the 968.

ealoken

It's a 2 year project.
Fist I'm going to use the 2.5 sleeved+++ engine untill im done.

Getting the engine next month, parts from Boost brothers during winter.
Intake kit already received.

Thom

Any update on the 3.0+ builds?
Mine did about 1,800 miles last week, it did not miss a beat.

333pg333

Well I suppose if you include a rebuilt motor an update. Am waiting on new (to me) S2 block to be MiD sleeved by a company down here. Then all the parts from previous motor to be installed and see what happens. Main conundrum is what headstud to go with. Currently am thinking of using some upgraded studs with tensile strength of circa 220,000 psi which is higher than stock but lower than 625+ material (280,000). These are also stock diameter. ARP won't reply in terms of getting some custom product made. I have contacted a company in the UK who can make some from the 625+ material. But am tossing up the various plusses and minuses of each. Obviously quite a few people have gone with larger diameter / stronger material studs and had success. Most of my previous motors had these but the larger diameter might be a partial cause of issues. Then I think of Sean's engines and he has always just run OEM studs and I believe stock torque values. Our main aim is not to push this motor too hard. So if it performs much like the previous one did then over 600whp @ 16psi is plenty. I'd really just like some reliability for once. We may yet decide to go with a different stud or just see how these go for now.

951TurboRS

I have a few theories on the head studs, taking in the lessons others have learnt on different platforms. The first and biggest issue we have is the 4 stud per hole layout. It's a poor design from the start that will give limited benefits to simply applying a higher torque load because of the distance between studs. You can clamp it as tight as you want but the head will still deflect between the studs. At this point you just have to control max torque within the tuning package. Find a torque number that works for your setup and stay below it. Backing off boost at peak torque and ramping it on with rpm.

I still believe you need more clamp load than the stock studs can offer. 625+ Need to be torqued to a minimum of 130ftlbs which needs special prep and can do more harm than good. I think the ARP studs torqued to 100ftlbs is about the sweet spot.

Another issue is the open deck design and rigidity of the bores. At the end of the day the head will always lift to a degree, the gasket is designed for this. The damage to the gasket is done when the cylinders are moving. I’m adamant the movement is not so much the cylinders walking around but more so the cylinders themselves expanding outward like balloon from cylinder pressure. The top hat, deck plate and Darton mid setup all add rigidity to the top of the cylinder preventing expansion/movement at the gasket face.

333pg333

I think that sounds pretty right. Add to the mix a 30 year old Alu block. Another thing to think of which was pointed out to me by Sean Buchanan (JET951) is that if the shop uses a torque plate during the honing process then you should co-ordinate with them to match torque values when clamping down the headstuds. That is to minimise the amount or possibility of cylinder distortion.

I've gone with deck plates on previous builds but we're not entirely confidant that these can't lead to problems via installation and varying expansion rates. Plus there's not a lot of leeway or meat at certain parts of the block. That's why I decided to go with the Darton MiD again. Despite having poor experiences with them in the past but I put that down to the machine shop who installed them not knowing what they were doing. We're also looking at a copper head gasket with independent firing rings. We've used these in the past with success.