ShawnSmith

I had not assumed siamesing the sleeves... that _could_ give you some of it (will you be able to keep those things cooled properly?), however I think you're gonna run into clearance issues trying to get to 4 inch or longer strokes with all the moving parts that are needed to make that stroke happen.

GregBBRD

You remove the cylinders, so that you can see how fast the uber brittle Alusil block can crack through the main webs. You might get lucky and not have this happen....not everything is going to happen every time, exactly the same...but Porsche couldn't do this with any reliablity and had to go to different alloy of aluminum, in order to make it work. It's very cool, when Porsche, with its vast resources, has already done the work that would normally take dozens of broken engines to confirm....which is what Porsche did.

90 S-4

This is a spare cylinder/barrel, it shows the stepped portion at the bottom as it
goes into the block with an o-ring. I had originally wanted a bigger bore that
would be 112.27 + 3.70 stroke = 7.44 ltr (454 cu-in)
But the wall thickness was going to be to thin at the bottom so we settled on the 4.286 bore.

ShawnSmith

yep, that looks roughly what I was expecting as a practical upper limit, with maybe another tenth available on the length of the stroke depending on exactly what combo of rods/crank/cylinders/pan you use.

90 S-4

Shawn,
Yep, it's pretty close to maxed out if you used the 3.75 stroke (mines 3.70)
max bore of 4.286 X 3.75 stroke = 7.09 ltr (433 cu-in)

90 S-4

But, if Russ can find a way to make a 4.0" stroke work than he would have...
4.286 bore X 4.0" stroke = 7.57 ltr ( 462 cu-in ) ( DAMN ) thats a big one !

largecar379

No Erik, your skills aren't lacking.....just quite a few combinations with BBC's. short deck, tall deck, different rod lengths....etc.





Yes, the confines of the lower end are tough to work with. Lots of grinding to be had.

The number are there, but as to whether the block can physically handle it is another story as I've not heard of anyone going quite this far-----






--Russ

Mark Anderson

let me know if you need more info

S4ordie

Ummmmmm, so I am a 44 S2 guy looking to upgrade to the 928 universe. the concept of a stroker is very appealing to me. Searcing the dscussion forums turned up this promising thread. Great intention here but I have read nothing of the requested OP.

As I am really interested in a stroked 928 and I am unfamiliar with the builders that post here, who are the best stroker engine builders for the 928 and any examples realtive to reliability and cost is appreciated. Sorry largecar for jumping/diverting this thread but so far there is little info of value here realtive to your original good post. Hopefully this will bump up the info.

slate blue

Just a quick thought, first you must have the cams and heads to be able to supply that type of air demand, if you don't it will be somewhat pointless. Also I feel that the bottom end power will make the car somewhat difficult to drive. Just in case you are not aware the smaller 2.4 liter V8 is much more drivable than the 3.0 V 10 monster they used to have in F1. The drivers and engineers agree how much better the V8 is suited to the chassis.

My 928 with a 2 valve has about 400 hp (flywheel) and first gear is a waste of time and that is with new 295 tires and Leda shocks, one thing I don't want is more bottom end power. What you may consider is a shorter stroke and higher revs. You will be able to stay in gears longer which gives greater flexibility. You also don't want excessive gear box busting torque.

Greg

P.S Greg Brown would be your engine builder, he responded earlier in this thread.

andy-gts

Greg Brown is the only stroker builder I am aware of with history that is worthy of your money.

largecar379

not a problem, just wanted more participation from those who have data to contribute.

I felt it would be good for all of us to be able to view the data and make choices as to which way we would like to go, but it's not happening (?)





--Russ

Louie928

Anything else?

slate blue

Russ I will cut you a break, I sense a bit of frustration there, after years of research, which is another way of saying making quite a few mistakes, I would be happy to advise on three issues. The first would be rod to stroke, I would have to correct some of my previous posts where I may have been overly critical of low rod to stroke ratios. The original stroker rod to stroke ratio was 1.56 to 1. I didn't think much of this due to excessive piston speed. You do require some very nice bolts and rods with a ratio like this. That being said it will produce great power upto 6,500 rpm. Beyond that you will need a higher ratio.

My stroker has a ratio of 1.75 to 1, and just for those who are not aware, the GT3 also has the same ratio, 1.80 to is the change over point to what most would consider a long rod to stroke ratio. F1 cars have a ratio of around 2.2 to 1. This does make a difference in the intake draw period and combustion at the revs outlined. However for the sake of completeness there is more mechanical stress with a low ratio.

The ratio I have at this point in time will not be fully exploited, as my pistons are not strong enough to withstand more than 8,000 rpm for extended periods with Mahle advising me that they were much more comfortable with 7,700 rpm (they ran my engine through their calculator). With a better piston the engine could see as high as 9,500 rpm. I have the heads to supply this amount of air too however they are not my 2V heads, as they can at present supply only 282 cfm at 0.542" lift. The heads I have flow tested were quite interesting.

These heads have the same included angle as the current GT3 heads, that being 27.4 degrees, well I measured 27 degrees on my heads with basic tools. They flowed a monsterous 336 cfm at 0.400" which is the standard GT cam lift, that amount of air supports almost 700 hp. The flow kept increasing too, my goal would be to make high lift cams. The GT3 street car has 12.7 mm or 0.500" lift and the race car has 13.75 or 0.541" at this point these heads my heads should in excess 400 cfm. or around the 800 hp point. The GT3 style cams have a very fast ramp like a roller cam.

Just to put the flow rate of these heads in context, I compared these heads to the best equivalent 2V heads, the RO7 Nascar heads, they outflow them.
So for me one of the areas high flowing heads addresses is the relatively low hp standard strokers put out and the cams, very low lifts. Please no offense is meant, it is just a fact. Remember the reason for this is we have restrictive manifolds and small cams is so that we didn't have too much power relative to the beetles.

I contacted Comp Cams and on of their engineers told me that 0.500" is quite common for 4 valve engines these days. The springs I have have found there way into many applications that the springs were not specifically designed for. He said that they have quite a few customers pushing past the 8,500 rpm level. He also told me to keep them cool, I already had planned to spray them with cool oil. Anyway I digress.

The last issue is piston material, only high silicon pistons will last in a street engine. The most common material that fits this bill is sae 4032 with around 12% silicon, it stops wear in the ring lands and pin bores. While it is technically possible to treat the 2618 material with coatings in these wear areas, it is costly and it still doesn't stop that material changing in a relatively short amount of time.

While it is true that 2618 has at the outset a higher tensile rating it is only a matter of hours and it is less than 4032. Mahle recommends M124 or for high end applications M142. This is what is supplied to high end OEM manufacturers. It has a very long life span and tight piston to wall clearance which is helpful if you are not using Nicasil. The Nicasil certainly helps avoid the galling that 2618 suffers from. I think the 968 pistons are made from M124.

Don't get me wrong 2618 still has its place, engines that experience detonation, 2618 is a more plastic material and is able to bend and avoid breaking ring lands and is fine for engines that get lots of maintenance like in drag racing, Nascar engines, it helps to remember its origins, it was invented by Rolls Royce and is sometimes called RR58, it was used because it could better tolerate the detonation the merlin engine experienced during WW11. It allowed more boost also. These engines had very short life's along with the brave pilots that flew them. Mahle is supplying high silicon pistons to F1 these days as the engines need to last more than one race, I would have thought that says something in its self.

Greg

John Veninger

how many liters/cubic inches?=6.4L

32V or 16V?=32v

turbo-ed, supercharged, or naturally aspirated?=NA

which piston/cylinder combination are you using? (Porsche or custom pistons, over-bored w/ Nikasil, sleeved, etc) 104mm 944S2 KS pistons Alusil bore

which rods are you using? (steel, titanium, SBC based or custom, etc)=Steel Oliver

how is the car driven? (track only, hard street driving, or just putting around)=track only

how many miles do you have on this engine since installation?= ?? Several races and track days

maximum rpm's you turn this engine?=6500

have you had any rod failures? ( broken, bent, etc)= No

have you had any excessive piston/cylinder wear? (skirt wear, where is it, etc)=None that I'm aware of at this time.

have you had any piston/cylinder failures? (broken pistons, gouged cylinders, etc)=No