Lagavulin

Finally, an interesting 928 thread; good job guys!

Fastest928

Having built ...ahhh, lots of strokers (all still running strong) over the last 10 years, using different base core engines...2V to S3 to S4/S5's, I have never seen a crack form in the head. The bmep (Louis gave enough info to calc that number) of my enignes are quite low (want to worry, check what happens to a 5L SC engine at 400 rwhp at 6000 rpm) and having recently did a head job (stem seeal leakage) on a 130K mile 6.0 stroker, with a 5.7 rod and 3.75 stroke, I can tell you that the bore was as near to perfect and parallel as can be made and the ring seal at all three positions was less than 2-3%. I have considerable less faith in the "majic ratio" as far as wear and reliability is concerned, but its perfromance characteristics are interesting! I have built the same engines with different rod lengths, the TQ curves are very different. I suppose that if I were reving the engine to 7-8500, I would be very concerned, but at 6-6500...not big deal.

BTW, that same engine that made the 550 rwhp, will make 600 rwhp with another ITB setup, at 6500 rpm...just waiting for the TB's to show up as I loaned them to Don Hansom for his engine.

The dyno sheet is on the DEVEK website FYI. And has anyone seen the Kelly Moss dyno sheet, and if so, can you please publish it or pass it on....

Thanks Louie for the remarks...time to make some more power? BTW, what is the rule of thumb for a rwhp of 600? Ahh...730-750chp?

It would be interesting to see the dyno sheet of this variable lift/timing 928 engine, no need for pics, but nice if possible, the TQ curve tells it all.

Marc
DEVEK

slate blue

Hi Marc, would you feel differently about the rev situation if you have much lighter components? Such as Je pistons, titanium rods and a lightweight valve train. Of course camming to take advantage of the higher revs. Could I ask you why does your dyno run start up at 3500 rpm? I would have thought that it would be valuable to see what power is available from lower speeds to which we drive most of the time on the street.

Fastest928

We were tuning for power reading at 6000 rpm, and we just started at 3500, for no particular reason.

BMEP goes up with increasing revs....550 at 6000 is less than 550 at 7000, regardless of the components used.

In addition, as the power is made higher up and up, the torque down low also drops...think honda S2000. Very difficult to drive on the street due to its high peak hp and tq ranges.

On the next goaround with our intake system, I will "estimate" 550 rwhp from 5700 - 7000 rpm. with a peak at 6500 - 6600

After about 400 rwtq, it is irrelevant how much more you have....it just spins the tires and costs money!



Lwt components have advantages and dis advantages. The downside is low rpm quality and tuning. If you go too low, the engine will not hold an idle at the normal 700-800 rpm ranges. I would go to Ti rods...but using JE pistons may be ok for the near term, but the 390 is very unfriendly to large piston to wall gaps. It produces maximum seal with tight piston to wall (no rock) tols...usually less than .001 for best seal and performance.

I already have solid lifter, wanna buy some?, config for heads....but again, Ti valves are considered a wear item in almost all street usage cases. Our last stroker had well into the 150K miles on the parts before water pump/overheat/head gasket failure...water and oil do not make good lubricants....hey, here is an advantage of using JE pistons and large gaps. Maybe would have saved the pistons and block!

Anyway, how much for Ti rods in Au? chevy 5.85 or 6.0?

Marc
DEVEK

slate blue

Last things first, Ti rods will certainly be cheaper in the States good ol mass production will see to that. I know what your saying about the close tolerance with a short skirted piston, it certainly worried me. My thoughts to counter this problem is to investigate carefully exactly what clearance I can get it down to without risking a seizure.

These are the facts as I know them, the Mahle pistons are basically 4032 aluminium. Mahle recommend a piston clearance with these of .00209" Now Je have on their site that they recommend for the same diameter piston about .0025" to .0035" The reason I believe this is larger is that they are usually going in iron blocks, i.e a different expansion rate. So then if we then look at Je reccommendation for the 2618a Aluminium. They say .0035" to .0045" Now I believe at this point and one of my engineer friends is looking into this, I believe 0.003" is possible to run, with the 2618a aluminium. One of the engineers worries was if the engine overheated it may seize. So we will need to build a tolerance for that.

So when we get this right at running or operating temperature the close piston to wall clearance is maintained. I wouldn't be putting the boot into a cold engine either with the 4032 or 2618a pistons. Obviously these pistons are very light and strong. I will have to make the best of this situation as I own them now.

Also I will look into DLC coating of the skirts of the pistons, of the problems of these strokers in theory at least is the high loading on short skirts. DLC coating reduce the friction to almost zero. So I may not have to coat the block with Nicasil. My concern is this, is the DLC compatible with the Alusil? At this stage I don't know, but if it is the whole problem of a very small selection of pistons will be over.

They are talking about the DLC coating for pistons in F1 right now. As you are probably aware all engines currently run Nicasil. Certainly one of its great benefits is its ability to retain oil. Alusil has no problem upto 8500 rpm. Maybe I should also include piston speed in that one? So revs should not become a problem, they don't believe that DLC coatings will work with Nicasil, the reason two super hard surfaces rubbing on eachother, hard and soft is best. Now nicasil doesn't need a coated piston whereas Alusil does, Alusil is soft in comparision to Nicasil, so maybe we may have some luck comming our way!

Fastest928

The Mahle/Kolbenschmidt, (i was given the material makeup long time ago by Mahle Germany, there is no material similar in theUSA), piston material is a higher content silicon than 4032, but 4032 is the closest used in piston manuf. I have made pistons out of 4032, used our proprietary coating and out of the 5 sets of pistons, one "supposedly" failed....the facts of the failure were unclear and clouded, and a frucus was caused by the additional influence of a competitor. In short, we no longer provide the coating except for ourselves and close associates. There is another material that was used in the US some years ago by chevy, but there are no more blanks available. That was the closest to the Mahle composition available.

The original Mahle or Kolbenschmidt uses ptw tols of .0006-.0008". 1/3 - 1/5 the 2618 specs.

What you want is the piston to wall clearance to remain constant within the operating range of the engine, and at elevated temps, provide enough clearance to prevent sticking/scuffing at overheat conditions. You can also drat the CTE of both materials, the starting dims and figure out what happens when cold/hot.

Marc
DEVEK

blau928

Hi Greg,

I checked into the Casidiam coating, and it is DLC, as used in NASCAR... I did not know the molecular composition when I asked you, but just heard very good things about it. So it seems we are on the same page, as I was wondering about using it on other items such as the valvetrain etc.. I also had a look at a valve stem from an F1 Ferrari (pics in EVO mag), and you can see the coating on the stems pretty clearly.. What I found interesting, was the shape of the Ferrari piston compared to street stuff.. The skirt is practically non existent, and these things rev so high, it's amazing..

In any event, are you using an S4 or GT or GTS block? I am curious, as I was wondering is deck heights were different for them, and also the 86.532v thick wall block...

Do you have to radius your skirts as well to clear the Crank? How many counterweights on the Crank? 6, 8?

Will you coat the crown of the pistons with DLC?

I plan on keeping the redline at 6500 for my build, as it will be boosted, and am concerned with durability, as the motor will have more than enough grunt to be a lazy shifter. I also plan on using an auto box, unless I can by some miracle have a Hewland or X-Trac appear at a significantly reasonable price..

Anyway, your posts are very helpful, and informative, and I would like to express my appreciation for your contribution..... Very interesting stuff...

slate blue

Hi to all, I have sent a request through for some info on this V-TEC, and we all are awaiting a response, fingers crossed lets hope for some photos.