bcdavis

Well, you still want the engine to run without restrictions.

Ideally you would have adequate air and fuel and intake and valve flow, so that the engine can produce the full amount of power it can. I'm not suggesting pushing the engine beyond those areas, by supercharging or nitrous. Just to make that particular engine run as good as it can. I just fear that slapping on stock heads, stock valves, stock cams, stock intake, will be restrictive for that block. It would not take a massive amount of work to port match the heads, add larger valves, cams, sharktuning, etc. But that stuff will probably take more time than Mark has before the next race. So it won't be a problem for him, since the engine will probably run better than his old one. But it will be down on *potential* power. My concern is that he won't want to take the whole thing apart again to redo the heads and intake. So he will just keep running it with mismatched parts, and it will never run the way it could.

Bill Ball

The heads are going to require some work. We had to have Dennis's heads welded and resurfaced due to corrosion, and there was no evidence of any problem until we removed the heads. Mark has some suspicion there may be an internal coolant leak.

Mark, you need to plan to have the heads resurfaced at the very least. Cometic gaskets may be great, but I have seen them leak after expert installation. If your heads need corrosion repair, the schedule is out the window.

Bill Ball

Yes, I'm much more comfortable with the stock gasket and I actually see no reason not to use it.

mark kibort

I understand the 968 stock gasket (that anderson uses) needs some modifications either on the block or gasket to work, due to the passages being slightly different. Ill have the heads re-surfaced to the tollerance needed by elsworth. they do good work and i know them, so they would probably be able to keep me on schedule.

mk

Bill Ball

Flow testing that Jim Morton had done showed the stock heads actually flow rather well. But once you attach the convoluted S4 intake manifold, flow drops about 30% IIRC, and it is rather unequal. Side spacers did next to nothing to improve flow.

BC

They may have moved the rivets at the one end, but mine had them.

BC

A normal "shaving" of the head leaves microscopically HUGE valleys and peaks which do not work with the more modern and STIFF MLS gaskets. Even the bandaids of copper spray and hylomar will not help.

The head shaving machines I have seen also have a tendancy because of user error to shave the head in a sometimes crooked manner.

The concern over the ~104mm bore is that under racing conditions, a stiffer head gasket and some head studs would never hurt.

BC

Even a 75k motor I disassembled had pretty bad pitting on the heads. Some other heads I Have personally seen with more miles didn't have any.

Todd does exemplary welding on the heads, and he can surface them properly as well. I don't know how much time he has right now, but he is the only one north of LA I would trust.

I can temporarily donate some very nice "head boxes" for the heads if you need to ship them. Cardboard boxes are not up to the task. My boxes are hand-made wooden "coffins"

Bill Ball

Andrew:

Can you get the Shrine out and dust it off? I think we're going to need it up and running for some prayer sessions at Mark's.

hacker-pschorr

Same thing I did for the two shortblocks in my garage. I purchased the parts to change them from a shortblocks to a long blocks.

Mark mentioned doing some hand porting on the heads / intake. That is an excellent idea.......is there time to do all of this before the next race? I doubt the valve guides are in the greatest shape in the holbart motor. Is there time for a valve job as well?

Bill,
You said yourself the SharkTuner has a steep learning curve. I agree 100%, still a noob myself with the ST. Now you want to toss in the variable of a rush assembly / install with a stroker motor while still learning how to sharktune?

On a side note.....any chance you guys have a brake chassis dyno available for tuning?


Mark,
Have you figured out the external oil cooler yet? Going to tap into the same connections as the factory? That should be the easiest way. Just have new lines crimped onto the factory fittings. That is what I'm currently doing on my 79.

mark kibort

all i have access to is a dynojet chassis dyno. good for general safety mixture checking.

Im going to try and find a small oil cooler and mount it in front of the radiator.

modifying the existing lines will be the easy way. we have some lines with custom ends and the stock block side mounts that scot has (came with his old euro motor rebuild but were not used), so maybe he will let me fit those with new lines.(lines look old and beat up)

mk

Bill Ball

Sharktune? Most likely it ain't happening for this build. We are still ironing out procedural issues. We're seeing some data logging anomalies. I need to go over to the Sharktuner thread and see if they have been discussed. It's not the digi-dash issue Andrew had, but just some general MAF, AFR and RPM logging irregularities.

mark kibort

Do you have the Piston diameters?

I'm trying to understand the tollerances and I know you guys probably did your homework on this one.

The bore mic's out to 4.080". The ring box said 4.085" and i assume the piston diameters are 4.075. I know you say that the tops of the pistons are narrower, but i wonder by how much. I know the tollerance from JE was .004, but thats on the piston skirt. If the diameter of the piston up top is .015" narrower, then it all makes sence.

mk

Tim Murphy

Piston diameter is 4.076" measured 0.5" from the bottom. I do not know if that is the max or the min since the pistons are not round. Yes the tops are smaller because of more material and thus more expansion, but I do not know by how much. Once again, I do not think they are perfectly round either. Call JE and ask them. We are not piston manufacturing experts so we left all those details up to them.

BTW, I vote keep running the engine you have in the car now. When ready, take it out and set the entire motor aside and drop in the new one. You will need to do some head and intake work to get the performance you are looking for. If you just bolt on the stock stuff the engine will make a bunch of grunt at low rpm but will fall on its face upstairs because it won't be able to breath. Look up some of the old Devek dyno sheets and you will see just what I am saying. Maybe you already have plans to do this but I have not seen you mention it anywhere.

slate blue

This is incorrect and a very common misconception that I think may come about due to the American piston aftermarket. I also do not understand why people use these sloppy pistons in a Porsche 928 engine when there is a better option for N/A engines at least, I, sure would grant an exemption for those going the high boost route, then fair enough use those sloppy 2618a pistons but for my two engines that I am building I will be running slightly less than one thou or that is what I am shooting for at least.

Let me explain why the high silicon pistons are better for most applications, this application list includes Porsche's top end current turbo models btw. Because the pistons that Porsche use are 12% silicon and are referred to as Mahle 124S, this make up of its composition is very very similar to what I use which is 4032. 4032 actually expands at a slightly more similar rate to our block material than the 124S but it is minute.

This similar expansion ratio allows the pistons to be run at a very tight clearance and as such the pistons do not slop around at all, especially if they have the offset piston pin. The 2618a pistons or Rolls Royce 58 expands quite a lot and because of this has a large clearance when cold and also requires a margin of error tolerance should the engine get hot!

That means that while you want the pistons to take up the slack when warm you need a clearance just incase you overheat the engine. Now the Nascar engine builders will not allow for that, that would cost power, due to increased friction and poor seating of the rings due to the piston not being perfectly in alignment to the bore.

Now people will say that 2618a is the best for boost, it is in general but just remember that 4032 as long as the engine is well tuned,( it can't take the knocks as well,) will be up to the task, they were even recently trialling using 4032 in the latest F1 pistons when the MMC pistons got banned, they were using 2618a before MMC came along. 4032 is good at reflecting heat to due to its high silicon content, the expansion rate doesn't change due to it being forged and the hyper eutectic pistons that are for sale cannot be forged as that material is too brittle. Hope this is of some help.

Greg