BC

For some ****s and giggles, I am going to put together an engine with high compression and then boost the hell out of it. This is just a motor of extra parts I have (except for the heads - they are new rebuilt)

So it will be an S3 bottom end, all stock except for some changes to the oil pan distance as well as the piston rings (standardized 951 rings)

The heads will be S4 (3R I think we call them here - from an 89).

So this should net a relatively high (but not for modern standards) CR of 12:1 or so. But I will be boosting it with a Novi 2000 as high as I can go.

The key will be three things, and I think with these three things it will run great and not blow anything up except for everyone's mind:

1) Aggressive cams - reducing the dynamic compression ratio
2) Adaptronic ECU and minute control over timing on each cylinder and injection into each cylinder
3) E85. (high octane, superior charge cooling, different burn and flame front characteristics)

One of my questions is this:

I don't actually think the S3 pistons need to be notched. I think that with the valve timing sorted, the piston never gets near the valves unless something is broken. Any comments on this?

This will be assembled quick and dirty (well, not dirty but surgically clean, but you know what I mean) and the only big hurdle at this point, well, two, are:

1) S4 intake with side plates welded to something so I can do a front mount throttle body
2) The ECU loom (which I am working on)

Imo000

What is your definition of high boost? 30psi and above?

NordicSaab

What's the goal here?

Do you have a HP figure in mind?

BC

The goal is to do some cool stuff and see if it works. High boost from the Novi is not like high boost from a turbo obviously. But around 26psi is what it's pulled for.

Fabio421

Of course they don't need to be notched. The factory just notched every single piston in every single 928 engine becasue they liked the way it looked. It is totally unecessary, especially since you are increasing the diameter of the valves. [/sarcasm]

BC

From what I have seen in these engines, the pistons are never that close to the valves to NEED the notch.

But you bring up a good point about the diameter of the notch itself - however if it needs to be a larger diameter, than it may need to be deeper - but we get back to my original comment at that point.

Fabio421

And you mention aggresive cams as part of the concept. Even more reason to notch the pistons. If you get to the point of mounting the heads to the bottom end you can clay the tops of the pistons and check the clearances for yourself.

I've got the parts to build this same engine and I've talked about the possibility for awhile but I don't think one would be able to feed it more than a moderate amount of boost. I could be wrong.

Are you still running that other car on E85? Have you ever sharktuned it for the E85 or are you still running with higher fuel pressure and/or larger injectors?

BC

That is the can opener car. Someone changed lanes and I had their wheel open the right fender like a can opener. So I sold it. It was on ethanol for over 10k miles from my count and it had zero issues. It had Porken 3.5 chips and 36lb injectors - which also were no problem.

This white S4 I have now for sale that had greg's hands in the transmission recently is not on ethanol. I may use it a bit to clean things out before I replace things like the fuel filter and injectors, but its not for the same purpose.

Yes, I understand your point about pistons. I may as well put it together. If it stops, I take it apart and notch a bit. My point is to keep the compression as high as possible for responsiveness and good power production. The aggressive cams are like 436 lift? I can't remember its been so long. Its elgin's cam grind on S3 cams made to fit S4 heads.

I feel as though from all the research I have done, the people I have spoken to, and the info I have about e85, there is almost no knock limit. So you will run into physical capacity from normal compression ignition on the structure of the block before you have any detonation. Pre-ignition can happen on exhaust valves but not on moderate rich mixtures. If it doesn't work, well, then I will use another engine and lesson learned.

I think the best way is to just put the motor mocked together and turn the crank with the belt on. If it stays turning, I'm fine. Put some clay in there obviously.

BisimotoSales

Wish you great success with your project. High static compression and force induction is a great combination when proper built and tuned. If you are in need of assistance with a custom set of camshafts be sure to reach us at our office.

BC

I have Elgin's Cam grind on S3 cams made to work in S4 heads, so yes there will be more lift. I don't have the sheet in front of me, but the intake is 437 or around there. I will indeed have to mock up the assembly and see what needs to be changed.

The purpose of this is high compression, so I wish to take out as little as possible to keep this compression high. Otherwise there is little reason to even do this.

FBIII

If it's unnecessary to cut valve reliefs on a running engine and engines bend valves when the belt snaps, what's the point of having reliefs?

BC

I think I understand your question, but I do not know the answer, at least 100%.

I do know that the pistons hit the valves when the belt breaks because the valve reliefs are not made for clearance at TDC for the pistons but Full lift on the valves. This scenario only happens when a belt has disconnected the movement of the valves from the pistons.

Usually the piston is chasing the valve.

Mike Simard

The pistons need to be notched, especially with more valve timing. The clearance concern happens in the areas near TDC as the valve is closing and the piston catching up to it (and vice versa).
Both intake and exhaust need it.
They could never prevent damage if a belt breaks though, they would be freaksihly deep to allow that and it would compromise other things.

BC

I have two paths as I see it with the resources and time I have.

1) I can notch them SOME with the larger diameter shapes of the S4 valves. How much I would not know until I mock it up or actually build it, take a deep breath and turn over the engine gingerly by hand.

2) Mock up the engine with two pistons - one for each bank with all old pieces and old rings, hook up the belt and turn it over with clay, as suggested in the other thread.

andy-gts

BC this is way cool....pushing the limits.....I never realized you actually were running and E85 engine....did you post dyno or was there a thread to follow . I would really like to read about the adventure!!!!