menlatin

I am wanting high compression on pump gas. Now, in forced induction, water iinjection is used to decrease heat and prevent detonation. Now isnt the point of using high octane fuel in high compression for the same reason. Has anyone else tried this successfully? I want to run a 11.6:1 compression iron head 355 shooting for 550-570 flywheel hp natural on a moderate 230 @ .05 / .590" hyd roller cam. I'd rather use iron just for the reason that i might want to run some nitrous (~100-200hp) and i dont like aluminum's ability to warp under high heat. And I can get the iron heads for about $250 less.

Mindgame

So you prefer cast iron's propensity for cracking?

I saw a post where Chuck commented on this subject here a few months ago. Seems he was using H2O in a really high comp LT1.
The point of high octane fuels in in the burn rate and the fact that the fuel is less volatile.... it has a more stable burn.
H2O injection as I understand it, reduces temps through evaporation in the combustion process. Effectively lowering temps in the combustion chamber which might lead to multiple flame fronts.
Hopefully someone with actual working knowledge of water inj. will chime in.

-Mindgame

WS6 TA

With a cam that size you’ll probably be very close to being able to get away with that compression with pump gas.

Water injection does very little cooling, instead it acts as an anti-detonant in the combustion chamber and causes the air/fuel mixture to work much like one using a much higher octane fuel. If you account for the latent heat of vaporization you’ll find that you’ll need a very large amount of water injected into the engine to give you any reasonable amount of cooling, something on the scale of 160lb/hour to get an 80* delta T for the intake charge on a 500hp engine, which would be way too much for the engine to run even close to well. We build a setup which injected water at roughly 31lb/hour triggered by one of the extra channels of a Haltech ecm (in this case at 2psi boost) and we didn’t measure more then a few degrees lower temp in the data logs,

menlatin

so you think i could run 11.6:1 with an iron head, and NOT detonate? I don't think that cam is big enough to allow enough blow off to be able to use that high compression. I've been told that iron isn't safe over ~10.5 with out high octane, and plus its only a 230 cam (274 adv), with i think a 110 ls. But back to the the WI, do you think could do like 15-20 lb/hr to get away with say.. 12:1?

menlatin

oopps.. just foud out that cma is 286 adv.... but still dont think its enough. BUt hey, im ignorant and may be wrong

WS6 TA

You are right there on the ragged edge, a little less compression, a little more intake lobe timing, even a slower intake lobe opening with the same .050" timing... and you'd be safe on 91 octane. If you've already got the parts I'd be tempted to try it, but you'll probably end up having to run the timing a little retarded on the street and top off with a little race gas at the track.

If you haven't looked at it, check out:
http://cochise.uia.net/pkelley2/DynamicCR.html
(posted by rkrause a few days ago in another thread) I’m not sure of the accuracy (I’ve always guessed before that), but it does give you #’s to think about.

WRT the water injection and slightly more compression… yes, I think you could get away with it, but I’m not sure that I would bother. I’m not a big fan of getting a fraction more power (probably on the scale of about 1%) in exchange for something else to keep track of that potentially if you’re making a hard pass and you run out you could end up burning a piston…

If I were you I’d probably shoot for getting the compression down to 11:1, tune the thing right and not worry about it.