I'm building a Tpi motor using ported 87 ally vette heads,
I'll be using a Tpis ZZ9 cam & 1.5 roller lifters /followers, Big mouth & runners & ported plenum etc. I need some advice on compression ratios on pump gas. I have some KB 120 'flat top' pistons which have a 7cc valve relief. This should give me about 10.8:1 static compression ratio with a 0.042" piston to head clearance.
Is anyone else running this much compression on pump gas, with a zz9 (or zz4/similar) cam. Tpis recommended 10.5-10.8:1 with this set up. Does anyone have any experience they might care to give on whether I will end up with a detonating monster or not.
[I tried a search, but couldn't find anything to help. so if I am going over old ground, please accept my appologies].
Any help/advice appreciated

 

I had serious detonation problems with the ZZ9 cam and 10.25 CR immediately after installation with only 6º timing. I ended up blowing a head gasket and after replacing it I now no longer have the problem and I'm at 8º. I did add larger injectors (24#/hr)at the same time the head gasket was replaced though.
Oh yeah I was running 91/92 octane pump gas

 

it's alittle high What is the highest octane fuel available in the pump in your area?

There is nothing stopping you from doing a bit of combustion chamber deshrouding on those heads to lower the cr a bit.

Right beside the plug near the intake valve is where they need it.

Would be a win-win thing.

 

Best check and verify your clearances and math I get
10.20 With .042" piston to deck clearance and a corvette L98
.051" head gasket.

here is a link to a compression ratio calc

Compression ratio

 

I have a 72 Chevy PU with a 350, Vortec Heads, .100 Domed Pistons which brings my compression ratio to about 10.65 to 1. I run 92 octane and octane booster in every tank full and have light ping at wide open throttle. My cam specs are 230 degrees @ .050 and .480 lift. I know it is a lot different than your car, but it shows how much compression you can get away with when you have a cam with enough overlap and cylinder heads with very efficient combustion chambers. Just my $.02


PS My Ram Air Clatters more than my truck does at full throttle and the only mods I have done to it are the SLP Airbox lid and Loud mouth Exhaust.

 

Thanks for replying guys, sorry for the delay in responding its been a bit hectic at the moment just managed to get on the computer at nearly 01.00 hrs.
DannyT, are you running ally or cast iron heads? As for octane here in good ole Blighty, we have 95 & 97/98 available but it is rated using a different system. I believe it roughly equates to 92 & 94/95 US.
F-Bird'88, I intend running 0.028" thick head gaskets with an approximate deck height of 0.012"-0.015" The block is yet to be machined. I have tried a little bit of unshrouding on one chamber as a trial and cc'd it, it measured just a smidgen over 58cc. I reckon I could get it to 59cc but am not sure I could make 60cc. Another option is to machine the piston tops to give another couple of cc's. I contacted UEM (KB-silvolite) and they thought this would be OK as long as I kept above the piston crown thicknesses they gave me. I would want to make that a last resort mod though.
JPK91rs, The zz9 only has a 270 degree advertised (216 @ 0.050") intake lobe, so this is a good bit less than your cam, I have thought about chucking in a couple of gallons of toluene with a tankful of 98, but have read conflicting reports about it even though it has a high octane rating. (Its about the same price as pump gas over here 5$/gal ) Please chip in anyone, all comments/advice welcome, especially zz9/4 cam users.

 

I have 58 cc heads on my sb400 it comes out to a rough 11.5:1 I run 93 and and octain booster in it. right now when it is nice and warm it will retard the timming 1 deg at wot. not bad being there castiron heads and the cam is very mild slp 480/487 112 I plan to try a couple other octain boosters yet. with out the boosters it retards 11 deg.

 

I have aluminum heads (AFR 190s)

 

Thanks guys, 88 350 tpi formula, are you running a tight piston to head clearance ? many say this is the secret to being able to run higher compression ratios, with 0.040" being the optimum. I was shooting for 0.040"-0.045". I feel this is pretty good compared to the 0.080" I had from the factory.

 

It is possible to run 13.5:1 compression on pump gas, IF you know what you are doing. You must have the right cam, the right heads, the right exhuast/intake and the right torque converter if you are running a automatic. IF you wish to run close to 11:1 on the street, i would recomend you to open the exhuast ports(port) and polish the intake ports very well. I would not recomend that cam, as you will have to much static compression with regular pump gas. Make sure you run headers to get the gas out of the cylander as fast as you can. And make sure the engine gets enough fuel and you will be on a good track.

 

Thanks chev496. I realise, that 10.8 does seem marginal, however I think we also know some combos simply work for whatever reason. Thats why I chose the ZZ9, it has more positive reviews than negative even if it is damned expensive. I have the cam and will be fitting it. Same with the heads & Intake components. I also have the pistons, but realise I may be building a marginal street engine , (which I want to avoid). So I really appreciate all your comments. I have seen magazine articles with engines using the zz9 cam and stating 10.8:1 compresion ratio's also running on pump gas, what I am trying to do is find someone who is actually using the zz9 at that comp ratio and gain a bit of knowledge. The zz9 applies strange or shall we say different logic to the valve opening points compared to other cams. 'Comp'. has just developed some cams almost mirroring this logic and they seem to tolerate higher comp ratios. Hot Rod ran an article recently on them although it was on an LS1 engine. However the same principles should apply. Please keep it coming guys, more zz9 users might see this. TIA.