is 11.2:1 compression too much for 91 Octane

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Call him (seller) or see him in person and ask some questions about what his procedure was for setting idle mixture. And what the initial timing and timing curve was? Don't comment or say anything negative or any criticism. Just listen to him talk.

Then ask around what year month the motor was built and running in car. And then approx mileage.

If he just set timing to what someone told him. Or had someone set it when the motor was build. There's a good chance this thing has been pinging for while.

If the it's been build for years, it's been pinging for years. With that cam and a loud muffer/axle dumps it's not easy to hear the pinging. So if he heard "rattling", it's been pinging pretty good. And more then he is just hearing.

A friend just took apart a motor with just 10:1 advertised badger pistons. The previous owner was not mechanically inclined showed by the hack work done on the rest of the car by him. Well... the top rod bearing shells are hammered. Some showed lots of copper. Even the top main bearings weren't pretty. This motor had obvious pre-ignition.

I'd be thinking about discounting the motor/car value if this rattling is not a very recent issue.
 
If that was my set-up, and it was already fully assembled, id just drive it and see.
Here in Manitoba 91 is E-10. And based on my sbm experimentation, I have concluded that E-10 is a little more compression friendly. Like was mentioned in post#2, I also ran 205psi. and with a Dc/r just under 9/1,IIRC, on 87E10 at 34 to 36*. Its gone 125,000 miles now, has never detonated at a normal running temp of 205*F, in my S-clone. I put about 8 runs on in total, 4 of them on what many would say, is crap fuel; the 87E-10.As a small block streeter though it may not apply to you. My Wot running is limited to 3 to 5 second blasts, and usually from 25 to 30 mph, beginning in 2nd gear at 2200ish rpm.
I see at least 2 options for your assembled combo, if it does happen to detonate;
1) Timing and timing curve, Obviously,
2) Carburetion
3) Loading
4) Temperature
5) Water/meth injection
-Oh wait, thats 5 things.
-On the other hand, if your engine is already apart and you are in the re-planning mode, different story.
 
Is there any way to easily up the octane of 91? haven't heard many good things about octane boosters... but haven't really looked into it either.[/QUOTE]


Yes.

http://race-gas.com/

It works. I have gone through 6 cans in the last year.

Call them yourself if you want more info they are die hard racers and engineers.
 
autoxcuda said:
If the it's been build for years, it's been pinging for years. I'd be thinking about discounting the motor/car value if this rattling is not a very recent issue.
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Defintely be finding this out and hope the guy is honest about it.
 
clinteg said:
Defintely be finding this out and hope the guy is honest about it.
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I wouldn't count on honesty.

Very well he could be honest. But still clueless on what was going on. It's hard to be honest about something you don't know about. Bypass the honesty issue, you just want to know the chances of the motor pinging and beating up parts.

A motor like that needs to be paid attention to by a knowledgable person to make sure it maintains it's tune. I'd be curious of the seller is "tired" of the car. Or wants to move on to something newer or tamer. That would be more clues it was too much car/motor for him. And clues he couldn't keep it in tune.

Fact of the matter that current state of tune of the motor is doing some degree of damage. Sure it could be just a little and insignificant or it could be longer and more significant. You need to weigh that risk.
 
Yeah I hear you autoxcuda. I will be practicing due diligence :)

Momoparman: I'll look into that link you sent. Thanks.
 
1970Duster said:
Ferrari 458 Italia

http://en.wikipedia.org/wiki/Ferrari_458


Super sorry I had that wrong, it doesn't have 13.5 to 1 compression, it has 14 to 1 compression! It's a very amazing motor that is used in the 458 Italia Speciale.
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My understanding is that direct injection let's you run a much higher CR because there's no fuel in the combustion chamber until it's time for ignition.
 
I run 10.2 staric and 8.8 dynamic cam is 251, 260 @50 and run 91 with 32 degrees timing
 
IMO it's boarderline runnable that way. If it's a std 505" kit it's running flat tops to get that high. 11.2 isn't that high. My 505 packages are usually 10.8:1 - but the cam is another 10° bigger at .50, and the LSA are a few degrees tighter.. If it uses dished pistons they will be close to the head, and quench will take care of it. If it's flat tops and they are .040 or more away you're boarderline with that cam. You might be able to tune it out like AutoX said. Sometimes ignorance works in your favor... But you might need to put in a larger cam or thicker head gaskets, so factor that into the choices. I stay away from additives. It seems too risky that you'll end up needing it somewhere and not have it...lol.
 
moper said:
My 505 packages are usually 10.8:1 - but the cam is another 10° bigger at .50, and the LSA are a few degrees tighter...
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But tighter LSA increases cylinder pressure and cranking compression thus more likely to detonate.
 
roccodart440: I'm not sure what the cranking compression is, but I'll try to figure that out.

moper: the stroker kit was purchased from 440 source and the pistons are diamond brand, not sure about the type but the owner must have had the machine shop figure out the compression ratio it had (based on all the internals), he said 11.2:1.

Thanks for all the input :)
 
roccodart440 said:
But tighter LSA increases cylinder pressure and cranking compression thus more likely to detonate.
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You have it backwards. Tighter LSA lowers cranking pressure.

To the OP,,,why the 113LSA? I will never understand that.

Call some other cam grinders and see what they say. I'd bet they would laugh at the 113 LSA.
 
madscientist said:
You have it backwards. Tighter LSA lowers cranking pressure.

To the OP,,,why the 113LSA? I will never understand that.

Call some other cam grinders and see what they say. I'd bet they would laugh at the 113 LSA.
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there is an additive that flat *** works. I used to carry a can of it in the trunk, and would add it at each fill up. it worked on a 600 horse 406 sbc. called MACH 1--qt to 16 gal. if I remember it right, use to be fairly cheap, but now is as hi as race gas. like I said, it use to work darn good,but I haven`t used it in yrs. something else that will work, b 12 chemtool , carry a can w/ you for every fill up. $2.99 a can at atwoods, used it after the mach 1 went up -----bob
 
madscientist said:
You have it backwards. Tighter LSA lowers cranking pressure.

To the OP,,,why the 113LSA? I will never understand that.

Call some other cam grinders and see what they say. I'd bet they would laugh at the 113 LSA.
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That's mad scientist. All other things the same, decreasing the LSA closes the intake sooner and increases the cranking compression. It's thought that increased overlap "bleeds" (I hate that word) cylinder pressure. Not true. Because increased overlap is generally associated with longer duration, the longer intake duration closes the intake later and that is what decreases cylinder pressure.

Keeping the same duration and decreasing the overlap opens the intake valve sooner. If it opens sooner and stays the same duration, it must close sooner increasing the dynamic compression.

From Comp Cams,

http://www.compcams.com/Technical/FAQ/LSAproperties.asp
 
IQ52 said:
That's mad scientist. All other things the same, decreasing the LSA closes the intake sooner and increases the cranking compression. It's thought that increased overlap "bleeds" (I hate that word) cylinder pressure. Not true. Because increased overlap is generally associated with longer duration, the longer intake duration closes the intake later and that is what decreases cylinder pressure.

Keeping the same duration and decreasing the overlap opens the intake valve sooner. If it opens sooner and stays the same duration, it must close sooner increasing the dynamic compression.

From Comp Cams,

http://www.compcams.com/Technical/FAQ/LSAproperties.asp
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Ok, keep on keeping on then fools. I have spent the last 20 years taking out the junk 268 comp on 110 LSA and using ANYTHING close with less LSA and they are easier to tune, have LESS cranking pressure.

Do some study and see what big HP engines are now using for LSA's (hint hint I've used them as tight as 98 and I know for FACT some have gone to 95).

And most of the people I know STILL use comp junk but the order the SAME lobe without the comp junk catalog standard 110 LSA.

And yes, I hate comp.
 
ITs all in the quench shape in the head. Many new cars run high compression with pump gas. Sure they control fuel to the Nth degree with EFI, but tis still possible to run higher than thought of ratios with AL heads and proper quench.
 
There are all kinds of variables in making a car run on hi cyl psi and pump gas, I think it's simply the load= car weight, gearing and engine effeciency. In my case it's a demon so it's somewhat light, 3.55 gear, and most importantly the 4,400 rpm stall. I have found running a very very cold plug also helps a lot, I run a NGK 9 I believe off the top of my head that's 3 steps colder than what a 70 10.5 cr 340 calls for, I do run a MSD 6al
 
madscientist said:
You have it backwards. Tighter LSA lowers cranking pressure.

To the OP,,,why the 113LSA? I will never understand that.

Call some other cam grinders and see what they say. I'd bet they would laugh at the 113 LSA.
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I bet they wouldn't. nor would one of the best engine builders around.

madscientist said:
Ok, keep on keeping on then fools.

.
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Pretty sure IQ52 isn't a fool. Pretty sure....
 
roccodart440 said:
But tighter LSA increases cylinder pressure and cranking compression thus more likely to detonate.
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Pressure is only one peice of a potential detonation problem - and it's not the most important one IMO. I never said the choice was to decrease cylinder pressure, my point in mentioning was simply to note the differences.

P.S. - I happen to like Comp Cams... In addition to a bunch of others... lol.
 
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