Thicker head gaskets/ less compression...

-
Kern Dog

Kern Dog

Build your car to handle.
FABO Gold Member
Joined
May 23, 2010
Messages
9,749
Reaction score
28,056
Location
Granite Bay CA
Hello all, first time in the racers forum here.
I'm looking to use a thicker head gasket to lower the compression in the 440/493. Currently I am at 10.7 and am having some detonation. I have chosen a bigger cam with a later intake closing and the thicker head gasket figures into this as well.
The engine currently has a quench distance of .056, so there isn't much quench happening anyway.
I'm interested in going from the .039 gaskets to a common .051 size. I've seen them listed with different bore sizes. I have seen 4.410 and 4.590. The 4.410 will drop the compression to 10.45 and the 4.590 will take it to 10.36. My question is.... Is there a problem with using the bigger bore gasket on a standard block? At .180 wider, I couldn't imagine that it would be at greater risk of blowing out. I have no intention of running nitrous or any other power adder.
Thanks, Greg
 
Wow...I didn't think it was that hard of a question.
When I get stumped on a subject like this, I figured that SOMEone out there is smarter and has been there.
 
The bigger bores are for the blocks that can accomodate the 4.500+ bores. They are not my cup of tea - but I'm fairly sure the bore centers are moved further apart on them so the gasket will not work on a standard B/RB. The one you want to use is 4.410.
 
Look to gasket thickness rather than bore size. Gaskets are a fine tune to get the rail you want and part of the build process rather than a after thought. Note that the ratio drop(a) with various gaskets are minimal. Good luck.
 
first off you probably built a very nice engine and it makes good power. why kill the thing with lower compression and less quench. have you given any thought to changing the timing curve to stop detonation. just doing that you can go back very easy and go racing with the better fuel and still use the horse power and torque you built into you motor. shoot having two distributors makes it even easier.
 
Bob, he is pining. The lower ratio is less of a HP killer than retarded/slow timing of a distributor.
 
Is this an iron head motor? If it is, you may actually end up increasing detonation by losing what quench you do have. At .056", there IS some quench goin on. Believe it. You should run all of the variables including the intake closing of the cam in a dynamic compression ratio calculator and make sure the DCR is below 8.5. I even like to see street engines under or right around 8:1. You need to factor in hot summer days idling in traffic with the engine getting into heat soak. I think you'd almost be better off leaving the quench and going with a different cam. It doesn't necessarily have to be "bigger". It needs to have a later intake closing event. That will have more impact than the head gaskets, IMO. But then, what do I know?

Nevermind. It just hit me you're the same guy driving everybody nuts with this same issue on FBBO. You're undercammed. Simple as that. With Eddy aluminum heads, you should be able to stand 10.7 with no problem with the right cam. A cam change will solve your problem, just like everyone over there has been telling you.
 
RustyRatRod said:
Nevermind. It just hit me you're the same guy driving everybody nuts with this same issue on FBBO. You're undercammed. Simple as that. With Eddy aluminum heads, you should be able to stand 10.7 with no problem with the right cam. A cam change will solve your problem, just like everyone over there has been telling you.
Click to expand...


HA! Exactly !
Usually with other aspects of the car I just forge ahead with things and they work themselves out. The cam issue has been covered a bunch, but I've had trouble getting anyone to help pin down a specific cam. I get some well intentioned responses with some " use something with around 260 degrees @ .050..." But I guess what I have been hoping for is to see someone with a similar build tell me the actual part number of the exact cam that worked for them.
It might be asking a lot. I know that there are fewer Mopars out there and there may NOT be many like mine.
I just spoke with a respected friend that feels that an MSD setup would help. He thinks that the Mopar Performance ignitions aren't as consistent or as easy to tune.

I PROMISE that once the engine runs right I won't keep posting about my problems all over the internet.
 
Well buddy, I'm fixin to pin you one down. Just gimmie a little time. lol
 
Thank you very much! The calls to Comp Cams were not very helpful in terms of cam selection. Maybe they didn't want to be held responsible if a customer isn't satisfied with a cam the Comp guy picked?
 
Frankenduster said:
Thank you very much! The calls to Comp Cams were not very helpful in terms of cam selection. Maybe they didn't want to be held responsible if a customer isn't satisfied with a cam the Comp guy picked?
Click to expand...

What is your engine combo? i am running 93 pump gas with a 11.1 440 and indy EZ heads. i have a comp cams solid roller that is 264 at 0.050 and have a cranking compression of 184 psi.my times are in my sig.mopar65
 
You East coast guys with your 93 octane!
We have 91 out here. I wonder what the 2 point difference means in terms of performance......
 
Your engine with aluminum heads should not ping with a 509.
Did you give any thought to a better carb.
I responded to you in the other post....

10.7 with aluminum is like 9.7 with a steel head.

I run 9.5 comp.with a steel head and the smaller .484 purple cam and can run 89 pump gas.

If it pings real bad i would think your engine is of a higher compression ratio then you think????

BUT...If your sure it's 10.7 then try a better carb before tearing into your engine.
 
T67POWER said:
Your engine with aluminum heads should not ping with a 509.

BUT...If your sure it's 10.7 then try a better carb before tearing into your engine.
Click to expand...

I think that if I has less compression, the 509 would be okay. The cranking compression is between 185 and 193. Many experts feel that a pump gas engine needs less than 190 cranking comp.
As I may have mentioned, the car produces no smoke and actually runs fine up to about 3/4 throttle. Maybe the secondary jetting or power valve are contributing, but there is no way around the high cranking compression numbers. I am too close to the edge for pump gas. I'd agree that if the carb and timing were optimized, it would run better.

The distributor timing curve could be slowed down and delayed. The jetting of the carb may be out of whack.
I have mentioned that I have a wideband air/fuel guage to aid in tuning but I have yet to install it. My goals were to use it after solving the detonation problems. I planned on using as a tuning aid to get better fuel economy and power.
 
The old adage that aluminum heads effect compression is an old wives tale. Couldn't be further from the truth. 10:1 with iron heads is 10:1 with aluminum heads or 10:1 with wood heads. All things equal, cylinder pressure will be the same regardless, so compression is totally and completely unaffected. Where the difference lies is Iron tends to hold heat in, while aluminum tends to dissipate it. That extra heat dissipation does absolutely not one thing to reduce compression. Nothing. All it does is allow the combustion process to run a little cooler. Nothing more. That is the only reason you can get away with more compression using aluminum heads. That's why an iron headed motor will spark knock before an aluminum headed motor.

Also, like I explained to you in my PM, that Mopar 509 cam does not map anything like it is advertised. It's well noted that Herb McCandless mapped all the Mopar cams back in the day and none of them came up as advertised. Mopar used a completely different measuring standard for their cams and most of them fall well shirt of that on the degree wheel. Herb himself found that the 509 only measured at 242* duration @ .050 rather than the 248.5* Mopar says it is. No telling where the intake closing is either. Obviously since you're having the detonation issues, it's a good bit sooner than the 74* Mopar says it is. That would be a HUGE hydraulic cam....and the 509 IS a big one, but it aint that damn big.
 
RustyRatRod said:
The old adage that aluminum heads effect compression is an old wives tale. Couldn't be further from the truth. 10:1 with iron heads is 10:1 with aluminum heads or 10:1 with wood heads. All things equal, cylinder pressure will be the same regardless, so compression is totally and completely unaffected. Where the difference lies is Iron tends to hold heat in, while aluminum tends to dissipate it. That extra heat dissipation does absolutely not one thing to reduce compression. Nothing.All it does is allow the combustion process to run a little cooler. Nothing more. That is the only reason you can get away with more compression using aluminum heads. That's why an iron headed motor will spark knock before an aluminum headed motor.
Click to expand...



You're on the right track in terms of affect on compression and pressures, but your conclusion is totally incorrect and with the example of Frankenmiester's issue I feel you are misleading him as a result of that conclusion.
What do you believe creates the power in an internal cumbustion engine?
 
RustyRatRod,

Compression is heat.
You can run aluminum heads at a higher compression ratio and have the same -heat in the cylinder -as a lower compression steel headed engine because steel retains heat more then aluminum.

The compression ratio is what it is.

How much:
-Air-Fuel-Pressure-Heat = Octane required to prevent pre-ingnition.

Low octane gas---------:rolleyes: lol
 
T67POWER said:
RustyRatRod,

Compression is heat.
You can run aluminum heads at a higher compression ratio and have the same -heat in the cylinder -as a lower compression steel headed engine because steel retains heat more then aluminum.

The compression ratio is what it is.

How much:
-Air-Fuel-Pressure-Heat = Octane required to prevent pre-ingnition.

Low octane gas---------:rolleyes: lol
Click to expand...

You repeated what I said almost verbatim. Look guys, don't just tell somebody they're wrong and back out. That's pussified. Ok so I'm wrong. Tell me why. I explained my opinion step by step. I'll tell you one thing I'm NOT misleading Greg on. He needs a cam with a later intake closing event. Period. End of discussion. That's my opinion and I stand by it. He's already gotten a thousand different opinions. Why make things more difficult for him by arguing some stupid moot point that's totally off track about what he needs? He HAS aluminum heads. The discussion aint about arguing the difference. I swear to almighty Christ, I think some of yall would argue about how best to screw your wife. Just jump in and do it.
 
Buy a drum of C12, 25% mixed in with your 91Octane, problem solved. Unless you are driving long distances. I have 12.2:1 on my street car, I mix half and half with C12, works great. Is it cheap? No, but I only put 100miles a month on it. Easier then pulling heads etc.
 
Frankenduster said:
You East coast guys with your 93 octane!
We have 91 out here. I wonder what the 2 point difference means in terms of performance......
Click to expand...

I sure wish you and everyone else would put your location in under your name so I (and the rest) can curve the answer best suited to your octane limitation.
I see the 2 point octane difference as at least .5 less on the ratio and maybe a few degrees change on a cam recommendation. Engines build combo dependent to this as well.

Mentioned earlier was the use of cosmetic gaskets. If there OK to use in just a straight swap, great. Call Cometic first to make sure there is no special prep for there gasket before use or you'll have fits like many others do since they often need a special finish before useage.
 
Rodzilla said:
Buy a drum of C12, 25% mixed in with your 91Octane, problem solved. Unless you are driving long distances.
Click to expand...

Thanks, but I actually do drive the car long distances. I make an annual 1000 mile round trip to Los Angeles and back every year.
I have already decided against the gasket swap. I have been grasping at straws in an effort to fix this problem. Sometimes I feel like the sick patient that is willing to see a witch doctor to find a cure, trying all sorts of unconventional remedies!
Thanks to everyone who offered help, Greg
 
You must log in or register to reply here.
-

Back
Top