With my current iron J heads I have 9.25:1 compression. If I swap to aluminum heads I should still have the same compression if the heads have the 65 cc they claim. From what I have read aluminum heads want a little more compression because they dissipate heat better. Would there be any concerns with the lower compression? Any and all advice is wanted.
Swapping from iron to aluminum heads
- Thread starter duster360
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I could be mistaken, but I don't think it's "want", I think it's "you can" run more compression because they dissipate heat better.
Good point.
UOP
Well-Known Member
The better heads will still outweigh the "want" for more compression. You can always have them milled though.
That is my reason for "wanting " alu heads , pings once in a while , especially if I can't find 94 octane (1.70 /litre ) . Plus the weight saving , every pound helps .
I was trying to clarify what was posted. I don't think aluminum heads want more compression as opposed to you can run more compression because of the heat dissipation, it helps eliminate the detonation.
They don't want more compression, they don't change compression all else being equal. You can get by with more compression, is the best way to put it. Don't worry about the compression. Worry about flow. It's the flow of the better ports that adds the power. Lastly, if I had the money to buy aluminum heads, I would also make SURE I had the money to have them professionally ported to take FULL advantage of them. Otherwise, you're spending all that money for less than 100 HP and that's kinda stupid, IMO.
I'd suggest that for the poster considering brodix heads, look at every pic you can.
Accessory mounting holes, spark plug access are two things that can be a royal PIA with those heads.
I'd put an Ede head on a street car with alt/accessories before a brodix.
Accessory mounting holes, spark plug access are two things that can be a royal PIA with those heads.
I'd put an Ede head on a street car with alt/accessories before a brodix.
1970Duster
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As RRR said you can get more flow out of them. Yes they are lighter yes they can handle more compression on pump gas yes they are a hell of a lot easier to work on/repair vs cast iron. One of the things that need to be thought about is the cam as well. Is the cam you have able to take full advantage of the flow produced by the aluminum heads?
And yes I have Edelbrock closed chamber heads on my motor.
And yes I have Edelbrock closed chamber heads on my motor.
100% right , would never put any new heads on without some porting , though a little less than 100 hp is nothing to sneeze at (without porting ) , I'm at 398 now anything close to getting up to 460 - 470 hp is good in my books . Where else can I pick up 80+ hp , plus the weight reduction ?
Less than 100HP is a small power gain per dollar spent. That's what I was referring to. With a good port job, that's a whole nuther ball game.
For the price of aluminums, A well done set of Edelbrocks,have a HUGE upside ported (personal exp,don't want to do it again.). A well done set by a good head shop, isn't much more than a new set out of the box .Send MRL /0U812 /Ramm/IQ52 ,a P.M. They KNOW Mopar, should respond.
I know what you were getting at , but I'm a bit insane , I want power , good gas mileage , 12sec 1/4 Mile and keeping it old school , no fuel injection .
Even close to 100 hp gain would be fine $ wise for me , but porting is just a given , once your spending the money might as well go for it .
So far I have good power , decent gas mileage and low 13 sec 1/4 mile , figure the heads will get me into the 12 sec bracket . If I could get bigger tires without butchering the body that would help as well . Running 235-60-15 MT drag radials , still spinning .
I do a lot of highway driving city is 50 miles away , now it takes a 1/4 tank to go there and back , would like to keep it in that range
At 106 it should be in the 12's already, has plenty of steam to get there.
60's around 2.00? That's where the losses are. Chassis is the issue, not the power.
60's around 2.00? That's where the losses are. Chassis is the issue, not the power.
Exactly right , 60 @1.956 - 1.988 , What has to be done in your opinion ?
Front end... loosen it up A LOT.
Tire pressures? My guess, run them up in the low 20's. If you are in the teens, it's likely too low. Sounds counter to what most think, seems to work well on et street radials. I've worked on some mid-high 10's 275/60 cars that guys ran mid teens pressures, boosted pressures and all the cars picked up 60's.
If you cut .1 out of the 60's, its usually at least .15-.20 on the other end
Don't want to hijack the OP's thread.
Tire pressures? My guess, run them up in the low 20's. If you are in the teens, it's likely too low. Sounds counter to what most think, seems to work well on et street radials. I've worked on some mid-high 10's 275/60 cars that guys ran mid teens pressures, boosted pressures and all the cars picked up 60's.
If you cut .1 out of the 60's, its usually at least .15-.20 on the other end
Don't want to hijack the OP's thread.
Front and rear chassis explained, as you have it.. What parts ,& have you set them up correctly....
I learned the hard way.....
pishta
I know I'm right....
ditto, youll actually lose HP going from an iron to AL if the CFM and CR are identical due to said heat dissipation. You may want to look into MLS gaskets too as AL on an iron block will have more movement.
The above statement is not correct as proven here.
http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/viewall.html
And here.
http://www.superchevy.com/how-to/83858-iron-vs-alloy-engine-heads/
http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/viewall.html
And here.
http://www.superchevy.com/how-to/83858-iron-vs-alloy-engine-heads/
ir3333
Well-Known Member
IQ..would the engines respond differently hauling a 3600 lb car on a hot day?
i.e...cylinder heat would be higher as well as cylinder pressure.
..one thing for sure though,aluminum heads will lighten your wallet!
i.e...cylinder heat would be higher as well as cylinder pressure.
..one thing for sure though,aluminum heads will lighten your wallet!
They also lighten the front end by 50 lbs or so , with alu intake , headders and other weight saving parts it adds up . Wish they had an alu block to match .
1970Duster
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Someone did make an aluminum block, riddler I think. Don't know if it's in production but do remember seeing pictures of it.
moper
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The articles are Chevy because you can get virtually identical Chevy heads in both. With a Mopar you can't. Even the machined full chamber can be taken advantage of more than an open chamber as-cast iron head.
So what does aluminum do for us then? It allows a Mopar builder to incorporate certain details into the build that will produce more power when exploited, and they give an instant relevant weight reduction. If you just bolt them OOTB they may give you a little more power, but the feel and performance improvement will be from the weight reduction. If you have a professional performance shop check an correct them they will give you more of a gain as a really good valve job translates into more cfm and more power - but again I think in general the gain felt will be more from weight reduction than actual mammoth increses in power unless your iron heads were really that worn or screwed up. If you use them and plan to rebuild the shortblock too then they can make a good improvement without porting but with correcting. Even more so with porting. I'll still prefer an aluminum head to an iron for any build not restricted by class rules.
So what does aluminum do for us then? It allows a Mopar builder to incorporate certain details into the build that will produce more power when exploited, and they give an instant relevant weight reduction. If you just bolt them OOTB they may give you a little more power, but the feel and performance improvement will be from the weight reduction. If you have a professional performance shop check an correct them they will give you more of a gain as a really good valve job translates into more cfm and more power - but again I think in general the gain felt will be more from weight reduction than actual mammoth increses in power unless your iron heads were really that worn or screwed up. If you use them and plan to rebuild the shortblock too then they can make a good improvement without porting but with correcting. Even more so with porting. I'll still prefer an aluminum head to an iron for any build not restricted by class rules.
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