I have a fresh 340 that I just broke in but have an issue with one of the heads. Since I will be pulling the top end off of the engine I am considering making some changes and installing edelbrock rpm heads, RPM airgap intake and a 750 holley avenger carb. With the iron heads I had calculated them to be 9.25:1 compression. With the edelbrock heads it would be 9.6:1. Would that ratio work good with aluminum heads? Generally I see around 10:1 used but that just may be to wring all the power out of it on 93 octane at the pump since the heads run cooler. It does have a six pack setup at the moment but I am considering selling it in favor of easier tuning. Throw me your opinions.
Thinking of changing direction with my engine. Opinions needed
- Thread starter duster360
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Woods74
Broke Senior
There are a couple points that help here
Aluminum is known to handle higher compression on pump gas, 10:1 is common; it's all about dynamic compression.
Good quench distance helps in the quest for wringing power out, and keeping octane down, but not the be all end all.
Keep the dynamic in the 7.5-8.5 range, enter your intake valve close ABDC value on your cam card, along with bore x stroke, static compression, elevation etc, here:
http://www.wallaceracing.com/dynamic-cr.php
After this, you'll have your answer, and the knowledge you need to improvise. After you figure all that out, call your cam grinder and tell him where you want to go with what you have, and work it out.
Enjoy!
Aluminum is known to handle higher compression on pump gas, 10:1 is common; it's all about dynamic compression.
Good quench distance helps in the quest for wringing power out, and keeping octane down, but not the be all end all.
Keep the dynamic in the 7.5-8.5 range, enter your intake valve close ABDC value on your cam card, along with bore x stroke, static compression, elevation etc, here:
http://www.wallaceracing.com/dynamic-cr.php
After this, you'll have your answer, and the knowledge you need to improvise. After you figure all that out, call your cam grinder and tell him where you want to go with what you have, and work it out.
Enjoy!
The dynamic was 8.5 with the iron heads. The iron heads were 65 cc as are the aluminum heads. The compression would be 9.2:1 just like the iron. The reason I calculated 9.6:1 was I thought maybe I would need to bump up the compression a little using a thinner head gasket (.039 ). Currently Felpro with .054.
PA Dodger
Well-Known Member
I don't know your engine specs so I can only offer a generic opinion. If it were my engine I wouldn't put aftermarket heads on it. My cam is a fairly mild .480+ lift cam with 10:1 compression. Aftermarket heads wouldn't be enough of an advantage to be worth it. If you have the engine built up enough to benefit from the Eddy heads go for it. If I'm in your shoes I'm fixing the head issue and taking the car to get it professionally tuned and enjoying it as-is.
Put a chebbie motor in it.
furyus2
Well-Known Member
If this is not a resto, I would put the Eddys on it. If you plan on more mods in the future, you will be dollars ahead compared to fixing 50 year old technology. As far as the 6 pack, if you have a 4 barrel setup that you can swap on to get everything sorted, then go back to the 6 pack. If you don't want the hassle, sell it and put on the 4 barrel setup.
Engine is a 340 with balanced rotating assembly, SRP forged pistons, Lunati voodoo 268* I 276* E, .497" I .513" E lift, Hughes roller rockers, cheapo hooker headers with 1 5/8" tubes, 4 speed with 3.91 gears.
Woods74
Broke Senior
Yup. Don't even need a crazy cam either, I bet a 220-230 dur @ .050 would thump.
goldduster318
Overzealous Car Modifier
My car has Edelbrock heads which are untouched other than a valve job by MRL performance (who also built the engine), and the Air Gap (and a 750 Double Pumper), and it made 470hp/455 lb-ft on the dyno. I have a roller cam and custom pistons (zero deck forged), and K1 rods which are much lighter. I love this engine. Runs amazing.
http://www.forabodiesonly.com/mopar/showthread.php?t=241854
The stock edelbrock head valvesprings really stink (and apparently the valve job isn't great). Mike from MRL said he could assemble some edelbrock clone heads which he thought were nice (I think they were Proform??), and you could get some beehive springs (I have them). Would probably make the most power that way.
http://www.forabodiesonly.com/mopar/showthread.php?t=241854
The stock edelbrock head valvesprings really stink (and apparently the valve job isn't great). Mike from MRL said he could assemble some edelbrock clone heads which he thought were nice (I think they were Proform??), and you could get some beehive springs (I have them). Would probably make the most power that way.
Woods74
Broke Senior
^ Thanks for putting up the bucks, MRL ain't cheap. It better run amazing for the price he wants for them..
A streetable 470 hp 340? Yeah, I think it runs pretty amazing. You get what you pay for.
OOTB Eddy's are known to have quite a few issues that should/need to be addressed before install.
goldduster318
Overzealous Car Modifier
The thing is - for what I got and the fact that I didn't assemble it, it wasn't that expensive. Sure, if he built it from parts he had to find, it looks pretty expensive at $9000. I saved a considerable amount of money by buying stuff a little at a time...yes, it still cost $7800, but if you've priced any other engines that make 470hp and have nice street manners, good luck finding one that good. He's willing to work with what you give him - or even just supply heads. Compared to someone like Best Machine, etc he's a very good value.
You'll find out really fast that H-beams, custom pistons with modern ring packs, and hydraulic roller cams get spendy fast. If you want cheap, buy a Chevy. 340s=$$$
goldduster318
Overzealous Car Modifier
The cost was also fully dyno'd BTW. You can take about $500 off for that alone.
13" of vacuum at 900 rpm with the clutch out. Great street manners even with tall gears and a 4-speed.
13" of vacuum at 900 rpm with the clutch out. Great street manners even with tall gears and a 4-speed.
Woods74
Broke Senior
Hey man no need to sell it to me, it ain't my b*tch. I can think of many things to spend 10k on besides a v8. If your happy then good on ya.
Sounds like some buyer's remorse.
2 Darts
A-body Addicted
The first question should be what do you see yourself doing with the car when it's finished?
IMHO, aluminum heads will tolerate .75-1.0 additional compression before detonation (knocking) will occur. The reason is largely due to the superior heat dissipation of aluminum.
As far as problems with the air gap, they pale in comparison to what I've seen of the Chinese knock-offs.
FWIW, I saw a comparison of the air gap to the M1. Engine was a 300/360 crate motor with Eddy heads. Both manifolds were gasket matched, the M1 had some work done to clean up the plenum as well. Final Results: The M1 didn't beat the air gap until about 5200 rpm.
IMHO, aluminum heads will tolerate .75-1.0 additional compression before detonation (knocking) will occur. The reason is largely due to the superior heat dissipation of aluminum.
As far as problems with the air gap, they pale in comparison to what I've seen of the Chinese knock-offs.
FWIW, I saw a comparison of the air gap to the M1. Engine was a 300/360 crate motor with Eddy heads. Both manifolds were gasket matched, the M1 had some work done to clean up the plenum as well. Final Results: The M1 didn't beat the air gap until about 5200 rpm.
JoeDust451
Well-Known Member
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I ran 10.3 compression on a 370 sbm i did up for a dart, I installed the comp XE284H cam, I ran the stock 915 iron heads, just installed 2.02 intake valves, It had great quench & ran great on pump premium, They were KB 190 pistons. 36* total timing, 2800 stall & 4.56 gears, That engine pulled to 6400.
Now this was at 3700ft. alt. You can get away with higher compression at higher altitudes, I'm sure at sea level i would have needed 110
Now this was at 3700ft. alt. You can get away with higher compression at higher altitudes, I'm sure at sea level i would have needed 110
moper
Well-Known Member
The question is will it run well with the aluminum heads - yes, it will work fine. Probably make a little more power than you currently do. Will it pass 400hp? Who knows. What does it make now (measured, not a desktop hp number)? With that cam, RPM heads, built well with good ring seal and good machining - it should be close to 400hp. No clue if yours does now tho.
In terms of the six pack - tuning is the same as a 4bbl but the intake is restrictive so you could make more power with a quality dual plane. There are guys on here that can help with tuning any engine combo. It starts with timing, and ends with carburetor.
In terms of the six pack - tuning is the same as a 4bbl but the intake is restrictive so you could make more power with a quality dual plane. There are guys on here that can help with tuning any engine combo. It starts with timing, and ends with carburetor.
moper
Well-Known Member
With the right work its possible. There's no way RPMs will give you a 50hp gain on their own.
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