Compression ?????????
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GoodysGotaCuda
Mr. Goody
Aluminum or Cast Iron heads? High or low octane?
mullinax95
Well-Known Member
I'll take a guess and say 10.1 with cast iron head and 93 octane. That's the highest octane we have around here. A little more with aluminum. I had a big block that was 10.1 and didn't have any trouble.
CORRECT with cast heads^^^^^^^^^^^^
AdamR
Big Member
It depends on the entire combo, Gearing trans, car weight, Cam, heads, altitude.
A safe bet is 9.5:1 with iron heads and 10.5:1 with aluminum.
A safe bet is 9.5:1 with iron heads and 10.5:1 with aluminum.
C130 Chief
Mechanical Genius
Careful prep of the combustion chamber surface can make a HUGE difference in detonation tolerance. Make sure to thoroughly deburr and smooth all sharp edges.
Thanks alot Guys Im new and HAPPY to be a mopar owner ,i just dont know much about building a SB mopar.
Im planning to keep it 4spd gears 3.91 stock wt.and i have been reading about cams so far im planning a voodoo cam, AIR GAP intake,750 holley carb so far
9.5-1 is a safe area still capable of makeing excellent power. As a note, in the Crafstman NASCAR truck series, the trucks engine were limted to a 9.0-1 raio and made 700+ HP. Of course there hardware was booo-kooo expensive and modified, but, it was 9.0-1.
Actual ratio can vary on a lot of factors. For a basic street combo, without problems, everyone is right in playing safe @ 9.5-1 as a max. 10-1 (Or higher) is doable, but pump gas has it's limits and other things about the engine that make a higher ratio doable on a street you may not like.
Extra large cam, retarded timing and mixing race gas in with 93 octane just so you can drive it.
Actual ratio can vary on a lot of factors. For a basic street combo, without problems, everyone is right in playing safe @ 9.5-1 as a max. 10-1 (Or higher) is doable, but pump gas has it's limits and other things about the engine that make a higher ratio doable on a street you may not like.
Extra large cam, retarded timing and mixing race gas in with 93 octane just so you can drive it.
dgc333
Well-Known Member
Or, if you want to go with a closed chamber head like a the magnum heads from a late model truck you can go to 10.6:1 and run 89 octane like I do. The benifits are a better flowing head (more power) than the 340 came with and the closed chamber combined with a zero deck flat top piston for a very detonation resitant engine.
mikesduster
Well-Known Member
13:1 !!!!!!!!!:yawinkle:
THE SUMMARY:
9.5 with cast iron heads if i want to be safe
10.5 with aluminum heads
10.6 with magnum heads
Now the hard part CAMS
AdamR
Big Member
The Magnum heads are cast iron but they have a better combustion chamber design. They are also closed chambered so if you run a lat top piston its easy to set your quench up right to help with detonation resistance. Thats why max compression is really combination specific.
Cams are not really hard. Everyone will have an opinion on them and have a valid point to there choice. Key points for your own choice in a cam would be;
Duration. This is the power band it will operate in. If your thinking is to have the car perform in the 2,000 - 6,000 RPM range, then you'll look at cams in that power range. Durations will be slightly different since Hyd. , solid and roller cams all perform alittle differently with there given duration.
Lift. You'll want to find a lift that will work with your head. If it is a stock head, generallly, the stock heads flow stall at around the .500 lift point.
This is why knowing how a head flows is so important to alot of people here.
Theres no real sense have the valve lift to .570 when the heads flow stalls or gets real crappy @ .500.
Hyd. or Solid or Hyd. roller or Solid roller?????? UGH! Theres alot of grinds out there. Choice on style is made easy but not limited to any one style. For a basic street machine, a regular standard Hyd. cam will do well. Don't expect a miricle from it, but it can make nice power, be easy on the wallet and free from constant adjustments or hang up from long duration cams with heavy springs and adjustable rockers etc...
Duration. This is the power band it will operate in. If your thinking is to have the car perform in the 2,000 - 6,000 RPM range, then you'll look at cams in that power range. Durations will be slightly different since Hyd. , solid and roller cams all perform alittle differently with there given duration.
Lift. You'll want to find a lift that will work with your head. If it is a stock head, generallly, the stock heads flow stall at around the .500 lift point.
This is why knowing how a head flows is so important to alot of people here.
Theres no real sense have the valve lift to .570 when the heads flow stalls or gets real crappy @ .500.
Hyd. or Solid or Hyd. roller or Solid roller?????? UGH! Theres alot of grinds out there. Choice on style is made easy but not limited to any one style. For a basic street machine, a regular standard Hyd. cam will do well. Don't expect a miricle from it, but it can make nice power, be easy on the wallet and free from constant adjustments or hang up from long duration cams with heavy springs and adjustable rockers etc...
Which one of the purple cams will give me good power and a nice exhaust note.
All the MoPar cams are ground on a 110 centerline except a few of the updated ones which are on a 112 for improved drivabilty.
The narrow centerline (Lower number) will have a muscle sound, like chop chop chop.
Now, what power band are you operating in?
What size tire?
How fast in the 1/4 do you want to go?
The narrow centerline (Lower number) will have a muscle sound, like chop chop chop.
Now, what power band are you operating in?
What size tire?
How fast in the 1/4 do you want to go?
moper
Well-Known Member
No purple cams can equal much designed after '00. You're better off sepnding money on something that will do what you want with little or no down side, rather than compromising.
Only thing i have bought is EDELBROCK Air gap intake and holley 750dp
1/4 if i see 11's im happy with a 26 10.5 15 tire I really dont want much out of her just to look good and sound MEAN.(LOL)
AdamR
Big Member
Its going to take a good amount of motor to run 11s
yeah i know,how about 12's
moper
Well-Known Member
I'm not sure what kinds of cars you were previously interested in, or if you have any drag racing experience... But, it takes more than an intake, an over sized carb, and a cam to un a 340 in the 12s. 13s is fairly easy with basic nolt ons, mild to medium gearing, and a basically stock convertor. 12s needs a bit more of a commitment in terms of the whole package. What exactly is your budget on this, and what are you starting with?
dont have a budget i just want a nice street car with a little power.Sorry I didnt think it would be that hard to get 12's out of a duster but I am new to the mopar world.I am Toyota and TurBo regal owner as well,Both run deep in the 10's with little $$$ but they are turbo cars.
So far im reseaching what i need and go from there:
My wife bought me a holley 750dp and air gap intake thats
all for now
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