DusterBoy15
THE WISE(guy) MEMBER
when i build my motor i want to run pump gas and the max is 91 im in CA so go figure. So i want to know what the max i can bore the motor to increase the C.I and would using a 340 crank help thanks
boring my 318
- Thread starter DusterBoy15
- Start date
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The 340 crank is the same stroke as a 318 crank.
The '73 crank is a cast unit and extrenally balanced. This is a 1 year only item. It is possible that a late '72 crank could be this way. The machinest will know when he see's it.
Otherwise, a 340 crank is fordged and early 318 cranks are as well. I'm not sure about what year they are cast. (I forget and I do not have a book infront of me. )
Overboreing should be keep to a min. While it doesn't really contribute to a ratio increase, it will in a most modest manor. It is more of the piston height that changes the ratio. Just ask for a 9.0-1 piston with the head you have or the amount of cc's the head has.
Max bore is actually a changing amount determined by the thickness of the cylinder wall which can be check by a (Good) shop with a machine. It's called sonic checking. You don't want to max out the bore. Thin walls can lose power by flexing under stress. A thicker wall is prefured. The amount of cubic inchs gained by an overbore and power gained is nothing and if gone to far, will offset and modest gains achieved.
The '73 crank is a cast unit and extrenally balanced. This is a 1 year only item. It is possible that a late '72 crank could be this way. The machinest will know when he see's it.
Otherwise, a 340 crank is fordged and early 318 cranks are as well. I'm not sure about what year they are cast. (I forget and I do not have a book infront of me. )
Overboreing should be keep to a min. While it doesn't really contribute to a ratio increase, it will in a most modest manor. It is more of the piston height that changes the ratio. Just ask for a 9.0-1 piston with the head you have or the amount of cc's the head has.
Max bore is actually a changing amount determined by the thickness of the cylinder wall which can be check by a (Good) shop with a machine. It's called sonic checking. You don't want to max out the bore. Thin walls can lose power by flexing under stress. A thicker wall is prefured. The amount of cubic inchs gained by an overbore and power gained is nothing and if gone to far, will offset and modest gains achieved.
DusterBoy15
THE WISE(guy) MEMBER
so how do you increase CI
7demon2
Registered User #1824
change the crank out.
DusterBoy15
THE WISE(guy) MEMBER
to what kind? and year
7demon2
Registered User #1824
overbores of the cylinders will gain you about 6 ci per a 30 thousandth overbore.....
DusterBoy15
THE WISE(guy) MEMBER
so what crank should i use
7demon2
Registered User #1824
you could go with a custom crank. mopar performance makes quite a few different ones. many other places also offer these. a 360 crank will also work as well
DusterBoy15
THE WISE(guy) MEMBER
what size are these cranks and do i jsut bolt them in after having it balanced or what thanks. also does this increase my compression?
7demon2
Registered User #1824
the cranks will vary depending on how much you want to go and how much your engine can take. there are stroker kits available that you can get through places like mancini raceing, hughes engines, flatlander raceing ect....compression will change as the piston travels with a longer stroke.
7demon2
Registered User #1824
a good book for you to look at is called " how to build big inch mopar small blocks" written by jim szilagyi. lots of info for you there.
GoodysGotaCuda
Mr. Goody
360 crank would need the main bearing journals milled down, and special pistons if i remember right. adding more than a couple cubies usually isnt cheap. So depending on your budget...
7demon2
Registered User #1824
very true.....GoodysGotaCuda said:
7demon2
Registered User #1824
here is a link to a 318 stroker kit from rpm machines. you can get the picture from this ad as to the cost and the parts needed. i think this will punch a 318 to 349 ci
http://www.rpmmachine.com/318-349-chrysler-stroker.shtml
http://www.rpmmachine.com/318-349-chrysler-stroker.shtml
GoodysGotaCuda
Mr. Goody
$1800 for a balanced 318 > 390cu kit here
http://speedomotive.com/ps-138-13-mopar-318cid-to-390cid-forged-piston-stroker-kit.aspx
http://speedomotive.com/ps-138-13-mopar-318cid-to-390cid-forged-piston-stroker-kit.aspx
I told him to get the books. These are easy questions answered in the books. But since the unasked question is the biggest mistake.......
As you see, a cut down (On the mains) 360 crank will increase your displacement some. IMO, it would be easier and cost effective to do a 360 block instead.
A 318 stroked with the 360 crank or a 4 inch crank will require expensive pistons. This is a "You wanna do it" project.
The cranks do not increase compresion because the need for a custom piston. The piston needs to be speced out.
You'll need to balance the crank with pistons when you get a stock crank or stroker. Not doing this is bad.
As you see, a cut down (On the mains) 360 crank will increase your displacement some. IMO, it would be easier and cost effective to do a 360 block instead.
A 318 stroked with the 360 crank or a 4 inch crank will require expensive pistons. This is a "You wanna do it" project.
The cranks do not increase compresion because the need for a custom piston. The piston needs to be speced out.
You'll need to balance the crank with pistons when you get a stock crank or stroker. Not doing this is bad.
ValiantMike
Well-Known Member
Heres a good 318 street build.
http://www.geocities.com/alwest_83/318?200721
http://www.geocities.com/alwest_83/318?200721
My fav. link to point out the 302 head vs a 360 head.
ValiantMike
Well-Known Member
Yea Rumble, thats some substancial difference in the bottom line. I'm still seaching for a set of 302s. Can't find much around these parts. Mike
7demon2
Registered User #1824
hey rumble if you didn't change the pistons the compression would increase would it not? changeing pistons would also only be necessary if you stroked it out alot also would it not? i thought a small stroke would be able to keep the current pistons......
You technically have a very good point with the minor exception of what piston sits that far down in the hole to be used with a stroker crank. If there is one, I'm not currently aware of it. It is possible to do if you can find that piston. Otherwise, it is going to be popping out of the block.
Do the math.
Yes, compresion would increase.
Do the math.
Yes, compresion would increase.
7demon2
Registered User #1824
i can live with that.....good point. :headbang:
One way of doing it (Figuring it out) is measure how far down in the hole your piston is.
Thats the amount of room you have left. Then do some math.
3.58 - 3.31 = .27 / 2 = .135
If your piston is @ .135 down in the hole or greater, then the piston could technicly (sp) be used.
Thats the amount of room you have left. Then do some math.
3.58 - 3.31 = .27 / 2 = .135
If your piston is @ .135 down in the hole or greater, then the piston could technicly (sp) be used.
I read the responses twice and everybody forgot Duster Boy's original question. Most 318's came with 8-1 to 8.5-1 compression ratio. If the best you can get for gas is 91-92 I would keep the compression at or below 9.5-1.
How do you bump the compression 1-1 1/2points? New pistons with a higher
compression ratio would do the trick. Cylinder geads with a smaller combustion chamber will raise compression also. (like the #302 heads with the heart shaped combustion chambers) You can also mill the heads and or machine the block and also the intake (so it will fit).{I don't recomend} You can also install thinner head gaskets for a slight increase. Boring the block doesn't actually raise compression and neither does a different crankshaft. Those two options just force you to install different pistons with the ratio you want.
How do you bump the compression 1-1 1/2points? New pistons with a higher
compression ratio would do the trick. Cylinder geads with a smaller combustion chamber will raise compression also. (like the #302 heads with the heart shaped combustion chambers) You can also mill the heads and or machine the block and also the intake (so it will fit).{I don't recomend} You can also install thinner head gaskets for a slight increase. Boring the block doesn't actually raise compression and neither does a different crankshaft. Those two options just force you to install different pistons with the ratio you want.
toolmanmike said:
Dang, you read into the question somewhere.
DusterBoy15 said:
I read overbore max. Unless the first sentence is about ratio. I didn't really see the go figure part as a seperate question on ratio.
Stock engines came with the thinest head gasket.toolmanmike said:
toolmanmike said:
This is what I was trying to say earlier.
Two, 318's, 1 with a stock bore and 1 @ .030 overbore, while both useing the same flat top pistons and same cc valve reliefs, the overbored engine will spec out with a ever so slight increase in the compresion ratio.
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