Need info/help on a 340

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wheelman21

Mopar noob
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Bing NY
I have an opportunity to pick up a built 340. Here is what I know, it's a 73 Block with J heads. It has flat top pistons, and the heads have been worked to a 202 intake valve. It has a 3 angle valve job. It has an M1 intake, and mighty demon carb. It has a stock crank that I believe is undersized. It has a ultradyne 521 cam, the specifics of which I do not know. I believe the guy also said something about a recurve (?) ignition. According to the guy who built the motor it is tuned to run on 100 octane, including 100LL. While this is well and good, most airports won't let you fill up there since it's illegal, and I want a car that is streetable. Is there anyway to get this thing to run on pump gas? And if so what kind of HP are we talking and is there room for imporovement with say, a more aggressive cam?
 
you need to get more info from the seller what pistons and compression ratio is it?

if the engine needs 100 octane fuel the compression is to high for a street car, it sounds like a race only motor, you could de tune it, only thay will not be cheap

here is a link to ultradine/bulet cams you can contact them to find the specs

http://bulletcams.com/index.shtml
 
First findout compression ratio. I have flat top pistons in my 340 with x heads and stock stroke and rod length and ended up with 9.7 to 1
 
Duster,
Do you have stock piston size I.E. not bored? What kind of numbers are you putting down?
 
First findout compression ratio. I have flat top pistons in my 340 with x heads and stock stroke and rod length and ended up with 9.7 to 1

The seller isn't positive of all the small specifics (he didn't build it), but I ran all the various possible variations of variables and the max compression ratio should be about 10.37, but I believe it to be more around 10.2. So with that being said, what say you fellas?
 
If you can get access to the engine, you could do a compression test with a bellhousing, flywheel, and starter. I am not certain of compression limit for 93 octane but probably about 175-180 psi. That would also give indication of equality of all 8 cylinders. Someone with more experience could give pressure limit for premium fuel.
 
If you can get access to the engine, you could do a compression test with a bellhousing, flywheel, and starter. I am not certain of compression limit for 93 octane but probably about 175-180 psi. That would also give indication of equality of all 8 cylinders. Someone with more experience could give pressure limit for premium fuel.

The engine is currently in a car. I could start it, but I'm not sure if the owner will allow me to disconnect the tank (it's full of race fuel) and hook up a separate fuel line.
 
3406pk is right, also the RVP for avgas is different than in pump gas. Avgas boils at a lower temp than pump gas and can lead to vapor locking. Just my 2 cents.
 
how did you come to the conclusion that it cant be over 10.37 to 1? with available parts it is easy to go a lot higher than that
 
Duster,
Do you have stock piston size I.E. not bored? What kind of numbers are you putting down?

Bored .30 over using Ross racing pistons (forged aluminum) with total seal gapless piston rings.
Haven't ran it since I put the full roller setup in it.
 
how did you come to the conclusion that it cant be over 10.37 to 1? with available parts it is easy to go a lot higher than that

I know you can go a lot higher than that, I'm basing it on what I know about the motor. The only thing I don't know in calculating the comp ratio is head gasket thickness, and exact deck, but I know it's right around zero deck.
 
I know you can go a lot higher than that, I'm basing it on what I know about the motor. The only thing I don't know in calculating the comp ratio is head gasket thickness, and exact deck, but I know it's right around zero deck.


I have more information. The engine is stock bore, stock stroke, stock pistons and stock deck. It has j heads with 2.02 valves and 3-angle valves. Why on earth would this thing be running 100 octane? Shouldn't it be 8.5-1 compression it's a 73.
 
I have more information. The engine is stock bore, stock stroke, stock pistons and stock deck. It has j heads with 2.02 valves and 3-angle valves. Why on earth would this thing be running 100 octane? Shouldn't it be 8.5-1 compression it's a 73.

You should be able to run it on regular pump gas. 87 89 octane.
 
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