340 questions

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SwingerMan

SwingerMan

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Hi everyone,
I am new to the forum and have a few questions about my 340. I just purchased a 69 Swinger with a stock rebuilt 340 in it. The problem is the guy I bought the car from was the 2nd owner after the restoration and doesn't know what pistons were used for the rebuild. Is there anyway to check and see what compression the motor is with it in the car? I know there are some formulas that involve the combustion chamber volume etc but like I said the motor is in the car. I know from looking at the harmonic balancer that the crank is cast. The reason I am concerned is the guy sent a new .484/284 cam w/adj rockers with car. I would like to use this cam but I am worried that they used low compression pistons for the rebuild and I would like to know before we go through all the work. I want to put the car into the 12's, I have the above mentioned cam, a edelbrock air gap intake/holley 750 to go onto the car. I would also like add TTI headers and to ditch the 3.23's and go with 3.91's and a stall. The car has J heads and I am not sure if they are the 2.02's or not. Sorry this is so long just a new guy with a lot of questions :book: Thanks for any help and suggestions!! :salut:
 
Hello fellow Houston (LaPort) Dart owner AKA SwingerMan,
Welcome to the board. Sounds like a 73 cast crank j head 340. Check the passenger side of the block for the date. Sometimes it is easier to do if you stick a mirror down there and catch a reflection of it. If all they did is rering it, you have the 8.5:1 low compression motor. You did say "stock rebuilt". Maybe someone with a 10.5 or 8.5 motor will post a compression test number for you to compair to.
 
I would do two things. irst, do a static compression test..Warm it up, pull all the plugs, prop the carb at wide open throttle, and then do the test. Write down the results, and post them. If they are good, there are other parts you can use to get what you want easily. If they are low, then you really should pull a head, and peak around in there to verify what you have. As far as guidelines, I'd say (with a "stock" cam) you're looking for 160psi or higher. You cannot tell what the static ratio is by this reading. But it will tell you if things like rings and valves are decent, then you can choose parts that will work with lower ratios, or do the head pulling and get some real numbers. Even knowing which pistons were bought, doesnt ensure that they are in the way they need to be to get the advertised ratio. They are almost always on the low side.
 
gremlin said:
Hello fellow Houston (LaPort) Dart owner AKA SwingerMan,
Welcome to the board. Sounds like a 73 cast crank j head 340. Check the passenger side of the block for the date. Sometimes it is easier to do if you stick a mirror down there and catch a reflection of it. If all they did is rering it, you have the 8.5:1 low compression motor. You did say "stock rebuilt". Maybe someone with a 10.5 or 8.5 motor will post a compression test number for you to compair to.
Click to expand...

Thank you for the welcome it's good to see a local person. The block is a 1970 supposedly they bored it and put in new pistons I am just unsure of which internals they used. I think the compression test is about the only bet I have. I may end up pulling the heads to get a better look.
 
moper said:
I would do two things. irst, do a static compression test..Warm it up, pull all the plugs, prop the carb at wide open throttle, and then do the test. Write down the results, and post them. If they are good, there are other parts you can use to get what you want easily. If they are low, then you really should pull a head, and peak around in there to verify what you have. As far as guidelines, I'd say (with a "stock" cam) you're looking for 160psi or higher. You cannot tell what the static ratio is by this reading. But it will tell you if things like rings and valves are decent, then you can choose parts that will work with lower ratios, or do the head pulling and get some real numbers. Even knowing which pistons were bought, doesnt ensure that they are in the way they need to be to get the advertised ratio. They are almost always on the low side.
Click to expand...

Thanks for the tips I will give this a shot and post them here to see what we have.
 
moper said:
I would do two things. irst, do a static compression test..Warm it up, pull all the plugs, prop the carb at wide open throttle, and then do the test. Write down the results, and post them. If they are good, there are other parts you can use to get what you want easily. If they are low, then you really should pull a head, and peak around in there to verify what you have. As far as guidelines, I'd say (with a "stock" cam) you're looking for 160psi or higher. You cannot tell what the static ratio is by this reading. But it will tell you if things like rings and valves are decent, then you can choose parts that will work with lower ratios, or do the head pulling and get some real numbers. Even knowing which pistons were bought, doesnt ensure that they are in the way they need to be to get the advertised ratio. They are almost always on the low side.
Click to expand...

im STILL waitting for you 2nd thing too do??? :butthead:
 
Lookout now...you guys behave yourselves up there...don't make me have to come up there...LOL
 
Sorry guys, but most of the "J" heads came with the 1.88 and 1.6 valves. It was mostly the early 340's that got the 2.02's in the 915 castings. However, like anything else, there are exceptions to the rule. The only way to know for sure is to measure 'em up. :)
 
yeah sorry about that i got my crap mixed up the j heads came with both 1.88 & 2.02 intake valves but i was thinking about the z heads that were all 2.02 but they only came on 70-71 and some 72 340's where as the j's mostly came on 360s " i think but i am not sure " some one correct me if i am wrong
 
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