348 build

[63impalass409]

So building a stoke stroke, , 10 to 1 -60 over piston,hydraulic crower cam but still have not figured out the lift is as it came with a bunch of parts I bought but wondering if putting 817 heads on are going to out perform the stock 379's as I have a bunch of each. I could also go with 690's or 583's but see no point with a small stock type motor. Just a play motor with this one.

 

[Don Jacks]

Yes on the 817's over the 379's by 25-30 hp.Use a good intake and at least 2 1/2 in.manifolds.You need to degree that cam and find it's duration at .050.When it comes to piston to valve clearece lift doesn't matter but over lap will get you.The cast repllacement piston has a small valve notch,but not much,the Icon forging will have enough notch to handle about any hyd.flat tappet ever made.If your lift on the exhaust side exceeds .550 you must have the notches in the block deepened.

 

[1964SuperStocker]

Only you can decide what you want to do. Sounds like you walked into a box store and can't decide on what is for dinner because of the huge selection to choose from. 379's are good for cruisers only. If you are going with 10:1 then you are clearly thinking performance minded. You could just go with 9.5:1 and have a nice little running engine but 817s are way better. Clearly the 690's and 583 are going to give you the best performance but you really need to decide what you want to do and what parts you have currently to do it with and what you may need to get to finish the build. Start there because its easy to get caught up in the HP wars. If this is going in a small light car then use those 379's, they are still good heads.

 

[63impalass409]

Sounds like the 817's are going to be the heads I go with and I don't want to waste big port heads on a 348. The pistons are already bought and hung on my resized rods just waiting on the crank grinder this week. Thinking about a different cam so I actually know what I'm using.. I have 2 348 cranks and 1 409 crank and a 65 409 block at the shop all supposedly going to be done this week! Fingers crossed anyways so I have something to do this winter. I have 583's all ready done waiting for the 65 409 block and crank.

 

[scott hall]

The big port heads won’t be any good on a 348 unless you turn some big rpm and get the air flowing.

 

[1964SuperStocker]

The big port heads won’t be any good on a 348 unless you turn some big rpm and get the air flowing.

In general maybe but I guess without a test mule to swap (large/small port) heads on with a number of camshafts, intakes and exhaust manifolds, it would be difficult to know what kind of velocity can be had in/out of the runners. Big reason I'm cutting heads open because (in my mind) if the only difference between an 817 and a 690 is the small vs large port design then its possible that nearly identical flow numbers can be achieved. Then the argument for 817's would be about the same as bolting on 690's. Until the factory runners are measured for each head along with different valves then we can only guess and assume. I have heard that 333 and 817s have very similar runners. I have also heard that 817 and 690's have very similar runners. Either way 10:1 pistons and 817 heads with a modern cam should put you in the 400hp range though your camshaft will play a large roll where you end up. What size of valves are in the 817? I hope you pan to dyno this girl, we all want to see how you come out. Keep us up to date on the progress. It will be a fun combo.

 

[63impalass409]

The 817's have stock size valves

 

[Tim]

The 380 I built had 817. I ported them and cleaned up a lot of the runners, put 219/172 valves, used the 409 crank and KB icon pistons,eddy intake and a 600cfm carb. Also had stock 409 manifolds. Having said all that mine was a double notch and was trying to get as much as I could but it came out at 400hp/450 torque at the flywheel.