HOT 340 Engine rebirth....... maybe!!!!

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Brambles

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I bought an engine today 9-24-70 to go into my 1970 swinger 340.

The engine is all apart and has been sitting in a wharehouse for the better part of 20 years.

Its a .030
TRW L2322 12.5:1 Forged
Crane CCH-312-2 cam http://www.cranecams.com/index.php?show=browseParts&action=partSpec&partNumber=694571&lvl=2&prt=5
915 J heads with 2.02-1.60's, don't seem to be ported

Not sure what intake, carb or exhaust the guy was running.

The cylinders hopefully can be honed clean, there is some surface rust in the bores.

I'll have to mock everything up and CC the heads to find out what the actual compression is but I can always mill the dome down to get more streetable levels.

The questions I have, and hopefully someone can help are

1.) whats the most I can hone before piston to wall clearences get too large. I believe recommended TRW clearences are .005 but how large can you go before it becomes a problem...

2.) considering the cam and compression, what do you figure the output of this engine was, ballpark, I know without induction and exhaust it will vary some.

3.) How difficult do you think this combo would be to drive on the street. I want something hot but this might be too hot???
 
thats a pretty high rpm deal i would gues with that cam and a short stroke 340, i would cc the heads first with most cylinderhead volumes those pistons wont get anywhere near 12.5:1 anyway
with that kind of cam size make sure its a ballanced rotating assembly since it will like to spin high...
streetable is in the eyes of the driver i would drive something like that on the street without any hesitation then again thats me;)
as for clearance i dont remember the numbers but i have some stupid clearance with the same pistons in my 340 and it runs nice and isnt very noisy after warming up:)

now over to the guys with more knowledge and experience:)
 
340sFastback said:
Before you hone it I'd check those cylinder walls for taper.
Click to expand...

That's exactly what I was thinking. Even if it's ok before you hone it make sure after you hone it to make sure it didn't get out of round from honing too much. .005 is what I've always heard for clearance on those pistons too. If you go much more than .007 they'll be slapping around in there and reduce the power output by not allowing the rings to seal properly.

With that combo I'd guess it should've made 425-450 hp originally.

That is a pretty wild cam for a small cube engine on the street but like duster340 said streetable is in the eye of the beholder. You need alot of compression to make that cam have at least some low end torque. Even then it wouldn't be great and you'd have to run a pretty loose converter and real low gears. Can you also handle 3-5 mpg on race gas? That's another consideration. If your after basically a race engine in a street car sounds like you've got it. If you want a nice mannered street engine that still sounds tough and can back it up drop some 9.5 to 1 slugs in it (if yours can't be milled down enough) work the heads over and put in a cam with about 230 degrees duration at .050 and .500-.530 lift. That'll get you a good mannered stout 340 that'll run fine on pump gas, have decent torque so you don't have to run a 5000 stall converter and 4:30 gears and probably even get 10-14 mpg if you don't go any deeper than 3.73 on gears.
 
reducing the compression will kill that cam, and the performance......drop the compression for the street you need to go to a smaller cam.. but with the higher comp. that cam will scream ! . try to find the original speck on the piston clearance , i would go no more than .002 more to clean it up and as stated the bores must be straight . You may be able to clean up the bores using a ball hone , they work well without removing much material. you need to stay as close to the manufactures speck as possible .



sorry ..looks like fishy and i were typing at the same time....
 
I measured the bore and pistons and it looks as thought it was set up for Drag Racing Piston to wall clearances are .010 which is Nitrous or serious drag racing specs.

Ball park Compression seems to be 11.14 assuming a 72cc chamber, 4.100 head gasket dia., "0" deck and a .039 head gasket.

Pistons have a 10.7 cc dome and bore is 4.073.

So after I nail down the actual head cc's and find out the actuall deck height I might be alright for compression, I can even run a slightly thicker head gasket if I need to fudge the numbers down a bit.

The only thing is the Piston to wall clearance of .010, how noisy is this going to be on the street and is it advisable?

The other option is a set of KB243's and get the cylinders honed to 4.08 for a .040 overbore
 
The new piston deal looks like a better option. That cam is large, for a everyday ride. I've run cams that large in the street before. There best as a weekend cruiser deal.

You'll need to port the hedswell for best result.

The KB107 flat top will work with that cam. It'll give you 9.8-1 w/ a 72 cc head. You'll need 91 - 93 octane to make it happy for the street.

Speaking of which, if you want to run the street with this;

I'd do 4.10's at the min. for a max street effort, shy of tubbing the car, I'd look at 4.30's at a max. Mini tube and fat tires, 4.56's.

This set up would work well with a M-1 single or Holley strip Dom and large tube headers. You can get more than 450 HP with good head work.
 
KB107's are 360 pistons arn't they?

I'm actually working on 4 motors right now, overhaulin a 318, going over and improving a Built magnum headed 360 w/KB372 pistons and two 340's.

This motor were talking about is a 1971 340, so the KB243's are the only ones avaliable. I figure with a little head milling I can get 10 - 10.5:1 maybe have to run a touch thinner head gasket. I'm looking for Forged alternatives, somthing that can run with tighter clearances since I'm honing to 4.08 and one bore is already 4.075, by my calculations that only leaves 1 thou hone on that cylinder if the pistons have the tolerances already built in these days?

The cam that was in the motor was shot, one journal is rusted and pitted from sitting, I just listed it to see what the power potential of the engine was.

I'll be buying a new cam, thinking somewhere in the 230-235 @.050. I'll probably run a M1 or similar edelbrock single plane,750 carb I have 3.91 gears, A904 trans with Race parts and am thinking of 2800 or 3000 RPM stall.
I'll port the heads on the 1971 360 cause they are 2.02 915 J heads but the 1969 has the X heads so I might leave them virgin, time will tell.

Hoping to get into the mid 12's on street tires.

I'll run the 360 until the 340 is built, I need a new cam for that one too and going to mill the heads a touch to raise comp to about 9.8, and do some more porting, its got a dual plane M1 magnum intake and 600 carb right now. Don't know if I can get near 400 Hp with this combo but I'll try.
 
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