Piston swap?

[Spootch]

I have a 73 Cleveland that is stock. It leaks a bit ( rear seal and pan)so I'm thinking of throwing Gaskets at it. I'm wondering if anyone has just tossed in a set of higher squish pistons keeping everything else stock ? Up the compression a little over the dish pistons currently in there..

Thoughts?

 

[MeZapU]

It is more preferable to install heads with a smaller quench combustion chamber than only swapping the pistons. The piston swap would require the lower rotating assembly to need rebalancing. A head swap is simple in comparison and would likely yield more desirable results.

 

[Jeff73Mach1]

If you are going to go to that trouble, then a set of pistons with a dome cut to match the shape of the chambers would be a good way to increase compression, but since it will require a complete disassembly and rebalance of the rotating assembly, you would be doing yourself a favor in the long run to go ahead and have the block cleaned and machined as necessary and replace the bearings while you are in there.

There is a lot of focus on compression, and it is a huge part of improved performance, but a less expensive gain is available with a cam change. A leaky worn engine needs to be torn down and measured before you make a decision

 

[barnett468]

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you can just mill your heads a bit and/or install thinner head gaskets from cometic.

run a water bypass block off plate and a 180 thermostat.

ignition timing is critical . . curve your distributor advance so it is best for your setting.

if your carb is jetted properly, go up 1 size on the main jets.

 

[Spootch]

If I just swap out pistons, why does it need a rebalance? I only ask because when I was a young lad my brother and I swapped in HO 351w pistons into a regular windsor that had a buggered piston. Still runs ! And that was all we did with it. I can't say I noticed a huge power increase because we put the motor in a van but it did work

 

[barnett468]

If I just swap out pistons, why does it need a rebalance? I only ask because when I was a young lad my brother and I swapped in HO 351w pistons into a regular windsor that had a buggered piston. Still runs ! And that was all we did with it. I can't say I noticed a huge power increase because we put the motor in a van but it did work

you do not "need" a rebalance but it should be rebalanced . . it will basically change the vibration point if you don't . . if you do not rebalance it, you will certainly not feel a huge vibration.

 

[Jeff73Mach1]

at normal engine rpms, minor imbalances are highly amplified. Sometimes you feel them, other times you don't, but they are there.

Internally your crankshaft flexes in a wave pattern. Your flywheel and harmonic damper help to reduce this action and to keep your crankshaft from tearing itself free from the block.

There are different types of balancing of a rotating assembly-static and dynamic

In static, you essentially match all parts Pistons are all lightened to match the lightest one, rods are as well with the addition of big and small end weight

Dynamic balancing is more involved.

If the pistons are of a different design, you could try and match their weights, but they will be different than the old ones, so your assembly's balance will be unknown. You might be fine or you might build a motor that will self disassemble. The choice is yours.

 

[barnett468]

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i have never seen a major vibration from swapping pistons in 40 years and hundreds of engines but there is always a first time and there is a risk as i mentioned, but matching the piston weight as closely as possible is definitely a good idea.

 

[Jeff73Mach1]

and indeed if the piston weights are matched you may well be fine. Leaking rear main seals can be a result of the seal failing or the crankshaft to bearing clearance being too large from years of wear. (or imbalance) I'd have the assembly checked for straightness and main and rod journals addressed if necessary and go ahead and plan on new bearings while you are in there. From there, having the pistons pressed off the old rods and the new ones pressed on, it is just a little more to get it balanced.

As I have been told many a time-"it only cost a quarter more to go 1st class"

If your budget won't allow you to rebuild it completely, you have choices to make.

 

[barnett468]

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if you tear it apart . . have a crank shop look at the crank as mentioned . . obviously it is working ok now but if it has small grooves etc, they can polish it a bit . . if it ends up undersize, you can buy bearings that are .001", .002" and .003" thicker . . if you plan to beat fairly hard, i would run around .00225" - .0025" clearance.

 

[Spootch]

I can't remember who made it but I thought I seen an add for a balancer that adjusted for most bottom ends (not fluid either)?? Anyhow, I think the shit kick would be the debate on how to freshen the cylinders. I wonder however, what it would take to get it to a 350 hp rating? At 170 some hp now, it won't get out of its own way. Up the compression with pistons to 70s era specs, then what? I should add that it's a q code so it should breathe.....

 

[barnett468]

I can't remember who made it but I thought I seen an add for a balancer that adjusted for most bottom ends (not fluid either)?? Anyhow, I think the shit kick would be the debate on how to freshen the cylinders. I wonder however, what it would take to get it to a 350 hp rating? At 170 some hp now, it won't get out of its own way. Up the compression with pistons to 70s era specs, then what? I should add that it's a q code so it should breathe.....

you can simply buy a set of trick flow 195 heads and a comp xe284h cam, vic junior intake, 2600 rpm stall converter, if your trans is an auto, build it to handle the hp, run 3.91 gears and you will have at least 350 hp at the crank.

 

[Jeff73Mach1]

What gear ratio is the rear end in the car now?

 

[Spootch]

No idea what the rear is. It's an 8. And it's a manual 4 out of a t bird I'm told. The car was an auto but was changed by the P.O. In the 80s. It lugs bad in first and does about 50 @3000 rpm:dodgy:. Looks a lot like Jeff's car!

It runs fine but it leaks. Just wondering how much hp higher comp pistons would give it? Or if its worth it? It sucks when my wife blows my doors off in her cobalt..

Like a lot.

 

[barnett468]

No idea what the rear is. It's an 8. And it's a manual 4 out of a t bird I'm told. The car was an auto but was changed by the P.O. In the 80s. It lugs bad in first and does about 50 @3000 rpm:dodgy:. Looks a lot like Jeff's car!

It runs fine but it leaks. Just wondering how much hp higher comp pistons would give it? Or if its worth it? It sucks when my wife blows my doors off in her cobalt..

Like a lot.

increasing the compression by 1 point might increase hp and tq by around 4% thru the entire rpm range.

you are doing 3,000 rpm at only 50 miles per hour? . . this would mean your rear gears around 4.11

is your speedo accurate?

what year t bird is the trans out of.

changing rear gear ratio will increase acceleration rate much more than increasing compression will.

 

[Jeff73Mach1]

if you put the car up on axle stands, transmission in neutral, you can rotate a tire one full turn while counting driveshaft rotations-this will tell you your rear end ratio. It helps to make a chalk mark on the driveshaft. If opposite wheel turns same way you have posi, if it turns opposite, the rear end is open

in the 8" there was a 3.40 gear available that I ran in a coupe 25 years ago behind a 302 and it was a very nice ratio. Good acceleration, good top end power decent cruising speed. (I made it from Memphis, Tennessee to Atlanta. Georgia in under 5 hours going through Nashville and about 3 tanks of gas)