Piston choice

[Jack A.]

I am rebulding a 61 315 H.P. motor. I am going 30 over and will stay fairly stock with the 097 Cam. I am looking for the best source for the Cam and recommendations on a good set of Pistons and where I might find them.

Thanks as always,

Jack 35730

[Jim L.]

Re: Piston choice

I am rebulding a 61 315 H.P. motor. I am going 30 over and will stay fairly stock with the 097 Cam. I am looking for the best source for the Cam and recommendations on a good set of Pistons and where I might find them.

Jack,

If you want to maintain something like the original compression ratio, these KB-brand hypereutectic pistons would be a good choice:

http://kb-silvolite.com/performance.php?action=details&P_id=41

You can get these from Summit or Jegs.

If that were my engine, I'd buy a new set of rods, too. You just don't know how the original rods were used or abused. Neither can you be sure the original rod bolts weren't over torqued sometime in the past.

Jim

[Dick W.]

Re: Piston choice

Jim, I believe that those pistons would be a little on the low side (9.6) with 64 cc heads.

[Ray C.]

Re: Piston choice

Jack,

I am also in the process of restoring a 1961 FI 315-HP car. I purchased the cam and lifters from Carquest. I used the Federal Mogul Speed Pro # CS-113R cam with listed solid lifters. I believe the engine machinist purchased KB pistons with the same specs as the originals. (At least that is what I requested from him)

Ray

[Jim L.]

Re: Piston choice

Jim, I believe that those pistons would be a little on the low side (9.6) with 64 cc heads.

If that's the chamber volume of the early 461 heads, then I agree.

Although I've never measured them personally, it's been my understanding the chambers are no larger than 62cc. My spreadsheet says he can get almost exactly 10:1 with 62cc heads and .018 steel shim gaskets, and of course more with .015 gaskets and more if he mills the heads.

I think this will be about as good as can be conveniently achieved. If there are off-the-shelf pistons that yield the original 11:1 claimed compression for a 283/315, I'm not aware of them.

Jim

[Clem Z.]

Re: Piston choice

Jack,

If you want to maintain something like the original compression ratio, these KB-brand hypereutectic pistons would be a good choice:

http://kb-silvolite.com/performance.php?action=details&P_id=41

You can get these from Summit or Jegs.

If that were my engine, I'd buy a new set of rods, too. You just don't know how the original rods were used or abused. Neither can you be sure the original rod bolts weren't over torqued sometime in the past.

Jim

if you want the original "clonk clonk" sound from your engine when cold you will have to used forged piston

[Tom D.]

Re: Piston choice

Ray and others: What compression ratio are you expecting?

Thanks
Tom D.

[Duke W.]

Re: Piston choice

The only forged piston I know of for the 283 is the Speed Pro L2163, but it's a flattop with valve reliefs, 1.795" compression height and will not give adequate compression.

With a Duntov cam I recommend a target not to exceed CR of 10.25:1 which should be doable with the KB 166 and since the compression height is 1.805" the nominal deck clearance is .020". Also the -4 cc volume must be entered into the CR calculator I've referenced a zillion times as a positive number. KB lists "domed" pistons as negative, which is opposite most other manufacturers. Install them at the upper end of the skirt clearance recommendation, which may yield enough piston slap to duplicate the acoustics of the OE forged pistons.

Of course, to target a true maximum CR you must know the actual deck clearance, which you get by MEASURING. Nominal 461 1.94/1.50" valve set head chamber volume is about 61 cc, but they must also be measured. Then you select a head gasket to get you in the target range and do some addition chamber grinding to knock down the high cylinders to no more than 10.25, and shoot for no more than 0.1 min/max variation or .05 if you're a perfectionist.

Duke

[Jim L.]

Re: Piston choice

if you want the original "clonk clonk" sound from your engine when cold you will have to used forged piston

A quick survey of Jegs and Summit failed to turn up any domed, 283 forged pistons at all.

If authentic cold-engine start up sounds are important, it looks to me like the choices come down to:

1. Pay extra to have a set of forged pistons custom made. JE and others are skilled at doing this.

2. Clearance the KBs loose, say .004 on the skirts. Me, I'd struggle with the decision to do this since one of the big selling points of the KBs is that they can be fit very tightly in the cylinders.

Jim

[Duke W.]

Re: Piston choice

The OP should contact United about maximum allowable installation clearance.

The OE forged pistons are fit "loose" because the skirts expand quite a bit resulting in much tighter operating temperature clearance than cold fitting clearance.

Hypereutectic skirts expand much less, which is why they are installed tighter.

I've seen too loose clearance break piston skirts due to the piston slapping back and forth.

Another lesson here is that engines with OE type forged SHP/FI engines should be allowed to reach full operating temperature before demanding high load and revs.

Duke

[Clem Z.]

Re: Piston choice

i would think that you should be able to get 4" bore forged pistons from FM. make it a 302" those 283 block can be bored to 4"

[Ray C.]

Re: Piston choice

Ray and others: What compression ratio are you expecting?

Thanks
Tom D.

Hi! Tom

I am using the KB 166060-8 Pistons. The bore is .40 over. There is a chart at the following location, but I am at work and have not had a chance to play. The engine machinist thinks it will fall between 10.5 to 11.1 Compression ratios.

Ray

http://kb-silvolite.com/performance.php?action=details&P_id=41

[Duke W.]

Re: Piston choice

The CRs listed on the site are based on a specific head gasket thickness, which is buried somewhere in fine print. Your actual CR may vary significantly.

The ONLY WAY to determine true CR is to measure deck clearance at assembly, which a 12-year old can do, and choose a gasket to achieve the target, but BEWARE, most "engine builders" don't bother with this step and just throw the engine together with a thick gasket, which can leave a lot of torque across the rev range on the table.

As I have said a zillion times before, deck clearance should be measured at DISASSEMBLY so you can compute actual deck height and understand if the decks are parallel to the crankshaft and whether one is higher than another, but, again, most "engine builders" ignore this important step.

Unfortunately, most of the time you don't "get what you pay for".

It's up to the individual owner to be sure that a target CR is selected and the easy steps to manage it and achieve the target are accomplished.

Duke

[Greg G.]

Re: Piston choice

Hi! Tom

I am using the KB 166060-8 Pistons. The bore is .40 over. There is a chart at the following location, but I am at work and have not had a chance to play. The engine machinist thinks it will fall between 10.5 to 11.1 Compression ratios.

Ray
http://kb-silvolite.com/performance....etails&P_id=41

Ray, You better check your pistons the part number KB166 is the piston the next three digits are the bore the last number is a set of eight (8). What you posted is that your bore is .040 and your pistons are .060.

BTW, With a deck hieght of .018 and a head gasket of .019 you should be right at 10 to 1. I would not run much more compresson than that on a street engine with todays fuels.

Greg

[Ray C.]

Re: Piston choice

Thanks! Greg

I will check tomorrow. The block and engine components are still at the engine machinist. I called him this AM to check on the pistons for this post and that was the numbers he provided. Maybe he had to take the cylinder bore to .060 over, but I had thought he told me .040 over.

Ray