C1 283 Quelch question

[Mark P.]

If my deck clearance is only 0 to .010" (my deck is not square with the crank) is this good for quench since it is smaller than what was original ? Will this lead to LESS detonation ?

I plan to go with a .015" shim gasket (FEL-7733SH1). Block and heads have been resurfaced. Deck height has been checked.

I am trying to get to the 9.5:1 CR and maintain the originality a shim gasket provides.

The CR with this gasket is 9.043 to 9.264 which is the best I can get with the available pistons and gaskets.

Felpro recomends using Permatex High Tack spray to seal the shim gasket and said I should not need to do a retorque unless it was a race motor. Does this make sense ?

[Timothy B.]

Re: C1 283 Quelch question

Mark,

I don't think that will be enough quench clearance. You don't want a collision between piston and valve. GM recommends .035-.040. Does the engine have #'s on stamp pad?? If not have the deck trued properly.

If you can't deck, try a .035 gasket and look for a piston with same height and two valve reliefs or slight dome. I agree with Duke's statement if using a GM 929 clone cam, static compression at 9.75 and will yield dynamic compression approx. 8. I think 58*ABDC is good closing point for 929 cam for estimating C/R

What is cc of heads??

[Jim L.]

Re: C1 283 Quench question

If my deck clearance is only 0 to .010" (my deck is not square with the crank) is this good for quench since it is smaller than what was original ? Will this lead to LESS detonation ?

I plan to go with a .015" shim gasket (FEL-7733SH1). Block and heads have been resurfaced. Deck height has been checked.

If the minimum deck clearance on your engine really is 0 (i.e. the top of any one piston is dead even with the block deck), then you want a gasket thicker than .015. If that were my engine, I'd use an .039 gasket, albeit composition and not steel shim, and take the deduction.

With an .015 gasket, I'd be real concerned about the piston top getting overly friendly with the head if you rev the engine.

Felpro recomends using Permatex High Tack spray to seal the shim gasket and said I should not need to do a retorque unless it was a race motor. Does this make sense ?

Re-torquing a head gasket isn't fun. I get that. However, I can't think of any situation for which it isn't a good idea.

If you do use a steel shim head gasket, for sealer you need nothing better than old fashioned silver spray paint on both gasket surfaces.

One question.... if you had the block decked, how come there is .010 variance in deck height? The machine shop I use can achieve .002 easily.

Jim

[Clem Z.]

Re: C1 283 Quench question

If the minimum deck clearance on your engine really is 0 (i.e. the top of any one piston is dead even with the block deck), then you want a gasket thicker than .015. If that were my engine, I'd use an .039 gasket, albeit composition and not steel shim, and take the deduction.

With an .015 gasket, I'd be real concerned about the piston top getting overly friendly with the head if you rev the engine.

Re-torquing a head gasket isn't fun. I get that. However, I can't think of any situation for which it isn't a good idea.

If you do use a steel shim head gasket, for sealer you need nothing better than old fashioned silver spray paint on both gasket surfaces.

One question.... if you had the block decked, how come there is .010 variance in deck height? The machine shop I use can achieve .002 easily.

Jim

stack up in machine specs can cause .010 difference as this was the problem in the original olds diesel engine. in the old days i used to check rod length,piston pin to piston crown distance and crank throw length and move the parts around to get the deck all the same or as close as posible.

[Mark P.]

Re: C1 283 Quelch question

My block was decked and is perfectly flat. It was decked because I needed it restamped because it is not original to my car. The problem is the shop that decked it did not make sure it was square to the main journals. They just made sure it was square to the original deck surface. The shop that is rebuilding it did not deck the block. Deck heights that at .010" different on blocks that have never been decked are common and will have no impact on the performance I have been told.

My pistons are the KB165030 piston which have two valve reliefs which are 6cc. My heads are 62 cc. I am going .030 over.

[Jim L.]

Re: C1 283 Quench question

stack up in machine specs can cause .010 difference as this was the problem in the original olds diesel engine. in the old days i used to check rod length,piston pin to piston crown distance and crank throw length and move the parts around to get the deck all the same or as close as posible.

I understand the problem of tolerance stack up. To compensate for it, I mix and match rods, pistons, and cylinders when I build one of my racing engines.

The OP seemed to be talking about .010 variance due to the deck not being parallel to the crank. Maybe he could get lucky playing mix-and-match too. In any event, if that were my engine, I wouldn't assemble it with such a wide variance in deck heights. I'd find a way to fix it.

Jim

[Mark P.]

Re: C1 283 Quelch question

We will check it. With new Eagle rods and new KB Hypereutectic pistons he is doubtful they will be any variation. Probably less than 1/2 a thousands of an inch.

He says for 15 years they got a new machine and have since always decked based on the center of the crank line. Unfortunately, they guy that sold me my decked block uses a shop that decks it the old way.

[Mark P.]

Re: C1 283 Quelch question

Should I strive for .035" to .040" Quench height ? Is .015 too low, even with a stock cam ? If so I'll need to go with the .039" gasket and average compression drops to 8.6 from 9.15.

[Joe C.]

Re: C1 283 Quelch question

Should I strive for .035" to .040" Quench height ? Is .015 too low, even with a stock cam ? If so I'll need to go with the .039" gasket and average compression drops to 8.6 from 9.15.

Mark,

Quench has nothing to do with the cam (unless you plan to use one with very high lift and long duration)................it defines how close the flat portion of the piston comes to the head @ TDC.
Some engine builders play "Russian Roulette" with quench, believing that less is better! Problem is, if you go too tight, then the piston will hit the head, or, in time, carbon buildup will cause contact.
The general consensus is that .035-.040 is optimal (all else being equal; i.e SCR), as far as deterring detonation................anything less has no added value...............anything more will deter it to a lesser extent.
A very well built SBC, using cast pistons (requiring tight clearances>>>>>>>less rocking), with tight bearing clearances and good, strong con rods and max RPM limited to say, 6000, can probably be built with quench as tight as .022-.025.............but why??
If I were you, I'd have the machinist true up your decks parallel with the main journals......if he can't do so, then I'd take the "job" elsewhere. I would build in .035 quench.

[Mark P.]

Re: C1 283 Quelch question

Ted - I am replacing a crate 350. My original engine is long gone.

The replacement engine block was decked and was restamped.

Since 283s typically were not decked square with the centerline of the crank (.010" variance was common), and the machines to deck them squarely with the centerline of the crank are still not used everywhere and hit the scene just about 15 years ago, I am not sure why having the deck squared with the crank is important.

I can tell you it seemed nearly impossible to achieve an acceptable CR once the block was decked. In hindsight I should have went with the KB domed piston and a .050 thick gasket. I was shooting for the originality of the shim gasket and missed the minimum quench issue.

I appreciate all the help from the TDB during this process.

[Timothy B.]

Re: C1 283 Quelch question

Is this engine put together now? Why not use a .035 gasket and get pistons with a small dome to achieve compression ratio.

Or is there a piston with smaller height and dome and .015 shim gasket??

[Duke W.]

Re: C1 283 Quelch question

Are you sure the head chamber volume is 62 cc? Did you measure them? That's the nominal chamber size for a standard valve 462 head - 283 small valve head chambers are smaller.

Duke

[Mark P.]

Re: C1 283 Quelch question

Hello Duke - yes, the rebuilder measured one chamber 3 times using the plexiglass technique with a syringe. He tried it with "Listerine" as well as Marvel Mystery Oil. He sealed the plexiglass to the head with grease and filled it until the solution came out the small hole in the plexiglas. He used an AC 45 spark plug. He owns the shop and has been doing engines for 25 years and has a good reputation.

Here are the head details.

Left Head 3774692 D280 28-Apr-60 Right Head 3774692 E2 02-May-60

The rebuilder said they have been rebuilt at least once before based on the tool markings on the surface. These are the right heads for my 1960 283 based on the JM but I am not sure they ever came on a Corvette.