SBF Deck Height ?

[Scott Calabro]

Hi Everyone,
Hope Thanksgiving went well with all !
I have a question........Does anyone know the maximum amount of material that can safely be removed from the cylinder decks of a mid 70's vintage, 302 SBF ?
Thanks,
Scott

 

[Bill D]

You shouldn't deck a block more than .010. If you do, you'll have problems with the pistons rising too high and protruding out the top during running. Second, the alignment of the heads and intake manifold will be off, causing more problems.

Why do you ask?

Bill D

 

[Scott Calabro]

Thanks Bill,
I want to stuff the longest rods in the engine as possible without using custom length rods. If necessary I will machine the intake to fit this combo. Here's what I want to do.....
1. Scat 5.4 " H beams
2. Scat 3" 4340 ultralight crank
3. Mahle 4032 pistons with a 1.245 " comp. height
This will require that I deck the block .055" for a "0" installed piston deck height. This results in a very favorable 1.8 to 1 rod / stroke ratio. Does any one know if the stock 70's block decks will safely support that amount of decking ?
Regards,
Scott

 

[Bill D]

.055 is way too much. Why not use custom pistons with the pin hole relocated?

 

[Scott Calabro]

Its cheaper to deck the block.

 

[Scott Calabro]

Anyone have any blueprint specs on the 302W, i.e. stock cyl. deck thickness?

S

 

[Jac Mac]

Its cheaper to deck the block.

Not if you think it thru Scott- Deck Block, Machine intake manifold, Procure shorter pushrods, Extra time to ensure head bolts dont bottom out, and now you have a collection of parts that are specific to 'that' block only.

It might pay to check with Scat about the possibility of some longer custom rod's or as Bill suggests taller pistons, compare cost difference on those options.

Here is an even better combo--- 302 crank, 1.090" piston ( 3.4" stroke type ), 5.625" rod ( Aussie Holden .927" pin-2.125"journal- Scat Make Them- B.E. will need to be narrowed or you could get them built in 2.100"chev size & grind crank to this or Scat could configure BE to ford bearings).
This will give Stack height of 8.21" [302 deck dim ] 1.50"+ 1.09"+5.625". Rod Ratio 1.88 to 1.

Jac Mac

 

[Scott Calabro]

JAC MAC,
That won't work ..... the block needs to be decked anyway to square it off, its a used block that has never been re built, so unless the decks are perfect (doubtful) it needs to be done. If they were perfect the combo you suggest would leave the pistons .015" out of the bores. With a compressed gasket of say .040, leaves only .025" @ TDC....Too scary for the RPM I wan't to run......., .055" is less than 1/16" ! Can the decks on a SBF be that thin to begin with, that that small amount will be detrimental ?
I'd like to use off the self components. Pushrods come in several lenghts from several mfg's, and I think SBF headbolts go into the water jacket anyway.



Thanks though !
S

 

[Scott Calabro]

HELP!!!!!!!!!!!!!!!!!

 

[Jac Mac]

JAC MAC,
That won't work ..... the block needs to be decked anyway to square it off, its a used block that has never been re built, so unless the decks are perfect (doubtful) it needs to be done. If they were perfect the combo you suggest would leave the pistons .015" out of the bores. With a compressed gasket of say .040, leaves only .025" @ TDC....Too scary for the RPM I wan't to run......., .055" is less than 1/16" ! Can the decks on a SBF be that thin to begin with, that that small amount will be detrimental ?
I'd like to use off the self components. Pushrods come in several lenghts from several mfg's, and I think SBF headbolts go into the water jacket anyway.



Thanks though !
S

Early Blocks are 8.210", Later 8.200". Early have Blind Head Bolt/stud holes, later crap blocks go thru to water. I would be happier to machine 0.015 off a piston crown than take 0.055" off the block. If you have the later block check out how much material there [is not] around the main bearing bolt boss/webs to that of an early block.

Jac Mac

 

[Scott Calabro]

I just wan't to know what the blueprint deck thickness is !


S

 

[Scott Calabro]

Hi All !,
I'd still like to know the answer to my last question if anybody has the correct tech data, but I think I found the answer if anyone is interested.....
J&E makes a flat piston P/N 170232 that has a comp. height of 1.280"
So....1.280" c/h + 5.4" rods + 1.5" stroke = 8.18", with SBF stock height of 8.2", I'll have .020" to work with to square & "0" the decks... perfect !!!

epper:

S

 

[Lynn Larsen]

Don't forget to include the compressed head gasket dimension! Doesn't seem like much, but as you can see, it all adds up. And, within reason, this is another dimension you can manipulate.

Regards,
Lynn

BTW, custom pistons aren't nearly as expensive as they used to be as long as they aren't too exotic. It just struck me that you may be asking what the miminum thickness of the deck can be. I have seen this number before and .750" comes to mind, but don't go by that! Call the guys a DART and I am sure they can tell you.