Cylinder head question

[Rembrant]

With the exception of the cam and pistions, My Bronco is a stock 5.0/ 302 EFI. Not that it really means anything to this conversation, I build my own dirt track race engines and have been for the last 25 years so I do have some engine building experance.

Hey Steve,

I know that you mentioned you installed 10:1 pistons in the 302, but the actual compression isn't 10:1, is it? With the stock heads?

I have flat-top pistons in my '84 302, and GT40 Explorer heads, and my compression is only around 9:1. Maybe the pin height in your pistons is different from mine. Mine are just a stock replacement, the same as what was in the truck factory, but for 0.020" bored over.

[old55pete]

Hey Steve,

I know that you mentioned you installed 10:1 pistons in the 302, but the actual compression isn't 10:1, is it? With the stock heads?

I have flat-top pistons in my '84 302, and GT40 Explorer heads, and my compression is only around 9:1. Maybe the pin height in your pistons is different from mine. Mine are just a stock replacement, the same as what was in the truck factory, but for 0.020" bored over.

No Cory, I am going to say with the stock heads it is around 9: 75 to 1 compression ratio. I put in .010 over Wisco pistions in a .010 over sized block.

[Rusty_S85]

Hey Steve,

I know that you mentioned you installed 10:1 pistons in the 302, but the actual compression isn't 10:1, is it? With the stock heads?

I have flat-top pistons in my '84 302, and GT40 Explorer heads, and my compression is only around 9:1. Maybe the pin height in your pistons is different from mine. Mine are just a stock replacement, the same as what was in the truck factory, but for 0.020" bored over.

Bout like mine, 302 with a 0.030" over bore I dont know the deck clearance as I havent gotten the short block yet but the builder claims that short block with a 60cc head would produce 9.0:1 compression and with my 58cc heads should be around 9.2:1 compression. But I dont know what thickness head gasket he is using for his figuring of 9.0:1 compression with 60cc heads. But his short blocks are flat top pistons with four valve reliefs.

 

[Lima Delta]

Hey Steve,

I know that you mentioned you installed 10:1 pistons in the 302, but the actual compression isn't 10:1, is it? With the stock heads?

I have flat-top pistons in my '84 302, and GT40 Explorer heads, and my compression is only around 9:1. Maybe the pin height in your pistons is different from mine. Mine are just a stock replacement, the same as what was in the truck factory, but for 0.020" bored over.

I put off any decisions until Monday, and in the meantime came up with this compression estimate using the calculator on the Summit website and based on stock 351w specs and the following assumptions:

- E7TE combustion chamber size: 62CC (table says 62-65CC)

- Sealed Power 336P pistons (.040 over): +6CC valve relief, 1.719 compression height

https://www.summitracing.com/parts/slp-336p40/make/ford

- Fel-pro head gasket compressed thickness: .040 (just a guess based on a review of different parts sites)

At 8.9:1 compression comes out lower than I imagined. Anyone see any glaring errors here?

Lucas

 

[Gary Lewis]

I put off any decisions until Monday, and in the meantime came up with this compression estimate using the calculator on the Summit website and based on stock 351w specs and the following assumptions:

- E7TE combustion chamber size: 62CC (table says 62-65CC)

- Sealed Power 336P pistons (.040 over): +6CC valve relief, 1.719 compression height

https://www.summitracing.com/parts/slp-336p40/make/ford

- Fel-pro head gasket compressed thickness: .040 (just a guess based on a review of different parts sites)

At 8.9:1 compression comes out lower than I imagined. Anyone see any glaring errors here?

Lucas

I've gone back through your calculations and I don't see anything wrong. But I'm no pro at this.

[Lima Delta]

I've gone back through your calculations and I don't see anything wrong. But I'm no pro at this.

Thanks Gary, much appreciated.

[Rusty_S85]

I put off any decisions until Monday, and in the meantime came up with this compression estimate using the calculator on the Summit website and based on stock 351w specs and the following assumptions:

- E7TE combustion chamber size: 62CC (table says 62-65CC)

- Sealed Power 336P pistons (.040 over): +6CC valve relief, 1.719 compression height

https://www.summitracing.com/parts/slp-336p40/make/ford

- Fel-pro head gasket compressed thickness: .040 (just a guess based on a review of different parts sites)

http://forum.garysgaragemahal.com/file/n85634/compression.jpg

At 8.9:1 compression comes out lower than I imagined. Anyone see any glaring errors here?

Lucas

Looks right, after all the guy I am leaning towards doing my short block offers them in 0.030" and 0.040" overbore and states 9:1 compression with 60cc heads using flat top pistons with I believe the valve reliefs are typically are 6cc. With 62cc 8.92:1 sounds pretty accurate in my book, I estimated mine should be 9.2:1 with 58cc heads but without knowing what compressed thickness headgaskets he use for his figuring of 9:1 @ 60cc chambered heads I have no way of knowing if mine really will be 9.2:1 or if it would be 9:1.

I did look up his pistons he uses in the photos he provided on the ebay listing and got things such as compression height for the pistons and I know he uses reconditioned stock rods and stock crank which gives me a good idea of the build, down side is he makes no mention of if he zero decks the block or if he brings the block down to a specified quench figure. All his ebay listing states is

then they all get squared up by our BHJ fixtures which gives you a truly squared up deck surface after we mill them (a plus for holding a head gasket tight under high stress applications)

His add also states the one I am looking at for $1,884 states the pistons are coated sealed power hyper pistons and the photo reference shows the short block with a H273CP sealed power Speed Pro hyper pistons which has a 1.605" compression height and a +8.00cc piston head volume.

This coupled with OE rods and a OE stroke comes out the following for me.

Rod Length : 5.090"

Stroke : 3.00"

Deck Height : 8.206" (OE not accounting for squaring or decking)

Deck Clearance : 0.011"

This combined with my 1011-1 recommended headgasket from AFR for my Renegade 165 heads with 4.100" x 0.041" head gaskets come up on Summits Compression Calculator as 9.15:1 and with 60cc heads 8.95:1 which tells me his 9:1 compression has to be with a thinner head gasket than the one I am running which is the thinnest recommended one for my AFR heads. That also is assuming he doesnt deck the block that much. If he decks the block down to 0.008" - 0.009" deck clearance he could get 9:1 compression with 0.041" thick head gaskets. If he did that then I would still be right around 9.2:1 compression.

I will see if I can find this other compression calculator I found years ago, you actually punched in all the measurements and it did all the work for you, no math having to be done to figure things such as deck clearance.

[Rembrant]

I put off any decisions until Monday, and in the meantime came up with this compression estimate using the calculator on the Summit website and based on stock 351w specs and the following assumptions:

- E7TE combustion chamber size: 62CC (table says 62-65CC)

- Sealed Power 336P pistons (.040 over): +6CC valve relief, 1.719 compression height

https://www.summitracing.com/parts/slp-336p40/make/ford

- Fel-pro head gasket compressed thickness: .040 (just a guess based on a review of different parts sites)

At 8.9:1 compression comes out lower than I imagined. Anyone see any glaring errors here?

Lucas

Where did the deck clearance number come from? Is that typical for a 351w? My ‘84 302 was 0.014” stock, and was decked down to 0.005” when the shop built it for me.

[Rusty_S85]

Where did the deck clearance number come from? Is that typical for a 351w? My ‘84 302 was 0.014” stock, and was decked down to 0.005” when the shop built it for me.

Deck Height : 9.503" (71-96 351W)

Stroke : 3.50"

Rod Length : 5.956"

3.50" / 2 = 1.75"

1.75" + 5.956" + 1.719" = 9.425"

9.503" - 9.425" = 0.078" Deck Clearance.

Thats assuming the block height is 9.503.

I ran into this problem years ago when trying to piece together a 351W build as I wanted to hotrod my 351W some, just about all piston combos with rods gave a huge deck clearance like as seen here. Only way to really correct it would be to throw in a longer than OE rod or deck the block quite a bit.

[Rembrant]

Where did the deck clearance number come from? Is that typical for a 351w? My ‘84 302 was 0.014” stock, and was decked down to 0.005” when the shop built it for me.

Deck Height : 9.503" (71-96 351W)

Stroke : 3.50"

Rod Length : 5.956"

3.50" / 2 = 1.75"

1.75" + 5.956" + 1.719" = 9.425"

9.503" - 9.425" = 0.078" Deck Clearance.

Thats assuming the block height is 9.503.

I ran into this problem years ago when trying to piece together a 351W build as I wanted to hotrod my 351W some, just about all piston combos with rods gave a huge deck clearance like as seen here. Only way to really correct it would be to throw in a longer than OE rod or deck the block quite a bit.

Ahh, OK Rusty. That math works out for my engine as well then. I ran my specs through the Summit compression calculator, and it's pretty much bang on with my previous calculations which my engine builder confirmed. My '84 302 now has 65cc GT40 heads, 3cc flat top stock replacement +.020" pistons, and they decked the block down to 0.005", which puts it right at 9:1 compression.

Hey Lima,

Can you find a set of pistons with smaller valve reliefs, or different pin height? With a deck clearance of 0.078" you have some room there. I'm no expert though...lol, all my experience is with the 302;).