Vortec heads and the quench factor

[boatnut74]

No salt water for me. What's the maximum I would want to run for compression on this motor? There's a few pistons available but it seems like a lot of them have compression heights of 1.540-1.548 which would put me .045-.037 in the hole

 

[alldodge]

No salt water for me. What's the maximum I would want to run for compression on this motor? There's a few pistons available but it seems like a lot of them have compression heights of 1.540-1.548 which would put me .045-.037 in the hole

I think your really going to make me do some Ciphering here (already loosing my hair and gona start scratching some more). As before I have not done a 4.3 but will provide the following:

Original deck height is 9.025
Con rods are 6.000
Stroke 3.48

9.025 / 2 = 7.5125
9.025 - 7.5125 = 1.5125 max piston height for zero deck
Add a .039 head gasket to zero and we get .039 quench

As I see it 1.540 would be bending some things

 

[boatnut74]

I believe the stock rods in a 4.3 are 5.7, the same as a 350. To make things easier a 4.3 is the same as a 350 minus 2 cylinders. 9.025 deck height, 5.7 rod and 3.48 stroke.

 

[alldodge]

No No No I messed up 3.48 stroke / 2 = 1.74 + 6.00 = [FONT=&quot]7.74 - 9.025 =1.55

So 1.55 is max piston height to top of deck, your correct

My bad

Edit:
If they are 5.7 inch then the final number would come to 1.585[/FONT]

 

[boatnut74]

My current pistons are 1.548 and sit .037 in the hole ( I measured)

I guess what I'm looking for is a smooth good running engine. I'm not trying to build a race car. If I don't have to deck the block that would be nice. I do know I want a maximum of .060 quench. I'm at .076 now.

I'm not trying to be a nuisance, just trying to do this right.

 

[alldodge]

Well were starting to have a meeting of the minds, your numbers and my numbers match on .037. I hound a 1.565 height piston with a 18.60CC volume. Using your .039 gasket should bring the compression to 8.65 using 64CC chamber. If it turns out to have some 68CC chambers compression goes to 8.35.

Deck to 000 and you have 9.0, Go to an .032 head gasket and compression numbers goes to 9.1
http://www.summitracing.com/parts/uem-ic6726-030/overview/make/chevrolet

There could be some other pistons but the 18CC to no less then 14CC keeps you in the ball park. With 18CC your on regular gas, Mid grade with the 14CC or 10.1 compression

 

[boatnut74]

http://www.summitracing.com/parts/uem-kb193-030

These are 12cc with 1.561 compression height. If I put them .005 in the hole they calculated to about 9.73. The heads are 64cc and were surfaced. They took no more than .010 off of them

 

[boatnut74]

The current (wrong) pistons calculate to 9.59:1
I always run premium (91 octane) fuel in my boat

 

[alldodge]

http://www.summitracing.com/parts/uem-kb193-030

These are 12cc with 1.561 compression height. If I put them .005 in the hole they calculated to about 9.73. The heads are 64cc and were surfaced. They took no more than .010 off of them

Looks good to me, see what Bondo and Tailgunner have to say. You would also get 2 extra pistons (set of 8).

From what I've found the heads are calculated at 64CC but in actuality they are between 64 to 68 according to what I've read (casting thing).

 

[alldodge]

The current (wrong) pistons calculate to 9.59:1
I always run premium (91 octane) fuel in my boat

Well if you always run 91, punch the compression up to 10.1 (go 14CC), that way your getting more for your money

 

[Bondo]

http://www.summitracing.com/parts/uem-kb193-030

These are 12cc with 1.561 compression height. If I put them .005 in the hole they calculated to about 9.73. The heads are 64cc and were surfaced. They took no more than .010 off of them

Ayuh,.... The heads Were 64cc's, but they've been surfaced, so now they're Smaller than 64cc's,....
The only way I know of to see what they are is to measure 'em,....

If ya have the block decked to .005 down the hole, it oughta be a good set up,... That's .046" quench,....
.003" down the hole would be Better with the .039 gaskets,...

 

[boatnut74]

Here's what I came up with on the compression calculator for the 193 keith blacks I was looking at.



Seems like it would be a good setup with these .003 or .005 in the hole

 

[Tail_Gunner]

Getting above 9.5 get your quench at 040 to 045 dead on or run forged piston's...It's of more importance to get the 9 to 9.5 than getting quench dead on this is not a high strung rever...Deep dish and quench along with high compression will give you a crisp throttle response. Some of this I don't understand factory timing on a 4.3 are fairly tame detonation is not a high priority.

 

[boatnut74]

Getting above 9.5 get your quench at 040 to 045 dead on or run forged piston's...It's of more importance to get the 9 to 9.5 than getting quench dead on this is not a high strung rever...Deep dish and quench along with high compression will give you a crisp throttle response. Some of this I don't understand factory timing on a 4.3 are fairly tame detonation is not a high priority.

Keith black does make another piston around 14cc that would get me around 9:1 I can get my quench between .040-.043 smooth and crisp sounds good to me

 

[Tail_Gunner]

http://www.beckracing.com/page07.htm

PUMP FUEL


8.5:1 - Quench head engine for tow service, motor home and truck.

9.0:1 - Street engine with proper .040" quench, 200? @ .050" lift cam, iron head, sea level operation.

9.5:1 - Same as 9:1 except aluminum head used Light vehicle and no towing.

10:1 - Used and built as the 9.5:1 engine with more than 220? @ .050" lift cam.
A knock sensor retard is recommended with 10:1 engines.

 

[boatnut74]

So according to that chart 8.5:1 would be optimum since a boat operates under the same basic load as a tow truck. Looks like I'll shoot for around 9:1. The pistons I found were 9.7:1 which may be a little much. Again, thanks for all the help!

 

[Tail_Gunner]

Keep it up 9 and below 10...8 would be very tame or lack luster in any engine.