Vortec heads and the quench factor

[boatnut74]

I recently buttoned up my 4.3 build but now after some research have some questions. Engine is a '90 4.3 roller motor with speed pro flat top pistons and I upgraded to vortec heads. From what I have found the optimum quench is .040. From what I calculated mine is .064. Ami going to have issues running it this way? I have to much money tied up into this to have catastrophic failure.

 

[alldodge]

You want it between .35 to .50 and wanting .40 is perfect. Your .64 may be a bit to much unless your running high octane fuel, and it can still be an issue.
What is your compression ratio?
What is your head gasket thickness?

 

[boatnut74]

Compression ratio is around 9.5:1 .039 compressed gasket thickness. There aren't very many head gasket options for the marine 4.3. Upon further research I found the pistons my engine builder put in are not to be used in a 4.3 so I have to get that issue resolved.

 

[alldodge]

Compression ratio is around 9.5:1 .039 compressed gasket thickness. There aren't very many head gasket options for the marine 4.3. Upon further research I found the pistons my engine builder put in are not to be used in a 4.3 so I have to get that issue resolved.

That bites big time.
So your pistons are in the bores at .025. To reduce quench may need to deck the block if the pistons can not be changed

 

[boatnut74]

From my calculations the pistons are about .037 in the hole plus the .039 head gasket. I talked to the machine shop and he said if I bring in the right ones he won't charge to swap them out and would refund me for the others.

What piston is recommended for this motor? I'm running vortec heads so I think I want a d dish piston but if I could find the lcq style I would prefer that but choices seem limited.

 

[alldodge]

From my calculations the pistons are about .037 in the hole plus the .039 head gasket. I talked to the machine shop and he said if I bring in the right ones he won't charge to swap them out and would refund me for the others.

What piston is recommended for this motor? I'm running vortec heads so I think I want a d dish piston but if I could find the lcq style I would prefer that but choices seem limited.

To my calculations are .037 (piston to deck) + .039 (gasket) = .076 Quench

I would always prefer flat top over dish due to turbulence issue, There are quite a few pistons out there and found ,021 gasket for 4.060 bore (don't know what yours is). Never rebuilt a V6 so I wouldn't know right off which to advise, but would also need to know about your build and what your wanting in the end. I'm assuming your block started as 4.00 bore and 3.48 stroke

 

[boatnut74]

4.3 bored .030 with vortec heads. Really just looking for a stout 4.3. Running stock roller cam with full roller rockers. I read that running a d dish piston with the vortec heads is preferred

 

[alldodge]

4.3 bored .030 with vortec heads. Really just looking for a stout 4.3. Running stock roller cam with full roller rockers. I read that running a d dish piston with the vortec heads is preferred

Never did a V6 but will look into and see what I can suggest. Hopefully someone which has done it will help out later. Right now I see with all the volume in the compression chamber (quench and dish pistons) the motor will be a real turd. Now if you put a blower on, it will run great with the low compression it currently has (as I see it).

 

[Tail_Gunner]

4.3..... 5.7 same thing.. opps the 5.7 oiling is a tad better..... dish piston with 9.5 to 10.1 compression get your squish to .040. what piston's were used if I may ask.

 

[boatnut74]

The d dish pistons I was looking at would yield around 9:1 compression.

 

[Tail_Gunner]

http://www.superchevy.com/how-to/46778-engine-compression-guide/

If you?ve never computed compression ratio before, this is worth experimenting with on a number of levels. For example, stroke has a much greater effect on compression than bore, which is why the short stroke/small displacement engines require such small combustion chambers. Other areas worth investigating are variables like gasket thickness. Replacing a thick 0.051-inch composition head gasket on a 350 with one of Fel-Pro?s 0.024-inch rubber-coated head gaskets can pump the squeeze factor from 8.68:1 to 9.16:1.

Read more: http://www.superchevy.com/how-to/46778-engine-compression-guide/#ixzz3OqNSwN4B
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9:1 is fine just play with gasket thickness

 

[boatnut74]

H345dcp speed pro pistons are what was used. Looking on a few sites they say do not use with 4.3 v6. That's the whole reason for investigating. I found some keith black d dish pistons that would yield around 9.5:1 with my 64cc chambers

 

[boatnut74]

Did a little searching for pistons. My current ones have a compression height of 1.548. To help with the quench I would need 1.560. I found the speed pro h631cp's that would work. They are a flat top with 2 valve reliefs. Would these be a good choice? Also are there thinner head gaskets available for a marine 4.3? All I can find are .039 compressed thickness.

 

[Bondo]

4.3 bored .030 with vortec heads. Really just looking for a stout 4.3. Running stock roller cam with full roller rockers. I read that running a d dish piston with the vortec heads is preferred

Ayuh,.... That is correct,....

Quench is set by measurin' all yer parts, 'n Deckin' the block, to bring the pistons, Up in their holes,....

Without Deckin' the block, there's no way to get where ya wanta be,....

 

[boatnut74]

Ayuh,.... That is correct,....

Quench is set by measurin' all yer parts, 'n Deckin' the block, to bring the pistons, Up in their holes,....

Without Deckin' the block, there's no way to get where ya wanta be,....

Since I have to tear back down to replace the pistons I am planning on decking the block to get my quench where it needs to be. What would the preference be between flat tops and d dish pistons. Keith black has the lcq style d dish but they run around $300 for the set. I can get the 2 valve relief speed pros for $150. They both have the same compression height.

 

[Bondo]

Since I have to tear back down to replace the pistons I am planning on decking the block to get my quench where it needs to be. What would the preference be between flat tops and d dish pistons. Keith black has the lcq style d dish but they run around $300 for the set. I can get the 2 valve relief speed pros for $150. They both have the same compression height.

Ayuh,.... If ya deck the block for a .040"/ .045" quench, you Have to use a d-dish, or inverted dome piston to bring the compression ratio down,...

With flat-tops the compression will be pushin' 11:1,...

 

[boatnut74]

I guess these are what I need then. I asked the machine shop about running the d dish and he seemed to think the compression would be to low. He does however build race car engines and not so much boat engines.

 

[Bondo]

I guess these are what I need then. I asked the machine shop about running the d dish and he seemed to think the compression would be to low. He does however build race car engines and not so much boat engines.

Ayuh,..... You've gotta do the Math,.......

Anything else is just a Guess, 'n leads to junk motors,.....

 

[alldodge]

I ran the numbers and came up with the following using Summit Racings calculator
http://www.summitracing.com/expertad...ion-calculator
With a 1990 4.3L engine, specs are as I take it:

Bore 4.00 and bored out .030 yielding 4.030
Stroke 3.48
Vortec head between 64 and 68CC using 64 as baseline
Using a deck clearance of .001

Compression ratio numbers using dish pistons, subtract about 0.3 to compression numbers for 68CC volume (Did not use negative number pistons)
22CC = 8.71
18CC = 9.04
14CC = 9.42
7CC = 10.15
6CC = 10.27
5CC = 10.38
0 CC = 11.04

All the above numbers came from pistons found at Summit
http://www.summitracing.com/search/p...2%2B4294882357

Edit: let me add, this is keeping with the .039 head gasket and not decking the block so much. Your engine but personally but I would think about using a non-marine gasket unless your in salt water.

 

[boatnut74]

With the keith black 193 pistons sitting .005 in the hole it computes to 9.73:1 That would give me a .044 quench