High compression ratio

[gregaba]

Looks like my compression is going to be higher then I expected. I was thinking of 11.4-1 with my set up.
I did my final set up on the short block yesterday and I was finally able to measure the piston height. They stick out above the block .006.
 Cometic .040 gasket's.
Using a online caculator I come up with 12.26-1 compression ratio using the Edlebrock cc of 76 cc.
This will increase after the heads are re surfaced as they are not flat enough for me.
I have a couple cases of 105 race gas booster which will be OK for what I will be using the car for.
I was going to use Rocket fuel but the price just got to be to much.
This should hold me untill next year when my CNG conversion will be ready. I guess I will find out if everything works next year.
Greg
 

[frnkeore]

I don't know your engine specs so, I can't tell you how much a .051 thick head gasket will lower the CR but, here are three available gaskets .051 and one .050:

Clevite 3389 .050 x 4.33 12.065cc

Cometic Gaskets C5840-051 .051 x 4.44 12.71cc
Fel-Pro 8045 PT .051 x 4.200 not round 11.86cc
Fel-Pro 8554 PT .051 x 4.330 not round 4.33 x 4.57 est 12.70cc

If this is your Cometic gasket, you can figure the reduction, using the above:
Cometic Gaskets C5835-040 .040 x 4.25 9.30cc

[gregaba]

Thanks Frank
Engine spec's are
bore 4.164
stroke 3.98
Blocked decked to 10.155
Scat forged h beam rod's
Race tec flat forged pistons.
block square decked and blueprinted.
internal balanced to 1 gram.
TCI Rattler balancer.
Edelbrock heads with 2.19-1.73 ss valves.
Harland sharp rockers
POP stand's.
POP hv oil pump.
Jays intake adapter'
Jays timing cover and adjustable timing set.
CVR electric water pump and Jays adapter's.
Trick Flow track heat 351 intake.
1050 dominator carb.
Will be pushing 6r80 tran's with speed gem's adapter.
Circle D torque converter 3400 stall.
Rear is
Strange with 4.11 ratio.
Greg

[blykins]

You'll have to wait until your heads are clipped before you can do a final compression ratio calculation.  Then you can determine what kind of fuel or fuel mix you'll need.

However, you'll for sure need a set of .050" head gaskets.  A .034" piston/head clearance is too tight IMO.  I have tried .036" and saw imprints in the carbon on the pistons.

[frnkeore]

Greg,
This is what I came up with using the minimum valve relief of 5cc and a top land with of .250.

I use the Diamond Piston calculator, the most accurate that I've found.
 
Looks like you have plenty of room to cut your heads.

PS
The Fel-Pro 8045 PT .051 x 4.200 not round 11.86cc is probably to small for your bore.

[Chrisss31]

Out of curiosity, are there any octane boosters that actually work?  Something you could carry with you to throw in the tank if you were running on the edge with 94 octane and you were out of town and couldn't get "good gas?"

[gregaba]

Brent
Thanks for the reply. I knew I would have to wait for my heads to be finished to get the final ratio.
When they are done I can cc the head's and clay the pistons and see what I have.
I was just a little concerned about getting a 12.26-1 before I did the head's. I think I can live with the 12-1 but not suer about 13 to one.
Frank
Thanks for the chart's. They are very usefull. I saved them for reference.
Chrisss31
Not sure if any of these booster's work.
Nothing I have tried in the past seemed to work.
I just read some good review's on the engine lab's site and decided to give the Race Gas booster a try.
The bad thing about living here is I can only get 91 octane locally and have to drive 70 miles round trip to  get anything any higher.
No E85 available without making a 160 mile round trip.
I do have a local source for 100% methanol if I wanted ro spend the small fortune to convert to it that but I would have to buy 55 gallon's at a time and srore it in my shop which I am not comfortable doing.
That is the reason I decided to run CNG in the car.
Greg

[Tommy-T]

Out of curiosity, are there any octane boosters that actually work?  Something you could carry with you to throw in the tank if you were running on the edge with 94 octane and you were out of town and couldn't get "good gas?"

I have had very good performance with VP's Octanium octane booster
I see many good reviews about the Race Gas product.
Lots of folks swear by the Torco octane booster and have for years.
Might want to look into a water/meth system if you're running 12:1 on the street. I had a Snow system on my blown car and liked it very much.

[gregaba]

One of the future upgrades is a Snow system. It will be installed when the engine is installed.
I just have not seen much about people running them here, but with anything over 10 1/2 to 1 I think on pump gas they are a must.
Greg

[My427stang]

I wouldn't hesitate going with a .060 gasket if you need to pull a little compression.  .054 quench is still good quench and can let you buy back some compression

[gregaba]

I am considering that but will wait and see what I have.
I am just using the car for a toy and not a daily driver, it will just be something to hit the road on a friday or saturday night with a occasional trip to the car's and coffee show.
It will hit the strip about 2 or 3 time's a year but that will have to wait on the cal track's and other upgrade's.
Greg

[My427stang]

Just to reiterate what Brent said though, .040s won't work...you need something different regardless of the compression if they are .006 proud

[6667fan]

Race Gas Ultra quieted things down for me. ( 11.3 compression as shown by Whistler).
A box of 6 quarts goes for around $175.00

[gregaba]

Ross
I am afarid you and Brent are right. I guess I will have a new set of .040 Cometic's for sale soon.
I still want to wait untill my head's are done and I can do a final check on them.
JB I ordered the Race Gas 105. It doesn't say Ultra anywhere on the can, Cost was the same.
Greg

[My427stang]

We have been around the block once or twice

However, I cannot come up with the numbers you are coming up with

If I use a .040 gasket, .006 deck, and no valve relieve at all, with 74 cc (all guesses), I get 11.74 ....not that you can run it that way, but certainly tighter than what you reported

If I use a .060 gasket, 4.40 gasket bore, (realistic for a .006 proud piston), a 74 cc chamber, and 5 cc of valve relief (which seems low for a Racetech), .006 proud deck, I get 10.59.  CORRECTED

If you could provide a picture of the label on the Racetecs to show exactly the compression height and valve relief, we can see if makes sense.

ON EDIT: The reason for my last comment is that it is very difficult to measure deck clearance without a dual dial deck bridge.  Often even being careful with a single you can induce rock.  I like to do it with the degree wheel on, with TDC found with a piston stop and a dual dial to take all possibility of rock out of it