luckyou03

My cam is the LE1.6 ( .573/.568 lift )

I'm looking at the Trick Flow® GenX (TM) Street/Strip Cylinder Heads for GM LT1 part number TFS-30400010.

I see that they have 62cc chambers and

Intake Runner Volume (cc): 195cc
Exhaust Runner Volume (cc): 75cc

I did a little computing and I came up with this:

with the felpro 0.039 head gasket I will get

* Cylinder head Volume (CC) = 62.00
* Piston Top Volume (CC) = -3.50
* Cylinder Bore (Inches) = 4.030
* Cylinder Stroke (Inches) = 3.48
* Piston to Deck Height (Inches) = 0.030
* Head Gasket Thickness (Inches) = 0.039

Compression Ratio is 11.0 to 1
__________

With the impala 0.029

* Cylinder head Volume (CC) = 62.00
* Piston Top Volume (CC) = -3.50
* Cylinder Bore (Inches) = 4.030
* Cylinder Stroke (Inches) = 3.48
* Piston to Deck Height (Inches) = 0.030
* Head Gasket Thickness (Inches) = 0.029

Compression Ratio is 11.3 to 1

Does this compression ratio sound good? I'm not sure what an ideal compression ratio is.

bombebomb

I think maybe you should ask lloyd for a "really good" anwser. Its not bad, from the small amount I know.

I am guessing you are going N/A or nitrous.

wrd1972

11.1 is no problem with a decent tune. An excellent tune is further icing on the cake. I run 11.1 with no knock retard.

1989TransAm

Are you sure your piston to deck height is .030"?

bombebomb

I thought he was asking if the cam would like 11:1 not if he could safely run it lol. If that is his question, then I am running 12:1.

You just sparked an idea, I wonder if that is why my car blows black smoke at WOT, I think its just the tune needed fine tuned though.

Injuneer

Are you sure you entered the data correctly in the calculator? Using -3.5cc for the piston top means its a reaised dome. If that's what you have, you are at 11.0:1. But if you have a 3.5cc dish (or valve reliefs), you would be at 10.1:1

red94chicken

yeah i don't think you are going to get 11:1 with a 62cc chamber and a stock piston without your block decked.

mdacton

depends on what calculator, I have seen them both ways,


I have never seen a .030 deck ht. or a -3.5 cc piston.

Injuneer

Appears he used the "Bowling" calculator linked on this site. What I said applies to that calculator.

luckyou03

Thanks for the responses I'm a little confused as you can see. The pistons I have in my motor are:

Manley
Piston Specifications-
Bore size: 4.030"
Rod length: 6.00"
Stroke: 3.480"
Compression height: 1.260"
Wrist pin weight: 119g
Dome volume: -3.5cc
Piston rings: 1/16", 1/16", & 3/16"
Piston weight: varies between approximately 421-427g



The way I got the pistons to deck height was I just used a straight edge over the block and used a feeler gauge at the piston tdc.

I'm using manley pistons and my block is decked.

bombebomb

Maybe I just don't know pistons, but I see no dome. My pistons had a -3cc dome, and you could clearly see it. That looks like a flattop to me.

luckyou03

Yes they are flattop with two valve reliefs.



I found a new calculator that says to "Enter a negative number for a domed piston. Enter a positive number for a dished or dimpled piston." so that would make my pistons +3.5 and my compression ratio 10.1:1

Ok so here is my new question. What is a good compression ratio to run on the street? I will need to get these heads milled so the chambers are 54-58cc. That will put my compression to anywhere from 11.1:1 to 10.6:1

JP95ZM6

Depending on the calculator, you may need to call the 3.5cc positive or negative. Easiest way to figure it out is to try both ways, and use the method which gives the LOWER CR. since the 3.5cc valve reliefs are adding volume to the chamber, they are reducing the CR.

To see what static compression ration a motor wants, you need to consider the cam's intake timing and figure the resulting dynamic compression ratio (DCR). Read this:

http://members.uia.net/pkelley2/DynamicCR.html

With that cam, I suspect the CR will want to be higher than 11.0. Use a DCR calculator. Here's one I used:

http://www.rbracing-rsr.com/comprAdvHD.htm

You need to know intake closing point, rod length, and the usual stuff. You will want that DCR around 8.5 for good performance and not too much tuning trouble. Search DCR and learn more. I have a couple old posts on the topic. My LE3 is close to 12.4 CR and 9.0 DCR, and was pretty tricky to tune for knock. Works great, though.

Question will be cake for Lloyd.

95Blackhawk

Really glad to see DCR is coming up in these discussions more. DCR is what you have to consider just as much as SCR. To parallel above, check my sig for CR's.

Injuneer

Did you use a dial indicator to verify your piston was at TDC?