I tried to figure out the DCR of my budget build 327 and I`m pretty sure I`m doing something wrong. I was using a calulator at the KB site. Here are the specs,

327 standard 4.00 bore with .025 deck height
.016 compressed steel shim head gasket with 4.10 bore
GM .125 dome pistons with -5.30cc`s according to similar pistons at summit

I get a static compression of 10.94 but when I entered the cam timing it said the DCR was around 10.5. I don`t think I`m doing it right. I`ve got 2 cams available to me cheap

Isky 292 mega on a 108lsa
Isky Z70 solid on a 108lsa

I was planning to run the 292 mega but I think the compression is going to be too high for pump gas. Can someone help me out? Thanks.

Dynamic will always be lower than static.

Dynamic will always be lower than static.

Yes I know that but should it only be about .5 point lower? Every other post I`ve read about DCR shows about 1-1.5 point difference from static to DRC. I`ve never worried about DCR in the past and I`m tryin to get the hang of it.

You didn't list your cyl. head combustion chamber volume.. did you add -# for domed piston in the calculator?

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

Use pat kelley's calculator. It rocks.

Even with iron heads, you should be able to run 10:1 with no worries. Aluminum heads can run up to 12:1 on pump gas. I've done it. If your using nitrous on top of that, that'll boost your dcr and you'll have to run race fuel.

12:1 with pump gas will be VERY dependent on intake closing point and tight quench. IMHO Don't try it with a stock hydralic like 929.

I thought more along the lines of 11.5. Depending on cam size to bleed off pressure. I am under the impression that 8.4 is a good pump gas motor. Anything around 8.5 up to 8.6 is border on pump gas. Anything higher is race gas territory.

I could bad info also.

You didn't list your cyl. head combustion chamber volume.. did you add -# for domed piston in the calculator?


Your right, forgot that. Thaey are 186 casting double hump heads. I listed them as 64cc`s on the calculator but I think they are really closer to 68cc`s which will drop the compression some. I entered -5.30cc`s for the piston head measurement. I got that number from summit from the TRW .125" dome pistons, they are pretty much the same as what I`m using.

My last motor ran KB .100 domes on 91 pump gas no problem. these pistons have a little bigger dome and I was worried that I would have too much compression. I know I`ll be over 10.1 compression with the domes.

I don`t plan on running anything close to a stock cam but I don`t know if I can get away with running the cam I wanted to run which is the Isky 292 Mega hydraulic. I`m not sure if it will bleed off enough compression to run on pump gas.

The DCR is where I get lost because when I tried to enter the cam info, I don`t think I did it right and the DCr came out only a half a point less than the static.

I did look at Pats calucator but I`ll try it again and see if I can figure out where I messed up. Thanks.

Anthony on his calculator

Do the middle tab first (Cam timing)

The left tab second (Dynamic Stroke)

The right tab last (Compression Ratio)

I think a 292 cam would need around 11 to 11.5 compression to run best.

Anthony on his calculator

Do the middle tab first (Cam timing)

The left tab second (Dynamic Stroke)

The right tab last (Compression Ratio)

I think a 292 cam would need around 11 to 11.5 compression to run best.


ok well for some reason I can`t get his calculator to work right now. I should be very close to 11.1 compression but I`m afraid the 292 cam won`t bleed off enough compression to run pump gas. I`ll just have to keep trying to get the calculator to work and see where I stand with my set up.

Make sure you are not entering a negative sign on the pistons. Just enter a number like 6 instead of using -6.

Make sure you are not entering a negative sign on the pistons. Just enter a number like 6 instead of using -6.


well that might be my problem because thats what I was doing since that was how I saw them listed. I`ll try again and see what happens. Thanks.

ok tried it again and came up with a static of 9.5.1 which I know it not right. oh well, i`ll figure something out.

Cam timing tab you should just fill out the advertise duration the LSA and ICL, then hit calculate

On the Dynamic tab enter your stroke and rod size and hit calulate.

Go the compression tab and fill out the info there. If you check that small box then it will calulate you DCR if you do not you will calulate your SCR.

Cam timing tab you should just fill out the advertise duration the LSA and ICL, then hit calculate

On the Dynamic tab enter your stroke and rod size and hit calulate.

Go the compression tab and fill out the info there. If you check that small box then it will calulate you DCR if you do not you will calulate your SCR.


I can`t even get the calculator to open so I don`t know whats going on. The KB calculator doesn`t have a spot for the advertized and LSA. I`ll just keep trying unless you would be so kind as to run the program for me. The 292 has a advertized of 244@050 and a 108 LSA. I`ll keep trying though.

Sure, I will run it.

Post your bore, stroke, rod size, head gasket thickness, deck height, gasket bore, head cc, and piston volume

Also give me your advertised duration on intake and exhaust as well as LSA and ICL.

You have to download Pats calculator and then use it.

all the specs are listed in my first couple posts, it`s a single pattern cam.

Yeah I tried downloading it but I could`nt get it to work.

ok, I`m a idiot. Still can`t get pats calculator to work but i figured out what I was doing wrong with the KB one. I came up with a 8.66 DCR using the Isky 292 mega.

A tad high for pump gas is what I have been told.

Either go with a bigger cam or lower the the compression for pump gas.

You can run that I think if you spike in like 2 gallons or 3 gallons of race fuel with each fuel up.

well I figured in the solid version of the 292, the Z50 and it gave me 8.125. I`m also not 100%sure that the chambers are 64cc`s, I need to have them measured.

That sounds like a fairly good DCR.

Are you running iron heads?

8.0 to 8.1 for irons

8.0 to 8.4 for aluminum.

cc the heads will be the true tell sign.

yeah they are iron heads. old 186 camel hump heads. I`ve seen them listed as 64cc and 68cc. i need to measure these. my old 041`s had the same chamber and ended up at 64.5 after having .020 shaved off.

Sounds like the bigger cam is the way to go.

Should be a nice motor!!!

Sweet sounding also!

my buddy is running the same cam in a 350 but has better heads. he is pretty happy with it. I might just go with that one instead of the hydraulic version. I wanted to keep the motor simple and I can get the mega cam really cheap but I would feel better knowing that I got the right cam in there.