Hot Rod Forum : Hotrodders Bulletin Board - Reply to Topic -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine> Another DCR question.
User Name
lost password?   |   register now

Thread: Another DCR question. Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options
Miscellaneous Options

Topic Review (Newest First)
08-04-2005 01:00 PM
Hippie Thanks Keith, I'm "pretty sure" it will be OK but I only want to build this one once, there's no room in the budget to do it over.
08-04-2005 12:50 PM

I have found that i need to play with the altitude on that one to get the cylinder psi to come out but once i found the correct number it's always with-in 5 psi for me....

If you keep the engine cool and have the correct timing curve it will be fine...

08-04-2005 12:47 PM
Hippie Thanks,
I ran my current 350 through and the one I plan to build, my current motor came out at 8.1 DCR and 162 PSI, actual cranking compression is an honest 160 so that's pretty darn close. I have run it with 87 Octane with no trouble. The one I am planning came out at 8.4 DCR and 170 PSI. Think the extra .3 DCR and 10 PSI will make that much difference? I'm thinking the "real world" numbers will probably be a bit lower. The new motor will have headers, better ignition, intake manifold and will be backed with a 200-4R and 3.73 instead of the tired TH350 and 2.73.
08-04-2005 11:43 AM

try this one

08-04-2005 11:24 AM
Hippie Thanks, the ones I used didn't give me cranking compression. I know my current 350 has an honest 160 PSI and runs fine on 87 Octane. I'll check out some other calculators and find one that gives cranking compression estimates. I'm thinking I should be OK but I'd hate to get this all done and find out I have to run 93 all the time.
08-04-2005 11:09 AM

Don't get all to excited over your dcr number. There ia alot about this subject that many people including most of the web sites and my self that is not understood.....

One of the problems is that those calculator give you a one cycle number,,,, this all changes when the same engine is at 5000 rpms......

The deal with a dynamic compression calculator is to help you avoid detonation.... Now we all know there are at the very least 6 or 8 major factors that can change the engines ability to resist detonation. So if you build a engine with a perfect dcr for the fuel you are going to run but have all the rest of the combo wrong it's not going to work anyway....

You don't have enough info for me to figure it out but, what do the calculators tell you the cranking compression is going to be..... That is a much better indicator,,, to me anyway....

I have run engines with the dynamic over what is recommended for pump gas with no issues, but the rest of the contributing factors were correct....

08-04-2005 10:56 AM
Toyman My very minor understanding of DCR tells me that you need to find a cam with the intake valve closing (IVC) a little later.
08-04-2005 10:47 AM
Another DCR question.

OK I did a search and waded through some very interesting threads on the subject but came to no conclusion only more confusion. I am gathering parts to build an 8.9 to 1 355 SBC. I will be using a set of 416 casting 58cc 305 HO heads with 1.94/1.50 valves, a set of -22cc D-cup pistons and probably a Summit K-1102 cam. I ran this through a DCR calculator and came up with a DCR of 8.16. This will be going in a 4200 Lb. vehicle with a 200-4R OD and 3.73 gears. Question..... can anyone tell me if this DCR is too high to run with 87 or 89 Octane? My static CR tells me I'd be OK but the DCR seems higher than what I've seen some others post for Satic CR's in this range. I used 2 different calculators and got nearly identical results. Do I need a cam with wider LSA to bring the DCR down? HELP !!!!

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -6. The time now is 11:02 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.