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> ported vacuum vs. manifold vacuum
User Name
lost password?   |   register now

Thread: ported vacuum vs. manifold vacuum 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)
06-13-2006 01:53 PM
ko.17 i'll try to reply to 2 posts here. the distributor is an hei in a 76 350 sbc. i have a retro fit roller cam 228 @ .050. 288 advertised. and i also have 4.10 rear. so maybe this setup will work. i do not think that i have the old springs, if i can recall, many years ago we played with the springs on my old distributor. i just bought this new distributor, it was set up with an adjustable vac advance. i will continue to test performance using both ported and manifold vacuum. it does not seem to idle bad, the cooler temps would be nice, but i don't expect to do a whole lot of idling. i think it's time to get things back together and let her loose!!! hopefully, i can answer the problem of gas getting into the manifold vac tube.
06-13-2006 07:43 AM
JohnTN I experimented with my mechanical advance by buying a Moroso advance kit (weights and springs). I found the Moroso weights were lighter and the springs were not as strong as on the original stock HEI distributor.

If you have the original heavier weights and try using weaker after market springs the mechanical will come in very fast like you are experiencing. Do you have the original stock springs?
06-12-2006 10:19 PM
potts You haven't indicated the type if dist. I've found many aftermarket perf dist are set up that way with a relatively small amount of mechanical advance. They expect that you have a longer duration cam and will run alot of initial advance.
One thing ported or manifold the initial timing is the same with the vac hose plugged. Manifold is fine for a cooler idle and simpler set up. It's stock on a 283.
I find that with any amount of cam duration, it makes the idle a pain cold and the engine wants to hunt (rev up and down). I prefer the ported. Take your maximum available mechanical advance in degrees and subtract that from 32. That should be your initial to start . If you get knocking in any med or heavy accelleration back off the initial 4 degrees at a time until it stops. Any light throttle knocking is the vac advance not backing off soon enough and requires an adjustable vac advance to get the vac pot to advance at a higher vac reading.

Rule of thumb : short duration cam or tall gears mechanical advance comes in slowly. all in at 3000

long duration cam or low gears ie 411/1. mechanical advance comes in quick .all in by 2000

good luck
06-12-2006 08:00 PM
acr You seem to have done your research. As you prbly know, every engine is different. All you can do now is "Trail & Error" testing (that you can verify), changing only one thing at a time.
Good Luck! acr
06-12-2006 02:13 PM
ported vacuum vs. manifold vacuum

hi everyone, i've been doing alot of reading on ported vs manifold vacuum. i've also checked out some of the old posts here on the site. from what i understand, the only difference is at idle. is this correct? i've always used manifold, however i keep finding fuel in the hose on manifold. i was thinking of changing to ported until i can find out how the fuel is getting in the mainfold port.

i've recently tried to re-curve my distributor, but haven't really been getting the numbers i expected. i've set my initial timing at 20* which the car seems to like. and i've adjusted the vacuum canister to limit my vac advance. however, my mechanical timing has 2 issues. 1: no matter what combo of weights and springs i use, timing is all in by 2000 rpm. from what i've read, this is too early. i was shooting for 2800-3000 rpm. 2: it doesn't appear as though i am getting any more that about 16* mechanical adv. again, i was expecting to see 18*-20* mechanical. the only real difference i've seen trying different combos with the springs and weights has been the actual numbers between idle and full advance, which is really only about 1000 rpm. any thoughts on this?
thanks for your time.

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 07:04 PM.

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.