Register or Log In To remove these advertisements. |
|
|
|
Thread Tools | Display Modes |
|
03-20-2012, 02:52 PM | #1 |
Registered User
Join Date: Oct 2011
Location: phoenix, az
Posts: 508
|
Driving Without HEI Vacuum Advance!
The HEI vacuum advance on my mid 70's 454 went out so I plugged the manifold vacuum, advanced the timing and I'm driving it until I find the correct vacuum advance. It still doesn't drive right but it drives better. My question is, will it hurt the engine driving it this way?
|
03-20-2012, 03:58 PM | #2 |
Registered User
Join Date: Sep 2010
Location: Lake Tahoe, Nevada
Posts: 755
|
Re: Driving Without HEI Vacuum Advance!
Yes it can. However, you can drive a certain way to limit your risk and damage, but it's still an ever-present risk.
Background engine theory: Without getting too technical, your throttle is controlling the density of air getting into the engine. It can be thought of and explained as the AMOUNT of air getting into your engine. At idle and low throttle positions, less air means less fuel, and your carb controls all of this. Really dense air/fuel mixture will burn fast, air that is less dense with less fuel burns slower. So when you're at idle and low throttle positions with very little air and fuel, you need lots of advance to give it enough time to burn, that's why you have the vacuum advance. You're firing the spark earlier to give it enough time to start the combustion process and build pressure. However, if you start it TOO early, you run the risk of detonation, and it will destroy your motor rather quickly.
__________________
I know a little about cars, but if you have a question about electricity or sport quads, I'm your man!!! |
03-20-2012, 04:05 PM | #3 |
Registered User
Join Date: Sep 2010
Location: Lake Tahoe, Nevada
Posts: 755
|
Re: Driving Without HEI Vacuum Advance!
Now here is how it affects YOU and your particular situation. If you stab the throttle wide open, you're going to get LOTS of air and LOTS of fuel, which will create a really dense mixture inside your engine, and that really dense mixture will burn really fast. If you couple that with lots of timing advance, you run a serious risk of detonation, which can destroy your motor in a matter of minutes.
Of course, I highly advise you to figure out the problem and fix it. If you continue to drive it like this, my advice would be to stay off the throttle as much as humanly possible, even if it takes you several minutes to get up to 60mph, and even if you have to downshift and crawl up every hill at 25mph. A heavy foot and max timing advance is a recipe for disaster. I imagine you can overcome the grief of people honking and flipping you off much faster than you can overcome the headache of a blown engine.
__________________
I know a little about cars, but if you have a question about electricity or sport quads, I'm your man!!! |
03-20-2012, 05:46 PM | #4 | |
Registered User
Join Date: Oct 2011
Location: phoenix, az
Posts: 508
|
Re: Driving Without HEI Vacuum Advance!
Thank you for the advice! I don't redline the 454 much so hopefully it will last until I find the correct vacuum advance which I'm having problems doing. My vacuum advance is about a 1/4" longer than the ones Autozone, O'Rielly's, Napa and Pepboys have and I can't find the HEI distributor casting numbers online anywhere so I'm kinda at a loss! I guess the junkyard is next to find the right one then go back and physically compare the units!
Quote:
|
|
03-20-2012, 06:33 PM | #5 | |
Registered User
Join Date: Sep 2010
Location: Lake Tahoe, Nevada
Posts: 755
|
Re: Driving Without HEI Vacuum Advance!
Quote:
If everything was working correctly, your engine would have the least amount of timing advance at wide-open throttle around 1000 rpm.
__________________
I know a little about cars, but if you have a question about electricity or sport quads, I'm your man!!! |
|
03-20-2012, 07:15 PM | #6 |
Registered User
Join Date: Nov 2009
Location: Sonora California
Posts: 860
|
Re: Driving Without HEI Vacuum Advance!
Go ahead and put the new one in. The difference is in the stroke of the advance unit. The new one appears to have a little longer stroke to it which will give you just a little more vacuum advance than your old one, which is more low rpm power.. If you end up with pinging back your timing up by 1 or 2 degrees. Set timeing at factory specs after you install it.
Note if you have problems at the smpg station just keep in mind you did this. I doubt that it will show up on emissions check. |
03-21-2012, 06:33 PM | #7 | |
Registered User
Join Date: Oct 2011
Location: phoenix, az
Posts: 508
|
Re: Driving Without HEI Vacuum Advance!
The problem is that the new one won't fit and I'm having problems finding the correct one!
Quote:
|
|
03-20-2012, 05:50 PM | #8 |
Registered User
Join Date: Feb 2012
Location: Austin, Arkansas
Posts: 248
|
Re: Driving Without HEI Vacuum Advance!
I just replaced the one in my '85c10.Itcaused shift problems/converter lock not engaging,spark knock/bad mileage.
Since replacement it's back to my sweet truck!
__________________
Always expect the unexpected,....but don't expect the unexpected to be the unexpected you expect ! I'm busier than a one-legged cat,in a sandbox! Veteran..and proud ! I can't fix what ain't broke....you want I should break it? |
03-20-2012, 06:28 PM | #9 |
Registered User
Join Date: Feb 2007
Location: Austin, TX
Posts: 3,930
|
Re: Driving Without HEI Vacuum Advance!
I would set the timing back to stock specs. Running without the vacuum advance will just give you bad gas mileage. Running with the whole distributor over advanced is not a good idea.
__________________
1977 GMC Sierra Grande |
03-23-2012, 12:01 AM | #10 |
GM Addicted
Join Date: Jan 2009
Location: Visalia, Ca
Posts: 2,294
|
Re: Driving Without HEI Vacuum Advance!
Easy fix man go on ebay and just slap in one of the hei untis from there. I have one on my truck there not too bad im sure there not the best but for the bang for the buck it will work.
__________________
..Mac’s Garage.. 73 GMC, 54 Caddy, 2010 Silverado, 68 C10 RIP DAd My 73 GMC Truck Build Pic 2010 Silverado 4/6 on 24s IG:MacsGarage |
Bookmarks |
Thread Tools | |
Display Modes | |
|
|