Gain extra benefits by becoming a Supporting Member Click here find out how!
Silver
Gold ***Platinum***
deek01BigDogSS (6)jk56chevy (11)WarrenL (2)Jens (10)
edad2000Custom_Deluxe_20VetteGyrl (2)JohnB (2)
speedygman (7)rickityfiftyMafo971Clifford Lao502drfleetline
Jud Leowish Non-synchronized
gary635g (6)
johnhem (10)
axmaker (3)
socalarch (3)
usmile4 (8)
Classic Performance Products Classic Parts
Ciadella Interiors American Auto Wire Art Morrison.com
Exile® Battery Keeper™ 6/12 volt charger w/ LED battery monitor
Low priced Genuine GM Auto PartsHarbor Freight
Hellwig Products IncPerformance Rod & Custom
Impala Bob's Bob's Chevy Trucks Bob's Chevelle Parts Bob's Classic Chevy

Recent Hot Topics
Current Quote
"Let's ALL do what we can to TOOT THE HORN for ChevyTalk - OUR BOWTIE BROTHERHOOD IS THE BEST ON THE 'NET!!!"
~ Supporting Member
Recent Topics
Join the Community today







Username Post: Please explain the heat riser...        (Topic#12837)
Mistress 
Senior Member
Posts: 437

Reg: 11-05-02
12-13-02 01:10 PM - Post#84437    

...because I think someone I talked to may be misinformed. I know it stays shut while the engine warms up, and I already have my idea of how it behaves after that, but I wonder if someone would please go ahead and tell me how the heat riser behaves after the engine is warmed up, and exactly when it should be open or closed and why. My engine does have the passage for exhaust fumes to go under the carb, plus I have dual exhaust. The fellow I spoke with said the heat riser was meant for the exhaust system with the y-pipe. I've forgotten why he said that was so. Isn't the larger spring on the side of the heat riser a bimetal spring like those on the old automatic chokes - they heat up and go one way, they cool down and go another way? Thanks for your time, and thanks for your help!! A hug and kiss for you all!!

 
This Forum is Sponsored by
bobschevytrucks.com
Visit Impala Bob's forum on ChevyTalk
JimKshortstep4x4 
Chevytalk Moderator & "10th Year" Silver Supporting Member
Posts: 4593
JimKshortstep4x4
Loc: Muskegon, MI, USA
Reg: 03-28-02
Re: Please explain the heat riser...
12-13-02 02:24 PM - Post#84438    
    In response to Mistress

You pretty well have figured the gist out on heat risers. They have a butterfly valve in them that the spring holds closed when the engine is cold and as the engine warms up the spring, being bi-metallic relaxes and lets the butterfly valve open up. I have never seen one that the valve opens up completely, the spring tension just reduces and the exhaust will push the valve open. The
closed valve forces more exhaust to pass through the intake manifold and heat it up faster, according to theory.

Because they either stick closed or they are so loose they rattle and leak, I have always eliminated them on my vehicles. They restrict the exhaust flow, even when they work and it would not matter, functionally if you have duals or not. I cannot tell any difference in cold performance between having a heat riser or not. If they contribute to cold weather running, it is minimal.

When the heat riser sticks closed, performance is adversly affected and they are prone to sticking.

Jim

Member 65-66 Full Size Chevrolet Club

65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/TH 350
71 Snow plow, 4x4, 350, TH 350
72 GMC Shortbed, stepside, 427/TH 400


 
Coley 
Super Senior Member
Posts: 3973

Age: 72
Loc: Milledgeville, IL. 61051
Reg: 11-23-00
Re: Please explain the heat riser...
12-13-02 06:27 PM - Post#84439    
    In response to JimKshortstep4x4

They do help a lot in cold weather whether you have dual exhaust or not. They keep the carb from running cold and wasting gas. If you have the hot air tube from the cover on the RH exhaust manifold going to the air cleaner, that air cleaner snout valve will also help in cold weather. When temps get down to 0 or less they can keep your carb from icing up. This is not as much a problem on a V8 powered vehicle but with a 6 cyl the carb can actually form a thick coat of ice on the carb body and run really poor....
So, depending on how cold it gets in your area will decide if you should have one.....
Any man that thinks he is too old to learn new things, probably always was....


 
BowTiePaul 
Member
Posts: 63

Loc: Pasadena,Md.USA
Reg: 08-26-02
Re: Please explain the heat riser...
12-14-02 04:07 AM - Post#84440    
    In response to Coley

Coley, you couldn't have said it better! I had duals put on my '72 Cheyenne and for some reason the installers removed the heat riser. The area under the bimetal choke coil(thermostat per GM) never got hot enough to fully open the choke plate.


 
0utlaw 
Very Senior Member
Posts: 2047

Loc: New Hampshire or Florida
Reg: 09-10-02
Re: Please explain the heat riser...
12-14-02 05:51 AM - Post#84441    
    In response to BowTiePaul

And more---
The big problem with heat riser systems is that exhaust residue passing up and thru the heat riser passage, eventually can clog up the passage rendering the heat riser system useless. Moreover, to clean them out requires removal of the intake manifold. The way to know if it is effective, is after you start a cold motor,note that the heat riser should be closed, then feel the outside of the passage and see if any heat is transferring.
If your engine does any amount of icing, there is probably a manifold heat problem.

------------------
69NovaSS427,87Z28,73Vette
Stgry,94S10,94P.Ave,40 F**d PI freak, blown 400

I'm the master of MOUSE...you got any duck tape?


 
Mistress 
Senior Member
Posts: 437

Reg: 11-05-02
Re: Please explain the heat riser...
12-14-02 10:45 PM - Post#84442    
    In response to 0utlaw

Well, what was surprising to me was that I remembered having a heat riser years ago and the way I remember it, when the engine warmed up, the valve opened up and stayed open until you got back home or whatever and then sometime later it cooled off and closed again. I could be wrong on that but somehow that really is the way I remember it!! Then this friend told me what Jim said here, that while you're driving, the exhaust pushes the valve open. Anyway, you have all taught me some more nice things, and I appreciate that very much!! My engine is 283 with a 2 bbl. I don't have that stove and tube going to the air breather. In a few days I'm supposed to get one of the little 4" air cleaners for the 2 bbl. anyway. I've had this engine apart recently and I know the passage through the heads and under the carb is not blocked, so I don't have to worry about that for sometime. Winters are not rough where I'm at, and so while I recently took the heat riser off because I thought it wasn't working right, I think I'll go ahead and leave it off. But I thank you all so very much for your time and for your help!!!! I appreciate you all very much!!!! Smooooooochies

[This message has been edited by Mistress (edited 12-14-2002).]

 
sixtynineGMC 
Member
Posts: 37

Loc: Fairbanks, Alaska
Reg: 12-03-02
Re: Please explain the heat riser...
12-15-02 01:25 PM - Post#84443    
    In response to Mistress

IMHO they actually detract from cold weather performance, because as you are zipping down the road in an Alaskan winter, enough cold air is blown past the riser that it will not open, effectively making most the exhaust from the right side run under the carb, greatly reducing the flow.

My 283 got a lot more power when I removed the guts from the valve, and very little increase in warm-up time.

Theres no replacement for displacement!


 
0utlaw 
Very Senior Member
Posts: 2047

Loc: New Hampshire or Florida
Reg: 09-10-02
Re: Please explain the heat riser...
12-15-02 03:42 PM - Post#84444    
    In response to sixtynineGMC

About icing----
Actually, icing can occur anytime it's 50 degrees or below, and humid. My supercharged 1940 truck iced up so bad that the throttle butterflies jammed and idle system froze.
Lots of frost would build up outside the carb.There is no heat riser valve.
Because there was very little heat coming up thru the blower, and no radiator in the front to throw heat, the longer I drove, the worse it got until conditions changed..
I ended up running a 2 inch spacer with heater hose wrapped around it and a transmission cooler in the airstream of the injector scoop. I can turn on those together or shut them off from inside the cab. A heated air cleaner would solve it too, but it wouldn't look pretty as a Hilborn style scoop. World of difference in how it runs....

------------------
69NovaSS427,87Z28,73Vette
Stgry,94S10,94P.Ave,40 F**d PI freak, blown 400

I'm the master of MOUSE...you got any duck tape?


 
Coley 
Super Senior Member
Posts: 3973

Age: 72
Loc: Milledgeville, IL. 61051
Reg: 11-23-00
Re: Please explain the heat riser...
12-15-02 07:11 PM - Post#84445    
    In response to 0utlaw

The heavy carbon deposits in the intake crossover passage is not from a heat riser working...it is from a heat riser NOT working. The exhaust carbon will go in from both sides under a non working riser condition and just bake fast there...A working heat riser will keep these burned out...
Any man that thinks he is too old to learn new things, probably always was....


 
sixtynineGMC 
Member
Posts: 37

Loc: Fairbanks, Alaska
Reg: 12-03-02
Re: Please explain the heat riser...
12-15-02 09:37 PM - Post#84446    
    In response to Coley

Okay, maybe I`m just stupid, but a couple things about outlaws post got me thinking.

First, if the carbs are on top of the blower, a riser wouldn`t work anyway. But you never said they would, so thats no biggie.

However, it seems to me the blower would magnify or even create icing problems. The reason a carb will freeze at 50 degrees is because airflow pulls the heat out of the metal, in laymans terms(the only terms I know!). The blower would move air through the carb much faster, and pack in that much more humid air, resulting in much faster icing. That is probably one of the reasons production cars seem to prefer a turbo over a supercharger.

I think that problem has little to do with a heat risers pros and cons, and more to do with the pros and cons of a blower.

P.S. this post is not ment to be rude!

------------------
Theres no replacement for displacement!

Theres no replacement for displacement!


 
raycow 
Honored Member
Posts: 18645

Age: 71
Loc: San Francisco, CA
Reg: 11-26-02
Re: Please explain the heat riser...
12-28-02 11:39 AM - Post#84447    
    In response to sixtynineGMC

Actually, the carb cooling effect isn't caused by airflow, but rather from the fuel changing from a liquid to vapor. It absorbs quite a bit of heat in doing this. You won't see carb icing on an engine running on propane, for example. But the propane tank/valve can ice up for the same reason - fuel changing from a liquid to gas.

Ray
Bacon is the gateway drug for vegetarians - Bridget Lancaster


 
This Forum is Sponsored by
bobschevytrucks.com
Visit Impala Bob's forum on ChevyTalk
Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

10790 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.229 seconds.   Total Queries: 13   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 09:30 AM
Top