Heat riser

[jst]

Hi
Can someone tell me exactly how a heat riser works on a dual exhaust system such as on the 1952-1955 Cadillac ? What is the route of the exhaust when the damper is closed ? I don't understand how it goes to the carburetor and where it goes after passing the carb. Thanks
Joe T

[TJ Hopland]

I dont know that car or vintage specifically but the typical design is there is a exhaust passage in both heads that connects to a cross over passage in the intake that passes under the carb.   When the exit flow is blocked in one of the exhaust manifolds it forces the exhaust from the blocked side through the crossover to then escape into the other head / manifold / exhaust.    In later years this was also the passage they used for the egr. 

[jst]

If the damper was stuck shut, could it cause the engine to overheat after a short while of driving ?
Joe T

[TJ Hopland]

If the damper was stuck shut it would cause the one side to be restricted which would cause those cylinders to run at a higher than normal temp.  It would cause more than usual temps in the intake and carb.  I would imagine it would also slightly raise the temps in the other head.   If everything was factory fresh I doubt it would make a huge difference but at this age if you factor in the normal efficiency losses in the system and then add extra load to it I could see it causing overheating.   

[Caddy Wizard]

Stuck heat riser would make the car run a little hotter, but would really heat up the carb and lead to vapor lock/percolation problems.  It also should make it slightly imbalanced, as one side will be breathing easier than the other.  But that would be hard to notice.


I have a few 49-56 spacers left to eliminate the valve.  $26 including postage.


Art G
404 375 3750

[jst]

Hi Art
Email sent
Joe T

[R Sotardi #11719]

Me too, Ron

[Caddy Wizard]

Joe T,


I didn't get an email from you.  Please re-send.


Art G

[jst]

Hi
Email sent again through forum Email. Just in case   jusmct@att.net
Joe T

[jst]

Would it hurt anything to completely block off the passover port going to the other manifold and do away with all that extra heat in the middle of the engine ?
Joe T

[John Washburn CLC 1067 Sadly deceased.]

Joe T,

That is what I did on my 53 Cadillac. I had Olson Gaskets (Info@olsonsgaskets.com) make me new intake manifold gaskets that blocked the crossover ports. I then added a phenolic spacer between the carburetor and the manifold. Starts about the same but reduced the problem with the hot start demons as discussed in the SS.

John Washburn

[Raymond919]

John,
I've been following your various comments and articles here and in the SS about the hot start problems since I own a '49 series 62. May I ask how thick was the phenolic spacer gasket you got for under the carburetor? Did Olson Gaskets make the phenolic gasket as well as the intake manifold gasket for you? My hot start problem isn't so severe but it does exist. I'd like to address it.
Ray Schuman

[John Washburn CLC 1067 Sadly deceased.]

Ray,

I also added a phenolic spacer to my 1949. I used a 1/4" spacer with a gasket on top and one on the bottom. You can also get 1/2" spacer. 1949 starts much better when hot.

Go to e-bay and search for "phenolic spacer" you will find many variations. Stromberg, Carter, and Rochester spacer will fit the 49. Some come with a kit, both gaskets and the longer studs.

If you have a hydromatic you might have to readjust the TV rods for shifting due to the extra length, with the 1/4" spacer I did not have to readjust.

Good Luck

John Washburn

[John Washburn CLC 1067 Sadly deceased.]

Yikes,

It should read TV rod and height of the spacer...

jw

[Raymond919]

Thank you, John, for that information. I'll go looking for it.

I'm not sure what previous owners of my car did, but the TV rod is slightly short (by about 3/4"). Checking it carefully, it appears that the bends in it are not neat, clean factory bends. I suspect it had been removed and slightly bent to make it short, perhaps. I plan to remove it and slightly bend it to the correct curvature making it about 3/4" longer. In this way I can complete that adjustment per the shop manual. If I'm treading where I shouldn't go, please yell at me. I don't plan to do this for at least another week or so, however. The tranny shifts just a slight bit harsh only in certain gears but very smoothly in others.

Thanks again and keep up those great articles,
Ray Schuman

[jst]

John
Did your phenolic spacer have a gasket on either side and also, did you use gasket sealer (permatex) ? Also, did you get the phenolic from Olsen Gaskets ? Thanks
PS Great suggestion. According to Olsen, blocking off the exhaust manifold crossover is done quite often.
Joe T

[John Washburn CLC 1067 Sadly deceased.]

Joe T,

I think I answered your questions in my earlier post, except on using sealant. Nope no sealant usede.

john W