I'm interested in knowing,if the exhaust manifold is the hottest part of the engine and what temperature it gets to ? The block and heads are cooled . Is that why they cast the exhaust manifold ?
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Re: Engine temperature
It depends on the engine configuration and operating condition.
On pre-exhaust emission controlled engines with proper total idle timing (20-34 degrees with high overlap cams requiring the upper part of the range) the manifold temperture at idle should measure no more than about 500 F with an IR gun.
On exhaust emission controlled engines with ported vacuum advance and only the initial timing value at idle, the manifold temperature at idle is typically several hundred degrees higher.
Under maximum load, such as a chassis dyno test the manifolds can begin to glow, and starting with a dull cherry red (about 900 F) they can achieve a pumpkin orange, which begins at about 1200 F.
Duke -
Re: Engine temperature
Thanks Duke, wasn't sure how hot it got ,but thought it wasn''t much more than 1200 degrees .Comment
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Re: Engine temperature
Say Duke;
I have an I.R. meter and I will sometimes check mine while it is running after I get back home. I've noticed before I removed my heat riser valve, I'd get a higher temp in the left manifold than the Right by some 140 degrees (engine fully warm at idle). Since I have removed the riser, they are much closer to the same temp. I would have thought the right one would be hotter with the riser in place, what with the restriction there. If I were to continue having higher temps on one manifold than the other, what would you think the cause would be?
As I'm still having some gas perculation after shut down, I'm considering blocking the crossover passages in the manifold as well. We used to do this by cutting a piece from a tin can that is large enough to block the passage, then bend the rolled or beaded end over to form a handle/stop, snip off the sharp corners, loosen just the two bolts that straddle the passage and slip it in and retighten the bolts. Is that something that is still feasible today? Heck, I'd settle for some old Fuelie gaskets with the restrictors in them if I could get some.
Stu FoxComment
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Re: Engine temperature
Many of the 'full line' engine gasket kits come with exhaust manifold gaskets (a good throw away part) and two sets of intake cross over plugs. One is typically a full port plug to totally block the cross over passages while the other has a small hole in the center of the plug to 'partially' block the cross over.
Personally, I prefer the partial plug because there IS a small pressure relief passage that's generally good enough to handle engine idle exhaust should the heat riser valve stick...
Some who buy these gasket kits don't recognize the 'extra' parts and simply discard them. I'll bet a local machine shop that does turn key engine overhaul will have some cross over plugs to GIVE you for the asking...Comment
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Re: Engine temperature
Jack;
I believe the gaskets or plugs you are referring to would be the type where removal of the intake manifold would be required, which is probably the best way. What I was describing is what we used to do as a quick modification, say like for the summer only, just to make more noise and get the best cheap performance improvement. If you do it right, you can remove them, say for the winter, without loss of seal.
My manifold has never been off my engine although I have considered doing just that. Last time I changed the oil fill tube (due to the tube for the PCV air intake broke out), I pounded the new one in too deep and cracked the boss around the tube in the manifold. It doesn't show or leak, but I know it is there and want to have it heliarced some day. I believe I can grind down the weld and sand blast/paint to cover it up ok.
Stu FoxComment
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