Hey guys, total noob here. Been lurking since March though:)

My 1st question (of which I have about 1 million) is about the heat riser in the sl6.

I've always been taught that heat+fuel=bad. ie. cool cans and such. Why is the heat riser necessary in the sl6 engines?

Is this only really necessary in the winter? Would a fully warmed engine run ok without the riser, during the winter?

Thanks,

Chris

You asked a two part question that needs a two part answer.

The 'why' of it is partly to prevent condensation of the air-fuel mixture in the manifold. There are lengthy and sometimes heated, metaphorically, discussions on the need for one all over the site.

The 'how' is in the design. When the engine is cold, exhaust gases are routed via the heat riser to the underside of the intake manifold. As the exhaust manifold is warmed, the riser diverts the gases away from the intakes bottom. This is done with a spring that reacts to the heat causing it to move.

Try doing a search on the subject in the forums. Lots of better explanations than I can give. I do have a few pictures of my manifolds off the engine in my link below. In several you can see how the flap points up to where the intake joins the exhaust. This is the natural 'cold' state of the flap.

_________________
The Old Goat '83 D150 225-2

AKA Ice Titan

Thank you.

I do understand the "how" it is more the "why" I was after,

So condensation is an issue? So is it more of a heating the mainfold than the fuel thing?

I know I am probably a noob beating a dead horse here, but if anyone will take pity on me, I'd sure love to know more!

Thanks

When the carb is cold, the air fuel mixture hits the cold metal in the manifold and the fuel condenses out. This will kill the engine, causing that early morning stumble, and stall. Also, the rapidly evaporating fuel will literaly freeze on the throttle blades when it is cold. The heat riser helps prevent both of these things from happening. It is an essential part of drivability with a stock slant. When it is fully warmed, the heat riser makes no difference.

Sam

_________________

I ran a manifold for about 3 years without a heat riser. My original ('72 manifold) was cracked and the manifold that came with my current engine (a '73) was frozen solid from sitting out in the elements. So I removed the flap valve and shaft, and installed a nut and bold on each side. Never a drivability problemin cold or hot weather, mainly because I still used (and continue to use) the stock air cleaner with the heat stove around the manifold outlet. This draws in heat from this area through the bottem of the air horn and into the carburetor. I have since switched to a manifold with a functional valve in it, and can really tell no difference between having one and not having one. I think the diffenence is in using the stock air cleaner.

Eric, How cold does it get where you are? That is probably the more critical question. And second, is the warm up driving stop and go,or steady state? I could never get me slants to run well without a heat riser until I switched to EFI. In Maryland it gets down to the 20's routinely and into the teens from time to time,and once in awhile down to zero for short spells. In this kind of weather, without the heat riser, my slants were undrivable until they warmed up. You would get to the first stop sign, which is one block away, and it would die when I opened the throttle to start back up. The hot air stove certainly helps there as well. But, that device was not on the earlier models. I think it started around 1970. My '69 did not come with one stock. It was only when i switched to the 2 bbl from a 78 Volare that I had the good air cleaner.

Sam

_________________

Eric lives 20 miles south of me. So we have the same climate. Eliminating the heat riser will lead to carb icing, especially in high humidity, low temperature weather. What happens is that when the air/fuel mixes, the mixtures, temperature drops, if it drops below freezing, the water within the mixture will freeze, i.e. carb icing.

With an inline engine the carburetor is about 5" from a heat source. A heat source is vital for the proper operation of the carburetor on an inline engine. Over the years many solutions have been tried. The \6 uses a diverter valve to force the exhaust gases up against the bottom of the intake manifold. As the diverter is heated, it opens up, letting the exhaust gases flow freely out the tailpipe. Thus regulating the heat for the carburetor.

Eric's setup worked because he had a heat source, i..e. the stock air cleaner and the heater tube to that air cleaner. On the other hand. I removed the heat riser and had real problems with carb icing. I was also using a stock '65 air cleaner, no heat source. Once the temp dropped below 50*, the carb would start to ice up. My solution was a water heated base plate for the the MC 2100 that I swapped too.

A V style of engine has the opposite problem. The carburetor is sitting within a large heat pump. Removing as much heat as possible, will increase the power available without a carb icing problem.

The evaporation and expansion of the fuel as it leaves the jets will further cool the mixture so you don't even have to be down to freezing to have problems with icing. Probably anything below 40* F will be problematic. Even above that you can have trouble with fuel puddling on the manifold floor.

_________________
David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

This 1935 Jam Handy cartoon, "Down the Gasoline Trail", would be a real trip to watch even if it didn't contain a sequence specifically answering this question about the manifold heat (at 5:37).

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Hey, that was cool! I love those old informational videos. A year or so ago I saw one about the pushbutton shifter from Chrysler. I'll have to see if I can dig it up.

_________________
David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

That pushbutton video got TOSsed off YouTube

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I wonder why? It couldn't be copyright issues surely. I think I may have it on my hard disk somewhere; I'll look.

_________________
David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

You wouldn't think so, but when I try to access it, I get "This video is no longer available on YouTube due to terms of service violation."

Something similar happened when I posted a really funny segment from the British car magazine show "Top Gear". Jeremy Clarkson tested a Ford F150 and was astounded at what a pile of junk it was. Over the course of the year or so after I posted it, I kept having to delete idiotic comments like "FORD'S RULE...U SUCK!" and "GO BACK TO ENGLAND". Eventually someone complained that the video violated some provision or other -- amusingly enough, they didn't complain that it was a copyright violation -- and YouTube apparently just yanks videos upon one complaint rather than spend the time to look into the matter, so it's gone. I do still have it around here somewhere, I think.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Cut 'em some slack Dan. If all you'd ever driven was a Ford, how would you know they sucked?

_________________
The Old Goat '83 D150 225-2

AKA Ice Titan

The video worked for me. Does anyone else know of any other old car basics videos??

_________________
Chris'
Autobody
Restoration
Service