Two heat riser questions.

[Barbecue]

Hi, all.

Last weekend I finally brought my '86 Silverado home. I couldn't be happier and am looking forward to sharing my progress on here.

My first order of business is replacing the "computer controlled" carb (q-jet) and distributor with a regular (rebuilt) and regular HEI distributor. While I'm at it, I'm throwing on an old edelbrock intake, rams horns, and removing most of the smog equipment.

In the process of doing this work, I've removed the heat riser from the passenger side exhaust manifold. It seems to be a vacuum controlled unit, as opposed to one of the older style ones with by bi-metallic spring. Question: have people had success just removing this heat riser and not re-installing it? Does it just take the carb a little longer to warm up?

In the process of switching to rams horns, I'll be losing the heat collecting shroud on the passenger side. This shroud collects hot air from around the exhaust manifold and sends it up into the air cleaner as a means of assisting the carb warming up. I would like to continue to use the stock air cleaner (I like its pseudo ram air design), so does anyone have experience in mocking up some type of heat collector for around rams horns?

Thanks everyone in advance for any insights you can offer.

Barbecue

PS, I live on the west coast (very mild winters), so that plays into the above to questions seeing as I won't be trying to warm my engine up in -20, just around freezing at the lowest. Thanks

[Dead Parrot]

The heat riser works with the intake manifold crossover. If you are going to block off the crossover, there is no need for the heat riser. It helps the gas vaporize quicker when the engine isn't fully up to operating temps. The vacuum unit was supposed to be an improvement over the spring system as the spring system tended to rust in place after a while. If it rusted mostly shut, then the carb often overheated and suffered damage. Plus performance suffered as a lot of exhaust was forced through the small intake crossover.

When I replaced stock manifolds with headers and a performer intake, I drilled a 1/4 hole in the crossover block offs provided with the intake gaskets on the theory that a small amount of exhaust gas would warm the intake a bit faster without overheating once everything was hot. Don't have a heat riser valve. Don't know how well it works but have suffered no harm in the 15+ years since setting it up that way.

Rigged up a heat stove for the Thermac system out of a cheap heater core and a random aluminum box that didn't hide well enough. Works well enough but I keep thinking something that captured some heat off the headers would be better.

[KQQL IT]

No choke. No heat riser. Starts fine.

[beamn7]

Congrats on the truck!

The vacuum controlled heat risers are better than the old bi-metal spring type as all you need to do is block off the vacuum supply and now it stays wide open whereas the spring operated ones were closed until it warmed up.... Not having it should not have much if any effect on your vehicle at all.
As for the stove pipe, there are a couple universal kits out there available. I had to build one once and went to the junkyard, got the two pieces to the heat shield off of the exhaust manifold from an early 90's G van and then tack welded them back together. Looked factory and sufficed for the California smog guys...
If your interested in selling that quadrajet, PM me the 170 number off it as I may be interested.

[rich weyand]

You should understand that your carb is continuously being refrigerated by the vaporization of gasoline. At 30 degree temps, the carb may never warm up, with attendant losses in mileage and performance.

The thermac air cleaner is the way to go. I made a hot-air pickup off the headers from a stainless steel exhaust tip. I'm sure you can do something similar with the ram's horns. See article below.

http://www.fullsizechevy.com/forum/g...d-headers.html

[geezer#99]

You're in for a surprise or two Barbecue!!
Once the temp starts to get below 45F you'll have cold running issues. You won't be able to jump in it, fire it up and just leave. It'll want to quit on you. You can two foot it. Keep the rpm up with your right foot and brake with your left. Or slip it into neutral when you need to stop while keeping the rpm up.
Once it warms up it will be good. It'll take awhile.
It's not the carb you need to warm up, it's the intake plenum. That cast iron or aluminum takes awhile to get warm enough to keep the fuel vapour from reverting back to a liquid. The vapour travelling along the cold intake runners starts to puddle. The remaining vapour that makes it to the cylinder is too lean and you get misfires and rough running and it might quit.
THat's the joy of running an unheated intake when it gets cooler out.
I have headers and a stock quadrajet. I expect it to be a cold blooded beast and prepare for it.
My method is to start him up, let it run on high idle for a few minutes or until it starts to run a bit rough, shut him down for 5 minutes for a heat soak (hot air rises from the lifter valley and heats the intake) and then restart. Usually good to go but sometimes he'll still be cantakerous. It's usually caused by the humidity we live in. Moist air.

If you know it's going to happen and guard against it, you'll be fine.
Now for those who say adjusting your choke will fix it, it's not true. Like I said. It's the plenum, not the carb.

[Barbecue]

Thank you, everyone, for sharing your wealth of knowledge. Some seriously impressive insights and I'm very appreciative.

After wrenching on the truck today, I'm changing direction a wee bit. I'll be sticking with the stock intake and exhaust manifolds for a few months while I get things running smoothly and take care of some other issues (small amount of rust). That will certainly take care of the heat stove, as I'll just continue with the current set-up.

I removed the air pump assembly today and the EGR from the intake manifold; last task today was fabricating a heavy gauge plate to block off where the EGR was. I still have to plug the air pump's ports in the exhaust manifolds. In light of all your great feedback on here, I think I'll be sticking with the stock exhaust heat riser set-up for now. Currently, the truck has a single exhaust system (3"). I'll likely make up a dual system in the spring, and I can re-address the heat riser issue after experiencing a winter behind the wheel.

Geezer, thanks very much for the locally-specific intel! Our moist climate, while not the coldest, does present some challenges.

Thanks again!

[rich weyand]

If you are removing the air pump, move the vac advance to manifold vacuum. It should only be on ported vacuum if you are running the full emissions kit.

[Barbecue]

Originally Posted by rich weyand

If you are removing the air pump, move the vac advance to manifold vacuum. It should only be on ported vacuum if you are running the full emissions kit.

Great advice, Rich. Thank you! I'm hoping that by swapping out the "computer controlled" (can't remember what three letter acronym starting with E its called) carb and distributor, I'll be able to turf some of the vacuum lines. Its a bit of a rats' nest of lines at the moment.