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all the cars ive had, ive never seen one with some kind gate looking thing on one exhaust manifold. its got a vacuum line going to it, appears to operated by that line. not sure what its purpose is. is this part really neccessary????
I think its called a butterfly valve. Alot of the older cars had it, and its meant for carbureted cars.
When you start your car, its cold, so the heat from the manifold is carried up through a pipe to the opening of the air cleaner. (the old kind with the snorkel). There is also a valve in the air cleaner.
When its cold, the more heat is passed in, and less air, and when the car warms up, the heat is closed off, and the fresh air is let back in.
EFE valve (Early Fuel Evaporation, IIRC). I don't know if its removal would adversely affect emissions or not. Without maintenance, the butterfly is probably non-functional and as a consequence frozen open.
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
It is an emmisions item. When the engine is cold it closes the butterfly, causing the exaust to be forced through the intake manifold crossover. The fuction is to force the engine to warm up faster.
When you start your car, its cold, so the heat from the manifold is carried up through a pipe to the opening of the air cleaner. (the old kind with the snorkel). There is also a valve in the air cleaner. When its cold, the more heat is passed in, and less air, and when the car warms up, the heat is closed off, and the fresh air is let back in.
Thermac system.
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
Well, the thermac system on my LO3 uses a vacuum controled valve inside the air cleaner snorkel to divert the intake charge so that it is coming up the stove pipe.
I have never heard of another valve on the heat stove, but I guess I learn something new every day. BTW my LO3 runs fine without the Thermac. I let it warm up in the driveway every morning so that probably helps in the cold weather.
__________________ -Adam
1990 Firebird Formula
Bone Stock 305TBI, T5 tranny, 62k Origional
UMI subframe Connectors
He is talking about the heat riser valve that goes between the left(?) manifold log and the y-pipe. Here is a picture of one from a different vehicle, could find the correct pic.
Yea i think im talking about a bunch of things and mixing them up. The point is, its in an e-missions thing.
One of the things in the exhaust manifold is just for heat, it doesnt circulate gas. The manifold crossover stuff is all internal (but i dont know how its activated). And theres also that valve in the air cleaner. They all work together though.
The important thing to check is that either it works, or that is not stuck in the closed position. If it is stuck closed it will choke the engine down.
The important thing to check is that either it works, or that is not stuck in the closed position. If it is stuck closed it will choke the engine down.
yea thats what im talkin about. ive got it disconnected, and judging by the amount of carb build-up in not only the manifold, but the amount it shot out of the muffler when i first got in it, i dont think its working anyways. i disconnected the vacuum line, being i took out the snorkel for the air cleaner (going to aftermarket chromie cleaner eventually) and re-did alot of vacuum lines near the carb anyways (i hate vacum lines clogging up my vision ). not sure how to tell if its stuck open or closed, or at all, but the car seems to run fine without it being hooked up. the only thing i did notice is if i remove the air cleaner all together i get a high RPM stumble, like the motor flat lines for some reason, even happened when i inverted the air cleaner lid to get more air. but that issue went away when i put the air cleaner back on the normal way. also got a "ticking" sound comming from the carb. <shrug> but it seems to run fine despite needing plugs, wires, and a cap and rotor something terrible. they'll be comming though, just fixed an oil leak at the sending unit for press. *whew* im very impressed with the knowledge here at thirdgen :-)
hahah pretty much...in process of deleting smog stuff, i went and checked the cap rotor....the inside fo that white rotor was completely black with carbon, and the contact point has a burn pretty deep in it, i cleaned it up as best i could, but i still get a hesitation at low rpm cruising down the higway, but if i was a motor, and my plugs were so old they had rust on them and my rotor was rpetty shot, i prolly wouldnt run at all, too much like work haha
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sorry for typos...ive got an over energetic 14 month old sittin my knee, trying to beat the keybaord up...for no apperant reason. wish i had his energy haha
Last edited by BlackFormula; 02-17-2008 at 10:49 AM.
Reason: Automerged Doublepost
The important thing to check is that either it works, or that is not stuck in the closed position. If it is stuck closed it will choke the engine down.
Well yea, first of all it is not a vital part in fact on my camaro i just scrapped it entirely, (and soon i hope to get headers and get rid of the manifolds.) Second the only way it would be stuck shut is if it had been sitting for a very long time w/o being run. And even if it were stuck shut you said it was running fine? Well if it was shut the car would either blow open the valve due to pressure, or else die due to extreme backpressure. Therefore scince it is running fine the valve must either be working right or it's stuck open. The only benifit is like mentioned earlier, it helps warm up the engine faster.
yea its runing fine, despite the obvious tune up parts needed, and the misfire issues that come with 21 year old plugs and other ignition components. i just know i see alot of rust on the manifolds and i know the car didnt get driven much at all, i mean i got it with 50,551 miles on it haha
A few details to make sure everything is clear (just in case someone comes in some time in the future and takes everything that's been said as gospel).
The valve is called "EFE" for "early fuel evaporation", as stated. In days of yore, it was called the "heat riser valve", but that's a bit of a misnomer. The purpose is to force some exhaust gases through the exhaust cross over passage in the head (connected to the two center exhaust ports), through a passage under the plenum of the intake manifold, and out the other head's cross over passage and out its exhaust ports. As the name implies, it promotes fuel evaporation during early running when the engine is cold. It isn't totally an emissions thing, as it predates the SBC engine, even. Without it, your engine will be a little sluggish off-throttle before it's completely warmed up. I haven't run it since I put headers on the car in 2001. Since I drive the car year-round, it is a bit of an issue for the first several blocks on cold winter mornings. The valve is operated by a thermal vacuum switch (TVS on your vacuum decal) in the intake manifold.
"Thermovac" is typically referring to the "heat stove" system in the air cleaner snorkel. Similar to the EFE, it uses warm air to help off-idle stumble when the engine isn't fully warmed up. It also predates emissions. I keep mine operating except when I'm at the track.
Your user information says you have a 1987 with 305 "HO". The "HO" wasn't offered in 1987. If the 8th character of your VIN is an "H", that's the baseline 305, commonly called the LG4. There's a thread on the FAQ forum that discusses the differences between the 305 engines, you might find some helpful information there.
thats good information. it doesnt get too cold down here in charlotte, and usually if i let the car warm up for about 5 minutes before driving it, it works good. as per the HO stuff, i was going by the H vin code, plus the origonal window sticker and bill of sale. <shrug>
Hi,
Ive got an lg4 and so now I know what that thing at the manifold is...There is a metal tube the diameter of a vacuum line coming out of it , but it isnt hooked up anywhere..So, where do I connect it?
Any pics?
Took mine out when I installed my SLP headers. Saw the thing, and tossed it into the trash. I just plugged up the vaccum source to it and my car runs fine.
i actually deleted mine. car runs fine without it :-) plus in deletion (complete removal), the exhaust doesnt sit as low to the ground
Did you use the 'donut' in its place that the TPI cars came with? TPI cars used the same exhaust manifolds as the 4bbl cars, but because they are EFI, they had no use for the EFE valve. Since GM used the same manifolds and Y-pipe, they just used a spacer 'donut' inplace of the EFE valve.
If you deleted the EFE valve, you should have used the donut in its place, otherwise you may end up with an exhaust leak.
Did you use the 'donut' in its place that the TPI cars came with? TPI cars used the same exhaust manifolds as the 4bbl cars, but because they are EFI, they had no use for the EFE valve. Since GM used the same manifolds and Y-pipe, they just used a spacer 'donut' inplace of the EFE valve.
If you deleted the EFE valve, you should have used the donut in its place, otherwise you may end up with an exhaust leak.
I installed SLP headers and it didn't need it. Everything lined up perfectly. Now, the new Bosch O2 sensor, that's a piece of junk. Gonna get a walker brand.
i had this EFE valve on my old 84 z28, b4 i did all the work too it. i did the same thing (i.e.- toss the piecer) then again, i had a completely rebuilt block, camel hump heads, air gap manifold and an edlebrock 750, not too mention a plethora of other crap that i now miss terribly just get some headers and a y pipe n u dont have to worry bout it. also, dump the q-jet pile. they suck, specially the half-*** computer controlled ones, garbage. u can find a used 600 for like 75 bux on craigslist or something. all the emissions stuff can basically be removed on a carb car really easy. mostly cuz none of it is necessary to run the car if you just have a standard carb with no electronic hookups. be careful with the distributor though. make sure you get a non comp controlled one at a swap or online, cuz that thing sux when it gets error signals from a fiddled w/ carb engine.
lol i think i seen that on a 82 and an 85 that i put headers on ...... i was like WTF looks like a diesels exhaust brake send this directly to the scrap can
lol i think i seen that on a 82 and an 85 that i put headers on ...... i was like WTF looks like a diesels exhaust brake send this directly to the scrap can
exactly my though when i was doing the exhaust on mine. completely worthless unless you live in alaska or north dakota.
they usually run better without them, as the car gets older. Everyone i've ever seen either has been stuck in one position or another. I have an all original '65 cutlass and the only "mod" is that the valve is tack-welded in the open position as it was stuck half-closed. I've seen that a lot also.
It is an emmisions item. When the engine is cold it closes the butterfly, causing the exaust to be forced through the intake manifold crossover. The fuction is to force the engine to warm up faster. 
). not sure how to tell if its stuck open or closed, or at all, but the car seems to run fine without it being hooked up. the only thing i did notice is if i remove the air cleaner all together i get a high RPM stumble, like the motor flat lines for some reason, even happened when i inverted the air cleaner lid to get more air. but that issue went away when i put the air cleaner back on the normal way. also got a "ticking" sound comming from the carb. <shrug> but it seems to run fine despite needing plugs, wires, and a cap and rotor something terrible. they'll be comming though, just fixed an oil leak at the sending unit for press. *whew* 
im very impressed with the knowledge here at thirdgen :-) 
just get some headers and a y pipe n u dont have to worry bout it. also, dump the q-jet pile. they suck, specially the half-*** computer controlled ones, garbage. u can find a used 600 for like 75 bux on craigslist or something. all the emissions stuff can basically be removed on a carb car really easy. mostly cuz none of it is necessary to run the car if you just have a standard carb with no electronic hookups. be careful with the distributor though. make sure you get a non comp controlled one at a swap or online, cuz that thing sux when it gets error signals from a fiddled w/ carb engine. 
send this directly to the scrap can 
