Inliners International Forums General Discussion Engines Good carb for mpg

While I have not even started my trucks new motor yet, I am thinking gas mileage and what can I do to improve it. I currently have a stock rebuilt 250, although the head has been milled .40 and has a near stock RV 1 cam. Anyways, I have held off on installing the stock manifolds thinking maybe a offy/webber and a header might help me get some better gas mileage. So, what should I do, stick with the monojet 1 barrel, a webber 32/36 or the 38/38. Overall power is not a major deciding factor, just best economy I can get out of a fullsize 4x4.

I have the 32/36 but have never been able to tune it right. Was going to have it done by a high performance shop but couldn't see spending the money when I'm going to a 4bbl anyway. I always got better tuning and mileage from my 1bbl, but the Carter carbs rebuilt ones suck!!!! You'll have to take about 3-5 back until you finally get a decent one. I've heard Holley brand new ones are good but waaaaaay expensive. At that price you should get the Webber IDK(???) carb. Someone here has one and is pretty happy with it on their truck.

i have found that it is better not to concentrate on the carb for increased fuel economy as it does sacrifice power....there are other methods of achiving better gas mileage without a high mileage ccarb...i have a carter YFA on my 250....easy to tune and rebuild....if u dont mind building a few things then nu can increase gas mileage without losing power by building a PCV gas condensator...this is a jar inbetween the PCV valve and the intake where the oil and crap that normally goes straight into your engine will be cracked and turned into fuel...all the other junk will stay in the jar and not go into the engine....this results in better mileage since more fuel and less crap is entering the engine...typical mileage increases for these jars is 25% better but there are ones that get 40% better mileage...the one i build gives me more than 40% im sure of cause i went 200km per 1/4 tank with it and about 80km without it...also depending how the engine is tuned will effect your gas mileage...same with the vac advance..u need vac advance....some carbs dont have enough vacuum to utilise the vac advance so then it should be hooked up to the intake manifold...take a look at page 3 of my website for more info on the pcv jar....

www.geocities.com/davevandrunen/ind3.html

fascinating! will this rob the engine of power? can it be used on an engine without a PCV valve... like my 59 235?

it wont rob the engine of power and cannot be used with an engine without a pcv valve...although a pcv valve is cheap and easy to put on...just drill the proper size hole and get a rubber grommet and pcv valve...to tell u the truth i never actually heard of an engine without a pcv...but i'm not too knowledgable on all things....so yes it can be used on your engine if u want to install a pcv valve...otherwise no cause it uses the oil vapors etc..from the crankcase to be cracked into fuel...although the hydrogen thing can be used without the pcv system but u wouldnt see as good of results without using the gas condensor...hydrogen alone only gives about 25%-35% better mileage...but requires more maintanence than the gas condensor...both units as standalones give about the same mileage....but when used together its doubled or more since the hydrogen being cracke with the oil and enter the manifold together....so mileage will be way better...

hmm, Interesting reading. I just have a hard time believing that a pvc trap can add that much fuel mileage. But I have never tried it either. I may build somthing of the like just to find out. I have heard other statments about water injection helping to. Cool reading slayer! Hey Brad, Is that webber one of the rebuilds from Stovebolt or is it a "webber"? What intake are you running, and have you tried different jets?

water injection does help if u plan to run a high compression ratio....but for mileage gains it doesnt really do all that much....the pvc gas condensor doesnt work exactly the same with every engine...it depends on the oil used...how well the engine is running...i think the reason it was such an amazing difference is cause i dont hava any emmisions controll devices at all...maybe its just the way i built it...its probably 3-5 times bigger than production units and is a more interesting design so the way the unit is built makes a difference too...i used 4" round by 10-12" high...the actual thing that cracks the oil is about 1.5"-2" round by 6-8"long so it holds quite a bit of material to crack the oil...also the stuff used to crack the oil makes a difference...silica gel beads and zinc i find are the best combination....

ive heard webber carbs are quite good....on my website if u go to the main page there are a bunch of links...one of them is how to install a webber carb and electric fuel pump...check that out as well....i would like to convert to a 2bbl holley or webber...webber probably being my first choice although they are tougher to tune supposedly..

Rayzors68, I have a Webber, not the HW version. I've tried using different jets, and spent $20-$30 doing it, but never could make it run as well as folks here made it sound. There's a shop near me that specializes in foreign cars that would have come with Webbers and was going to take it in there, but I'm going with the Holley anyway. I might try putting it on my Camaro someday and having it tuned professionally. I would bet I'd feel the difference on that.

Oh, also I'm running the stock manifold with the Stovebolt adaptor and that may be my main problem really.

I have seen those 2 into 1 adapters before. They seem like a real bottle neck for air flow compared to the 2 barrel. I dont know, I am thinking about the 38-38 webber as its a little larger then the 32-36. I guess I need to get a different manifold like the clifford though. I have not seen a offy close enough to tell, but it looks like they are setup for a 4 barrel only. I do have a brand new edelbrock 600 sitting here but that may be to much carb for the amount of motor mods I have.

The Offenhouser manifold has a plate on it that the carb bolts to. The plate is bolted to the manifold. If you wanted you could make a new plate for the 2bbl and bolt it onto the offy. You wouldn't need an adapter. The offy will bolt to the stock exhaust manifold, the Clifford does not.

this is a picture of what a few people are doing with the log head to make it fit their carb desires....the one drawn will fit 6 small carbs...you can make the aluminum plates to work with whatever carb setup u want.....just an idea which would be bwtter than a 2-1 adaptor....u wouldnt have to shave the whole head for just 1 carb....just shave down the origional section where the 1 bbl carb goes and make a flush surrounding for a plate that can hold a 2 bbl carb...if u do try something like this...get a shop to shave the intake for u cause it needs to be flat as poosible....sorry the pic is so big....

That makes alot of sense thetrueslayer! Although the GM 194/250/292 intake is about 4" square, if a guy could come up with a way to chop the top off the square portion, then bolt or weld on a plate it seems the idea would work.

Btw, Rayzors68, what part of Oregon are you in?

the design is for ford integral logs....i have seen a chevy 250 log and its about the same....it wouldnt be too hard to think something up though for the GM...i dont know exactly what it looks like though...for the 4" square part do u mean the part the carb sits on or the actual log itself? i'm sure if u brought it to a shop u could easily get the intake shaved...then just do some grinding and drilling at home...

I looked at the top of the manifold thinking I could do this. It would seem there is enough room. I would have to cut up a spare first to find out though. Brad, I am in a town called Holley. Its near Albany.

I dont get the part about hooking up the vaccum advance to manifold vaccum.you just made it a vaccum retarder that way.

Marc:

your right...and the effects are different...u can achive better cruising mileage when cruising and smoother idle than the other way....supposedly you get a quicker off the line start with vacuum manifold but top end performance isnt as good...but only really matters if racing...the timing does need to be changed when switching to manifold vacuum....i actally prefer manifold vacuum to carb...but thats cause my carbs vacuum is nothing so its useless and makes no diff when the hose is on or off....if your engine changes RPMs by about 60 RPMs when the hose is disconnected then your vac advance is working and doesnt matter...i think it would be fine running the hydrogen from the manifold...just not as completely evenly distributed...

do you have any drawings or pictures of this oil Cracker?Is it patented?Sounds interesting.

Its not patented...i would suggest taking a look at the high performance section for the 'hydro-boost' thread...its got a fair bit of extra info....but here is the link to my site anyways....

www.geocities.com/davevandrunen/ind3.html

Marc...just found out today that it is patented..so u cant sell the things...but the plans and ideas are free if u want to go ahead and make your own or help others make them...just dont try to sell them...