350 with a carb what kind of gas mileage are you getting?

[Guest Killer Zx]

Ok so I know it is kind of a stupid question but i plan to use my car as my daily driver and I just wanted to know from some of those who have already performed the swap what type of gas mileage are you getting? My engine is a carbed 350 with about 325 horsepower and 350 torque with a 700r-4 auto if that helps.

 

thanx guys

[Bri]

:malebitchslap:

 

LT1 engine, trans, and ecu - $2,000

 

Chevy 350 with Edelbrock 650 carb - $1,000

 

Lt1 gas mileage average - 15 to 20 mpg

 

Chevy 350 gas mileage average - 5 to 12 mpg

 

paying for your LT1 swap

with the gas money you saved in 1 year

from using fuel injection - priceless

 

[Guest Nic-Rebel450CA]

Chevy 350 gas mileage average - 5 to 12 mpg

 

Whew, someone doesnt know how to tune a carb! I get better than that in my carbureted 65 GMC with an 88 350 in it and a TH400 with 4.10 gears! Who did you get that number from?

 

Gas mileage is primarily dependent upon the weight of the vehicle and the moving losses that it has to deal with (wind resistance due to size, aerodynamics, etc.) Since the car is the same car, and a properly done swap wont change the weight that much, you can get actually get close to the same gas mileage no matter what the engine as long as you dont put on too much weight. Granted, an engine with smaller bore and fewer cylinders will have less mechanical loss, and manual transmissions can get better mileage than auto transmissions.

 

Bottom line is if you get it adjusted right you should be able to get good mileage. Check out the JTR manual, I believe it mentions between 18 and 22 mpg which would be about right.

[Pyro]

As for my car, I didn't notice a change in mpg as long as a didn't step into the throttle too much.

 

I'm running a +400 hp, 11:1 cr, comp cam 292, dart heads, full length headers, 2.5 in dual exhaust, 362 cid small block with a GM T5 and 3.90 gears in a 240Z.

 

It is very important to make sure the jetting is right for your carb and it would help a little more if get the converter to lock up in OD.

 

I also believe that MPG is more of a function of weight, drag, and gearing. However, not when is comes to big block chevys which always seem to suck 1/3 more gas than their 350 little brothers.

[EvilRufusKay]

My overbored sbc with 650 cfm drinks like I do. Waaaay too much!!!!

 

I have never bothered to figure it out because life is already depressing enough!!!

 

I know my primarys are too big but since I don't know the cam configuration I have not messed with them. I dream of an LT1/T56 and hope that if I was ever able to come up with the cash it would not only increase milage but also get rid of the rich exaust I breathe every day to and from work.

 

All that said I would not stop using my Z as my daily driver even if I only got 2 mpg!!!

 

The price of gas ...1.75/gal.

 

The price of speeding tickets...still counting

 

Being able to pass whoever / whenever.........PRICELESS!!!

[Guest Nic-Rebel450CA]

EvilRufusKay, why dont you adjust your carb? Running to rich is just a waste, it doesnt give any more power, in fact, it actually takes power away. What kind of carb is that? It shouldnt be very hard at all to adjust it to a great AFM. Let me know what kind of carb it is and I might be able to help you figure out how to adjust it.

[EvilRufusKay]

It is an Edlebrock 650. I think it is a performer but I am not sure. I have many hours into adjusting the idle mixture screws and trying differnt timing advances/idle speeds and I think I have it about as good as it will get. As far as tuning I belive that has to do with the size of the primary needle valves which I think are probably too big.

But don't you need to know the cam lift/duration to select the correct ones?

I purchased the engine and carb used and the previous owner did not know the info. The main reasons I have not torn it apart is it is my daily driver (until it starts snowing) and I would really like to go EFI over the winter.

That said I would still be appreciative of the help. I actually started a thread asking for help a while ago

http://www.hybridz.org/phpBB2/viewtopic.php?t=24262&highlight=

 

Maybe we should talk about it there as to not take over this thread? Don't want to peev the people in charge!!

 

Thanks in advance

Rufus

[dmanzo57]

I average 18-20 MPG on my commute, about 400 miles per week.

 

'72 240Z, 383ci SBC, 200-4R, 850 CFM Q-jet

1/4 mile: 11.6 @ 120

0-60: 3.2 seconds

 

Don

[danc]

I have a 2930LBS ZX, 430 H.P. SBC/w 770CFM Holley Street Avenger, 700R4, 390:1. 17-19 on the highway. In town 10-12. Both calculations were semi-normal driving and not getting into it toooo much..

[Guest mikey_clark]

For another reference, my Barracuda that weighed about a thousand pounds more with a 383 with mild cam and big 4 barrel got about 12 -14 mpg highway driving it around 80mph. So I'd think a carbed 350 in a lighter and higher geared car would get considerably better than that.

[Corzette]

Mine gets exactly 7.2 MPG cruising around. Dont know on the highway yet...I have a 750DP though with 71/80 jets. I changed them to 68/76 so far because it was so rich. It seemed to help. Can I go lower on the secondaries without trouble. I heard deJetting is not such a good thing because it makes the carb run lean at full throttle under load....Is this true?

 

CZ

[Guest Perry]

To all you carb guys with Holleys, hot cams, and real bad mileage...

put a vaccuum guage in the car and make sure your cruise vaccuum is suffecient to keep the powervalve shut. The power valve should open at a set vaccuum which is closer to atmospheric than your cruise vaccuum. I think my 750 Holley w/vac secondaries is 6 inches Hg to open power valve, it is marked on the power valve.

with a big cam you may not pull much vaccuum at idle or low cruise which lets the power valve open and it runs real rich.

 

 

My carbed 350 was getting phenominal mileage because I pushed it by hand everywhere it went for 2 years. now it's still not street legal so all my gas is used idling in the garage or doing short burn outs down the alley... real bad for mileage..

But seriously my uncle's 240 with V8 was in the 20's and with a light weight car/decent gears I'll expect good mileage when I get it all set up properly. anything less than 10-12 or so (maybe even 15ish) even with fairly aggressive driving I'd start looking things over.

My 93 camaro with LT1/6 spd rarely sees more than 16-17 with my driving. Once on the highway it got 22, but usually lower cause I cruise at pretty high speed. so unless your on the highway a lot I don't think mileage is that big a difference between the Lt1's and carbs, and who builds a V8Z to sedately cruise the highway with?

Perry

[Corzette]

So if my idle vaccuum is 13 I would divide by 1/2 and add .5 right? I would need a 7 power valve or 6.5 right? I have a 4.5 in there now so maybe thats the culprit....still made 380 RWHP

 

Corzette

[Tim240z]

Oh hell...with a Z, a carb'ed 350 should be getting you at least 15+mpg. My 3/4 ton 71 Cheyenne with a 750 double pumper and mildly built engine gets me 10-12 MPGs in a fair state of tune!

Tim

[Guest Perry]

improper power valve size will not effect full throttle power usually. just cruise/idle mixtures.

Mine is a 6.5 inch, that's what come stock in my 750 Holley with vac secondaries. I haven't had the car running long enough to set this up properly, but my cam isn't too radical so it'll probably be OK.

The point is to set power valve so it won't open at normal idle or cruise conditions. I'm mostly book knowledge on this one so I don't know a good rule of thumb for choosing one that I've actually tried. The Holley book I have says "experiment for best results" using a vaccuum guage and a mixture meter. Another book I have is aimed at race cars and says subtract 1.5 inches from idle vacuum, this would give an incredibly rich part throttle I would think for a street car. Maybe someone with more experience can help us with a rule of thumb.

When I set up a carb I have O2's and a vac guage in the car and tune the main jet for lean cruise then setup power valve so it won't open at normal cruise and tune the power valve circuit for my full throttle mixture. according to Holley book the PV adds 6 to 10 sizes to main jet under load, and this can be adjusted.

Main trouble is with big cams that open the stock power valve setting under light loads. Then at cruise you're running full power mixture which if jetted right is like 12:1 or so, if not jetted right Holley tends to be even richer in stock trim.

 

Perry