Need help "De-hotrodding" my truck

[crawdad]

Hi folks. I just aquired my young teenage nephew's '86 SWB truck that he had bought about a year ago. Well, he wound up having a 4-bolt main 350 built for it with a radical cam, headers, etc. I don't know all of the stuff that went into it, but it was all high performance stuff. He's suppose to get with the builder and get a list of everything so that I'll know what I got. The thing is an absolute gas hog, and the cam is so wild, it lopes and vibrates everything in the cab. It became too much for him to buy gas for and finish up the things that remain to be taken care of (paint, etc.), so I took it off his hands. I am wanting to "de-tune" or "de-hotrod" this thing so that I can make a more decent daily driver out of it and get the gas miledge up. I would like to get your advice on how to do this and spend the least amount of money. I think it has a Rochester Quadrajet carb in it, and I know it is not running right as I think I can smell an overly rich mixture on it. Other than trying to get the carb right, how would you go about dealing with the rest of the stuff to make this beast more driver friendly? Thanks for any advice.

[bigarmzz]

decent rv/tow cam for starters...unless he ported the guts out of the heads....then it would probably fall on its face

it probably has a high rise intake on it....just put on a performer...ya can get those anywhere from $25 to $50 used


just those two things should help ya alot

what are the rear end gears? he's probably swapped in some 4:11's or 4:56's....put in some 3:08's or 3:42's

Originally Posted by crawdad

Hi folks. I just aquired my young teenage nephew's '86 SWB truck that he had bought about a year ago. Well, he wound up having a 4-bolt main 350 built for it with a radical cam, headers, etc. I don't know all of the stuff that went into it, but it was all high performance stuff. He's suppose to get with the builder and get a list of everything so that I'll know what I got. The thing is an absolute gas hog, and the cam is so wild, it lopes and vibrates everything in the cab. It became too much for him to buy gas for and finish up the things that remain to be taken care of (paint, etc.), so I took it off his hands. I am wanting to "de-tune" or "de-hotrod" this thing so that I can make a more decent daily driver out of it and get the gas miledge up. I would like to get your advice on how to do this and spend the least amount of money. I think it has a Rochester Quadrajet carb in it, and I know it is not running right as I think I can smell an overly rich mixture on it. Other than trying to get the carb right, how would you go about dealing with the rest of the stuff to make this beast more driver friendly? Thanks for any advice.

[r0lf-]

Yeah, we'd need some more info, but what is prolly killing your milage the worst is that cam. The headers are good. Change the intake like bigarmz said and the cam and it should get pretty good milage with the right compression. 9.0:1 would be good to shoot for. Well flowing heads and a good RV cam will result with great reliability and milage.

And for the carb. If its a quadrajet, thats a WONDERFUL milage carb if you can tune it right.

[86swb]

"a good RV cam will result with great reliability and milage."

What is the deal with the RV cam? These cams really give you better milage and reliability?

[Boog]

And just how is an RV cam different from a factory stock cam? Is it no more than a stock cam advanced 4 or 5 degrees to build more low end torque? I am wondering the same thing 86.

[r0lf-]

Well, compared to a radical cam its gonna be a lot more streetable, reliable and definitely good for milage, better than stock even. I guess my words could be taken out of context. Its no magic cam.

[hotrodhomi]

What is your idea of bad mileage? You might not be able to improve it that much.

[crawdad]

Right now the truck is getting around 10-11 mpg. I don't know for sure what the rear end ratio is. I'll pull the cover and check it out. I can't tell for sure when I'm driving it, but it seems to be geared pretty low. It's hard to tell though because of the cam and the sorry, LOUD, exhaust system on it. Makes it seem as though it's reving higher than what it actually is. I think pulling the cam is beyond my level of expertise, not to mention the time factor. I just work too many hours a day. What do you think it would cost me to have a shop pull and replace the cam? Thanks for your help folks.

[hotrodhomi]

you are not going to get much more that 14-15. I would say you should change to exhaust if you dont like the sound. This wont help with the gas issue but you will enjoy the truck more. Maybe change the rear end to a 3.08. Other than that, I would leave it.

[87 Shortwide]

Cam and carb setup will help out the driveability and gas issues, also a gear ratio if it is not stock.

[Tlynde]

like everyone else say's, change the cam unless your motor is pretty radical you shouldn't need more than an RV. The Quadrajet is a good economical carb, IF, it is working correctly, and IF you keep your foot out of it.

b.t.w. I get between 15 & 17 with my 383 and 3.73 rearend, If I drive like Grandma moses but who the heck can do that.

It's like I always say if I was worried about gas mileage I'd drive a V.W diesel

good luck.

[runsthingsover]

you mentioned that it sounds like its revving up higher than it is, did he have a stall converter? stalls will murder your gas mileage, i have a 71 el camino with a 496, it never got good mileage ( i dont know of a stroker big block that does) but went from 7 mpg around town to abut 5 now with a 3200rpm stall, they help alot if your hot rodding but are wastefull from an economical standpoint. just a though

[84slopwaggin]

I was wandering if any of you guys could post the lift and duration specs. of a R/V cam? I would like to compare one of these to other mild performance camshafts.

[Tom]

Originally Posted by 84slopwaggin

I was wandering if any of you guys could post the lift and duration specs. of a R/V cam? I would like to compare one of these to other mild performance camshafts.

There is no such thing as an RV cam- its just a term applied to any cam thats a step bigger then stock but not radical. This means just about ANY cam with under 220* @.050 duration is an "RV" type cam.

If your already getting 11mpg with a non-overdrive, then I wouldn't change the cam myself. Get a stock torqe convertor if you have a higher stall one, and a good tune up. Other then that your doing average and won't find much more milage in the combo IMO. To answer your Q, no the 350 was not stock, they weren't avalible at the time.

[86 Red_Bowtie]

a good tune up may help you out.

[piecesparts]

Reading what you have written here and I can feel for you. First of all, get the motor detuned (So to Speak). To do this I would look at a moderate cam around the profile of a Crane or Comp Cams 275 size. Second I would definitely go to a Performer intake or one that is a dual plane style to get a good flow characteristic. Third get rid of the Quadrajet unless you really understand them. They are a great carb, but most people have a really hard time setting them right. A Performer carb or a Carter AFB is a good base unit to get a decent flow profile and keep the truck running. (For a truck you need to keep the air flow up on the carb and not it gewt sloppy, so I would recommend using a 600 to 650 cfm unit) If you get to big of a carb (750 cfm, for example lets the fuel and air flow in lazily and gives you a sloppy around the town acceleration. ( I discussed this with many of the manufacturers Holley, Edelbrock, Carter and they all agree) If you have very low gears and want to perform at the race track then keep the bigger carb. Look at your rear end gears, at 3.73 or lower gear ratio will kill you if you have a 35o or 400 tranny. If you have a 700R4 then the 3.73 is just right. A 700R4 with a 3.08 gear is just the worst thing going the other way. The road manners and acceleration is so lousey that you kill your gas mileage trying to get a smooth performance out of the truck. EXAMPLE: we took an 86 Chevy truck with a 700R4 tranny and a 3.08 geared rear end to 3.73 gears and picked up two (2) MPG. The Chevy engine likes to be at their optimum power curve and this appears to be around 2200/2500 RPM. The 1900 rpm at 70 MPH was hard on the motor and the acceleration was bad. The cruise control worked hard all of the time to make up for any inclines it encountered. I presently have a 84 GMC Short Widebed with a 383 stroker with a 700R4 and 3.73 gears and I get 15 MPG average (driving like it should be driven) and I can stomp the daylights out of most vehicles on the road (If needed). Look at your timing, set the timing at 36 degrees (TOTAL ADVANCE) and then drive the vehicle, see if it works better for you. Do you still have the computer driven distributor? If so that may be part of your problem you might look at a HEI for a replacement.

[crawdad]

Piecesparts, thanks so much for that excellent reply. Lots of good advice, and information that I haven't even thought about. I'm going to go ahead and order the Performer intake manifold. This engine doesn't have EGR on it, so I'm going to get the non-EGR type manifold. I am not at all familiar with the Performer carbs. What is your experience with them? Are they a good street carb? I'll be checking the rear end this weekend to see what I've got back there. As far as the distributor, how do you tell the difference?
Runsthingsover, I don't know what kind of converter is in there. I'm trying to get my nephew to contact the builder to get all of the specs on the truck. I do know it had a Turbo 400 transmission in it, but it now has a T-350.
BTW, was the 350 CID engine stock to the 86 SWB Silverado trucks?

[piecesparts]

Yes I do have some experience with the performer carbs. First of all, I have tried the 750 carb and I had all kinds of problems with stumbling and poor acceleration at the stoplights. The 750 gave me a good top end when driving, but you don't usually run your truck at 4000 RPM. The Performer 625 CFM carbs (That is what they are actually rated at not 600 CFM as advertised) is a good all around street carb. I bought the extra needles and springs to tune the carb for optimum performance. They are easy to work on and mount onto the performer manifold easily. If you have a cruise control then you will need to get the Chevy cruise adapter kit that Edelbrock sells. Go to their website and look before buying. The distributor issue is different. If you have an HEI unit it should have a square plug connection on the side of the cap and not a big flat plug setup. If that is the case then all you need for the distributor is a hot power wire to spark it. The coil is in the cap and there is a tachometer connection on the cap also. I would rcommend having someone disassemble this and clean it, while you are replacing the intake manifold. While they are at it, put in a set of new advance springs to help it advance sooner. The computer is in the cab of the truck (behind the glove box), there is a big wiring plug on the firewall behind the distributor that the woring comes out to connect to the engine. I have completely disposed of that mess in more than one truck. As for your engine; Most cases the trucks came with 305 engines and they were a bit weak on performance, the 350 has a better power curve and more torque. The torque converter is another story, if you have a healthy cam, then there is a chance that there is a "Stall" converter in there. If it was stock then the truck would be trying to pull through a stop light when you were stopped at it. Most converters "stall" at 1500 RPM (Stock) and if there is a good healthy cam then it may be set to engage at 2200 or 2400 RPM. The truck has to idle at a higher RPM to keep it running for the cam overlap. That is why you have a rich gassy smell around it while you are idleing. The carb is adjusted to where the idle circuit of the carburetor is partially transtioning into the power circuit, so that you can get enough air to the cylinders for an idle. Get rid of the cam and the smell goes away and the idle will smooth out when you adjust the carb back to where it works right.

[cliffsta]

You're complaining about 10-11 miles to the gallon? BAH!! My poor old truck is getting 11 to 13 most tanks (in town). The rare times I actually do mostly highway, it goes way up to like 15 or so (thanks to 2.56 rearend).

11 is not too bad for a brick like these, especially with the rad cam you got.

[piecesparts]

Sounds like there is a lot of disatisfaction out there.... I get 15 MPG with mine as I said earlier, but I'm pushing well over 400 HP and 3.73 gears...

[white82]

i have a balanced 350 bottom end in my truck i used to have a .510 solid cam with 1.6 rockers, a 3500 stall ,350 turbo,and a holley 750 it got about 9mpg. i put one of summits .440 lift cams with the 1.6s put it about .460 lift .i put a stock coverter with the t 350. i run about 2500 rpms at 70miles an hour and get about 14mpg now but i want more im thinking my next step is to build a 700r4 to lower my rpms on the highway my power curve starts at 1300 rpms so i figure if i can get it around1800 rpms at 70miles an hour would be a good round number and still have plenty of torque