View Full Version : 350 engine build advice.
I'm looking for some ideas on rebuiding a '75 chevy 350 for my '83 pickup. The truck has a camper on it and has a 4-speed trans with 4.56 gears, 16" wheeels. I need to know what cam, intake, headers, etc would work good with this (and maybe some that wouldn't!). Thanks.
12-12-2000, 10:16 AM
As far as intake, I think the Edelbrock Performer is definitely the best for your application. Really helps off-idle power and throttle response, and will help on the top end a little as long as you don't want to rev past 5500 RPM, which you shouldn't with your setup.
DynoMax CeramCoat headers are great for you application. They are ceramic coated with 1-5/8" primary tubes. 1-5/8" are great for low-end torque, which I am assuming you will be wanting lot's of. Again, they are not the best above 5500, but for your truck they should be perfect. They are about $215 (already coated) or so through Summit or other performance outlets.
Cam selection is a little bit trickier. That really depends on exacly how you plan to drive truck. I have a personal preference for Comp Cams. I have a 268H in my '74 Corvette, and plan to install a Comp Cam in my '76 Suburban one of these days. You can call them and tell them what intake, headers, compression ratio, gears, tranny etc you have and they will tell you which cam they recommend.
I would stay away from the Edelbrock cams. The Performer cam is hardly an improvement over stock, and the Performer RPM cam makes very little power below about 3500 RPMs, although it makes good top-end power.
Remember, the low-end torque is what will get your truck around town easily. Trucks are generally not expected to rev past 4500 or 5000 RPMs, although with your 4-speed you can do just about whatever you want.
What heads do you have, and do you know what compression ratio you have, or want to have?
You can check my website to see info on my '74 Corvette 350 buildup, although it's a bit more than you will want for your truck (lopey idle, likes to rev).
12-12-2000, 10:38 AM
I agree with all Jeff's advice,but you might want to go with the 260H Cam,it will idle better and work better at lower RPM's.If your willing to sacrific it a little,the 268H will come alive and outpower the 260 on the midrange and top end.The performer is a great intake for a truck.Your heads will more than likey work fine the the cam/intake setup.As you already know this thing will drink gas with 4.56 gears and no overdrive.
12-12-2000, 09:17 PM
Might I suggest doug thorley headers? They are some of the nicest Ive seen and arent too outrageously prices.. Their tri-Y pipe design is supposed to do quite a bit for low end power
Doug Thorley's are nice, Ive had them on my big block for 6 years now and no problems. Lots of low and mid range torque and they beat manifolds for the high range. 14g, industrial chrome plating, thick flanges. They are like $400 though they are money well spent.
12-12-2000, 11:04 PM
I agree with the guys here about the Thorley headers but I couldnt seem to justify there price. I just bolted a set of Hooker Competition headers on my 350 and was very suprosed by the results. I had always heard headers were made for top end but they will put a big kick in the bottom and mid rpm's. I believe the 125 I spent was the best dollars I have spent on my truck yet.
12-12-2000, 11:11 PM
No definitions found for "suprosed", perhaps you mean:
hmm.. supposed, no..
hehe I dont usually get too anal about peoples spelling but depending on what word you really meant to use, you could have meant two completely different things.. so: what did you mean?
I've never had this engine apart and don't know whats wrong with it. Its got a Q-jet, and dual exhaust, thats about it. The symptoms are it just doesn't have any power. You'd think that with a V-8, 4-speed, and 4.56 gears (even with the weight) it would be able to maintain speed going up some of the Misouri hills at 55mph, but sadly this is a challenge. I only use it a few times a year and get by, but wow, it would be lots more fun to drive if it had a better performing engine. The cam could be worn out....I need to examine for this. I'd like to pull it and work on it this winter. I assume compression ratio is low since its a '75, and I'm not familiar with chevy heads that much to tell which ones they are. A 5,500 redline sounds about right since it already turns around 3,000rpm at 60mph (I love the sound of a small block winding up though!). The body on the truck is near perfect (no rust Arizona sheet metal that hasn't been used in the crummy weather here in Iowa) so I'd like to keep it for a long time.
12-13-2000, 02:55 PM
Sorry about the grammatical error. I typed that at about 3:00 a.m. after a long night of studying. It was supposed to be suprised. Also how much did you pay for your Thorley headers cause I wanted some but all the prices I saw were ridiculosly (I dont even know if I spelled that right) high.
12-13-2000, 07:10 PM
ahhh surprised.. I dont know why that word didnt click in my head.. but anyway I dont have thorley headers (yet) but a good friend of mine just got them a few months ago for his truck and i beleive they were in the high 3's, definately under $400.. i also remember him looking around quite a bit to find em that cheap.. but, like was already stated, they are very high quality with THICK flanges... one thing you dont want to deal with is a warped flange.. I had endless headaches with an old set of headers and thin flanges.
good luck, if I talk to my friend with the thorleys any time soon i'll ask him where he got them and how much he payed exactly..
Are truck headers a special application, or are they the same as some car applications? I have factory A/C and would probably need some type of bracket right? Does anyone have some part numbers? Another thing is the carb, I've been considering the Demon 625 with electric choke and ditch the Q-jet.
12-14-2000, 02:20 PM
You will probably need some kind of special bracket to mount the A/C, but it really depends on the configuration of the brackets. The small-block trucks I beleive bolt the rear of the A/C to the intake manifold, so that isn't a problem. I think the front bracket is clear of the exhaust manifold, so it's not a problem. There may be a lower rear bracket, but I don't see where it is really necessary with the other brackets in place, but you could buy an adapter from the header manufacturer. After you pick your headers ask the manufacturer to give you the part numbers for any brackets you may need.
Truck headers are a different application due to the distance from the exhaust port to the underbelly of the body. This distance is usually short for cars. Pretty much every car or truck has a different header due to problems with the locations of the brake master cylinder, steering column, and various other underhood components. I had a '72 Olds Cutlass with a Pontiac 400, so I ordered '72 GTO headers, as the GTO and Cutlass were based on the same platform. I finally got them in but there were some exciting moments while "modifying" some stuff under the hood to clear.
Personally, I prefer QJets, I am running a slightly modified Qjet on my '74 Corvette with ~350HP. The Demon is supposed to be a really good carb, too, but I don't have any experience with it myself. Electric choke sure would be nice...
12-14-2000, 05:59 PM
Yes Mike I have noticed that the Thorleys do have thick flanges on them. The Hooker seem to me to be just as well made in that department as well. The only problem I have had with them is leaks around the collecter flange which I know could be fixed by better gaskets and tightening up. The topic of the AC is interesting. On my truck (95 4x4) the AC was not a problem. I am sure our mounts are different since you are looking into an 83 but you might have the same problem. My problem was with the alternator. One of the bolts for the flange was under the mounting bracket for it. And the bracket seemed impossible to remove without removing the engine. NO WAY! Aint worth it. So I simply cut part of the the bracket with a Sawzall mounted the headers and welded it back together. Another mounting problem I had was the rear bolt on the driver side. It was nearly impossible to get to especially if you have big hands like me. I fianlly got to it with a 3 inch box end was able to turn it maybe a 1/8 turn at a time. Like I said my truck is a 95 and Im sure it differs from an 83 but I would definetly check for these problems.
Thanks to those who have posted to this topic. I am reading each one and check here often. The guy I'd trust to rebuild the Q-jet wants $150 plus parts, so for that price I'd rather start out with something new that might fit a new manifold better than the Q-jet. Headers will also be part of the plan. Are some brands better than others when fitting with a manual trans? I have cut the header flanges off between the ports over the years to provide better sealing and easier installation. Has anyone else done this? I've never done it on a chevy though.
12-15-2000, 07:14 AM
I put dynomax ceramicoat headers on my 84' 3/4 ton 4x4 350.
it has the 4 speed tranny w/granny low. no trouble at all putting them on, took me about an hour in my driveway including removing the manifolds (i was VERY lucky that the man. bolts came right out) no mods required for me.
12-28-2000, 02:49 AM
I can't say much in the header department but I can say the Q-Jet should stay there. The demon carbs look nice but with all the headaches i've had on the holleys I mostly try to avoid all of them. Q-jets are had just about everywhere from scrap yards to the swaps so parts are never a problem. They are just particular about their tuning and enough can't be said about that aspect. If you tune it right there is nothing else on the market that'll compare with the economy and adaptability of a good q-jet. If you absolutely want nothing to do with the tuning give jet performance in huntington beach, ca. a call and they can sell you one thats tuned to your specifications right out of the box. There are a few tricks to getting them right and I believe hot rod mag went over all of them. I got the one on my vette rebuilt when I did the 383 buildup and it runs flawlessly. I did the rebuild myself and did all the little tricks to it. Even went as far as smoothing out the casting marks in the bores, and epoxying up the drill plugs. This is all the same stuff jet does to theirs, also it will bolt right up to an edelbrock performer manifold with no adapters. Edelbrock also sells a new q-jet that is in the box.
12-28-2000, 02:48 PM
I definitely agree about keeping the Q-Jet. I am running the factory original Q-Jet on my 350+HP '74 Corvette. I sent it to The Carb Shop in Ontario California for their Stage II rebuild. I haven't finished dialing in the engine yet, but the carb transitions perfectly from idle, to part throttle, or full throttle, or from cruise to full throttle...it feels like fuel injection or something!
I will be keeping the Q-Jet on my '76 big block suburban, although I bought a rebuild kit to freshen it up. If you have your stock Q-Jet rebuilt I think you will be happier with it than any aftermarket carb, including reproduction Q-Jets. They will not be calibrated to your engine the way the original is.
12-28-2000, 07:50 PM
DITTO on the qjet. Trust me the last couple posts were right on the money.. any aftermarket holley/demon might run OK but will never run as well as the factory qjet.. gas mileage will definately be best with the Q.
Q has to be the most underrated carb, people dont associate Q with good performance, but they should.
granted, the holley will be easier to tune. Dont get me wrong I love holleys, Ive had many but Q has its place on certain vehicles..
The rationale behind a possible carb change is if I have to spend around $200 to have the Qjet rebuilt, I was considering the Demon 625cfm street carb complete with electric choke for about $300. The current Qjet seems to work ok as it starts up and idles good when I haven't started the truck for a month or so, but it hasn't been looked at or rebuilt for at least 10 years! so you'd think at minimum it would need something. Either I learn to rebuild this carb myself and keep it, or changeover to the Demon. One think about the cam, if this engine is running low compression (8/1?), what duration cam would sound like it has some lope to it but not be overcammed? When it fires up, I'd like it to sound like its got a cam in it if you know what I mean. Thanks for your responses, I know there are oddles of small block chevy buildups in the store magazines, but hearing first hand, real world what you guys have tried and are pleased with is more meaningful to me.
Stick with the Q-jet. $200 seems a little high, but you will do better with this than with the Demon thing. Go with a mild cam. If you can hear the lope, its too much for a truck. If you will be doing any type of towing or truck like things stick with an RV cam. They move the RPM range a little higher than stock, and keep cylinder pressure up, and with your 4.56:1 (yikes) gears, this should do fine. Check out the Edelbrock system. Cam lifters chain, performer manifold, and headers. They are designed to complement each other and they spend big bucks on R&D, why should you? Stay simple and mild. This is a truck, not a bracket racer. IF you really want that lopety lope sound to impress your friends, pull one plug wire, or ****** the timing a bunch!
12-29-2000, 09:31 PM
I hate to do this, bring up something that I heard, when I cant remember details, but there is a place, it MIGHT be the carb shop, that will work over your carb for CHEAP.. I remember it was a place with a very good name/rep. I think it was in California, but I may be wrong. They will do anything and everything that it needs, from rebush the shafts, to rejetting for your particular application. At any rate I remember it being MUCH cheaper than buying a new carb, especially the edelbrock qjet.
as for rebuilding it yourself, if you're mechanically inclined, and are detail oriented, you really should have no problem doing it yourself.. Id get Doug Roe's quadrajet book first and skim thru the qjet section.. another thing that is REALLY good is to have an old (complete) carb that you can take apart first, and familiarize yourself with whats coming up.. Thats what I did. It also helps so that you can look at the spare carb if you get stuck with how something goes back together (like the choke parts) AND you can steal parts from the donor carb if needed.
What do you guys think of a GM Goodwrench replacement engine for my application? You know, the 250hp standard 350 with 3yr/36Kmi warranty. Would that have an RV type cam in it? If I were to keep the q-jet, put a performer intake, and headers on it, would it make a little more power than 250?
12-31-2000, 02:38 PM
You can check with the GM dealer for the exact cam specs, then compare to some aftermarket cams. If you kept the cam, but swapped the intake, added headers, and had a fresh rebuild on your QJet I would say you could pump some extra ponies out of it. I would *guess* that you could pick up as much as 50 HP depending on the cam they are using. Some cams appreciate mods more than others. At least 25 HP, though I would say. And better throttle response, which feels like more HP, too. Probably a pretty good plan you have there.
I found the cam specs for the standard GM Goodwrench 350: 195 intake/202exhaust@.050" with .390"I/.410"E lift. Its a 8.5/1 compression and torque is rated at 304lbs/3500 rpm. This seems like a RV type cam to me. If I put a performer intake and headers on it (and keep the Q-jet), do you think it would be a good combo?
Good combo...yes. This however is not the IDEAL cam. You could go a notch higher and still be a stump puller. I had one in my old '76 and pre installation put a Crane Cam (little too much cam)490 lift, forget what duration and separation, and it ran like a raped ape. It was dead until 2500rpm, but would wind up till the valves floated. Kind of tuff shifting that HD 4speed when your cranking out 6400 rpm. It had a Performer intake and 4 into 1 headers, HEI ignition, im guessing 325 or so horsepower. It would have been real fun with a 700r4 or TH350 or 400. Looking back, it would have been much more truckable with a milder cam. But it was cool as hell pulling into the local hangout at 16 years old with a cherry '76 4x4 that could turn 15's and sounded like a dragster...lumpety-lump. Ahh to go back to those good old days. Wish i'd never of sold it.
I decided to go with the Goodwrench engine and picked it up yesterday. It probably won't go in until March or April though because I can't pull the truck in my garage. That will give me time to diagnose the problem(s) with the current engine and time to detail the compartment. I'm real excited about this engine and looking forward to having a top running truck this summer. There will be many more questions to come, so thanks in advance for the responses.
vBulletin® v3.8.6, Copyright ©2000-2015, Jelsoft Enterprises Ltd.