71 350 Rebuild advice needed - Head and Cam Suggestions
 

Hey Guys, I've been scouring the local classifieds for months to find a nice SBC to swap into my truck eventually.

I ended up finding a super clean complete 79k mile all original 71 2bbl 350 out of a Chev Biscayne(saw the video of it running in the car before being pulled) . There's still cross hatch in the cylinders and all the crank bearings are in great shape. I'm hoping to get away with polishing the crank, new bearings, new rings and a very light hone in the cylinders for the bottom end.

So my question is.. I like originality and want to keep the stock heads which are ok ish. The stock engine made 245hp with a 2bbl and it seems the 4bbls of that year made around 275hp. I have a 4bbl QJet and manifold to install for it.

I'd like to end up with 300-325hp, just a nice little bump up from stock but how do I pick the cam to match the heads? The heads are 76cc 1.94/1.5 inch valves which I know are just ok.

Is it realistic to have the machine shop do the heads and have a slightly bigger valve installed, nothing crazy but just a slight bit more flow. What cam would go well with this setup. I'd like a very very mild cam, something to just give me the extra 25-45hp from stock.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Heads have come a long way in the last 52 years. It's not really economical to put bigger valves in those heads that won't flow that great anyway (and probably need a set of guides and hardened seats). If it were me and I was stuck on a carburetor, I would put a set of Vortec heads on it. You would have to buy a special intake since the Vortec heads have a weird bolt pattern. You would need center bolt style valve covers but they are easy to obtain. Vortecs have limits on what cam you can use but there are many articles about building a carbed 300+HP 350 with Vortec heads. My .02

https://www.youtube.com/watch?v=Xm2JnOrQeMc
for instance

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Yeah, I've heard the Vortecs are great but also prone to cracking. I'd want to stay with my stock heads and go from there

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Here’s some info for you.
Looking at the chart you’ll see your stock cam is spot on for your compression right now.


https://www.crankshaftcoalition.com/..._compatibility

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

It's gonna be hard to get 300 HP out of those heads. A cam will help but if the heads don't flow and the exhaust is restricted and all of the other things with it then you won't get the power out. Not to mention the problems these days with flat tappet cams eating lobes. I don't do carbs anymore. I don't do flat tappets anymore. If I was going to build a 350 today for anything it would be fuel injected and I would start with a roller cam 1-piece seal block. I doubt you want to go that direction, but even the TBI 350s have more HP and torque than a carbed 350 truck engine. So you want a carb. A Q-jet is a good choice. Good driveability, lots of CFMs wide open. Nothing wrong with that. You have a nice bottom end it sounds like, but it won't do a factory roller cam. You have to decide how to best spend your money. But me (and again if I absolutely had to use a carb), I would find a 1996-1999 350 Vortec truck engine to build and put a Q-jet intake on it. There are some Vortec castings that cracked worse than others. Vortecs are generally cheap, maybe you could get a guarantee that they were good and get them cleaned and magnifluxed? No good-at least maybe you get money back on the heads? Even the pick-a-part would at least exhange them so you were only out cleaning and magniflux cost. If you do use a flat tappet cam get the right oil and follow the break in procedure to the "T"-no shortcuts. Good luck with your build.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Thank you guys for all the advice to switch to Vortec but I'm going to have to stick with and work with what I've already have. Yes fuel injection would be way better but I don't have that budget and I want to keep the truck the way it came, with an old school engine.

Wouldn't these heads breathe a little better if the machine shop puts a little bit larger valves in? Are there decent quality affordable aluminum heads that might be a better fit? I've checked Summit and I have about 700 different head options..I have no clue how to choose.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

OP

you are absolutely going to want to get new lifters for any new cam. Use Valvoline VR1 or Joe Gibbs break in oil as they have a high zinc content.

Those heads are not great candidates for going 2:02/1:60 valves but at a minimum get hardened exhaust seats, and a complete valve job

A mild cam in the 218/224 range or even smaller.

I know you are set on that motor but IMHO a later year 1 piece RMS full hydraulic roller cam with vortech heads would, be what I would have done

IMHO even with a cam, that motor will be in the 275ish HP range unless you get a more modern head. Heads and cam should be a compatible package. One without the other really leaves a lot of HP on the table

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Yes, a machine shop can get those things flowing better than stock. Nice thing is, they will look like stock when opening the hood if that's what floats your canoe. Upgrading the manifold and carb, cam and lifters, and getting a little more spark will probably get you to that 300 goal.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Some off the shelf aluminum heads wouldn't cost much more than trying to change to bigger valves and doing the head work on those (at least here in the states). You'd also be way light and you can pain them to look stock.

If the engine runs good, slip the 4BBL on it and run as it is. Your're talking way more power than the old 250 had.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

The engine in your picture has a Quadrajet on it. It also has what appears to be provision for an EGR valve, so pretty sure it is not a '72 engine. I'm pretty sure EGR was installed starting in '73. Can you get some numbers off the block?

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

>>I want to keep the truck the way it came, with an old school engine.<<

The 250 is an old school engine. Stick the 4bbl on it. Cam, headers, lump ports.
That's old school and it's original and different than the run of the mill SBC.


>>I ended up finding a super clean complete 79k mile all original 71 2bbl 350 out of a Chev Biscayne(saw the video of it running in the car before being pulled) .<<
>>the crank bearings are in great shape. I'm hoping to get away with polishing the crank, new bearings,<<
If the bearings are in great shape, why do you need to replace them and polish the crank????


>>There's still cross hatch in the cylinders and all the crank bearings are in great shape. I'm hoping to get away with polishing the crank, new bearings, new rings and a very light hone in the cylinders for the bottom end.<<

You pulled the heads and can see the crosshatch at the top of the cylinders or used a borescope. A very light hone is needed because?
A 300,000 mile engine will still show crosshatch at the bottom of the bore.

To me that 350 sounds like a money pit, with gains proportional to $$$$$$

Either run it in as is or play with the 250.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Very true, I'm tempted to just run it but I am in no rush as my L250 runs great right now. I'm tempted to just buy some aluminum heads and be done with the old but I will have to research which heads to go with since there are so many options. I do like having the engine mostly original like the way it would have came with the old heads though

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

The aluminum intake and Quadrajet you see in the pic are off of an 81 Vette. I have the original 2bbl and cast iron intake sitting on the floor.

All the block numbers check out. It's a 3970010 Casting with an engine stamp of CGC which comes back to a 71 350 245hp 2bbl and auto tranny which is exactly what the Biscayne was it came out of.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Any chance the heads would do ok with a bit smaller valves than the 2.02/160 you recommend or is that the only bigger step up. I'll have to call summit to see what they'd recommend for an aluminum head and cam I guess. I've heard they are good to chat with?

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Yeah, this is what I was hoping! Definitely want it to look stock when I open the hood. I've got everything I need, just missing a stock 4bbl Air Cleaner.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Geez, you sound like a Police Interrogator! Lol The bearings and cylinders are in great shape for 79k, it never hurts to deglaze the cylinders, polish up the crank and put in new bearings and rings to freshen it up. What I was trying to get across is that I should be able to get away with avoiding the machine shop on the lower end. I could probably run it the way it is but freshening it up is worth it

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Oh, OK. One never knows...

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

hi, I have a cgc 245 hp 350 also. came in a elcamino. I put a 4bbl on it and it ran very well. the origanal tax code that came in my 70 gmc I rebuilt and put a 204 214 420 442 cam in it it ran great. the next 350 I put in the gmc is a goodwrench vp code I put a performer intake q-jet headers and the same 204 214 cam. it runs on regular and has more than enough torque to pull my trailer up hills. that engine was dynoed for chevy high performace magazine and at 8.00 comp with a 4bbl headers and duels got 265hp and 350 ft lbs. any of these engines should do what you want. good luck, chuck

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

A original April 1971 400 sbc (4 bbl had 255 hp rating)
I am not finding any 1971 SBC engine made 245hp stock with a 2bbl
This is what I could find, (Horsepower net: 165 hp (SAE net)/ 4000)

The final straw was the passage of a 1971 California law requiring that any reference to engine horsepower in advertisements, brochures, owner’s manuals, or sales manuals for 1972 or later gasoline-powered cars and light trucks state only the as-installed SAE net rating. Faced with that reality, manufacturers decided it was time to abandon the gross rating system entirely, at least in the United States. For 1971, many U.S. manufacturers listed both SAE gross and net ratings..

The heads are low compression and low flow. I would be temped to reseal the motor and run it (as is). I wouldn't put any money into the motor except to seal it up ad paint it.
Save your money for some of the better options others pointed out.
Cheers

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Just had a small block 400 redone , went .30 over so 406 now , 2 bolt main, for my 72 C10. Pictured are the heads cam and lifters that were used in the build. Yes the aluminum heads are great but these are cast iron and complete and ready to bolt on and know of someone that has used them on a 350 like u have and its been driven over 10,000 miles and no issues. Sending old heads to a machine shop will probably cost u as much as getting a pair of the pictured ones.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

I have an original 72 Z28 and it has from the factory an 010 block and 487 heads. The heads are 202 valves and the bottom end is a 4 bolt, steel crank, pink rods and a gm solid lifter cam. My point being the combo you have can be made to GOOOOOO!
It would be costly but very doable. Good luck.

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Here`s a youtube video by Richard Holdener that dyno tests all the components you are looking for. This guy does tests on various motors (GM, Ford, Dodge) with various performance upgrades and combos.

This vid starts with a stock 2 bbl 350 and goes from there. 2 bbl to Q-Jet, stock cam to mild cam, stock heads to ported heads and gives dyno tests when each component is added. Then adds alum heads, bigger cam, better intake and carb. It should answer all your questions.

https://youtu.be/NAuHAmzyEvw

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Very interesting video and results, thanks for passing that along! His stock 4bbl dyno numbers are bang on with GM's published results for a 350 with a 4bbl of that year, 275hp & 350lbs of torque. I haven't made a decision yet but just keeping it stock and adding the 4bbl might be the way I go as I'm not looking for crazy power..

On the other hand, a good set of heads and a little cam could bring me above 300hp reliably and closer to 400lbs of torque!!

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Interesting, Thanks!

Re: 71 350 Rebuild advice needed - Head and Cam Suggestions
 

Hey Greg, thanks for the suggestions! That's the kind of info I was hoping for :) So no issues running the same set up on your 400 SBC vs a 350?

Summit sells these head individually correct? My local machine shop gave an estimate of $400 per head to fully rebuild..wish shipping across the border wasn't soo expensive through Summit though..

What kind of HP do you think your buddy is getting with this setup on his 350?

BTW, I found my 350 in your fair city! Drove the old girl up there and back in an afternoon and she didn't miss a beat. Calculated my US MPG for the trip and I got 15.8! Not too bad for the old girl..