mattbhm

I have a few questions about the Chevy double hump heads.

I found these on CL earlier today, and was wondering how they'd work on a street only SBC 350.

When I saw "racing" I thought high RPM that you'd never see on the street, but is this the case?

I'm going to ask him how recently they were rebuilt.



I know, chances are these are something not to ever be used on the street, but I thought I'd ask.


I just think they'd be cool cause they're kinda different. And cheap.

Jorlain

iTrader: (4)

Back in the day, 291s were pretty swank. Now days though, I would run Vortec heads. Cost is usually similar if you can find a set assembled that doesn't need any work. Frankly, though, I'd just get yourself a set of brand new vortec style heads and be ahead of the curve... And be able to use your accessories, since they'll have the holes in them, unlike the 291s.

mattbhm

Yeah, different isn't always better haha..

Can't beat new Vortecs for like <$600.. New Vortecs with new valve springs would probably be a better setup.

Thanks!!!

I'll be happy if anyone else would like to throw in some more opinions!

AlkyIROC

Double hump heads are 1960's technology. They will work but are not as good as more modern parts such as the already mentioned vortec heads. Even some iron Dart Sportsman heads right out of the box are far better than those antique heads.

Those CL heads are listed for $375. It doesn't say exactly what valve springs are installed or what they've been set up to so you have no idea how much camshaft you can use. It doesn't say what size the valves are either so they can still be the smaller stock size. Saying they've been ported and polished etc means nothing unless they provide flow sheet to back up claims. You can easily try porting some heads and make them worse or useless.

I'd offer $100 for the set without valves and springs and proof that they've been magnafluxed to make sure there's no cracks.

With more modern parts available and the cost of better aluminum heads being a lot more affordable than they were 20, 30 or 40 years ago, the only people who really need these camel heads are old car builders who need period components.

sofakingdom

iTrader: (1)

You don't want em, at ANY price, for a motor to put in one of these cars.

They don't have the accessory bolt hole bosses.

Pass.

mattbhm

Thanks for all the info!! I appreciate it!!

Thanks man! That's over with.



Would you guys just recommend getting the money up and buying a set of new Vortecs and a new set of valve springs then?

I was hoping to get the engine swapped with the 305 in the next 2-3 months and I don't see being able to get an extra $700 for them in that time.. I still have to finish paying for the car.

I've seen some sets of vortecs for 300-400 that supposedly have new springs and haven't been run very much on CL, but I don't know if it would be worth going that route over just saving up the money and going new.



Where would be the best place to buy new if that's the best?

sofakingdom

iTrader: (1)

What sort of a car are you building? What are The Rules? (class, emissions, whatever) What induction system? What are your tuning skillz? What's the rest of the car? What cam, REAL ACTUAL TRUE MEASURED compression including taking into account the deck clearance not "catalog" "10.3:1 pistons" compression, CID, gears, converter, weight, tires? What supporting mods are you willing to do or have already done? (chassis, subframe connectors, suspension such as LCARBs, etc. etc. etc.)

Vortec heads are BY FAR the best stock heads EVAH for the SBC; but before just slappin a pair of em on yer ole wore out POS 305, best to figure out a total plan and direction.

johnbhm

iTrader: (1)

On my fathers acc because the power is to iffy for my desktop to stay on.

I'll try and answer all the questions.

Well, to start off it's a 1985 Trans am.

As of now, when it's done it's going to be a fun weekend driver with as much power we can make out of an L83 on a budget. Not a daily driver, but not something that can't be a daily driver if needed.

We live in Alabama if that says enough. I was told that there really isn't much for rules here.

It's going to be an NA carbed engine. Quadrajet.

Errr..

The rest of my car.. Isn't really there. It has a 700R4 that we plan on getting built to handle 350ish(I think that's the most we could make on a budget, if that much?)

We'll be using a 2002 Z28 rear end we picked up complete with brakes, with black 17/18/19" corvette rims.


Don't have a cam picked out yet, nor do I no compression. We just picked this engine up a few months ago and it's still sitting on the basement floor.

350

3.43

Stock right now.

Stock right now.

Mismatched right now.


No mods have been done, but we definetely plan on SFCs.



This is a Resto-Mod in progress. We just got the car last year, it's barely running with the original 305 and completely trashed.

zraffz

I like how they rattle canned under the valve covers... that's a nice touch.

skinny z

Did you say L83? As in a GM Gen V 5.3 litre LS?

mattbhm

1984 Corvette SBC L83.

skinny z

I should have known that. Had to ask. (duh).
Anyway, if you have interest in the Vortecs, there are a couple of ways to go about it.
My first build with them was using them as they came out of the box. No spring up grades. Kept the pressed-in studs. I had a flat tappet cam, .454" lift, which is about the limit with the stock valve springs, retainers and guides, and duration of 218 @ .050". Static compression was close to 10:1. That engine ran very well and also got pretty decent mileage. RPMs were kept to less than 6000 although a 5500 RPM redline was probably really the limit. The only trouble I had was on a missed shift (to 6500+) and I bent a couple of valves. Still the motor was a decent one. Also budget friendly. It wasn't until the cam got wiped out from using the wrong engine oil, that I made the next move.
The next step for me was to modify the Vortecs with screw-in studs and upgraded valve springs. I also got rid of the self guiding rocker arms and went with guide plates (personal choice but not necessary). Then I added a hydraulic roller cam with .550" lift and 224 @ .050" duration (the spring upgrade allows for a greater cam lift). My compression ratio went up a little to compliment the larger cam and I drove the wheels off that combo. Took my car into the 12's too.
The Vortecs are probably the best bang for the buck but they do have their limitations. I'd certainly build another Vortec headed 350 if the right vehicle came along. I sold my original set last fall and they went right back into service in some other hot rod.

mattbhm

Thanks for the info!!

In the end we'll probably end up at least replacing the springs to allow for a larger cam lift, I've heard the .454" limits you quite a bit, and like I said I'd like to get all I can safely get outa this engine.


That brought to mind another question, I heard somewhere that the old SBC 350s like mine can't use a roller cam without major modifications? This could be wrong, I just heard it somewhere..



I could always wait for a set of aftermarket aluminum heads to pop up on CL for cheap, but when they get put up for $600 in like new condition, they're gone in a few minutes..



Thanks so much again everyone so far!! You've all been very helpful!

skinny z

My block (two actually) both were "converted" to roller lifter. There are several manufacturers that make retro-fit rollers for the old blocks. The lifters are a little pricey but the swap is simple.
And regarding valve springs, there are also several springs out there that will drop right in without any modifications. The Comp 26915 and 26918 Beehive springs are examples. Most folks, myself included, go the added step and machine the valve guides to accept a more traditional positive style seal. This adds even more room for additional lift. But don't fool yourself, the Vortecs and .450-.460" lift cam (with the right amount of duration) can make plenty of torque and horsepower. Talk to any circle track racer that's limited to an OEM production iron head. 400 hp is not at all out of the question. Certainly enough to boil the tires off of the car.

mattbhm

When you say 400HP isn't out of the question, is that with a roller lifter conversion? Sorry, I really am just learning this stuff as I go along. I don't barely know the differences, let alone if they make a huge difference..

Those comp springs are what I was looking at, but even just buying them and the heads puts you near a new entry level set of aluminum aftermarket heads.. We're getting a new intake either way so that doesn't matter.


But after you said even using .450" lift cams, you can still make a ton of power, that does raise my hope for just getting some vortecs and bolting them on. I don't think anymore then 400HP is needed for what I'm building, although I don't think I'll see quite that with stock internals and it being NA.


Thanks!!!!

skinny z

Carb, the right intake (I like Edelbrock's RPM Air Gap), a flat tappet (non roller) cam with the stock Vortec lift limit, arguably .460"-.480" (but .460" is known to be safe), the right duration cam and compression ratio, (which is the key to the HP target), a proper ignition curve and a good exhaust system consisting of headers (1 5/8 in this case) and dual exhaust (the OEM single muffler setup is a real choke to performance and I'm dealing with that in my own build) and you'll not be too far off 400 hp. (The exhaust will make or break even your best efforts). But, the torque production from the excellent low lift flow of the Vortecs is what really makes that combination. That's what you'll feel as you get up to highway speed. Put some decent gears in the rear end, 3.73s and a 700R4 is a very good combination and you'll fly through first gear.
I'll qualify all of that with this though. If you want to make more power, and reliably, a roller cam is a step in the right direction. Modify the Vortecs (no porting required), use a bigger cam and the rest of the above ingredients, and engines built along those lines have surpassed 400 hp mark on the dyno. Some builds boast 450+ but that's a dyno number and difficult to reproduce once the engine is in the chassis.

mattbhm

You pretty much summed up the exact build I had in mind. Only issue I found is that I've heard the Vortec RPM air gap with a quadrajet can hit the hood.

We plan on running either a custom or pre made true dual exhaust, the stock one is halfway rusted off anyway.

As for a gears, we got a 3.43 rear end which I've heard works "almost" as well as 3.73s with a 700R4.

Also from most people I've heard that it's so much cheaper that they just buy a roller block instead. I'll need to do some research into this.. They're saying atleast $400 for the conversion? That's threads I've found from a few years back.


If we make 350-400HP/TQ I'll be more than happy!!



All of this has got me wishing I had the money and time to do it right now! I'm so excited! Only issue now is slowly putting aside money as I'm going to college next year.

skinny z

Yes, the Air Gap and any carb with a 3" element air filter can have clearance issues. Mine did. I had to trim away at the hood brace on my IROC steel hood and take a little off the fibreglass from my early Z28 hood. A Performer RPM may give you equal results. I believe it's a little shorter. Edelbrock has that info in their catalogue.
Dual exhaust, or a large single and free-breathing muffler is the only way to go. Anything else and you will not realize the full output.
The gearing isn't as important as getting the compression ratio and cam choice sorted out. That's where you'll make power with Vortecs (or any head for that matter).
Yes, a roller block , if you have the option, will save you dollars in the conversion. I think Comps retro-fit lifters are pushing $450. Add to that a timing cover that has a provison for a cam button, and it starts to add up. From a short block perspective, there's no to choose between an old block and a newer one. In fact the newer blocks, with the one piece rear main seal, are just a little better.
350 HP is easy. You'll have to work to see 400. Somewhere in between is likely.
Put your money aside, shop CL, stuff comes up all the time. Half the fun of this hobby is researching and shopping for the parts you'll need.
Go to college.

mattbhm

Thanks man.

That's where I'll probably end up going flat tappet for now and just get the heads/cam/etc. Just because we have a complete ready to run 118k mile recently honed and new rings, just ready to bolt in. The when we pull it out in a few years we'll get a roller block, turn it into a 383 and roll with that.

Couldn't pass up a 118k mile L83 complete with carb for $350.



Thanks again for all the help!!!

skinny z

Pay very close attention to how you break in that new cam. And do some research (reliable research) on what kind of oil you're engine will need to keep the flat tappets alive. People's notion of "high zinc" varieties of engine oil isn't entirely accurate. There are options on what lifters to get too. The best choice (if best means durable and economical) are lifters with a hardened face. The August issue of Car Craft has an article on flat tappet lifters. You may find it interesting. It's called Flat Tappet Lifter Paranoia by Steve Magnante. I have a paper copy. Not sure if it's on-line.

mattbhm

Ah, it'll probably be a close to year before I break in whatever I get. But I'll be back here for every step of breaking it in.

I'll try to find that article!

skinny z

Keep us posted.