regardless, I respectfully disagree

 

Lies, Damn Lies, and Pre-1971 SAE Gross Dyno Rating Statistics.
https://www.hagerty.com/media/archived/horsepower/

 

Running a dyno test without an air filter or even the housing, accessories, and "dyno headers" isn't realistic?!? ;-)

It cracks me up that Auto manufacturers decided it was too misleading to advertise super unrealistic gross HP figures using a methodology like that, but it's basically the EXACT rating methodology used for crate engines and all? magazine tests.
Then you've got weird manufacturers like BMW who seem to be escalating how much they UNDER rate their engines...

Adam

 

Yes, I have been pounding my fist on the desk for years about the ludicrous GROSS HP figures that often are thrown around which are pretty meaningless since they don't represent anywhere near the realistic HP of said engine as installed in a car. GM and all the others were forced into NET figures in 1972 by the government (hysterical by the man) that are a better representation of the HP/TQ a given engine makes at least with all accessories installed and a full street exhaust. RWHP is the real deal but difficult to implement on a widespread basis. At the very least I would like to see aftermarket engine manufacturers have to report some semblance of NET figures and GROSS should be retired......

 

You are totally correct on all counts, but I still desire one. 😁

Thankfully my brother is a whizz with engines & mechanical matters. I have asked here as he has a lot on his plate with a severe family illness at this time. 😞

He & others will kindly do any work and he will assist me in choosing a good one to start from.

To be clear, I'm not looking to have a dragster, but would like more bhp than the later stock 70's put out.

I really appreciate everyone's feedback & comments.
Thank you. 👍😎🇺🇲

 

compare apples to apples. Gross to Gross. Different test methods are just that; different test methods: and as expected, return different results.
GM published Gross specs for both MY1970 & MY1971
I see nothing, Nothing in that article which disputes GM's Gross specs

so, what's your point ?

 

OP, all these C3s are "old cars". You're NEVER "going to be done fixing it". IMHO, there's a different mentality required to enjoy one; not be driven crazy by one.

The overwhelming odds are there's going to be things to fix every year even if you do a ton of work upfront, it's going to drip oil, it's not going to instantly start. Half of the things in these cars run off of engine vacuum and vacuum hoses (head light pop-up mechanisms, windshield wipers, switching from vent to heat to AC, cruise control, the transmission shift firmness, etc...). Tuning a carburetor is some witch doctor voodoo magic to someone who's not used to it (me).

The brakes system literally fills with air through the calipers and stops working if the rotors get out of spec and THEN you find that GM riveted the rotors on and you have to drill through rivets to even replace them. -Magical surprises left by clearly high 1970s era GM engineers await you to discover them at every turn!

-If you want a C3 that can handle like a more MODERN sports car, be prepared that full modern suspensions can cost as much as many people pay for complete plastic bumper C3s. (You can still get a very good handling C3 without paying a ton, but it's good to set expectations. A full Van Steel suspension setup will be $7-$8k and SOMEONE's got to install it.)

If you're not ok with that get a C5 or newer Corvette.


If you can come to grips with it and reset expectations that C3 ownership is a journey of finding the flaws and slowly improving your car over time, including the potential to make it far better than it came from the factory, (and improving your own mechanical ability as you improve your car) then the engine questions start to become relevant. C3 ownership is either buying a finished car exactly the way you want it, a giant money pit of labor $$$, or choosing to become handy and buying tools and going at a snail's pace, AFAIK.

I think most C3 owners fall in the 3rd category and then C3 ownership looks a lot like buying year old dog from someone else and planning to address it's bad habits early on and then hanging out with it a LOT and cleaning up it's crap and taking it on midnight trips to the vet for many years into the future, but you'll end up with a heck of a friend when it's all done. Ever seen how much "dog stuff" dog people end up with scattered all over their house? -That'll be you too unless you just want to throw money at the car to make it go away; they're money hungry beasts, though.

Small Block Chevy engines are Small Block Chevy engines and I'd say that a good MAJORITY of C3s have been modified and unless you're going for some classic sought-after BigBlock chrome bumper model, how they came from the factory is mostly irrelevant. If you want to make power, you're going to need new heads and you're going to need a good exhaust. If you're not mechanical and don't want to pay an arm and a leg in labor, buy a crate motor with a warrantee from someone like BluePrint and find someone to drop it in for you, so the engine the car comes with matters even less.



Adam

 

A fabulous post Adam.
I have had a C5 & two C6's, so yes, the C3 will be nothing like them.

I hope to get one that has had all the major work done & am happy to pay for additional work and expect issues, but I want the 'big smile' experience of owning one.

I grew up around race cars with big thumping V8s and am used to oversteer moments from my racing days.

Its an itch I have tried not to scratch for 40 years, but it may be time to take the gloves off and wear that smile.

I guess if it's not for me, at least I will have tried, time will tell. 😁👍😎🇺🇲

 

No idea where you got that, but it’s very wrong. Cars were sold with carburetors in the US through 1990 (Olds, Buick, Cadillac, and Subaru for sure). And since you said “vehicle”, you’re WAY off the mark when you start looking at carbureted motorcycles and scooters.

 

Op what area are you in? I bet theres some members not far from you should you need a carb or timing tweak...buying one like you said where all (esp underneath) is gone through is money well spent. Few times over the years Id be suprised by some member I didnt know pming me, showing up and giving a hand.
Gawd...I remember those...Those lean burn systems were horrid....the funky ignition systems on Granadas, talk about a tow ride. Transitional era to EFI...it was then I figured best to keep this as a hobby.
Gotta say I love those old carbed cars wtih ice cold ac though, so many really were dead nuts reliable. It was common if one kept up on a Qjet, HEI and oil changes, timing chain every 100k to get 200k+ out of a 350 all day.

 

I have a slightly different opinion than Adam's about the C3's, having owned my L-82 4 speed Gymkhana car for 37 years.

Granted I have beed tinkering with cars since I was 17 and have strong background and training in the sciences and have road raced formula cars as well although my "day job" is nothing related to cars, mechanics, and corvettes. If you have some good basic automotives skills and the tools along with desire to learn, these cars can be quite reliable, fun, very old school, and rather inexpensive to maintain and upgrade.

The biggest annoyance for me over 40 years has been the leaks from the engine oil, power steering system, and 4 speed along with very minor drips from the rear diff. Aside from those issues, I have had zero issues with brakes after I installed VBP SS calipers in 1985 (LONG TIME AGO), replaced the Qjet with the holley 4175 in 1985 as well, original vacuum hoses and system for the headlights, no electrical issues, no clutch/4 speed issues etc...It has been pretty darn reliable for its vintage, some occasional hip cups, but mostly solid!

I have also documented and posted numerous times how I have changed/upgraded the suspension and tires using the OEM suspension architecture over many years, with better or modern components and tires so that my car is almost modern sports car like handling for no where near big dollars $$, more like <$2k for everything, doing all the work myself.

I have know quite a few C3 owners like me with really great reliable cars BUT I also know C3 owners whose cars are a constant problem either due to the luck of the draw when that car was built, prior owners hands on that car, or hidden accident damage and collateral damage...you need to buy a good car, if possible

Lastly, I have a 10C6Z06 bought new, that is no where near the same experience, as the C3.

A C5/C6/C7 will all be much more comfortable, reliable, faster, etc BUT the pure visceral experience of driving a C3 is very different. You cannot get a C3 aura from a later C model car..no way. I love my 10 Z06 but I enjoy the C3 just as much but for different reasons....My 2 Corvettes could not be more different and both are a blast to drive! If you want the C3 total experience, you need to have a C3. There is no going to later models to capture that atmosphere in part or in total...........

 

LMBlue - back to your original question - a Good "street type" build (think 6,000 - or so Max RPM & the ability to idle at 1,000 RPM or less) and NO emissions - you can generally get 1.2 HP/cubic inch with a SBC based engine (and that's flywheel HP). Sure - there are ways to get more - but to go higher - you typically start losing more and more low & mid range RPM torque - and that is NOT what you want for the street. So - with a 350 - think 420 HP or so... A 383 gets you to around 460 HP

Now - having said that - you did not include headers in your list. If you don't include headers - you are effectively hurting yourself power wise - it's like a pro athlete breathing through a snorkel. How much you are hurting depends on how bad the manifolds your using are.

Your choice of a 650 CFM Carb is appropriate for this area. A 750 CFM Carb will start to be a restriction around the 500 HP mark - so the 650 will be good for 425 - 450 HP before it becomes the limiting factor.


Three final thoughts:

One thing that was not mentioned in the above posts is that all SBC Blocks are not created equal. In the late 1960's and early 1970's - Chevy made some pretty robust blocks. As the HP levels dropped, and fuel economy became more important - metal was taken out of the block, and the blocks were not as strong. Not really an issue at the 200 HP level, but a lot more of an issue at the 400+ HP level - particularly if you are using that HP more often. A good 1.2 HP/cid build runs some money - figure at least $4K in parts ( $1,500 for heads, another $600 for a carb, another $400 for the cam kit, $300 for the Intake, close to a grand for pistons, rings and crank balancing, another few hundred for rockers and good rocker studs, you probably want to get a new distributor that is compatible with an aftermarket ignition system ($300+) and of course another few hundred for head bolts and mail bearing bolts, a good oil pump, gaskets etc. etc. etc. etc.) Putting that $$$ into a "lightweight block" may not be the best plan.....

Two - after you build the motor - you really need to spend some $$$ to get the motor or the car on a dyno to get it tuned. When you start talking aluminum heads and aftermarket cams - the ONLY way to get a carb set up properly is to get it on a dyno where you can look at air/fuel ratios in real time. (and truthfully - it's harder to set up a steet carb than a real race set-up - because the race set-up doesn't care about light throttle air/fuel - it matters for a street set up. Then - once you get the carb set up - you can then look at getting the ignition timing right.

Three - C3's are notorious for cooling issues. A good aluminum radiator solves many of these, and a well designed cooling fan solves most of the rest - but those two are going to run some $$$$ ...

Bottom line ..... IMHO - spend half an hour talking to a reputable engine builder, and explain your goals, and your budget, and listen to what he says ...

 

Don't forget cubic inches builds HP & TQ more easily and more cheaply than small er cubes. A 383 can be less expensive and make more power than a 350, etc. But that does change when you hit Big Blocks. Their parts just cost more. A 400 SB can make the same power as a 396 Big Block, for less money. But then you can't get 496 cubes out of a small block.

So how much power do you really want? 300 (gross) is a fine cruiser. 350-375 feels pretty fast and feels more like a sports car or a race car. More than that gets very fast and becomes a lot for the street. 400 HP in a C6 feels very smooth and suttle. There are a lot of electronics helping you/it. The same HP in a C3 feels noisy, raw, sudden and brutal. DIfferent cars entirely. 500HP? You better have your A game on when you are behind the wheel.

 

Agree with Leigh above, mostly^^^^, again, but with some slight deviations. I have said this before:

If you are looking for Sub 400 Gross HP from the SBC Gen 1, in my opinion, if you have a serviceable, good condition 350 block and crank with rods, there is no need or real significant street difference between a 355 built correctly and a 383, unless the 383 is built for 475+ Gross HP. Unless the 383 is built with top heads, roller cam and compression for max street power (475+ Gross HP/TQ), a proper 355 with top parts will easily make the same power/tq within 200-300 RPM (insignificant at these power levels on the street) versus the additional 28 cubes. If you have to change to a 383 crank with rods and machine work to convert the 350 block, that additional money used for better parts for the same 355 will get you the same result in the 300-400 Gross HP range on the street at the lower RPMs. The power/RPM differences are VERY marginal on the street and not noticeable in that power range. Looking for 475+ Gross HP/TQ at the lowest streetable RPM, 383 all day.

The major engine manufacturers learned many many years ago that the displacement of an engine is only PART of the Hp/TQ equation. There are literally countless examples of engines of smaller displacements/Liters easily outpowering there bigger brother cube motors. The components used in the motors are actually a much bigger determinant of the final HP/TQ result than just cubes alone. A 383 will outpower a 355 only if built correctly with the better component parts. A 383 is and will not make more power just because of the additional 28 cubes.

 

peak hp can be close but that extra stroke is noticeable....Id rather have a mild 400 for instance then a 350 withou lousy manners...all depends on how its set up though
WIth roller cams and good heads we have today sure, for a fun 400hp a 350 will get it done easily
Remember in the 80s the proverbial 390-400hp 350 was 11-1, set of well ported heads, a 292 type cam single plane deep gears etc. a 13 sec car was impressive, 12 sec cars were on a trailer to the track.
now even a heavy challenger can run 12s or better with the AC on, depressing lol

 

I used to think this ^^^^ until I built my 355 roller cammed L-82 for max mid range torque with AFR heads and 10.2 compression. My engine with the 4 speed and 3.70 gears can pull IN 4TH GEAR with zero hesitation from 800-900 RPM all the way to redline, 6,000, with no problem. I have been in more than a few 383's in the same situation and driven them as well that will not pull mid range torque like my 355. This is fact, not theory.

A 383 again, in of itself, does not mean and it will not outperform a less displacement 355 if not built appropriately. Again, there are countless examples of less displacement motors V8/V6's over all time that will out power the large Liter engines, simply because they are built differently with better power components.

A max built 383 will out power a max built 355 all day long but the comparison must be very exact apples to apples...Having a longer stroke does NOT mean automatically the 383 will make more power. Its physics only, when all else is exactly equal, which is almost never the case.

 

Of course that's what the crate market does. What other method would you use? There's an infinite number of exhaust system combinations (resulting in an infinite variety of backpressure readings and flow restrictions), at least a thousand different airbox configurations (resulting in a thousand different AIT readings and pressure drops), and a few dozen different accessory combinations (large or small sized alternators and pulley ratios, p/s pump speed and pressure difference, a/c option or not). Which one of those thousands of combinations would you choose to make your net hp measurements, because my money is on you choosing a combination completely different than I would, or any of a thousand other guys.

Measure the gross hp of the engine. It tells the customer what level of performance the core engine will provide, and allows the customer to compare similar engines from multiple builders/sources. After that, the buyers get to decide how much performance they want to leave on the table by buying the exhaust system or accessories that are either efficient or cheap, heavy, and inefficient.

 

Here is a table which may help, from How to Resotore Your C3, Walt Thurn

I have a 75, 350 these are very low Hp and can be matched with equally underperforming Tans and Diff. I am going through whole car and wanted a car pre CA smog. This had some smog components but is the last year which does not require a bi-annual smog test. From what I see a 350 can go to 350 hp, big block much over. I would go 1972 just so I could keep out of smog checks and do what I please.

1972 454 270 hp
1976 350 165 - 210 depending on build
1980 350 uncertain

 

yep the late 70s, 80s and 90s gm cars put people to buying japanese cars and by 2009 gm was bankrupt there stock at 85 cents the government took over complete control of there company. Went from in the late 50s from having 52 percent of the entire world market with ford and chrysler making up together another 25 percent of the world market. To gm totally bankrupted.

 

from your parts list sounds like your thinking sbc. After 72 the vette kept gaining in weight was a real porker by 78/79 in 80 they put it on a diet supposedly 250 lbs. If you can find a 74 with the LS4 454 at a decent price go that direction. If not find an 80 model if you want an auto car. Only down side to 80 up is a little weaker rear end not as big a problem if you want an auto car. If your going with a sbc like most end up with get a good exhaust system aftermarket aluminum heads with no more then 64cc chambers a modern cam and use a dual plane manifold.