So I recently bought a 73, it's been awhile since I've been in the horsepower game. I'm looking to do a heart transplant and wanted to stick with a 383 pushing close to 425 HP. I talked with a reputable engine builder today and he didn't really want to back things down to 425, as he said it's the same money to make 550 as it is 425. I'm concerned to go with that much HP as what i read major problems begin with breaking stuff in the mid 400's. What is everyone's experience with a 500+ engine, what have been the major issues, Cooling? Rear ends? Mine has a M20 tranny, do i need to upgrade to a rock crusher? Please talk me into the higher HP engine. I'm looking for reliability and a fun driver

Thank you,
Mike

 

ok the real question here is what your giving up to get 550hp out of a 383... Its likely that you will be giving up some low end torque. for an engine with a higher rpm powerband with a 4 speed this wont be as big of a deal as it would with an auto.

 

I can't answer that, the company that builds these engines is Jensen Engine Technologies in Nescopeck, PA.

 

You can build a streetable low 500’s 383 that has enough vacuum to avoid running a vacuum pump. A 236/242 duration .550 lift roller cam, AFR 195 heads, 10.5:1 compression is a pretty common combo.

low 400’s 383 should almost idle like stock and will have a better bottom end from about 1500-3000 rpm.

I would probably opt for a 4 core aluminum radiator in either case.

How abusive it is on the drive train is up to you.

 

Yes to pretty much all you have listed. You can’t break the laws of thermodynamics, physics and conservation of energy. More power = more heat needs to be dissipated. Your research on the power handling capacity of the driveline is well founded. You can certainly build the components up to handle gobs more but it will take gobs of cash to achieve that.

My L-88 dyno’ed out at 505 HP and 500 lb-ft. I have a TKO-600 and built my differential using Gary Ramadei’s advice and best practices. I have a DeWitt aluminum radiator. I have owned the car for 50 years and have no plans to beat on it. It sounds like a coffee can full of rocks at idle and is a handful when applying all that power. I love the sound of it but it certainly is not a “daily driver”.

If you are looking for reliability and don’t want to worry about overheating and turning driveline components into junk, build your engine to your 425 HP target. You’ll have more than enough power on tap and you’ll not need to take out a second mortgage to beef up everything else.

 

I just finished tuning a customers car with a stock GM ZZ383 425HP, .Auto, 3.23 rear, 3" exh. We added EFI. You really don't need / can't use much more power than that in a street car, and it is very reliable and fun. It has 265 BFGs on it and will smoke 'em in 1st as long as you keep your foot in it. It will not "hook" at WOT in 1st gear. 2nd maybe. It ran 12.90s at Atco on street tires and 11.90s with slicks. Driving it on the street requires careful judicious use of the right foot, but yet it is not overwhelming. The TQ is very good at every RPM. The "mild" GM ZZ383 is very reliable and makes 15" of vac at idle. Yet the exh gives it an authoritative bark. My LT-1 had way more cam, less head, and less TQ and did not pull any where near as hard, but wound up much higher. The ZZ just pulls hard everywhere.

And yet in my own build I built a BBC with 100+ more HP & TQ. Why? ...just because.... I suspect it will not hook up well in 1st or 2nd on street tires....oh well!

If you are looking for reliability with a C3 IRS, once past 400HP just don't put slicks on it, let the tires be your safety fuse. LOL

 

I agree,
You'll always lust for more power.
just don't put sticky rubber on the rear till you have updated the driveline components.

 

Leigh, the answer to your “why” is simple - nothing can compare to a legendary 427!

 

ask your builder about using a 3.875 stroker crank to make a 396 ci. they make more tq than a wimpy 383 and they cost the same to build. mine is about 550 hp. AFR 210 heads, solid roller cam, team G single plane, 1 3/4 hooker headers, three inch exhaust, and tko 600 with 22 pound flywheel.

leigh1322, Automatic transmissions are TQ multipliers and cause take off traction problems. NOT comparable to manual trannies. I had to get rid of my 700R4 when I installed a 650 hp 427 even with 345 width rear tires.

 

The street tires are the safety valve. Slicks will make it much easier to break stuff.

 

So true!
And I have always preferred the extra "control" you have with a manual.

When I autocrossed with 265 slicks, my right foot became both the traction control device and the rear wheel steering device!
And that was with "only" 400HP.

 

With this as your last statement, I'm thinking your looking for a street cruiser with the odd spirited blast down the open road....am I correct?

The 550HP 383 is going to have a larger cam and be designed to reach that power level at 6000-6500RPM and it will be soft at 2000 RPM, whereas the 425 HP version is designed to be more of a street engine and going to be there @5000-5500 RPM while being crisp at 2000 RPM. If your looking for more of a street car, you'll want to choose an engine with a cam with less than 230 degrees duration @.050" so that it has mid range torque.....that is what makes the car fun to drive.

Don't get sucked into the horsepower game and ruin the fun driveability of your new to you car.

Just my 2 cents

 

What he said about the engine is basically true, but the 550HP version will make it's power at a much higher rpm, requiring matching mods & expense in the rest of the drivetrain. So it is still more expensive to you.

The real question here is how do you want to have your "fun"?
From 1500 to 6000rpm?
Or 2500 to 7000rpm? That will require you to get by the doggy 1500-2500 section before it takes off like a rocketship.
So what do you want the power curve to feel like?
A milder power curve is always more enjoyable to drive, and in more situations.
But the stronger power curve is always faster, if geared right, and you have enough room. And it's more "rowdy" so it has more of a cool factor. But it is very hard to stay in it more than a couple seconds without risking your license and jail! LOL
My 400HP high revving LT-1 was an absolute blast on a race course/autocross. It just sang at "full tilt", all the way to 7000.
On the street, not so much. I was "pulling back on the reins" almost all the time, or it was "doggy", under 2800, with virtually no "in-between". That was not as much fun as "letting it loose".

If you want that feel of a highly tuned race motor, with the doggy low end, and you need to apply some skill to nurse it to above 2500, where it really lights up and takes off like a mad-man from there, then you want the 550HP version.
If you want brute strength (torque) at almost any speed, practically from idle, then you want the 425HP version.
It is TQ that makes the low end very easily driveable.

I did eventually get tired of the high revving LT-1, but it took 30 years! I would still have it if I could afford both cars.
Now I am looking forward to the brute TQ of 550ft-lbs at low rpm. And never having to go past 6200.
LS6 454 550# @ 3500 and 500HP @ 5600.
LT-1 350 410#@ 4800 and 400HP @ 6400.
Look at the peak rpms and you see how much "milder" it is.

So only you can answer that question:
How do you want to have your fun?

 

I don’t understand how a 550 vs 425 hp motors can cost the same. Usually bigger intake = more money. Bigger/better heads = more money. I guess the internals could be the same.

 

This pretty much sums up the justification in my mind to build my 427 as a low end ......580 horsepower engine.



I went through several 355s, then the 406 in three versions, and can agree that you will be needing many more upgrades than you realize now. Gears, trannies, tires, cooling exhaust systems,....everything needs to be factored in........if you're going for horsepower.

Now if an ice cream cruise is what you are after.......keep the 350 and cam it small, like the Edelbrock Performer cam. Will pull to 5500 or so and roast the tires anytime with your four speed.

 

One other thing to consider is will the 550 hp 383 run on typical 91 octane pump gas? Around here we can only get 91 octane. I've kind of looked into a 383, 396 and 406 SBC combos for a project.
If it was me I would build a 406 just for the more cubes. Mild cam, Mild compression. Good heads like AFR. Roller cam. Roller rockers. Forged piston and rods. 2800-3000 stall converter.

 

This is also what I was getting at though I did not explain as well. The tradeoff with more hp..
My next engine will likely be a 406.

 

I would go with bigger cubes like the 396 gull was talking about but for me a 427 or a 434 and will be very user friendly for my 69 I am running a 650+ hp 434 that is as easy to drive as my 350 putting out 350 hp so yes on the 427 and 650 hp in a corvette is very fun and then there is this which is another story but very user friendly.

 

Looking at their site, make sure they understand you have limited hood clearance and the oil pan has to fit a Corvette.
https://www.jensensenginetech.com/en...t-engines.html

 

Their 421 looks good