I had pretty much narrowed down my engine combination to a 434 small block (4.155” bore by 4” stroke). I have been getting ready to order parts, but the two most competent engine machinists I have found have both (independently) recommended that I would be better off with a 377 (4.155”bore by 3.48” stroke). Their decision is based on the fact the motor is primarily aimed at autocross use and some street driving. They believe the 434’s excessive torque down low will be a problem when coming out of a corner while the 377 will rev to 7500 and be making power at the end of the straights, where you can really apply it. They also have been taking into account the relatively light weight of the Corvette and the fact the 377 will have plenty of torque to move the car.

I am leaning towards the 377 but I am concerned about the street manners of such a motor. To make the horsepower up high, the heads will have to be pretty large (210cc or bigger). Will the car have any umph down low? Will the throttle response be there at 2500 RPM?

Anybody running a 377?

 

The 377 is very popular with the circle track crowd. The stroker motor seems to be the craze for the street crowd today.

I autocross my car on ocassion and built a 388 (4.125x3.625). Most will recommend the bigger ci because the cost is about the small for both and you get the added torque down low from the extra cubes. I had no problem spinning the tires with my old 355, so I didn't think I needed the extra torque down low, although I did add quite a bit going from the 355 to the 388 anyways.

I have a solid roller cam. The lobe separation angle is 112 degrees. This cam has 4 degrees ground into it to improve the lower rpm torque so when it's installed at 108 degrees it will essentially be straight up at 112 degrees. The lift is intake .616"/ exhaust .622" with 1.6 rocker arm ratio. Duration @ .050 is Int. 248 & Exh. 254 . The cam timing events @ .050 are 16 52 63 11. With the standard shift transmission and the 3.90 rear gears I'm running, I've had nothing but a blast running this engine on the street and it has tons of power.

Do you prefer one builder over the other, and have you talked with others that have had work by them to find out about their reputation and knowledge?

Good luck and keep us updated

 

Smoked Tires:

Thanks for the response. Both the engine builders I am talking to are very involved in the local racing scene and have very good reps. The one I have chosen builds lots of motors (half the field) for the vintage stock car circuit. He has a dyno in house so he tests everything. Go to his shop and Earnhardt and Yates motors are lying around. This guy will do all the machining, I will screw the thing together, and then go back to his shop for a dyno session.

Your motor is very similar to what we are contemplating. We have kicked around cam specs close to what you are running. What heads do you have? How is the throttle response and pull at 2500 RPM? Any dyno data? DD2000 is showing a very broad torque curve for this motor.

 

The throttle response is great. I'm running AFR 210cc race ready heads. I haven't had the engine dyno'd, but this is what desktop dyno puts it at:

 

Smoked Tires: Thanks again. The AFR 210 RR's are a leading candidate for us as well. The engine builder would really like to see me in 18 degree heads for this motor. Not sure if I want to get that exotic.

The jpg is too broken up for me to read. What is your peak HP and RPM and what is your peak torque and RPM? I'll also run DD2000 tonight with your cam specs.

 

Exported your jpg and was able to look at it. Very nice numbers!

 

you running a stick or an automatic?

I think I'd still be inclinded to go with bigger cubes - even for AutoX - for more torque (4000 RPM isn't exactly "out of the powerband") especially if you're running anywhere near stock rear gears.

Bigger cubes is likely going to be more fun, with more usable power, and will be more reliable on a tighter budget.

Sure you could build it to scream at 7500 RPM - but why?

 

Im not really into autocross, or know much about it, but i was just thinking, if your stuck between a 377 and a 434, why not go in the middle with a 406 (4.155 bore, 3.75 stroke)

 

My thinking was that if I could just leave my transmission in gear, then I could concentrate on driving my car around the course without worrying too much about my rpms, and requiring less shifting.

I built my engine with all small journals to decrease the surface contact area and thus the frictional losses. By destroking and increasing the rod length to 6.0", I also improved my rod to stroke ratio. With the shorter stroke, my engine has less side thrusting when rotating than a stroker motor, this will also decrease friction as the rod pushes the piston straighter up the cylinder bore vs into the side of the bore. Another advantage to this is that you get less wear in your cylinders for longer engine life

I ordered my Dart block with the 4.125 bore and with the 350 main bearings. My rods are also the small bearing journal size so there is decreased rotating mass.

Nascar runs destroked engines, but they are limited to the class rules like any other racing organization, it'd be interesting if they would still destroke if they could run a larger displacement.

Here's an interesting article that one of the mags put out a while ago called "The 350 Chevy should have built".

 

I think the reasoning is pretty much what SmokedTires has said. You really can't use the power of a 434 coming off a corner so you would have to feather the throttle. At the end of a straight you would like the motor to hang in there as long as possible to avoid up shifting and then down shifting at the next corner. A 377 would have adequate power out of the corner but could hang in there until 7500 on the straight. At 7500 the 377 would be making as much power as the 434 (if you could keep the 434 together at 7500). It's about keeping the car in one gear on the entire course.

 

I'm puting one together now. It's not going to be an all out race setup; just something just for street fun. Another one I'm interested in doing is a 353. This is a 4.155 X 3.25. The same as a 377, except using a 327 crank.
Now before anyone sends me the "bigger is better" emails, and how de-stroking is not the way to go, I like the super high reving type motors and like I said, it's just for fun. I drive my car, a '63 FI conv. anywhere and everywhere, so a little economy doesn't hurt either. Email me in about a month or so and I'll have some G-Tech times for you.
loup1962@aol.com

 

if someone was building a SBC,

why would they
NOT
use at least a 3.75 crank?

 

There is no real reason that I could even imagin for building a destroked motor. Unless your in some class racing.

3000+ pound Vettes are not light. If you have a traction problem you don't have the correct tires.

I have a 7500 rpm 383 ci and now I also have a 7000 rpm 427 ci small block. I'd never build another sub 396 ci motor again.

Your not going to beat the 434/427 small block with a 377 if you have correct gearing. Lets say that motor "A" 377 makes an average of 500 foot pounds of TQ from 3500 - 7500 and Motor "B" 434 makes 520 lbs from 2500 to 6500. The power range is still 4000 rpm wide for both motors. So your logic about not shifting on the end of the straight is flawed. Change the gearing and the TQ monster will win every time.

When it really comes down to it the 4 .125 stroker small blocks are the best all around small blocks. They are the 441-454 small blocks.

Just because some engine shop has some big name motors sitting around doesn't mean anything to me, because BUBBA does not even grasp the theory of how or why it was built.

In local A-X racing one of the fastest cars week after week is a 71 Vintage racing Vette. It has 496 ci of solid roller big block and a 4 speed. He runs a 390 CFM NASCAR carb to limit TQ and HP for A-X and installs a 900+ CFM for road racing

 

I don't really understand anyone's reasoning for going with less cubes than more when it won't cost significantly more. Unless you just want to build a super high RPM motor because it sounds cool, there really is no point to go with less stroke than more.

 

And if you wait long enough for the next Engine Masters Challenge it is going to be engines limited to 434ci. Might learn something!

 

Guys, believe me, I was on the 434 bandwagon. I'm listening to advice from two independent engine builders on the 377. These guys spend a lot of time at the race track and I think I'd be foolish not to at least listen.

The point I think they are trying to make is that 500 ft lbs of torque is unuseable coming out of a corner at 2500 RPM. The 377 would have more than enough torque to spin the tires at 2500 RPM at low speed. DD2000 shows more than 400 ft lbs. The torque band of the 377 could extend to 7500, and that is a 3:1 ratio. On the flip side, you might argue the 434 will do that from 2000 to 6000, again the same 3:1 ratio, and it will have better street manners.

And no, I'm not running race tires. But I am running 315 Kumho 710's in a '66 corvette. Even with a 350 350 and 4.11 gears, I can lose traction in 1st. My biggest problem with my present motor is it gives up at 5500 at the end of a straight. And keep in mind this is an autocross car, not a road racer.

Just looking for pros and cons here. I appreciate the inputs.

 

Cris this statement doesn't jive with anybody that works on real race motors.

but the two most competent engine machinists I have found have both (independently) recommended that I would be better off with a 377 (4.155”bore by 3.48” stroke).

3.480 stroke is a stock chevy 350 length. high quality forged cranks are 3.500..................................4 .250

Smoked tires has a super Bryant crank 3.625 or something like that to get his 388 ci and it's small journal like mine for aftermaket blocks like Motown and Dart.

It's not the ci that determines the mannerisms of a motor. It's the whole A/F system and the cam. I tend to go big high flow heads and a smaller solid roller cam duration to keep it tame.

 

Sorry Gkull, that was me. I actually thought about whether to type in 3.48 or 3.5. Both machinists said they would specify a 3.5" light weight crank. I typed in 3.48" because I thought forum members would recognize the "classic" 377 easier. A 3.5" crank actually leaves you with a 380.

The aftermarket is pretty geared up for this motor. 3.5" crank, 6" rods, and 1.25" compression height pistons are standard catalog parts. This gets you to a zero deck height of 9". Flat tops (-5cc), a 68 cc head, and a .041 gasket land you at 10.5:1 with, of course, a .041 quench.

 

I've driven some low power to weight ratio cars, GoKarts and even road racing motorcycles. They might entertain a beginner. But things that you can drive with your foot on the floor most of the time get real boring in anything, but the slowest of turns.

I out grew hot rodded 383 even though first gear was worthless with my 315/17 inch tires. On an auto-X course I would just drive around in second. I found life after Auto-X and rarely attend SCCA meets. I decided that a higher power to weight ratio was needed.

You actually become a much better driver. Think of real race machines. Very few people can really drive them well.

 

I don't understand why more people don't realize how effective your right foot is as a traction control device. Whether you have 200, 500, or 1000hp, you can still modulate the limits of traction with the throttle pedal. Once you've gained some speed and traction is no longer limited, I can't understand why anyone wouldn't want more power available to them. I've never heard anyone wish they had less power. You'd think that the throttle pedal only works in 2 positions.