I Currently have my 91 L-98 motor out and am close to machining it to a 383 motor. I am considering scraping the block, getting a Bow-Tie block and going all out to a 420 or 427 CU In. motor. I can't decide if the extra expense is worth the 60 - 80 extra Hp. I am also considering going with a supercharger on the 383 with the $$$ saved on the Bow-Tie block. What is a better chioce for good solid power, torque and an ultra fast vette; a supercharged 383 or a normally aspirated 420 / 427 CU In. motor.

Bruce

 

Lingenfelter has a 420 ci with 236/244 cam that put out 525 hp @ 5500. It had port Corvette heads and ported superram. He does state the you can do this with a stock 400 block instead of the bowtie block.

A supercharged 383 or 420 are both good choices. The real decision is how much complexity you are willing to live with. A NA motor is much easier to tune and maintain. Lingenfelter put together a 383 that put out 607 HP at 6000 @ 11 psi of boost and 8.8 CR. I don't know if he had an intercooler. He states in his book that street car boost is limited to about 7-8 psi (with intercooler ?) using 92 octane. Shalin made somewhere in the low to mid 500s using a stock bottom end 350 with forged pistons, intercooler and 10 psi (I think).

 

A 434 (4" stroke in a bow-tie/motown, etc. block) with a solid roller, 18 degree or some good 215 rr 23 degree heads should be able to make 550-600rwhp pretty handily. NA motors are easier to keep in tune (as was pointed out above) than blower motors, and hopefully will be a bit more reliable (because of the ease of tuning).

A 383 with a blower can also make a ton of power. George baxter has a LT1 383 with a YS trim making 800+ rwhp, running 9.1's - in a 4000lb convertibly 97 SS!. 600 rwhp would probably be in the range of maxing out a S-trim on the motor, a T-trim would take you up to 750-800 max, and after that it's a YS-trim. Don't honestly know if they make brackets for the T-trim - YS trim is all custom for sure. If you get an s-trim make sure you get the Heavy Duty model.

I would suggest a good dyno tune by ed wright or shalin patel with the blower setup, as a good bit of your power is going to be in the tuning. With either setup, but the blower especially you will want to use an in-tank pickup and an aeromotive inline pump for fuel. Larger injectors, new intake, etc. will be required with any of the above combinations.

The real question is what kind of HP levels/performance levels are you looking for, as well as idle, emissions, shift points, etc.?

 

The question is how fast do you want to go? If you're going to build a rock solid 383, the additional cost associated with upgrading to a 420CID is minimal. Economically, I'd build a 406CID and spend the $$$ saved on the crank and bowtie block elsewhere. If you're looking for over 600hp, the blown 383CID is the ticket because you'll spend big $$$ on those 18DEG heads, intake, and exhaust parts for the 420CID. You can build a reliable 540hp 420CID using a stock 400 block machined to use 4 bolt splayed caps and 23 DEG heads.

 

I think the rotating assembly should be priced the same for a 383 or a 420, so the only additional cost should be the 400 block. Heads/Cam/Intake will cost the same for either setup.

I would go with a NA motor , it is easier to tune and will not have the additional stress of a blower.

I have seen Lingenfelter 420 Superram combo's go low 11's all day long.

Vic

 

If your serious, I have a 434 with all the good stuff I need to sell. I sold my project car and don't have a use for it. I never got to crank it, but it will run on pump gas and is estimated at 550+HP and 550+TQ.

 

WOW.... to have your problems :jester :crazy:

 

Bruce,
I chose the Bow-tie option with the 427 SB as the basis for my next motor. The reliability of NA motors was a big factor in the decisions I made. As previously posted, the only additional expense is only in the block directly. The cranks, rods & pistons will be the same whatever you build. Also, the machinist will still need to do the same preparation work, so that will be a wash in the expense.

Where you'll see the biggest gain in going with a better block is that they are designed to go bigger without compromising the strength of the block. A 400 block will not have the wall thicknesses you want for reliability. Beyond that, you'll most likely need to replace the block on the first rebuild, as the walls will be too thin after being punched to 4.125".

The aftermarket blocks also have some nice features to take advantage of. A raise-cam design will let you go with a larger base-circle for the cam. This equates into being able to have a more aggressive cam profile and still run higher seat pressures without twisting the cam into a candy-cane. They also address priority-main oiling, and other features that ensure the engine won't open new "expensive" inspection ports in the side of the block. They have spread pan-rails so the crank swing will clear without notching the bottom of the block.

Running the numbers on my combination with Desktop Dyno, we'll likely see 600+/- HP on 92 octane fuel. My machinist told me his job was to break everything BEHIND the engine. If he doesn't, he's failed. :lol: You can build a good motor, or a great motor...it just depends on how patient you are. The extra $1,800 for the right block will make the difference.

 

Looks like the bigger question for you is staying smog legal-since I see you also are from the smog natzi state! :conehead