House power from a 402 - Impala Tech
Performance Our High Performance Area

LinkBack Thread Tools
post #1 of 5 (permalink) Old 06-26-2014, 08:44 AM Thread Starter
Join Date: Jun 2014
Location: Titusville
Posts: 2
House power from a 402

I'm a novice to mechanical Issues. I just purchased a 1971 Impala with a 402 big Block. I'm rebuild the engine and adding a few high performance parts like a bigger cam, roller rockers, bored over 40, original heads valve job shave down 20, high rise intake, 750 Harley carb, 3200 stall. Compression should be 9 To question is how mUch horsepower can I realistically expect
1971lmpala_fla is offline  
Sponsored Links
post #2 of 5 (permalink) Old 06-26-2014, 09:42 AM
Join Date: Jan 2006
Posts: 12,362
With the stock heads you will be making about a bit more than stock power. It is the heads that makes the power. The cam tells you where you will make the power in the RPM band. With a bigger cam you can make more peak horsepower but it will be so high in the RPM range that you will not be able to use it on the street.

The only thing you have done to raise the horsepower over a stone stock motor is to make it marginally bigger. The greatest contribution to power was made by your raising the compression from the stock 7.8:1 compression ratio to 9.1:1. Bigger valves in your stock heads would also increase your power levels.

You have to keep in mind that it isn't horsepower that you want unless you are planning to take your car up on the high bank oval track. To accelerate your car you want to make gobs of torque. This is why the 406 SBC is so popular. It makes more horsepower than your BBC 410 (40 over 402), but the same torque because it has the better head found on the SBC, and does so for less money.

Torque is made by cubic inches. If you choose to make those cubes by relying upon a longer stroke you will make more torque than if you where to increase the bore spacing to maximize the bore to make the same cubes.

An example of this is the 496 which was the last production big block made to compete with light diesels in pick-up trucks. The 496 was a 454 engine with a quarter inch longer stroke crankshaft (it also used bigger, to fit on top of a Gen V big block, LS-1 heads with dedicated EFI). Chevy also offered a 502 which is about the same displacement, but makes it's power by boring out the motor to a 4.5 inch bore. The 496 pulls like a diesel. It makes lots of torque, but slow reving with all of it's power made below 4,200 RPM. The 502 made more horsepower, but less torque, and had to rev to 5,400 RPM to make that power.

This is why the 496 is so popular (it is the 383 of big blocks). The best big block that makes the most power for your money is the 540. It has the big bore and long stroke that can be assembled from off the shelf parts. Go bigger and the price doubles quickly, but bigger is better with a big block motor.

Big Dave
Big Dave is online now  
post #3 of 5 (permalink) Old 06-26-2014, 11:58 AM
Senior Member
Join Date: Jun 2014
Location: San Jose, CA
Posts: 279
On this one I am with Big Dave.
You will be $5-6k into the engine and still be at 400hp at the crank and not more than 300hp at the wheels. (Unless you can find a 427 crank and stroke it, which is damn near impossible).
Save your money, hit Craigslist, for the same amount that you are gonna spend on this engine you can find a monster that puts out upwards of 500hp. In my area there was couple of real nice roller 454's fresh rebuilt carb to pan for about $5-6k.
67SS is offline  
post #4 of 5 (permalink) Old 06-26-2014, 12:12 PM
Senior Member
Join Date: Apr 2010
Location: Monroe NC
Posts: 1,094
Ah the 71' 402 nice, but from my post's I'm a little biased to them. Nice little engine, back it with a 4sp auto or manual and a 3.73 and it's a good blvd. cruiser.
X2 with Big Dave.
68imp is offline  
post #5 of 5 (permalink) Old 06-26-2014, 11:30 PM
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,129
Blog Entries: 15
3200rpm stall on those stock heads seems like an odd combo to me.
I'm not as experienced as others here on the Big Block so my opinion is worth about a nickel.
I didn't see any details on the cam, nor if you had headers, what size, or stock exhaust manifolds but I would be surprised if your 402 was making more than 350-380hp.
Like they said, you want torque on that big car anyway.

BA. is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Impala Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome