Planning 402 build - help!!!

[GAc10boy]

So, I planned to keep my L6 intact in my '71 but after getting it up and running, I've decided it isn't going to satisfy my every want and desire. I'm looking to build a nice, streetable period correct 402 to match my th350, 3.73 gear, hei equipped swb stepper.

I've found a '71 402 w/ #820 heads and stock from there. Complete motor, pulleys, carb, intake & exhaust manifolds, etc.

After researching here and the chevelle forum, my plans are this:

Keep the #820 heads and stock pistons , etc.
Put the Lunati 60202 cam, lifter, and valve spring kit
Edelbrock Performer 2.0 intake
Edelbrock Performer performer 750 cfm carb
Sanderson small tube headers (I think they're 1 3/4 tubes)
2 1/2 inch Flowmaster 50 exhaust


Questions: should I upgrade to new rocker arms? How much hp should this make at flywheel? Shooting for 375-400 hp at the flywheel.

Thanks!

[72_swb]

I went with the harlen sharp rocker arms and comp push rods. I was getting very little oil to the top end with the stock rocker arms. I think the push rods were 7/16. Oiling much better with the new rocker arms. Im running a 402 with a summit brand intake (dont ever buy) and 700 DP. 280H cam and 373 rear. I think im close to 400HP. Heads were cut for the bigger valves. 10.2 to 1 compression. Im going to switch to a victor jr. I think big blocks love single plane intakes.

[GAc10boy]

Originally Posted by 72_swb

I went with the harlen sharp rocker arms and comp push rods. I was getting very little oil to the top end with the stock rocker arms. I think the push rods were 7/16. Oiling much better with the new rocker arms. Im running a 402 with a summit brand intake (dont ever buy) and 700 DP. 280H cam and 373 rear. I think im close to 400HP. Heads were cut for the bigger valves. 10.2 to 1 compression. Im going to switch to a victor jr. I think big blocks love single plane intakes.

Very nice! Appreciate the run down. Let me know what you find when you switch the intake.

[hugger6933]

Big blocks do love taller intakes! I know this doesn't help much but they really love Dominator carbs as well. I had a 1050 on a Chevelle I could reach inside the car and fire it off and walk away from it and it would idle as long as need be. I know that sounds crazy it was also in a 402 motor I had it street legal but bracket raced it and when I went to that carb, I changed from a 750 DP to that 1050and a SMALLER cam and picked up half a second in the eighth mile!! .5 full tenths Jim

[72_swb]

I agree with hugger. The bigger the carb the more power just that simple. I am actually going to get a 800 DP just had the 700 laying around at the time. It does run fine with the 700 but I know it will make more power with the 800

[myyamr7]

I just got done rebuilding a 402 for my 71, didn't go crazy but the guy at the machine shop says it should be around 350-375hp with what I have. I was just looking for a small upgrade from stock and didn't want anything crazy.
I had to bore the block .030 over and replaced the pistons with stock replacements, file fit rings and had to deck/square the block .007
I got lucky, the block for whatever reason came with a forged steel, cross drilled and hardened crank. It was all in spec, so just polished and new bearings.
I went with the comp cams 1000-5,000rpm range complete kit..cam, lifter, valve springs, retainers, locks, seals, pushrods, etc. The machine shop did a multi angle valve job and shaved the heads .020 The tricky thing was to find the correct thickness head gasket, something a lot of people overlook. I bought the felpro gasket kit and the head gaskets compress at .043, the OEM gaskets compress at .022 So not only would I have lost what I gained by shaving the heads, I also increased the area between the piston and the flat surface of the head had I used the felpro gaskets...which is not the best thing for an engine. After some research, I found that Mr Gasket makes a steel shim gasket that compresses at .020, which is exactly what I was looking for.
No plans for anything fancy as far as carb or ignition go, using an OEM 402 carb on a Weiand intake, and a Malory HEI

[FRANKENSTEINC10]

standard or auto?? if auto make very certain that you have the proper flywheel/flexplate. I an putting a 454 in mine and went out on Sunday to bolt the t. c. to the flexplate and this one only has mounting holes for the 400

[FRANKENSTEINC10]

Originally Posted by myyamr7

I just got done rebuilding a 402 for my 71, didn't go crazy but the guy at the machine shop says it should be around 350-375hp with what I have. I was just looking for a small upgrade from stock and didn't want anything crazy.
I had to bore the block .030 over and replaced the pistons with stock replacements, file fit rings and had to deck/square the block .007
I got lucky, the block for whatever reason came with a forged steel, cross drilled and hardened crank. It was all in spec, so just polished and new bearings.
I went with the comp cams 1000-5,000rpm range complete kit..cam, lifter, valve springs, retainers, locks, seals, pushrods, etc. The machine shop did a multi angle valve job and shaved the heads .020 The tricky thing was to find the correct thickness head gasket, something a lot of people overlook. I bought the felpro gasket kit and the head gaskets compress at .043, the OEM gaskets compress at .022 So not only would I have lost what I gained by shaving the heads, I also increased the area between the piston and the flat surface of the head had I used the felpro gaskets...which is not the best thing for an engine. After some research, I found that Mr Gasket makes a steel shim gasket that compresses at .020, which is exactly what I was looking for.
No plans for anything fancy as far as carb or ignition go, using an OEM 402 carb on a Weiand intake, and a Malory HEI

hahaha. he didn't go "crazy"!! says the guy that took the time and effort to find the perfect head gaskets! love it.

[hugger6933]

There is a difference between ocd and obd[overbuilding disorder]

[FRANKENSTEINC10]

lol. yeah I agree. I used a toothbrush to clean my overflow coolant bottle

[GAc10boy]

Originally Posted by hugger6933

Big blocks do love taller intakes! I know this doesn't help much but they really love Dominator carbs as well. I had a 1050 on a Chevelle I could reach inside the car and fire it off and walk away from it and it would idle as long as need be. I know that sounds crazy it was also in a 402 motor I had it street legal but bracket raced it and when I went to that carb, I changed from a 750 DP to that 1050and a SMALLER cam and picked up half a second in the eighth mile!! .5 full tenths Jim

Thanks for the feedback! I'll have to look into the 1050.

Originally Posted by 72_swb

I agree with hugger. The bigger the carb the more power just that simple. I am actually going to get a 800 DP just had the 700 laying around at the time. It does run fine with the 700 but I know it will make more power with the 800

Nice! Let me know how it goes once you make the change.

Originally Posted by myyamr7

I just got done rebuilding a 402 for my 71, didn't go crazy but the guy at the machine shop says it should be around 350-375hp with what I have. I was just looking for a small upgrade from stock and didn't want anything crazy.
I had to bore the block .030 over and replaced the pistons with stock replacements, file fit rings and had to deck/square the block .007
I got lucky, the block for whatever reason came with a forged steel, cross drilled and hardened crank. It was all in spec, so just polished and new bearings.
I went with the comp cams 1000-5,000rpm range complete kit..cam, lifter, valve springs, retainers, locks, seals, pushrods, etc. The machine shop did a multi angle valve job and shaved the heads .020 The tricky thing was to find the correct thickness head gasket, something a lot of people overlook. I bought the felpro gasket kit and the head gaskets compress at .043, the OEM gaskets compress at .022 So not only would I have lost what I gained by shaving the heads, I also increased the area between the piston and the flat surface of the head had I used the felpro gaskets...which is not the best thing for an engine. After some research, I found that Mr Gasket makes a steel shim gasket that compresses at .020, which is exactly what I was looking for.
No plans for anything fancy as far as carb or ignition go, using an OEM 402 carb on a Weiand intake, and a Malory HEI

Nice build! Throw a good intake manifold, a set of small tube headers, and a good carb and really capitalize on all that attention to detail.

Originally Posted by FRANKENSTEINC10

standard or auto?? if auto make very certain that you have the proper flywheel/flexplate. I an putting a 454 in mine and went out on Sunday to bolt the t. c. to the flexplate and this one only has mounting holes for the 400

It's an auto - th350.

[truckdude239]

Roller cam is all i want to add if your doing it xo it right and with a roller cam no worries about wiping a cam lope

[ho70]

look at what the factory 70-71 Chevelle 396 (402) used and use them as a guideline. Some modifications work against each other. 70-71 396 Chevelles were fast

[GAc10boy]

Originally Posted by ho70

look at what the factory 70-71 Chevelle 396 (402) used and use them as a guideline. Some modifications work against each other. 70-71 396 Chevelles were fast

Thanks! As of right now, this appears to be a relatively stock '71 Chevelle motor. It needs a cam and lifters (says the owner) so I thought I'd go ahead and update a few things before I put it in.

[FRANKENSTEINC10]

youre gonna want to absolutely sure that you have the correct flexplate! you don't won't to be like me and get finished building your engine, and rear end then you can't go out and drive your truck. the stock plate for my 454 doesn't have the th350 mounting holes. good luck and keep us posted.

[GAc10boy]

Originally Posted by FRANKENSTEINC10

youre gonna want to absolutely sure that you have the correct flexplate! you don't won't to be like me and get finished building your engine, and rear end then you can't go out and drive your truck. the stock plate for my 454 doesn't have the th350 mounting holes. good luck and keep us posted.

Thanks, I'll definitely keep that in mind. Where did you source yours? Were most of theses engines backed by a th400?

[FRANKENSTEINC10]

not sure on the 71, bit i know mine was. eBay has been a pretty good source so far. just make sure that the description says it has the bolt pattern for the th350 and the th400.

[Oly72C20]

Great info on here! I too have a 402 and will be watching this for future info and ideas when I'm ready to build.

Joe