1971 402 Big Block

[bigowl]

Hello All -

I have a 1971 suburban with an original 402 motor. Interested in creating more power. The casting number appears to be 3955287.

What are the group's suggestions for more horsepower / performance. An LS swap is a possibility, but I first want to consider what I might do to the original motor and how much more horsepower I can create without a lot of trouble / ripple effects through the rest of the drivetrain, brakes, etc.

I will static drop the vehicle as part of the process.

Suggestions and thoughts welcomed. Thx!

[04ls1gto]

Google BBC builds and there is everything mild to wild. Nice set of alluminum heads, intake manifold, camshaft exhaust and carb will wake that right up

[Average Joe]

I vote to keep the 402!

I'd add a dual plane alum. intake.
Get the timing dialed in. Add a good HEI and play with different springs and weights to dial in the curve.
Small tube headers. Tri Y's ideally and high flow mufflers.
If you dont like carbs get a Holley Sniper or FiTech efi.
If that aint enough, put a bigger cam in it.
Aluminum heads are great but run about 2 grand for a quality set for a BBC.

Just my 2 cents

[bigowl]

Originally Posted by Average Joe

I vote to keep the 402!

I'd add a dual plane alum. intake.
Get the timing dialed in. Add a good HEI and play with different springs and weights to dial in the curve.
Small tube headers. Tri Y's ideally and high flow mufflers.
If you dont like carbs get a Holley Sniper or FiTech efi.
If that aint enough, put a bigger cam in it.
Aluminum heads are great but run about 2 grand for a quality set for a BBC.

Just my 2 cents

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[bigowl]

I was thinking about doing a Holly EFI kit for reliability. How much HP gain am I likely to achieve with these various modifications. The local machine shop had suggested cleaning up / polishing existing heads. How much benefit do I achieve with aluminum heads. My sense is the motor from the factory was around 240 hp net (300 gross) and had a torque rating of 400.
Posted via Mobile Device

[Average Joe]

Originally Posted by bigowl

I was thinking about doing a Holly EFI kit for reliability. How much HP gain am I likely to achieve with these various modifications. The local machine shop had suggested cleaning up / polishing existing heads. How much benefit do I achieve with aluminum heads. My sense is the motor from the factory was around 240 hp net (300 gross) and had a torque rating of 400.
Posted via Mobile Device

I would guess 50-60 more HP. It really depends on how radical you want to go with the cam and intake. The thing to remember here, HP gains usually come with rpm gains. Meaning that 50 HP will likely be 500 or more RPM higher than what is stock.

You could probably go much wilder with cam timing and compression and see 400 HP with your stock heads. However, you will also kill power at a lower RPM if you choose this route. Personally I love low RPM torque and throttle response.

The beauty of aluminum heads is their ability to dissipate heat quicker than cast iron. This allows a higher compression ratio on lower octane fuel. Higher compression, without having to increase cam duration, = efficiency.

Please remember you are trying to push a 5000lb brick here not a 3000 lb drag car. Think low end & mid range torque for max smiles per mile!

[C130Nav]

Drop in a 454 crank for a 427 stroker.

[Dave]

Do you have any pics of the burban? Would like to see it

[bigowl]

Sure - here are a few; it's a recent purchase for me. About to have some work done on it, but not sure if I will do anything with the engine or not.

I had a compression test and 7 of the 8 cylinders show 180 psi. The #1 cylinder showed 105 psi. Wet test showed 125 psi. So, they thought it has a bad ring.

I am not a car guy but the engine seems to run pretty well from my perspective. Has good pickup. One thing I noticed on the highway (in addition to all the debris flying in through the kick panel vents) is that it seems to have an in and out kind of droning noise when it gets about 60 or so. No change in power; but some intermittent change in pitch.

Plans are to static drop, Ridetech shocks, rack & pinion steering, a/c, stereo, Dakota Retrotech gauge, new weatherstripping, new wheels and tires and some cosmetic stuff.

Not sure what to do on the engine part. Kinda want to stick with the 402 engine. Current plan is to add dual exhaust and just see how she runs for awhile. The torque of this engine is fun, and more would be even better.

[LEEVON]

Nice ride, welcome!

[Dave]

Nice clean original burb! You mentioned it was a recent purchase, did you find it within TX

[bigowl]

Spent all its life in California.

[sweetk30]

dont forget bbc if cam swapped from stock = new valve springs with cam kit .

find out what heads you have with casting #'s under the valve covers . 781 or 049 last 3 is great stock large oval port heads with a tiny bit of work .

as said more air in ( cam / intake / maybe efi ) = more power if you get it out faster with exhaust upgrades .

rember bbc make power low to mid and are not rpm monstors .

[bigowl]

I'm not really sure where to look. Here are a couple codes on ledge on the front left of the engine.

Larger letters/numbers: T0308IN
Smaller numbers: looks like 6L190319

Are either of these the codes you are referring to?

[bigowl]

Per my initial post, the casting number I located is 3955287.

[sweetk30]

Originally Posted by bigowl

Per my initial post, the casting number I located is 3955287.

thats the BLOCK

head casting #'s as i said are under a valve cover .