improvements to a 402

[ls70918]

OK, As I posted on an earlier thread, I'm no mechanic. I know a little, but there is a lot more I don't know.

So I have a 70 GMC Sierra Grande with a 402. At this point everything is stock. I want to change the intake manifold and carborator (and possibly put headers on it) to improve preformance.

I have to watch my budget so I'm not looking a super high-end stuff. I was thinking about an Edelbrok proformer intake. I'm not sure about the carborator yet. A friend has told me to stay away from Holly. And it looks like there are a ton of headers out there, makes, diamater, etc.

I'll take any and all suggestions. Try to keep it simple. . . I can lift heavy things, but I might have a hard time following some of you guys.

[67ctener]

I also know squat about motors... I do know Sanderson makes 67-72 big block headers that I've read are nice and fit well. I will also be running a 402
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[Littletony]

You need to let everyone know what you are going to use the truck for. Are you going to race it, tow with it or trying to just bet better gas mileage. That way they can give you a better ballpark on what you should use.

[kaycee]

I would post this in the engine/drivetrain section or maybe the performance section of this forum board

[ls70918]

My truck is a 2 wheel drive all stock 1/2 ton. I would like to be be dependable daily driver with some kick. I thought that eventually I'd drop it about 2-3 inches and level it out then through some nice wheels on it.

[GASoline71]

Your friend that told you not to get a Holley doesn't know how to tune one correctly is all. The main problem with a Holley is that they are infinately tuneable. So some cats will go a little too far and then not know how to get it the way they want it. Holley has realized that over the years and came out with the "Avenger" series of carbs that are a little more forgiving to the carb novice.

Holley is the best carb out there. Edelbrock carbs have a good following here, and are a decent carb. I personally don't like them. You could reuse the old Q-jet thats probably on the truck now. Just make sure it is rebuilt by someone who knows what they are doing. The Quadrajets are great carbs.

Just remember that doing all this to a 40 year old stock engine might not give you the boost in performance you think it will. It will help... but don't look for it to slam you back in the seat.

[bronze 72 super]

Just my 2 cents worth. I have to agree with Gasoline 71, on the Holley Carb. I have used Holley's for over 30 years and have had very little problems with them. Had one I run for over 20 years on a small block in my old '70 Chevelle. Car had over 200,000 miles on it when I finally sold it,(bad mistake '70's took off in value). A good hand held vacuum gauge works wonders on tuning a Holley. Q-Jets rank right up there too. Very good carb, just make sure it's been rebuilt my someone who knows what they are doing. Don't think much of Edelbrock carbs. Had new and used ones, don't tune up as nice as a good old Holley! Stay away from headers, run them for years, hassle to maintain.Stay with stock exhaust manifolds, lots easier to maintain. Good luck.

[So.Cal.Super]

I have to agree with Gasoline and bronze, Any Carb Needs to be sized and tuned correctly. I have had 3 since I bought my 72 with the 402. The 600 cfm edelbrock that was on it when I bought it ran it, but was starving. I had the q-jet for the truck so I had it rebuilt and tuned, swapped it out and she ran great.
I picked up a 770 avenger from a board member and had it rebuilt and tuned by my same carb guy and he warned me I wasn't going to be happy. I tried it for a few weeks and went back to the Q. Tuned right it's better on gas (if you don't start romping on it because your going to want to hear that 402 the intake and headers will make her breath so much better) I went with edelbrocks intake and full length dougs. I will need to make changes when I lower it for more clearance . I also did a cam kit but due to lifter failure a year later I'm building a 496 now. Like Gasoline also said. your only going to get so much out of that 40 year old motor.

you didn't mention exhaust, are you upgrading that when you do the headers or is it already done?

[ls70918]

It has dual exhaust now with some kind glass packs (i think)

How much do you think it will cost to change out the cam. I'll be paying someone to do it.

[So.Cal.Super]

Not sure on the cost, but your going to do lifters and valve springs at the same time. I will never use edelbrock lifters again. the clips in several of mine broke and ran through the cam. My new setup is isky roller.
How many miles are on the motor? your heads might be close to using an overhaul. Thats the problem with tinkering with a 40 year old engine. you can open up a whole new can of worms as you find the weak link.

[cjb70chevy]

if this is just a daily driver, i would just stay with stock manifolds, you can actually get a little more torque from a stock motor. but if your searching for sound and really want headers, just choose wisely. and i have heard from hundreds of people havn problems or always tightening them up. if you use copper gaskets your gona be tightening them up. i have always used just standard stock manifold gaskets. i've had my 70 chevy for over 2 years now, i put hooker comp headers on mine, and never had a loose bolt or had constantly tighten them up.

[hugger6933]

I wiil have to say that the Holleys are great carbs but I also love my Edelbrocks as far as setting and go for a ride,. The Holleys seem to be more sensitive to weather changes and such than the Edelbrock, I have often told ones that seek my advise is you want o runfast Holley if you want to ride go Edelbrock if you want economy go with a Quadajet. Now for a general hop up in the little big block with nothing special just more power and torque I say get a Comp cam 268 h cam Edelbrock performer rpm intake and a Edelbrock 750[#1407] and probably a mid length runner tube on the header, and they must have thick flanges to prevent leaking. Enjoy your new found power!!!