Re: Thoughts on the stock 402?
 

A example of stock form 402 performance is we used my wife's 1971 GMC Suburban 3/4 ton 2 wheel drive with 402 and Dana Posi 4:54 rear end as one of our vehicles pulling 1 of our trailers behind it to go to Carlisle 2 years running and it pulled a 12,000lbs load both years through the mountains running 70-75mph the majority of time and we had the A/C on non-stop in 95-100 temps outside. There were 2 sections in the mountain that had such steep long grades we did get slowed to 55-60 on but other than that no issues doing it.
So stock form there strong but they also can definitely have performance boosted.
Paul Sr @ GMCPauls

Re: Thoughts on the stock 402?
 

Go ahead and leave it stock. It will out perform the same truck with a 350/307 by a long shot. Your fuel milage will be terrible, but that should be offset by the huge smile on your face. Mainly because if you are like me, you will not be able to refrain from gunning it several times every time you drive it. Hence the poor fuel milage suffering even more. That is why i have a 350 in mine.

Re: Thoughts on the stock 402?
 

I'm probably the only guy on this board who has built one exactly to stock specifications with the stock heads and cam and dyno'd the thing on an actual engine dyno:

My take-away is that the cam is for tractors. No joke, it's really made to work well with a PTO. So any performance notion will come with a new cam. Then pocket porting the intakes of the little peanut heads. Then you're looking at better heads and intake.

With better heads and intake, it's a fine motor. With the stock cam/heads/intake it set up to idle and make torque.

Re: Thoughts on the stock 402?
 

.
Two bolt 1970 402 block, closed chamber #063 heads ( 101cc ), -15cc dome pistons.

That's all stock...mostly. Then I added comp xr270hr with matching springs, SS valves, proper valve job and setup, roller lifters, roller rockers and the correct length pushrods.

It idles at about 675RPM with a slight lope. Throttle response is IMMEDIATE with enough torque right off idle to pull a house down!

-klb

Re: Thoughts on the stock 402?
 

Those are good numbers Dave for a bone stock 402.
Looks to be close to 330hp on the engine dyno...which is slightly more than GM listed for theirs, which I think was 240hp? or something close to that and then, what....310hp back up to the 1970 rating system.
Correct me if I'm wrong on that.

Anywhooo, with all the accessories on and it installed in the chassis I assume the approximate loss to the rear wheels would be?....what about 20-25%?
Which still leaves you in the mid 200's which is not bad so long as the torque is there.
Interesting stuff! Always good to see some numbers around these kinds of things to provide a good datum point for power and torque requirements.

All good
Coley:canada:

Re: Thoughts on the stock 402?
 

Don't for 410 lb-ft of torque at 3300 rpm. I bet at 1500 rpm it was making 300+. The seat of pants feel has to be immediate. Gotta love a big block.

Re: Thoughts on the stock 402?
 

So what I learned is GMC Paul and Dave are fine with stock. Everyone else ... Not so much. And one member might as well have been talking about how many licks does it take to get to the middle of a tootsie pop because his post had zero to do with the subject at hand haha! I love this board =)

Re: Thoughts on the stock 402?
 

I'm fine with my stock 402. I like the grunt when pulling a 6000 pound trailer.

Re: Thoughts on the stock 402?
 

My 7 year old daughter could figure that out easily I'm sure, however, I did stand next to the 'Everyone else ... Not so much.' group in post #7 thank you very much.

-klb

Re: Thoughts on the stock 402?
 

Tell your daughter to be careful if she tries it. I tried it when I was a kid and ended up getting a raw tongue :lol:

LOL, yeah there were a lot of not so much's haha! What the heck, you never know if you don't ask, right?

Re: Thoughts on the stock 402?
 

I'm not sure exactly what changed on the innards over the 70-72 model years. I've never had a c10 with a 402 but I have owned the following years in that engine in Chevelle SS cars in my life. A 69-396/ 70-402/71-402/and a 72 with a 402. The 4 different cars were all automatic turbo 400 cars and the 70 had headers. Other than that, they were bone stock comparable cars. Grunt wise, the 69 and 70 were both hands down the faster, better performing engines. I only owned those two at the same time. The others were later. The drop in HP was very noticeable in the 71-72 although , I really don't remember much difference at all in the way those two were. Miles were all under 100,000 and none of the engines gave me much trouble. the gas mileage was NO better than 11 highway on any of them. I am like you, I would love to find a stock one that somebody pulled in favor of an LS and put it in my pickup. But I want a 70 model.

Re: Thoughts on the stock 402?
 

The biggest drawback on them is they are not a very efficient engine. Flat out use more fuel. I had a 68 396 SS Chevelle at the same time I had a 69 GTO. Both were T400 auto cars with comparable miles and mostly stock (headers). The GTO would get 16 to 17 mpg and the Chevelle was 11-12 mpg highway.

Re: Thoughts on the stock 402?
 

Yep I agree they are a reliable yet pretty boring motor with poor economy. Once I get the rest of my '72 C20 CS dialed in the way I want it the 402/TH400 with the DNE2 OD will go off to another home and an L96/6L80e will take up residence under the hood. Better MPG and way better SPM with over 360HP and 380FT stock. Once the Computer is reflashed and tuned plus headers and a few other tricks these are not unheard of to get 10% more in both HP and Torque numbers. The best news is I am seeing this combo pretty regularly for under $3000 with under 100K on them. My current has only 84,500. My '06 GTO with an LS2 has 161K on it and runs prefect with no issues at all and still delivers 18-24MPG and lots of Smiles Per Mile!
Bob

Re: Thoughts on the stock 402?
 

Give me boring any day--not that any BBC is boring. I don't want FI, I don't want computers, and I don't want late model.

Just my $.02 (possibly overvalued).

Re: Thoughts on the stock 402?
 

I'm a big fan of simple performance upgrades...ie: cam, head improvement, intake, correct/tuned quadrajet, dual plane intake, etc.

I'm not a fan of the 'full house' performance stuff....too much cam, usually way too much duration (typical), bad holley, etc, etc.....it seems these vehicles have driveability problems 90% of the time.:lol:

As for a 402, I wouldn't mess with it too much...but I would upgrade the cam, and give the heads/valves a 3 angle valve job, port-match them to a quality intake, etc...then tune the hexx out of the factory quadrajet.

Then, I would leave it stock appearing...factory GM orange....noting that the chrome stuff has been to overdone for my taste, but everyone's taste is different and there's nothing wrong with that;)

Coley

Re: Thoughts on the stock 402?
 

The 396 was my first favorite muscle motor. I loved the 66 SS396 Chevelles. I can agree they were anything but fuel effecient but they were fun. For an occasional use vehicle these days I’d still have the old big block with carb and all. For a daily driver it makes more sense to go modern I guess.

Re: Thoughts on the stock 402?
 

Any other thoughts on this cam that was mentioned earlier?:

Comp camshaft 11-106-3 or the GM #3904362.

According to specs, that's the cam used in the L78 or LS6.

Re: Thoughts on the stock 402?
 

My 71 3/4 ton had a factory 402. someone before me had installed hard valve seats in the heads. one came loose and wrecked the engine. It pulled heavy loads Ok. pinged and dieseled on low octane gas. guzzled gas. wasn't the fastest big block I ever owned. I installed a 454 that has lower compression ratio. Better all around. I was thinking of putting the 402 crank in a 454 block and building a 427.

Re: Thoughts on the stock 402?
 

BAM! This quote all day^^. Add headers & full duals & a cross over pipe, if you do anything to this 402 to allow it to breath. Around .500 lift cam-bingo. It should have the oval port heads. The peanut heads will be done at like 4200 RPM tow truck style & take a smaller cam.