Thoughts on the stock 402?
 

So been reading through the threads tonight and was surprised to read a few thoughts on the 402's in our trucks that were less then stellar heh.

For the most part I'm not really a performance guy when it comes to our trucks. Seems to me with maybe an upgrade to HEI and a good tune the 402 should be a perfectly acceptable engine. Am I way off?

Re: Thoughts on the stock 402?
 

A 402 is basically a 0.030 over 396 and was I think 310 or 320 horsepower pre-1972 re-rating to net hp. What's not to like? Good power band and plenty of torque.

Easiest and cheapest big block to build. I am currently doing a Mopar and a nailhead in other projects - parts are double on the Mopar and triple on the nailhead.

Re: Thoughts on the stock 402?
 

Those 402's are Strong.
I almost lost a drag race 30 years ago
because :lol:

Re: Thoughts on the stock 402?
 

If you are just putting around with a now and then romp on the pedal, then the 402 is ok. Any real performance then pick up 50+ more cubes and build that for the same cost. When I pulled the 396 out of my 68 and built a 454 for it the difference was night and day

Re: Thoughts on the stock 402?
 

I had a 454 in my last K20 and it was pretty stout engine even though it had a lot of miles on it. Livrat built it and he did a really great job.

I have a low mile 402/400 combo and was thinking that it would be a great engine with minor upgrades ... Not going in to the internals at all. I was surprised that some didn't think much of the engine.

Re: Thoughts on the stock 402?
 

I have one in a 72 that I bought and want to keep it as the power plant when I fix the truck. It runs well but certainly not real robust in its stock performance. I will be researching ways to get it's performance up.

Re: Thoughts on the stock 402?
 

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I'm real happy with the 402/396. In 1970 truck stock trim they weren't much to get excited about, but it doesn't take much to wake them up: intake, headers, cam and some proper tuning.

In my case, I wen't crazy with the roller setup! but that's not necessary.

-klb

Re: Thoughts on the stock 402?
 

I really love my '72 and it is a very well optioned, clean, solid Highlander.
However, if there is one thing I could have changed in the option group....it would have been to have had the big block 402 in it in lieu of the current 350.
That would make the truck darn near perfect in my opinion.

....gotta love that extra torque.

All good
Coley

Re: Thoughts on the stock 402?
 

Not an expert on motors and such but I would imagine you can make a 402 perform very well like all the rest of the big blocks if you wanted to.

Re: Thoughts on the stock 402?
 

396/402 is a hell of an engine , the truck version came with a wimpy cam , everything else about it , including the great heads that they came with is great , much better engine than a junk 220 horse 454 with peanut port heads , put an rv cam in there , 260 or 268 , and it will really wake up , your rear tires will hate it

Re: Thoughts on the stock 402?
 

Amen on the stock cam!!! The stock cam in my 396 had the groove cut in the rear journal. I thought that cam was only used in 65 and 66 engines, because their different oiling setup...not so... That cam was used after 66 for at least a couple of years (according to my engine builder, who's experience is second to none...):metal:
Any way that stock cam was used in likely every stock low performance big block made from 65 till likely 68 or 69...it's performance was very lackluster. Any good aftermarket cam would make it seem VERY weak in comparison.

a 260 or 268 High Energy cam would make a world of difference, however I do not favor the XE cams...:smoke:

Re: Thoughts on the stock 402?
 

I have been dealing with big block chevy engines just about all of my life until the LS engines came out. One thing to consider is this; if you are going to build it to run it hard. You need to run 6 quarts of oil in it, because the big blocks had the high volume oil pumps in them and the pump would keep all of the oil up in the top of the motor. Performance wise would be to put you a 454 450HP cam and lifters in it with a good Quadrajet carburetor. JMO. The 402's are good engines.

Re: Thoughts on the stock 402?
 

I just bought a 72 402 for my 70. Looking to do some upgrades as well. Has good compression so was just thinking a new cam and lifters. Any brand recommended? What's preferred, the 260 or 268?

Was thinking about this: https://www.jegs.com/i/COMP-Cams/249...791+4294829790

Re: Thoughts on the stock 402?
 

Do you know what the compression ratio is on your 402? What heads?

My 68 396 was a high compression engine. I couldn't put much timing in it because of such. I used some octane booster in it a couple of times, that helped. Whenever I get it back together, I plan to go with different heads to lower somp ratio, some...

I know that the Competition Cams 268H High energy cam (NOT the XE version) should work. There's many modern cams on the market these days, some are good, some ARE not. BUT your true compression ratio needs to be known before buying a cam...Hylift Johnson lifters are THE best. You will have to buy them direct. They are a little more expensive, but are by far the best quailty, American Made!!!

Re: Thoughts on the stock 402?
 

Look at the Comp camshaft 11-106-3 or the GM #3904362. The GM camshaft is the one I always ran, because I worked at a auto parts supply house for 13 years and I got them with a discount. The Comp cam should be just as good. A lot of people do not like this type of camshaft because it is a solid lift cam. I used what we called back in my days was poly locks, rocker lockers. (Rocker stud nuts with set screw inside of the nuts.) You should pick up a good 50-75 hp from the cam swap and using a 750 CFM quadrajet carb with headers.

Re: Thoughts on the stock 402?
 

It's a completely stock 72 402, so I believe it was 8.5:1 that year.

Re: Thoughts on the stock 402?
 

If purchasing either of those cams, should I replace the lifters and/or rockers?

Re: Thoughts on the stock 402?
 

Yes, anytime you replace a camshaft you need to replace the lifters unless it is a roller cam.

Re: Thoughts on the stock 402?
 

Put a new timing chain and gears. I have had 2 different 402s timing chains fail.

Re: Thoughts on the stock 402?
 

So far all ive read is that its potentially a good engine. None of you seem to like it in stock form.

Re: Thoughts on the stock 402?
 

great engine in stock form 310 hp and 400 foot pounds , but with a cam upgrade it is crazy good , might as well go thru it , new gaskets , timming chain [a must ] and springs to match the cam , and you have a monster

Re: Thoughts on the stock 402?
 

I saw a "but" in there haha!

Re: Thoughts on the stock 402?
 

My 402 was rebuilt in 1993 with rebuilt heads off a 396 HP (i.e. Corvette). Word is 10/1 compression instead of 8.5/1. High RPM cam and an HEI. Somewhere around 350-375 HP.

40K miles and many decades later it runs like a top. At least it did, I put it in hibernation 2 years ago. Didn't use any oil despite some leaks, but then I didn't drive it much. Oil is always clear.

Stock gears, a 402 is unimpressive off the line. But gives a nice chirp when it shifts into 2nd. Great response all the way around, Highway is very impressive. One of the cool things about these BBC is they gain speed going uphill without more acceleration. At least that's been the case with my SWB "sport truck". My other 402 is tired, its pulling a C20.

Only downside about old BBC is they're on the downhill slide after 60K. Maybe with today's synthetics and an HEI they'll go longer. 100K its time to think rebuild, but that's true for a SBC as well. That and gas miles is 8-12ish.

Great engine IMO. They look great, what's not to like............This isn't my truck, but it's somewhat the goal.

Re: Thoughts on the stock 402?
 

I built my 402 with the following specs; bored .30 over, Comp Cams 268H cam, lifter, springs and retainers in 1966 Impala 396 heads with a 3 angle valve job, double roller timing chain, performer intake and Edelbrock 750 carb. Runs like a raped ape!

Re: Thoughts on the stock 402?
 

In my day the word "BIG BLOCK" meant power. So go ahead and have a little power. (FUN) I keep saying in my day. I am 64 years old and I still love power from these old rides. I have had a few super rides in my life since I was 18 years old. Oh, the stories I can tell. I know this is a tread about the 402 big block, but the big block is the thing of the past in my book now. The big blocks where the power from the past, but the LS engines are far more powerful and better engines than I have ever known in the past. There are so much power from just stock engines than most build engines from the past. LS engines are the way to go now!!!!!! Performance and fuel efficient. JMO again.
I have now restored a 1985 Silverado with all of the new commodities from the new rides added. I'm also about to start on a 1972 with a 5.3 LS engine and transmission. Happy motoring.

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