Power difference between stock 1969 396 vs 1972 402?

[jumpsoffrock]

I'm just asking this as a random curiosity.
Because they had EPA regulations and changed from Gross ratings to Net ratings, is there a real tangible power or performance difference in these two engines if they were factory stock, hot off the assembly line? Was the 1972 version actually detuned?

Could a 1969 truck be able to pull more weight and faster than a 1972 truck with the 402?

[72c20customcamper]

Object of going to 402 was to avoid detuning and emissions . All engines over 400 ci had less requirements. I dont think you would notice a difference between the two. Even AMC made the 390 into a 401 .

[davischevy]

Mark is right, and there is no way to get either of them to run like a big block Chevy should without changing heads.

[jimijam00]

Originally Posted by davischevy

there is no way to get either of them to run like a big block Chevy should without changing heads.

500hp was easy to achieve on the L78 with just a cam, manifold, headers, and a carb tune.

[davischevy]

Originally Posted by jimijam00

500hp was easy to achieve on the L78 with just a cam, manifold, headers, and a carb tune.

Yep, one of my favorite engines, but those square port heads weren't really ideal for everyday driving in a truck. They were designed for higher RPM.


I used to watch a 69 Chevelle SS with the setup you speak of, running a class called showroom option, pull the left front wheel off the ground one every run.

That Chevelle is still around with the original engine in it.

[72c20customcamper]

Originally Posted by davischevy

Yep, one of my favorite engines, but those square port heads weren't really ideal for everyday driving in a truck. They were designed for higher RPM.


I used to watch a 69 Chevelle SS with the setup you speak of, running a class called showroom option, pull the left front wheel off the ground one every run.

That Chevelle is still around with the original engine in it.

Ya they didnt run like this stock
https://m.facebook.com/story.php?sto...09713&sfnsn=mo

[davischevy]

Originally Posted by 72c20customcamper

Ya they didnt run like this stock
https://m.facebook.com/story.php?sto...09713&sfnsn=mo

If that sound don't get your blood pumping, you need therapy.

[special-K]

The light truck 402 was an L-47, rated at 310hp 70-72. The '69 396 was an L-66 also rated at 310hp

[davischevy]

The 402 in my Longhorn got tired. I could have built the 402, but it costs the same to build a 454.

We bored the 454 .040, used 781 heads and installed a full roller valve train. It idles smooth and has tons of torque. Now it breathes free. It no longer feels "smothered".

[kwmech]

Originally Posted by davischevy

The 402 in my Longhorn got tired. I could have built the 402, but it costs the same to build a 454.

We bored the 454 .040, used 781 heads and installed a full roller valve train. It idles smooth and has tons of torque. Now it breathes free. It no longer feels "smothered".

I can attest to same thing with changing out the 396 in my 68 with a 454. No comparison in power, the 454 pulls like a freight train. AND I got rid of the headers and went with cast iron and a single 3'' exhaust. I can just about blow everybody away on the hills around here even with a 2000# pallet of block in the back

[jumpsoffrock]

^^^^.....And see, how will that much power be if my truck has an sm465 and 4.10 gears(she's a 1 ton) and I plan on daily driving it in the rain.
Would your kind of torque be usable in that situation, or a hazard?

I bought this truck to use as a work truck that I can/will daily drive.

I'm afraid of spending 2-3k on building an engine and ending up with a useless "work" truck that won't keep traction without a ton in the bed.
I was hoping to build a 502 if I decided against reusing my 402.

[57taskforce]

Originally Posted by davischevy

The 402 in my Longhorn got tired. I could have built the 402, but it costs the same to build a 454.

We bored the 454 .040, used 781 heads and installed a full roller valve train. It idles smooth and has tons of torque. Now it breathes free. It no longer feels "smothered".

My experience is very much the same even with the 454. In stock form 90% of them are dogs from the factory. 96-99 vortec 454’s are a great example… tiny ass cams that are retarded from the factory, and heads/intake that really don’t flow crap above about 4,500 Rpms…. Peak torque is between about 3500-4500 right where it don’t breathe the best. Gm really used all their decades of power train engineering experience to its full advantage there… I’ve got a vortec 454 on the stand that’s just waiting for parts to go back together. Trying to convince myself I don’t need another 6-700 Hp monster to go with the 402 stroker LS I’m building. Most of the 454’s were pathetic from the factory (certainly the early 70’s chevelles and similar for example don’t fit this bill) in my opinion mostly because of smog the era stuff they had on them. If they had been around in the early to mid 60’s I bet we would have seen some nasty factory power from them.

[kwmech]

Originally Posted by jumpsoffrock

^^^^.....And see, how will that much power be if my truck has an sm465 and 4.10 gears(she's a 1 ton) and I plan on daily driving it in the rain.
Would your kind of torque be usable in that situation, or a hazard?

I bought this truck to use as a work truck that I can/will daily drive.

I'm afraid of spending 2-3k on building an engine and ending up with a useless "work" truck that won't keep traction without a ton in the bed.
I was hoping to build a 502 if I decided against reusing my 402.

I'm running a 465 with an AA Ranger Overdrive, 3.73 gearing and a power-loc. does not feel like it wants to get away from me unless I want it to. I am actually restricting it some with a 650 edelbrock. I have a 750 on my flatbed and it will lite up the duals from a standing stop with a T400 and gear vendor

[Accelo]

"is there a real tangible power or performance difference in these two engines if they were factory stock?"

Max is 6hp, if they made 1ph per cubic inch which they didn't .
So I'll give it 4 to 5hp difference. Or 1.3% if you use the 310hp rating.
Withing the margin of error on most dynamos.

[davischevy]

Because I didn't want to run a stall converter in the 700R4, I didn't put a lopey cam in mine. It idles smooth as silk. Running 3.73 gears, it doesn't feel finicky at all.

If you stand on it it will get out of the way.

[jimijam00]

Originally Posted by 57taskforce

Most of the 454’s were pathetic from the factory (certainly the early 70’s chevelles and similar for example don’t fit this bill) in my opinion mostly because of smog the era stuff they had on them. If they had been around in the early to mid 60’s I bet we would have seen some nasty factory power from them.

I think it was 72 or 73 when the Chevy big blocks got their balls snipped.

[davischevy]

Originally Posted by kwmech

I can attest to same thing with changing out the 396 in my 68 with a 454. No comparison in power, the 454 pulls like a freight train. AND I got rid of the headers and went with cast iron and a single 3'' exhaust. I can just about blow everybody away on the hills around here even with a 2000# pallet of block in the back

First of all, I am very fond of the Ram Cummins.

A few years a friend of mine was going hunting in the Rockies, pulling a four horse trailer with living quarters in it behind his Ram/Cummins.

On the climb out of Denver west on I-70 he caught up with a 72 Chevy pulling a good size travel trailer. My friend struck up a conversation with the guy on the CB. After a couple of exchanges on the CB he passed the 72 Chevy. When he got around he made some comment on the CB about a gas rig not pulling like a Cummins. The guy in the 72 asked what he meant. My friend made some comment about pulling away from the big block Chevy. The guy in the Chevy came back with "Oh, I didn't know we were racing.".

My friend said he looked in the mirror just in time to see that Chevy freight train him. They pulled over at the top, and the guy had twin turbos on the Chevy.

[57taskforce]

Originally Posted by davischevy

First of all, I am very fond of the Ram Cummins.

A few years a friend of mine was going hunting in the Rockies, pulling a four horse trailer with living quarters in it behind his Ram/Cummins.

On the climb out of Denver west on I-70 he caught up with a 72 Chevy pulling a good size travel trailer. My friend struck up a conversation with the guy on the CB. After a couple of exchanges on the CB he passed the 72 Chevy. When he got around he made some comment on the CB about a gas rig not pulling like a Cummins. The guy in the 72 asked what he meant. My friend made some comment about pulling away from the big block Chevy. The guy in the Chevy came back with "Oh, I didn't know we were racing.".

My friend said he looked in the mirror just in time to see that Chevy freight train him. They pulled over at the top, and the guy had twin turbos on the Chevy.

Turbos on big displacement can mean stupid power if done right. I have no doubt that Cummins got its ass handed to it. That Cummins is nearly impossible to beat as far longevity and durability go. I’ve built a ton of 5.9’s from the ground up, they are very remarkable engines in simplicity, durability and longevity. We’ve got several 12 valve 5.9G compressor engines that have 15+ years of 24-7 runtime that have never been rebuilt. 90% of the 40-50+ I’ve built didnt need to be bored, just a .005 cleanup hone and run it again. I do wish the 5.9 had gotten wet sleeves like 8.3 and 855 did though.

[geezer#99]

Buddy of mine had his ‘74 Chevy ugly truck’ (his name for it) set up with a 12.5 to 1 454 with rectangular port heads and the old LS7 cam. Ran a turbo 400 and 4.10 gear. It got on the cam and really started to haul the mail at 3500. Pulled his fifth wheel holiday trailer.
Surprised a lot of folks when he’d pull out to pass uphill.

[davischevy]

My Longhorn has a 454, now it needs a posi trac.

[davischevy]

We have a late 69 dated 412 LS6 block in the storeroom. I don't know what happened to the heads.

A friend of mine bought a new 70 El Camino LS6. This engine came out of it. I wish I had the car. He special ordered it hugger orange.

[jgr]

basically, it is the same motor you would not notice any difference between the two. both are awesome motors. There is nothing like a BBC you will never go back to a small black LOL