Hey i finally got the number off my block...its 3999290....it says its a 1972 402.....and its rated at 240hp....is this why my car seems slow?.....i'm going to put it on my buddies dyno this week....I didn't realize that these motors came below 325hp...is this correct?? :confused::confused:

The block has nothing to do with it's power output. If it's build it to stock `72 specs (same cr, cam, carb, distributor curve, emission control, etc.) it should make around 240 NET hp. If built it to earlier L34 (396/350) specs it should put out around 350 GROSS hp. (At the flywheel, at the wheels will be less).

YES,CORRECT,THE 1972 LS3 402 HAD LOWER COMP AND THE SAME MILD FLAT TAPPET CAM LIKE THE 396/325HP HAD.

The 325hp had 10:25:1 comp and your motor is approx 9:0 comp .

But they were also rating the motors @ NET/NOT GROSS anymore in mid to end 1972 with all the accessories like ex manifolds/ps/alt/fan/air cleaner/etc installed with the motors on the dyno robbibg power. So the 240 net hp could easily be more like 270-280hp before the new power robing NET ratings hit in 1972. The new net hp rating better reflected the real world hp like as if the motor was in the car with all accessories hooked up and functioning that would normally rob hp from the motor.

So between the compression reductions and then going from gross to Net hp ratings the motors really took a hit in hp/trq #'s with the compression drops and in somecases milder cams too realy taking the steam out of the motors back then 1st time being in 1971 with 1st compression drop for GM, then more power lost in 72 when the NET ratings took place,then 73 even more power was lost.

Then by 1974 or 75 ish i believe the base vette 350 sbc had 160180 net hp/APPROX 200-220 gross hp & the vette 454 was approx 240 net hp/280+ net hp in its last yr in the vette,it was pitifull situation to say the least.

Back to your low comp 72 396 motor,Bolt on a set of smaller chambered 290 or 063 lrg oval port heads to increase compression,install a moderate/but still very streetable perf cam along with headers and your net 240-250hp/gross (pre 1972) 270hp + could easily become a very streetable 300-320 net hp/340-360 maybe even 370 +gross hp.

Heck,even if you keep the large chamber heads and lower comp you can install a mild flat tappet perf cam(like L34 396/350 gross hp 986 cam or 1 maybe 2 steps hotter cam tops with the low comp) along with small tube headers with your bbc which can easily inc the hp by 40-50+hp/25-30+lbs trq which is substantial.

But keep in mind these hp #'s i am throwing out here are just very rough estimates from past 37+ yr's exp with these motors so keep that in mind.

Scott

I know of a few 245 HP 454's that run low 13's/high 12's ;)

i've been keeping my eyes open for a 454 anyways...this is not numbers matching motor or anything so maybe someday soon i'll pull it and replace it.....if i can come across a good deal on a 454 or 427

A 454 would be great but wy bother to have to buy & rbld a 427 if you find when you can rbld/stroke your current 402 to 434 cubes with the speedomotive kit. A propely preped 434 will perf a lot better then the current low comp 402 you have.

Even if you built the 434 stroker for only 9:0 comp to run on cheaper low octane pump fuel with mild pocket porting the current heads your running/right cam -carb-intake choice/headers it would still run circles arround your current motor. It would put out a lot more hp/trq then you have right now,increase the compression to 10:0 with more cam for even more of an inc in perf.

Don't get me wrong 427's are great motors but for not much more $ you can stroke you 402 to 434 cubes and you know what you already have and dont have to buy someone else's possible problem.

My friend just bought a pricey completely rblt top to bottom bbc for his 70 chevelle ss 396,got it in the car and after running 15 mins it filled the area with white coolent smoke comming from the driver side bank,that was the worst experience i had had ever with respct to a newly rblt motor install.

After diagnostics i found a 2.5 " crack in #3 cyl,you know your current motor runs ok with no issues like that at this time which is why i suggested the 434 stroker kit rather then you buying an unknown 427 if you cant fine a known good 454.


My friend didnt want to take the time to rbld the current tired non matching bbc that was currently in the car waiting for me to diaasemble it/machine shop work/meto reassemble/then re-install the in correct motor but now he whished he had.

But the guys at the machine shop that sold him the motor are standing behind it sleeving the cracked cyl for free. They are also completely cleaning the engine out of the soupy light tan mix of coolent & oil mix and then installing all new bearings and what ever else it needs for free too.

My friend lucked out big time there because you know how buying a rblt motor can be when it comes to problems later on . But i have to remove & re-install of motor all over again in a mint car having to be extreemly carefull with every move i make.
(UMPH!!!!!)

So either get a known/gaurentee'd good 454 to rbld or if you cant fine a 454 when you need it rbld & stroke your currently running ok 402 to a 434 using the speedomotive kit,thats what i would do.

Scott

i'm going on the dyno tomorrow morning....if the numbers are way below 300hp...i'm going to keep an eye out for a 454 or maybe a 396 with 360hp.....i want something i can just drop in and not have to wait for my current motor to be rebuilt