Thread: 402+ Rebuild

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Hey all, been a long time since I posted here. New job, little time. Just dropping a line to let y'all know what's up with the Firebird this year. Dropped her off with my engine builder early February where she sat and sat and sat until he finally cracked her open yesterday. Of course, he finally gets to it while I'm out of town.

A few surprises: previous owner tells me I had a 1969 396+.030 but turns out it is actually a 1972 402+.030 with 1965 97cc heads (first/worst ever stock BBC head). So I was very surprised to learn I was running ~10.2:1 SCR as I was guessing it was much lower already.

Original plan was just top-end work (cam heads intake) to wake her up but not much I can do without giving up CR and #8 was a bit out of round giving a 30% leak down so getting honed and putting in new pistons.

So I'm looking for new pistons and wow, whodathunk nobody makes 396-402 pistons! SpeedPro looks to be the only game in town so I went with 36.6cc dome and am going with a trickflow 113cc oval aluminum head for a SCR around 10.8:1.

Cam will be Lunati roller .630/.630 255/264 @.050.

The goal is quickest ET (low 12's maybe high 11's), streetable on 91 octane at high altitude (Denver). I was running 13.2x@100 all day every day last season.

He got back to me today to tell me his machinist has a 2-bolt 454 block to sell for $400. As tempting as it sounds, I have this irrational desire to make this little BB fast. I told him when I'm ready to go big, I'll be going really big The big one I want to build myself, but currently I don't have the time or tools to do it right.

Anyway, thanks for reading and sorry for the epic post ... just venting and enjoying having the chance to be on the forum again.

-Chris

Originally Posted by skids72

Hey all, been a long time since I posted here. New job, little time. Just dropping a line to let y'all know what's up with the Firebird this year. Dropped her off with my engine builder early February where she sat and sat and sat until he finally cracked her open yesterday. Of course, he finally gets to it while I'm out of town.

A few surprises: previous owner tells me I had a 1969 396+.030 but turns out it is actually a 1972 402+.030 with 1965 97cc heads (first/worst ever stock BBC head). So I was very surprised to learn I was running ~10.2:1 SCR as I was guessing it was much lower already.

Original plan was just top-end work (cam heads intake) to wake her up but not much I can do without giving up CR and #8 was a bit out of round giving a 30% leak down so getting honed and putting in new pistons.

So I'm looking for new pistons and wow, whodathunk nobody makes 396-402 pistons! SpeedPro looks to be the only game in town so I went with 36.6cc dome and am going with a trickflow 113cc oval aluminum head for a SCR around 10.8:1.

Cam will be Lunati roller .630/.630 255/264 @.050.

The goal is quickest ET (low 12's maybe high 11's), streetable on 91 octane at high altitude (Denver). I was running 13.2x@100 all day every day last season.

He got back to me today to tell me his machinist has a 2-bolt 454 block to sell for $400. As tempting as it sounds, I have this irrational desire to make this little BB fast. I told him when I'm ready to go big, I'll be going really big The big one I want to build myself, but currently I don't have the time or tools to do it right.

Anyway, thanks for reading and sorry for the epic post ... just venting and enjoying having the chance to be on the forum again.

-Chris

I say buy the 454 block and order a 4.25 stroke crank and be done with it.
You will have about a 100 cubes over the 396 and all the torque you can handle.
Look at the Brodix oval port heads and keep your same cam.
Run a victor with a 850 dp and you should have one heck of a combo.
You won't need as much gear with the 489/496 so it just became that much more driveable.
My advice is always build the largest engine you can to try and kep the rpm's down in a street car.

if you build your 402 then i like your build better with the air gap intake the 396/402 are ok engines and can run. you could run the KB pistons and a gm 4.000crank that will get you more cid 427 that would help the bad thing with the 396/402 pistons are pricey for the same money or abit more you can get SRP 496 pistons and less for hyper pistons but a bigger engine would be nice LIKE Erik said.i have some stuff for that i posted on the parts form. that i would help you out on i am selling all my big block parts just keeping one .i like to keep them a round but alot of guys have there parts for me to machine so you can P.M me i would throw you a hell of a deal on a short block 496?or long block

thanks erik and pat for the replies. Looks like the 402 pistons are out as there are none (except custom) that will work with anything but a stock type head (valve shrouding and clearance problems). Getting a 454 block (should find out tonight if he can find a 4-bolt for the same price as the 2-bolt), reusing the short crank for a 427+. Pistons are on the way from SRP I think 30cc dome for ~10.6:1 with 113cc chamber Trickflow oval heads.

Was leaning toward Holley strip dominator intake. 850 carb is the way to go but I'm going to run my current 750 for the time being (shouldn't choke it too much but the 850 will be better).

I appreciate the advice and want to build a mountain motor in the future. I'm a bit bummed my 402+ plan was foiled but I think the short 427 (432/whatever) will suit me just fine for the time being and might even get me into the 11's on pump gas.

Already running 4.56:1 gears so she buzzes right along on the highway ~3500rpm. To clarify, this is a mostly strip car that drives 30mi to the strip. My next worry might be traction although I never had a problem hooking with the old motor.

I just wish these crises could have come up at least a month ago so I had more time to plan (first test/tune is next weekend). Doesn't help I'm going through this while on the road and away from my books and tools.

I appreciate the input...

-Chris

have one set of nice 427 used trw pistons 060 over 11to1 you really do not need a four bolt block

thanks for the offer pat! I agree, but the 4bolts extra insurance especially if I up the stroke and CR later... if it doesn't materialize that's fine and the 2bolt is all clean and ready go. little time for more machine work with the clock ticking so I'll have to pass on the pistons... as it is I'll be lucky to get 8 passes on it before the first race...

speaking of which, what's your opinion of quick break in procedure before running it all-out aside from the obvious cam break in and oil change...

thanks,

Chris

Originally Posted by skids72

thanks for the offer pat! I agree, but the 4bolts extra insurance especially if I up the stroke and CR later... if it doesn't materialize that's fine and the 2bolt is all clean and ready go. little time for more machine work with the clock ticking so I'll have to pass on the pistons... as it is I'll be lucky to get 8 passes on it before the first race...

speaking of which, what's your opinion of quick break in procedure before running it all-out aside from the obvious cam break in and oil change...

thanks

Chris

no the 454 two bolt main will hold more power than you think i know have built many468 496 and have seen them do just fine just say you want one the big block bottom end will take alot .the insurance is building the engine right .not two more holes in the main web .you will have a hard time getting the caps to move around if the caps set in the block good. two more bolts for the power you are putting thru it less you are dumping alot of Nos???? if so stud it. break in as alot with how it hone and how it is built the rings should set in soon if tq plated and plateau honed .the valve springs i worry more about. so they are broke in right

Originally Posted by skids72

thanks for the offer pat! I agree, but the 4bolts extra insurance especially if I up the stroke and CR later... if it doesn't materialize that's fine and the 2bolt is all clean and ready go. little time for more machine work with the clock ticking so I'll have to pass on the pistons... as it is I'll be lucky to get 8 passes on it before the first race...

speaking of which, what's your opinion of quick break in procedure before running it all-out aside from the obvious cam break in and oil change...

thanks,

Chris

I have a customer that has a 2-bolt 496 with a stud kit, 13.5 to 1 comp. ratio.
This engine has a 4340 balanced assembly and see's 7,500 every pass and runs 6.00's.
In two seasons I have only had to do one line hone and the caps where still tight.

thanks for the education... always thought 2bolts were not so strong. No n2o...of course that would have been the easy route... I think of it as cheating. I'll have to trust the machinist to do the job right... engine builder is trustworthy and touts building them right and claims his engines don't break because of it... he built the motor that was top qualifier in quick 16 here last year at 7s flat, of course the driver/owner got banned for life from the track for duking it out with someone in the pits...

what special precautions to take with the valve springs? should use weaker springs for cam break in but then I need to break in the new springs? Easy revs varied around for xxx miles or xxx minutes?

Originally Posted by erik erikson

I have a customer that has a 2-bolt 496 with a stud kit, 13.5 to 1 comp. ratio.
This engine has a 4340 balanced assembly and see's 7,500 every pass and runs 6.00's.
In two seasons I have only had to do one line hone and the caps where still tight.

i can beat that over 7000 with stock gm bolts in the mud and there has been some cast cranks that would have made GM proud

Originally Posted by pat mccarthy

i can beat that over 7000 with stock gm bolts in the mud and there has been some cast cranks that would have made GM proud

Stop it Pat. You are starting to scare me again.

Originally Posted by erik erikson

Stop it Pat. You are starting to scare me again.

do i really do you find me repulsive hey and them were stock 3/8 rods with arp bolts. Hey erik how is the slant 6

Interesting thread here. I have been running 396-402 combo's for a little over 20 years now. I raced a factory 70 L78 camaro with the stock closed chamber rec port heads, L-78/LS-6 cam, 11 to 1 comp, 4 speed tranny, and 4.56 gears and was running 12.40's@112-114 mph depending on the track. I am partial to the smaller flat tappet cams and have found that the smaller cube motors seem to like the dual plane intakes better. My most recent package is 1979 Z-28 with a 402 bbc, rec port heads, 12 to 1 comp, .570 lift solid cam, 4 speed box, and a set of 5.00 gears. I switched to a single plane intake and have been struggling with poor 1/8 mile times, but still running 12.30's @ 113 mph. I just switched back to a dual plane intake but haven't tested yet. Both cars were heavy weights also, The 70 tipped the scales at 3700 with driver and the 79 comes in at 3550 with driver. I also had some crazy itch to make the smaller motors run fast. Guess I just wanted to be different.

Rich