Author Topic: Smog Legal 350 Rebuild  (Read 1064 times)

Offline jksef1984

  • New Users
  • Posts: 2
  • Newbie
Smog Legal 350 Rebuild
« on: October 24, 2019, 01:35:27 PM »
Hey everyone. So Iím in the middle of a frame off restoration of a 84 step-side with my dad with rebuilding the ECM controlled 350 up next. Iíd like to build a nice daily driver that has decent power, maybe something around 300hp but I have to meet California smog requirements.

My initial plan is to bore/hone/prep block for flat top pistons with valve reliefs, freshen up stock 462624 76cc smog heads with stock 1.94/1.5 valves, install Edlebrock Performer EGR intake and rebuild stock computer controlled Quadrajet.

My question is has anyone used the 12-208 Comp Cams Dual Energy can/lifter/spring/timing chain kit in any of your builds? The cam is rated at .462Ē/.482Ē 211/221 @ .050 and comes with a CARB EO number which I need for smog. But I know the smog tester will never know whatís inside so Iím open to cam suggestions, just gotta make sure itís good idle and vacuum.

Iím concerned that the compression with the flat tops and cam setup will be too much for the stock heads or worse stock ECM to control and cause me to fail smog tests.

Appreciate advice anyone can give!!
Jeff

Offline 75gmck25

  • Frequent Member
  • **
  • Posts: 423
  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Smog Legal 350 Rebuild
« Reply #1 on: October 25, 2019, 05:44:15 AM »
It sounds like you plan to do quite a bit of work on the engine, but are trying to get by with using the old smog heads.  In the long run I think you will find this is a difficult mistake to correct.   You are giving up 30-40 hp right up front (vs. Vortec iron or aftermarket aluminum heads), and any future upgrades (exhaust, etc.) will not be as effective. 

I don't know how to calculate the expected compression with new pistons and heads, but I there are several folks on hotrodders.com that could do it for you.  You can also use different head gasket thickness to fine tune and change compression a tenth or two. 

The 221/221 cam will work better with more compression, but GM managed to make a similar duration cam work in the 350/290 hp crate that only has about 8.2 compression.  Its a bit of a dog, but it does okay if you keep RPM up.  Unless you have good low gearing (3.73/4.10, etc.) and stock diameter (30-31") tires, you might want to go with a more conservative cam to keep your low end torque in a heavy vehicle.

Bruce

Offline jksef1984

  • New Users
  • Posts: 2
  • Newbie
Re: Smog Legal 350 Rebuild
« Reply #2 on: October 25, 2019, 11:11:39 AM »
Thanks for the advice Bruce, Iíll definitely look into aftermarket heads hopefully thatís something I can fit into the budget.

Any suggestions on a more conservative cam in case I need to stick with the stock heads?

Offline roundhouse

  • Senior Member
  • ****
  • Posts: 1474
  • Newbie
Re: Smog Legal 350 Rebuild
« Reply #3 on: October 26, 2019, 03:42:06 PM »
Thanks for the advice Bruce, Iíll definitely look into aftermarket heads hopefully thatís something I can fit into the budget.

Any suggestions on a more conservative cam in case I need to stick with the stock heads?
A cam designed for a motor home will be the beat for stock heads
   Called an RV cam I think

Offline 75gmck25

  • Frequent Member
  • **
  • Posts: 423
  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Smog Legal 350 Rebuild
« Reply #4 on: November 18, 2019, 05:56:07 AM »
I upgraded to better heads and used a Howards 213/217 @ .050 duration cam.  It has very good low end, but still develops more total HP than a stock cam (usually stock are about 195/202).   My cam works well with about 9.2-9.4 compression, which can be achieved with 64cc heads (like a stock Vortec) and a thinner head gasket.

Bruce