Wondering what the stock cam specs are for an 81 (RPO L81)??
Also if these look like the correct gear ratios?
Automatic Transmission
Three-speed Turbo Hydra-Matic
floor-mounted gear shifter
gear ratios
1st = 2.52:1
2nd = 1.52:1
3rd = 1.00:1
Rev = 1.93:1
Final drive ratio: 2.87:1

Im looking to upgrade the cam without having to do much to the heads,
so Im wondering how much of a change it can handle.
Thanks in advance!

 

Also any suggestions on changing the gear ratios would be greatly appreciated!

 

I believe the cam that came in L-81 were the 'standard' 4-bbl cam of that era (L-48, '77-'81 Z28, and '82-'84 Cross-Fire ), with specs of .390"-lift intake / .410"-lift exhaust, 195* @ .050"-lift intake, and 205* @ .050"-lift exhaust, on a 112 LSA.

The gearing you show is correct for THM350, and probably the same for THM350-C (lock-up converter ), too.

Changing the cam-only will improve performance slightly, but you'd really need to upgrade the heads (smaller chambers to increase CR ) to see a sizeable difference.

Rear-gearing swaps will result in great off-the-line performance gain (especially with those 2.87s ), but limit all-out top-speed, and anything over 3.73s will kill MPG:
what is your intended useage for the car (highway cruiser, stop-light bandit, etc. ) ?

 

Mostly Street/Strip use, I wouldnt want anything too drastic in the gears, but first just doesn't pull as hard as I want it too and second hits pretty good. So changing out the first gear is all I really want to do. As for the heads I have access to a machine shop so would it be a good idea to mill them? If so how much?
Thanks,
Austin

 

'changing-out' 1st Gear in your car isn't an easy-fix, nor one you should do without considering a few things:
if the RPM-drop on the gear-change is too-severe, the car will fall on it's face once it engages 2nd Gear, unless you have a lotta power
(I have a 700R4, with 3.06:1 1st Gear, but 1.63:1 2nd Gear, behind my stock Croos-Fire..... ASK me how I know..... )


TCI (amongst others ) makes extra-low gear-sets for THM350 & THM400 transmissions, and I have them in both THM400s for my Z28:
they come with 2.75:1, 1.57:1, and 1:1 ratios, so it isn't-as-wide of a spread, and I also have a very-loose 8" converter, too.


Whacking material off those heads can be done, but I'm under the impression the castings are very-thin, and prone to cracking at the standard deck-thickness:
cutting them enough to improve squeeze ain't gonna help this situation.


In all honesty, those heads aren't worth investing much money into them, even if you can do the work yourself:
turn 'em into boat-anchors, and if you're serious, get some newer-style vortec heads and a matching intake, with a cam in the .460" - .480" -lift / 224*-230* @ .050"-lift range, a decent carb & exhaust, then shift the motor at 5500 RPM.....


with 3.73s and 26"-short tires, that'll put you just-over 100 MPH, which might be in the 13s:
(I think Red 69 goes 14-twenties @ 96 MPH with a somewhat similar gear/tire set-up, with less power/motor )
4.10s with 28"-tall tires will do the same, and give you a bigger foot-print on-launch.

 

Glen forgot more than I know about gear ratios and such, but I can share this. My 79 L-82 has some mild mods as follows, and it is drag raced. The stock heads have been ported with 2.01-1.60 valves and a 327-350 HP hyd cam. The stock intake has been port matched wearing a Holley 600cfm square bore carb. The trans is a TH350 with a shift kit and 2700 stall converter and 3.70 gear out back. It wears a 25.75 tall Nitto drag radials and gets a 2.03 60 foot and 14.20's @95 MPH in the 1/4. This is at 90 degree temp. It also has 1 5.8 long tube headers and true 2 1/2 inch dual exhaust.

That said, I was disappointed in the numbers and thought it could do better. After checking with forum members who have been where I am, the first suggestion is always dump the heads. One esteemed member of the forum said he had done exactly the same heads and mods as on mine, and found a dramatic improvement after installing better heads. Vortec heads alone would put my car in the 13's. Add the other parts and I'm looking at low 13's IMO. Your 81 is a little lighter and should do better. My 79 weighs 3445 with 3/4 tank of fuel.

My plan is to eventually swap in Vortec heads and Air-Gap intake and replace the cam with a roller unit. I don't see where replacing the first gear in the trans is going to get you what you are after. It is my opinion money and time would be better spend upgrading the engine parts mentioned. Glen has plenty of experience with the parts and what combinations work well. Good luck achieving your goal, we all want to go faster.

 

Thanks for all the info! I guess I will just have to bite the bullet and look for new heads. I already am running the Performer RPM intake and Eld. carb, so I may check out their RPM heads too.

 

Since you already have so-much Edelbrock stuff, you may-as-well piece-together one of their 'combination/kits' (heads and cam ), so you'll have some idea of the HP/TQ it'll make.


I think they have some head/cam 'kits' that make 325 HP/ 375 TQ from 9:1 350" SBC, which is what your motor will have w/ 64cc heads, using the Performer intake and 650 cfm 'Thunder' carb.