[Joe Corso]

Ok, my motor is a 60 over 455 with 670 heads. the cam is caomp cams 305H with 253/253 at .050" and .525 in" lift. I will be using a THM 400 and the rear is a 12 bolt. what is the ideal gear for this setup. would i benefiet by using the 1.65 rockers. i really need to get as much power as possible out of this setup. the car is an 81 TA. I will be putting a fiberglass nose on probably. for an intake im thinking performer. any other help or suggestions would be appreciated. I had my motor balanced and i have stock rods in there with ARP bolts. The pistons are ross. how high of a stall conv. should i go with.im looking for as much help as possible here. thanks

[Joe Corso]

Ok, my motor is a 60 over 455 with 670 heads. the cam is caomp cams 305H with 253/253 at .050" and .525 in" lift. I will be using a THM 400 and the rear is a 12 bolt. what is the ideal gear for this setup. would i benefiet by using the 1.65 rockers. i really need to get as much power as possible out of this setup. the car is an 81 TA. I will be putting a fiberglass nose on probably. for an intake im thinking performer. any other help or suggestions would be appreciated. I had my motor balanced and i have stock rods in there with ARP bolts. The pistons are ross. how high of a stall conv. should i go with.im looking for as much help as possible here. thanks

[Bill Boyle]

Joe--The 81 TA weighs around 3800 pounds. Your 455-670 combo will require racing fuel so I take it this car will be for the strip. If that presumption is correct, you need to test the car with the current gear ratio or at least determine the rpm you will be reaching going through the traps. Heck, a 3.23 rear gear may be right or any gear up to 4.11.You need to keep rpm in the 5500 rpm range with stock rods. Traction is a big question mark and that includes tires and traction bars etc. Please provide us with some more information to consider.

[This message has been edited by Bill Boyle (edited 01-09-2000).]

[Joe Corso]

I want to ask a question about that comp. ratio in this setup. The 670s are 72cc heads and have had a valve job. that should bring them to around 75. I have valve reliefs in my pistons of about 7cc. I also thought that i had read that 670s were actually 75 cc's to begin with. when i calc. out the compression i get 10.4 with the 78 cc comb chamber and a 7 cc valve relief. Now if i use a thick head gasket, i could easily get that down to about 10.15-10.2. i think that the high duration of the cam will help as well. I dont think that it would be too much of a strecth of the imagination to try running 94 and octane booster in this setup. Well, either way, my question wasn't really regarding the compression.

What i want to know is: Can I make this car really go. i had intentions of doing an A body, but could not find one that i could work with. I got this car for a good price, soooo..... Here i am questioning its potential.

basically what im looking for is someone to say "i ran that setup in this type of car and this is what i had for a stll, and gears, and i used 1.65s, and etc. I want to hear real life info.

I want to be able to squeeze every last bit of power out of this motor that is possible. thanks again

[Gach]

Joe, the 670 heads aren't 75 cc, more like 65 cc, even with a valve job they still won't be close to 72 cc. So your compression, even if your running a -.19 deck hight with .041 head gasket, is 11.39.1 With a 0-deck it's 11.88.1 and that's figuring it with a 72 cc heads. No addtive will help. you
need at least 110 actane gas.

The 1.65 rockers may help but you have to make sure the valve springs will handle the added .050 lift with out running into coil bined. That's also some thing I would try at the track. But my guess is your don't mention any port work being done to your heads, I don't think you'll pick up much if any
by going to a 1.65 rocker. If you still want to try, then I would try them on the exhaust side first.

As far what gear to run, I'd go with a 3.55, but in my honest opinion I think that cam is to much cam for the heads your running, unless you do some port work on those heads. The compression is right for that cam. My guess is mid 12's in a 3800 lb car, with some head work high to mid 11's

[Old Man Taylor]

As I started to describe combinations like yours, I realized they were enough different to make comparisons difficult. FYI, the 670's are spec'd at 72 cc's, and do normally measure 75. I installed RAIV valves in mine and got them to 78. That is in a 428 4-spd with nitrous in an A-body, and a 253/260 cam and .585/.601 lift with 1.65 rockers.

In your application I think you will find a gear between 3.73 and 4.11 the best. You will definitely need racing gas with those heads.


------------------
Jim

[Joe Corso]

ok, i must be a retard. every time i do calculation of the compression on the CP site, i get 10:1 with my setup if i use different size head gaskets. I was thinking a .071" head gasket, the 7 cc valve reliefs, the 75-78 cc heads, and 4.211 bore and 4.21 stroke. i left deck height alone and i will not be cutting the deck and it was never cut before. isnt it true that the thicker head gaskets reduce compression and that cams with higher duration help to relieve the motor a little when it has higher compression. Thanks

Below is the basic calculation. Mail me off line if you would like a spreadsheet where you can substitute different parameters and have it calculate it for you. I haven't used any of the web calculations because they frequently make asumptions for some of the parameters.

Compression space = (1) Combustion chamber volume plus (2) gasket hole volume plus (3) deck height plus (4) piston valve relief volume.

(1) 75 cc
(2) Pi Rsquaredxheight = 3.1416 x [4.211/2]squared x 0.071 = 13.93 x 0.071 ci = 0.99 ci x 2.54 cubed = 16.20 cc
(3) Same formula as (2), therefore 0.015/0.071 x 16.2 = 3.42 cc
(4) 7 cc

Total compression space = 75 + 16.2 + 3.42 + 7 = 101.62 cc

Swept volume = [bore/2]squared x 3.1416 x stroke = [4.211/2]squared x 3.1416 x 4.120 = 57.38 ci = = 57.38 x 16.387 cc = 940.3 cc

Compression = [swept volume + compression space]/compression space = [940.3 + 101.62]/101.62 = 10.25

If you substitute a 0.047 gasket thickness the result becomes 10.8.

At 0.035 gasket thickness and 0 deck, it becomes 11.45.

Where did you come up with 0.071 for head gasket thickness?

------------------
Jim

[Paul Spotts]

Joe - A friend of mine ran a 305h cam in a 400 with those heads in a 70 GTO good cam. I would run the 1.5 ratio rockers, 411 gears with 29.5 to 30" tall tires (assuming the car is untubbed) The 1.65's would be OK if you had better rods and some porting to take advantage of a higher RPM but too much for your application. Gach is correct in your compression - at least 11 to 1 depending on the variables. I suggested the tall gear because of your weight - even with glass up front. I would run a torker 2 or street dominator with a 2" spacer(hood clearance permitting) and a 800-850 carb. Also use the original leaf springs with long traction bars or similar traction device. Keep the car at the stock height in the rear. Scott Rex has a 70 TA with factory leaf springs and ladder bars - the car sits at the stock height (9.60's ET) - the best for traction. As for a converter - depends on how much you want to spend. A custom built unit will run about $800 but will gain the best ET. An of the shelf unit i would suggest would be around 2500 stall. I predict mid to upper 11's as described.

[This message has been edited by Paul Spotts (edited 01-10-2000).]