1962 Corvette RPO 675M

[Joshua C.]

Good morning,

I am new NCRS member. I own a 1962 340hp 4-speed posi red/black car. Really nice driver. I have the photo copy of the original dealer sheet with my serial number listing the following RPO:
923 Solid Red
STD Black Trim
470E Convert Top White
685B 4 SPD Transmission
102A Signal Seek Radio
1332A 670 x15 4 PLY WSW
396A 340 HP Corvette v8
675M Positraction Axle

My question does the "M" at the end of the 675 RPO designate gear ratio? If yes, when does M designate?

Thanks,
Josh

[David B.]

Re: 1962 Corvette RPO 675M

675M indicates car is equipped with 3.36 Limited Slip rear axle. Production data indicates there were 3,238 '62 Corvettes with this option.

[Joshua C.]

Re: 1962 Corvette RPO 675M

675M indicates car is equipped with 3.36 Limited Slip rear axle. Production data indicates there were 3,238 '62 Corvettes with this option.

Thank you for replying to my post. Like I said I am new to NCRS and I have owned my car for a little over a year. The 3.36 gear ratio is really interesting. Not what I was expecting. I know the car has 4.11 gears in it now and that the standard gear ratio for the 340hp car was 3.70. With a 2.2 first gear, 3.36 rear and Duntov cam would it have been difficult to launch the car (normal driving not drag racing)? The reason I am asking is my car currently has a 30-30 cam in it and you have to slip the clutch a little with 4.11 gears to launch the car during normal driving.

Long term I want to install the correct GM 97 cam but I have not found one yet. I probably need to change the cam before making any changes to the rear end, otherwise I am going to be miserable trying to launch the car with no low end torque!

[Richard G.]

Re: 1962 Corvette RPO 675M

[QUOTE=Long term I want to install the correct GM 97 cam but I have not found one yet. I probably need to change the cam before making any changes to the rear end, otherwise I am going to be miserable trying to launch the car with no low end torque![/QUOTE]

I own a 63 340 HP car with 3;55 gears. I never noticed any issues on take off. Are you confident of the information you have on the currently installed camshaft? Sound like it may be a lager cam than indicated.

[Joe R.]

Re: 1962 Corvette RPO 675M

If indeed he has the 30-30 cam that would be his problem as that cam has no low end torque. Should be offset by the 4:11 gear set. The 097 cam is available from Federal Mogul and would be perfect for his application.
The only camshaft worse then the 30-30 is the LT-1 camshaft! Don't use it under any circumstances. Even if it is recommended by the California distributor expert.

JR

[Joshua C.]

Re: 1962 Corvette RPO 675M

If indeed he has the 30-30 cam that would be his problem as that cam has no low end torque. Should be offset by the 4:11 gear set. The 097 cam is available from Federal Mogul and would be perfect for his application.
The only camshaft worse then the 30-30 is the LT-1 camshaft! Don't use it under any circumstances. Even if it is recommended by the California distributor expert.

JR

I am pretty sure I have the 30-30 cam in my car. The rest of the motor is stock including the right 461 heads, intake, carb, and distributor. My distributor obviously has no vacuum advance which makes dialing in the 30-30 cam near impossible. 20 degrees at 800rpm and 36 total at 2,500 is the best compromise I have been able to achieve (the 64-65 365hp distributors had I think an additional 16 degrees of vacuum advance). I am assuming the 97 cam needs less overall timing or is not as sensitive as the 30-30 cam? Is the Federal Mogul cam you are referring to the Sealed Power 113R cam? I was wondering if anyone has ran this as a 97 replacement? It is by car the cheapest option. Comp cam also makes a copy of the 97 but it is literally twice the cost. I was hoping to find a NOS GM 97 cam but I will likely need to settle for copy from someone else. Suggestions/advice on cam? One of the local Corvette mechanics recommended Comp Cams Nostalgic Plus L-79 cam with z28 springs. The car would likely make more power but at this point I think I am leaning toward stock solid lifter 97, especially if the Sealed Power 113R cam is any good as cam and lifters can be bought for less than $150.

Thanks for any help, suggestions or advice.

[Duke W.]

Re: 1962 Corvette RPO 675M

The only camshaft worse then the 30-30 is the LT-1 camshaft! Don't use it under any circumstances. Even if it is recommended by the California distributor expert. JR

Please explain.

[Joe R.]

Re: 1962 Corvette RPO 675M

Gosh, no reflection on you Duke. I thought that was explained by Michael Hanson many years ago.

Have a nice day!

JR

[Duke W.]

Re: 1962 Corvette RPO 675M

Hanson never tested any of the SB mechanical lifter cams, and the rest of the LT-1 cam naysayers never have either. I have and have the data. The LT-1 cam has about the same effective overlap as the Duntov (which is significantly less than the 30-30), so it makes more low end torque than the 30-30 with about the same top end power and revs, which is more than the Duntov. That's why I recommend the LT-1 cam to replace the Duntov and 30-30.

If you really know SB cams you know that the LT-1 cam uses inlet and exhaust lobes from two existing production mechanical lifter cams.

Do you know what they are?

If you hate the LT-1 cam then you have to hate the two cams that the lobes came from. That doesn't leave much left to love.

Duke

[Duke W.]

Re: 1962 Corvette RPO 675M

I am pretty sure I have the 30-30 cam in my car. The rest of the motor is stock including the right 461 heads, intake, carb, and distributor. My distributor obviously has no vacuum advance which makes dialing in the 30-30 cam near impossible. 20 degrees at 800rpm and 36 total at 2,500 is the best compromise I have been able to achieve (the 64-65 365hp distributors had I think an additional 16 degrees of vacuum advance). I am assuming the 97 cam needs less overall timing or is not as sensitive as the 30-30 cam? Is the Federal Mogul cam you are referring to the Sealed Power 113R cam? I was wondering if anyone has ran this as a 97 replacement? It is by car the cheapest option. Comp cam also makes a copy of the 97 but it is literally twice the cost. I was hoping to find a NOS GM 97 cam but I will likely need to settle for copy from someone else. Suggestions/advice on cam? One of the local Corvette mechanics recommended Comp Cams Nostalgic Plus L-79 cam with z28 springs. The car would likely make more power but at this point I think I am leaning toward stock solid lifter 97, especially if the Sealed Power 113R cam is any good as cam and lifters can be bought for less than $150.

Thanks for any help, suggestions or advice.

The "cam wars" have been going on for over ten years. Do a search for threads started by me, 327 LT-1. That thread will have links to the Corvette Forum that has more data and discussion.

Comp cams quality is poor, and I would never buy a cam from them even if it was cheaper than Federal Mogul. FM offers high quality, built to GM print OE replacement cams. The part number for the LT-1 cam is CS-1145R.

You don't need "Z-28 springs" that were designed for the first design ...140 Trans-Am racing cam and installing them will increase the chance of wiping lobes because they have much greater seat and open force. (The production DZ and LT-1 engines used the same springs as your grandmother's 283 2-bbl. as did engines with the Duntov and 30-30 cams.) The OE springs with proper setup will yield a valve train limiting speed of about 7200, but the engine won't make power that high unless you massage the heads, and you certainly don't want to rev it that high with the first design 327 rods that are weak and subject to fatigue failure.

There are ways to ID the installed cam, but I don't have time to write a long essay right now. Shoot me an email and we can discuss more if you like.

Duke