# camshaft



## simmons68 (Dec 22, 2009)

Hey guys,
I have a 68 gto, rebuilt 400 with 3,000 miles, pretty stock. Was wanting more power and better sound. Have a very mild cam in it now. How hard is it to change out the camshaft? Is is worth my time to do this? What is the biggest cam I can install without having head work done on my stock heads. Thanks


----------



## Mr. P-Body (Jan 20, 2011)

A cam change isn't a MAJOR operation, but isn't trivial, either. It requires the removal of the "front" of the engine. That is, the pulleys, balancer, and timing cover. No need to take the water pump off the cover. 

You need to know if steps were taken when the engine was built, to lower static compression to 9.5:1 or below, for using 93 octane gas. In stock form, compressoin is too high. A "mix" of 93 and "race" gas is required to avoid detonation. Adding a performance cam can compound the problem when the proper cam selection is made. On the other hand, an "old school" cam, fairly "rowdy", can "bleed off" some of the cylinder pressure, amking the higher compression engine a little mor 'friendly". It will do nothing for detonation in the higher revs, though. It, too, can actually make matters worse.

Aside from headers, a cam change can "net" you more power than any other single change. 

It is genreally accepted the stock valve train can "handle" up to about .470" lift (at the valve, hydraulic flat-tappet) before at least a spring change is needed. It is ALWAYS recommended, when a new cm and lifters are installed, new springs should be as well. This will give you a little "room" for a bit "more" cam. 

Perform a compression test and let me know what the readings are. I may be able to determine (at least an educated guess) where your compression is now. 

Jim


----------



## Rukee (Feb 8, 2007)

Maybe some high ratio rocker arms?? I have a set of COMP Magnum roller rocker arms 1.6 ratio that I never used, or couldn't with the heads I have.


----------



## geeteeohguy (Feb 2, 2008)

Simmons, by all means perform the compression test and post the numbers. You're in good hands here. What are the casting numbers on your heads, and is it the '68 GTO block?? Also, are there receipts for the engine/machine work? If so, the part numbers for the pistons used might be listed....


----------



## dimitri (Feb 13, 2009)

Mr. P-Body said:


> A cam change isn't a MAJOR operation, but isn't trivial, either. It requires the removal of the "front" of the engine. That is, the pulleys, balancer, and timing cover. No need to take the water pump off the cover.
> 
> You need to know if steps were taken when the engine was built, to lower static compression to 9.5:1 or below, for using 93 octane gas. In stock form, compressoin is too high. A "mix" of 93 and "race" gas is required to avoid detonation. Adding a performance cam can compound the problem when the proper cam selection is made. On the other hand, an "old school" cam, fairly "rowdy", can "bleed off" some of the cylinder pressure, amking the higher compression engine a little mor 'friendly". It will do nothing for detonation in the higher revs, though. It, too, can actually make matters worse.
> 
> ...


I hate jumping a thread but can someone tell me my ratio with 180 psi on my compression test?

thanks


----------



## geeteeohguy (Feb 2, 2008)

Dimitri, P-Body will probably chime in, but I'd guess close to 10:1. Ideal compression for today's fuels is in the 150-175 psi range (8--9.5). Depends on your camshaft, too.


----------



## dimitri (Feb 13, 2009)

I've got 96 heads flat top pistons 0 deck highth mild cam.


----------



## BearGFR (Aug 25, 2008)

dimitri said:


> I hate jumping a thread but can someone tell me my ratio with 180 psi on my compression test?
> 
> thanks


Not reliably. Cranking pressure is very dependent on the cam and resultant timing of the valve events (intake valve closing event in particular). It's even harder with a hydraulic lifter engine because unless the engine is running there's not enough oil pressure in the lifters so that affects all the valve events.

Having said all that, 180 psi cranking pressure is pretty high - right at if not slightly over the 'safe' limit. Ifn' I was you, I'd be watching my spark plugs VERY closely for any tiny shiny metal specs...

Bear


----------



## simmons68 (Dec 22, 2009)

*Cam*

Wow, thanks for the quick replies. My compression is 10:75-1. My engine is the original 400 WT motor, 365 horse, 415lb torque from factory. When I had the engine rebuilt I had standard bore (30) with a very mild cam, not sure of the specs. I believe the pistons were concave (pro-seal) pistons, does that sound right? I will get the numbers from the heads, but they are the originals. I did have the heads freshened up when the motor was rebuild (nothing at all aggressive) I have added headers, edlebrock intake, and a cold air system. The Comp Cam I was looking at was 525 lift and 305 duration, Is that too much. Like I said I do not want to do any head work if I can keep from it. Thanks guys


----------



## simmons68 (Dec 22, 2009)

*Camshaft response*

I have been reading about cams. Are the melling camshafts any good? I appreciate your help.


----------



## geeteeohguy (Feb 2, 2008)

Talk to Mr P Body about cams and combos. He is the "go to" guy!!!


----------



## BearGFR (Aug 25, 2008)

simmons68 said:


> I have been reading about cams. Are the melling camshafts any good? I appreciate your help.


When it comes to cams, generally the measurements (duration, lift, lobe separation, etc.) are more important than who make it, as long as it's a reputable company (and Melling is). Cam selection starts with how you plan to use the car (street, street/strip, highway only, race only, etc.), budget, and specifics about the rest of the car (manual or auto, converter stall if auto, rear gear ratio, vehicle weight, etc.)

For example - the 69-70 Ram Air IV 400 was a stout combination, but put a Ram Air IV cam in a 400 in a heavy car with 3.08 gears and a "tight" converter, and it will be a dog -- unable to get out of its own way.

So.... tell us about the rest of the car and how you plan to drive it?

Bear


----------



## Mr. P-Body (Jan 20, 2011)

The Melling performance cams for the Pontiac are all the "old" factory grinds. SPC-3 is "068", SPC-7 is "744" and SPFC-8 is "041". These are not "reproductions", they are the real deal. Melling was the vendor to GM "back in the day". 

If your compression is to stay "high", and you "mix" fuel, the SPC-8 is an excellent choice. If you choose to lower the compression for a "pump gas friendly" engine, none of the factory grinds are as good as the more modern stuff. 

FWIW

Jim


----------



## simmons68 (Dec 22, 2009)

*Camshaft*

Hey guys,
My 68 GTO is a weekend driver. My longest road trip is about 45 miles. I generally drive it around the town that I live in. I am not worried about fuel consumption at all. I am at a stand still point now. I have spoken to Summit techs, crane cam techs, and comp cam techs, they all tell me that if I do not know what cam I have now, they cannot help me. I wish I had that info. but I don't. The cam that I do have is very mild and very close to stock. I search online and found out that the stock cams had 516 lift and 280 duration. To me that sounds like a lot, is it? The techs tell me to put in a 480 lift and 305 duration, that should be ok. All I want is a mean sound, and more power, without doing head work (except changing the springs). Any ideas? My problem is that I do not want to put a cam in that is smaller than the one in it. And according to the information that I found, I would be doing just that. Any help is appreciated.


----------



## BearGFR (Aug 25, 2008)

simmons68 said:


> Hey guys,
> My 68 GTO is a weekend driver. My longest road trip is about 45 miles. I generally drive it around the town that I live in. I am not worried about fuel consumption at all. I am at a stand still point now. I have spoken to Summit techs, crane cam techs, and comp cam techs, they all tell me that if I do not know what cam I have now, they cannot help me. I wish I had that info. but I don't. The cam that I do have is very mild and very close to stock. I search online and found out that the stock cams had 516 lift and 280 duration. To me that sounds like a lot, is it? The techs tell me to put in a 480 lift and 305 duration, that should be ok. All I want is a mean sound, and more power, without doing head work (except changing the springs). Any ideas? My problem is that I do not want to put a cam in that is smaller than the one in it. And according to the information that I found, I would be doing just that. Any help is appreciated.


Ok, that's a start --- I gather you don't plan on much highway usage, nor racing, but you want something with some "authority" for street crusing that also has some personality in how it sounds ---- right?

I forget-- which transmission do you have, and do you know what your rear gear ratio is?

How about power brakes and A/C --- do you have one or both now?

Also, you said you have 10.75:1 compression ---- did you actually measure it (cc all the combustion chambers)? Which heads do you have? (large numerals, usually cast into the top of the center two exhaust ports.)

Bear


----------



## simmons68 (Dec 22, 2009)

*Camshaft*

You are exactly right, no highway driving, just in town with a good sound and some muscle. I do not have AC or power drakes, I have 3:55 gears 10 bolt 8.2 rearend, with a muncie 4 speed (m21). The heads are stock with all new springs, lifters, etc. I have full length headers with dumps. Thanks for your help. I appreciate it.


----------



## simmons68 (Dec 22, 2009)

I did not measure my compression, that is the information that the engine builder gave me when I picked up the motor. Thanks again


----------



## simmons68 (Dec 22, 2009)

Oh ya, The heads have a DN above the number 1 cyclinder and the letters JA038 on the passenger side


----------



## BearGFR (Aug 25, 2008)

simmons68 said:


> Oh ya, The heads have a DN above the number 1 cyclinder and the letters JA038 on the passenger side


4 speed, 3.55's, no power brakes or a/c --- that does open things up a bit for cam choice, for sure. Now if we can just get the correct head codes...
Look at this photo, see that big 6X on the center exhaust ports? That's where you should be looking --- tell me what you've got there.

Also, be thinking about how much you want to spend -- keep in mind that you'll be replacing cam, lifters, pushrods, and rocker arms at a bare minimum, probably best to assume you'll also be replacing valve springs too to make sure they're properly matched to the cam. I'd also recommend at least replacing the stock rocker nuts with poly-locks in order to get positive adjustment. All this stuff gets replaced because all these parts touch/wear against each other, and therefore establish a mated wear pattern.

Bear


----------



## Mr. P-Body (Jan 20, 2011)

One "correction" to be made here. There are no factory cams with .516" lift and 280 duration. The "big" one was the 041, .470" lift (1.5 rockers) or .519" (1.65s, some catelogs list it as ".520" lift). It also had 308/320 "advertised" duration and 230/240 @ .050. Where they get their "information" is beyond me...

The vast majority of factory cams (including the old solid cams for the SD program) were .408" lift (1.5s). 

Jim


----------



## simmons68 (Dec 22, 2009)

I will get the numbers from the heads tonight. I was hoping to spend around $250.00-$300.00.


----------

