Discussion Forum - Northstar Chevelle Club

BLUESS · Contributor

camshaft question

Bungy L-76 · Active Member

First off, Welcome to the club!

That makes sense to me. To get the overall lift, you have to subtract the base circle or diameter of the cam from the total height of the lobe. Measure the overall height of the lobe, then turn the cam 90 degrees and measure again. Subtract that measurement from the first and you have your lift figure. To get the lift at the valve, you would then have to multiply that figure by your rocker arm ratio.

-- Edited by Bungy L-76 on Monday 21st of February 2011 05:58:51 PM

Tony Hoffer · Moderator

Was the .542 lift cam ground on and undersize base circle? or was it specc'ed for a higher ratio rocker?

Lost in the 60s · President

Welcome
Bungy is right. To get the high lifts of modern cams to fit in old blocks, the base circle is smaller. The lifter lash is set on the base, so 2 lobes with the same HEIGHT will have different lift specs depending on the base circle diameter.

What cha got that the 400 is going into.... confuse

The Pontiac engines were built for torque and never were high revving with a crazy cam from the factory. You must have a pretty radical set-up to need/make use of a cam with .542 lift.... biggrin

BLUESS · Contributor

Thanks for the responses guys. I was thinking it had to do with the smaller base circle thing, but was not sure. It is my kids car and he was the one who saw the differance in the lobes. We were thinking bigger cam = bigger lobes. Will this affect the length of the pushrod?

Lost in the 60s: its in a 78 TA 400 with old 670 heads from the 60s. He says that I always go to small of a cam, so he wants to try this. The car runs 12.60s @107 but seemed to run out of breath 200-300 feet before the end of the 1/4 mile with the old cam. His motto is, there is no such thing as to much cam, just not enough motor. We can't wait to get it together and bring it to the track . Thanks again.

Lost in the 60s · President

Yes, there is a such a thing as too much cam........when it exceeds the limits of the other, related parts. Sounds like it was running out of gear ratio before track and the speed seems to indicate that too. The engine is reaching the max rpm before the trap. Does it have 4:56's ? I had a Chevelle that ran 12.65 at 118 mph with 3:73's. 4.10's would've helped lower my et as I was going thru the traps well below redline.

You will need a push rod checker to see what length push rod is needed to keep the valve train geometry aligned with the valve stem. The rods he has now will most likely be too short for the rocker arm tip to align in the center of the stem.

frank · Active Member

so if your running 12.65 what should your mph be. i thought that was about right. my car is really wackey it runs 11.54 @ 110 i have nothing at far end of track. you can feel the car slowing down. a gear vender od would be nice.

John D · 2K+ Club

His motto is, there is no such thing as to much cam, just not enough motor.

I'm really biting the inside of my mouth right now.... disbelief

Tony Hoffer · Moderator

again.. If anyone is picking up 25MPH or over on the backhalf of the 1/4 Mile ....Id like to talk.. But Ill have a look at your 60' first

When my car ran 12.0's it would MPH about 109-110-

Pontiac and Chrysler wedge engine always have a really ****ed off sound with a race cam.
Im guessing the wedge heads are a little on the restrictive side so they ramp the duration up to compensate. Much like an NHRA stocker.

Tony Hoffer · Moderator

When it ran its 11.38 it MPH'ed at 116.37 with a 1.551 60' it picked up 22MPH on the backhalf.

frank · Active Member

my 60' is 1.559 and half track is 93 so i'm picking up 17

-- Edited by frank on Tuesday 22nd of February 2011 08:02:47 PM

frank · Active Member

i have 400 tranny with ratchet shifter for years i have tried to shift at just the right time and squeezed out a 11'65 the daughter gets in just leaves it in drive and she ran the 11,54 what the heck. she is about 100 pds lighter.

-- Edited by frank on Tuesday 22nd of February 2011 08:08:53 PM

Tony Hoffer · Moderator

I still have the column shifter and it hangs up on the header in low... So I always race in Drive.. LOL

Ive done some secret modifications to the governor so Its shifts right where I want it.

SShink · 3K+ Club

frank wrote:

i have 400 tranny with ratchet shifter for years i have tried to shift at just the right time and squeezed out a 11'65 the daughter gets in just leaves it in drive and she ran the 11,54 what the heck. she is about 100 pds lighter.

-- Edited by frank on Tuesday 22nd of February 2011 08:08:53 PM

Frank, that makes sense to me. I've always heard that removing 100 lbs. from the car = 1/10th of a second in the quarter mile.

Chris R · 2K+ Club

frank wrote:

i have 400 tranny with ratchet shifter for years i have tried to shift at just the right time and squeezed out a 11'65 the daughter gets in just leaves it in drive and she ran the 11,54 what the heck. she is about 100 pds lighter.

-- Edited by frank on Tuesday 22nd of February 2011 08:08:53 PM

Its possible that 100lbs could be the difference.

frank · Active Member

i know all about the 100 lds. it was the shifting part that got me. i spent a lot of time perfecting that for what seems to be for no reason. i never evan tried just leaving it in drive.

-- Edited by frank on Wednesday 23rd of February 2011 06:11:40 AM

-- Edited by frank on Wednesday 23rd of February 2011 06:12:29 AM

BLUESS · Contributor

alright guys, both my son and I know it takes a thought out matched combo, he just says that to get me riled up. The cam we took out was only good to 5000 rpms. The new cam should go to about 5800 or so. As far as mph on the back half, we were only gaining 18-19 mph. I don't have the time slip with me right now, but I think it was 1.7-1.8 60ft, 7.95 1/8 @ 88 mph and 12.66 @ 107. The rest of the combo is a th400, 3500 stall, 3.90 gears , 28x9x15 slicks,in a 3700lbs car. We thought it was just a little short picking up on the back half of the track.

Lost in the 60s · President

As long as the rest of the valve train is up to the increased rpm and the valves don't hit the heads, the extra 600-800 in each gear should get him very close to hitting red line closer to the light... emote.img?ID=15282

Winston Wolf · Member

Here is my cousin's 68 GTO with a 455. In the second run, you will see the shift light that is set at 5,000. You don't need to rev them (Pontiacs) too much higher to make HP. This one runs to about 5500 and puts out just a tic over 500 HP. The first run is an 11.50 and the 2nd the in-car is a 10.90 using a small shot.

SShink · 3K+ Club

Winston Wolf wrote:

Here is my cousin's 68 GTO with a 455. In the second run, you will see the shift light that is set at 5,000. You don't need to rev them (Pontiacs) too much higher to make HP. This one runs to about 5500 and puts out just a tic over 500 HP. The first run is an 11.50 and the 2nd the in-car is a 10.90 using a small shot.

SWEEEET! That video makes me want to go to Rock Falls NOW!

Dave Seitz · Mega Poster

Are the heads stock, what do they flow, porting gets more flow then bigger valves and that has been proven on the dyno and track.