Retarded cam = low vacuum levels Q

[C9]

My pal who owns the SBF powered 46 Ford with the low vacuum and no shifting into high gear probs has the car at the trans shop now.

I'm beginning to think the cam may be a tooth off and perhaps retarded.

Anyone ever stuck a vacuum gauge on an engine that was found to have a severely retarded cam?

Right now, I think he's grasping at straws . . . he needs to run a compression check, firing order check on the plug wires etc.

He doesn't seem to have a vacuum leak.

The engine runs pretty good and pulls the big ol tub along pretty good.

I'm beginning to think the guys who put things together do hot rods as a sideline and their real job is at the circus wearing big shoes and lots of make-up....

[enjenjo]

I believe Ford had a factory cam retard for a bunch of years, on the order of 4 degrees. If they are a tooth off from that it could be a problem.

[tomslik]

My pal who owns the SBF powered 46 Ford with the low vacuum and no shifting into high gear probs has the car at the trans shop now.

I'm beginning to think the cam may be a tooth off and perhaps retarded.

Anyone ever stuck a vacuum gauge on an engine that was found to have a severely retarded cam?

Right now, I think he's grasping at straws . . . he needs to run a compression check, firing order check on the plug wires etc.

seems to me there is a difference between early and late cams as far as firing order
late used the 351 W firing order(i think)
just how low IS the vaccuum?
what's your altitude?
He doesn't seem to have a vacuum leak.

The engine runs pretty good and pulls the big ol tub along pretty good.

I'm beginning to think the guys who put things together do hot rods as a sideline and their real job is at the circus wearing big shoes and lots of make-up....

if it runs good, it's prolly not a tooth off...

[Dave]

My pal who owns the SBF powered 46 Ford with the low vacuum and no shifting into high gear probs has the car at the trans shop now.

I'm beginning to think the cam may be a tooth off and perhaps retarded.

Anyone ever stuck a vacuum gauge on an engine that was found to have a severely retarded cam?

Right now, I think he's grasping at straws . . . he needs to run a compression check, firing order check on the plug wires etc.

seems to me there is a difference between early and late cams as far as firing order
late used the 351 W firing order(i think)
just how low IS the vaccuum?
what's your altitude?
He doesn't seem to have a vacuum leak.

The engine runs pretty good and pulls the big ol tub along pretty good.

I'm beginning to think the guys who put things together do hot rods as a sideline and their real job is at the circus wearing big shoes and lots of make-up....

if it runs good, it's prolly not a tooth off...

I agree.. Not saying it will miss and pop but it sure should be sluggish..
Dave  

[C9]

Enjenjo:  Yeah, forgot about the retarded sprockets/cams.  If the engine was pretty worn and the chain stretched, that could add to it.


Tomslik:  Good call on the altitude, I'd forgotten about that.  Vacuum comes down 1" for every 1000' of additional altitude.

My Buick engine used to idle at 18-19" at 350' in Central California and started idling 16" or so up here at 3300'.
After some tuning and leaning my carb out a bit it idles a little over 17".

When I had a big cam in the Buick - and at 350' altitude - it idled about 10-11" vacuum at 600 rpm and when you spun the engine up to 1200-1500 rpm with no load it would level out at 18".
Backing off the throttle quickly it would go to 20-21" with no load and then drop to 10-11" at idle.

The SBF - a 302 of unknown vintage - idles at 10" vacuum and when spun up to 1800 rpm or so pulls 15" vacuum.
Letting the throttle off rapidly the vacuum goes to 17" then sags to xx".

Right now, it's starting to look like there is no vacuum leak.

The trans guy told him they'd found a modulater that operated at low vacuum and they would put one in for him.

Makes sense, perhaps some cars destined for a Denver dealer or the like would have had a high altitude device put in at the factory.
I know that Ford - back in the 50's - had lower gears and leaner jets for the Denver market and I've heard they had bigger brakes for mountain driving as well.
Probably went from the passenger car 10" brake drums to the station wagon 11" drums.
We used to swap out our Shoebox coupe drums for the station wagon drums and it made a difference.


One thing I am suspicious of, is the Lokar shifter that was recently installed.
He's installed several different styles of floor shifters for automatics in the past and swears this one matches the trans detents etc.

What I wonder is, if the Lokar has the wrong shift detent plate in it and he doesn't realize it.

Right now he's distracted by company, but once they leave maybe we can get the car up on the rack and run some basics.
Unless the trans guy fixes it.

[Dave]

I threw the vacuum gauge on the roadster last night to set the idle.. Idles at 20 and i just didnt check any further. Seemed good enuff for me on a used 305.
Dave  

[Bill Adkins]

Does your friend know how the engine is built? Is it stock or has it been modified. The modulator shouldnt prevent an upshift, by design it only directly effects the abruptness of the shift quality. The governor is more responsible for upshift with the throttle pressure adjustment modifying the shift timing sequence. A higher lift cam or one with close lobe centers will change overlap and decrease idle vacum signal but benefit from increased volumetric efficiency at increased engine speed. Hope that helps.
Bill

[tomslik]

I threw the vacuum gauge on the roadster last night to set the idle.. Idles at 20 and i just didnt check any further. Seemed good enuff for me on a used 305.
Dave  

you won't see that up here..... :cry:

[C9]

Does your friend know how the engine is built? Is it stock or has it been modified. The modulator shouldnt prevent an upshift, by design it only directly effects the abruptness of the shift quality. The governor is more responsible for upshift with the throttle pressure adjustment modifying the shift timing sequence. A higher lift cam or one with close lobe centers will change overlap and decrease idle vacum signal but benefit from increased volumetric efficiency at increased engine speed. Hope that helps.
Bill

He doesn't know how the engine is built . . . it's supposed to have a cam in it, but if it does it may be one of those fabled RV cams I'm always hearing about.

If it does have a cam and it's retarded a tooth it may idle fairly smooth.
Regardless, I don't think it has a hot cam.

I have a slightly stronger than stock cam in my roadsters Buick engine and you can barely tell it does have a cam.


The car comes from a guy who doesn't know anything about hot rods or cars other than how to apply stickies and bolt on chrome skulls and the like.
Nice guy, but he depends on others for his info.

Quite the trader he is.
First time I noticed him was as the owner of a very nice and well built full fendered 27 T roadster.
Then he had the 46 built or bought it from the builder, not sure there.
He swapped the 46 for my pals nice little full fendered 29 roadster and my pal was probably smitten with the shiny paint and tuck & roll and didn't look as close as he should have.

The 29 is a well built car with all the good stuff, but he got tired of being cold or hot or didn't care for the air blowing into the car.

Last time I saw the 46's original owner - original to us anyway - he was driving a full fendered A sedan hot rod.
I think he may have swapped the 27 T for that.
Now it's looking like he swapped my pals ex 29 for something else.
God knows where the 29 is now.

Anyway, thanks for the info on the governor.

I'm hoping the trans guy gets it ironed out.

If the modulater isn't the problem, the trans guy will have to fix the trans and we'll have to do the R&R on it.

[wayne petty]

just a few thoughts.....

is the modulator tube steel   with vacuum hose at each end???/

vacuum hose run the full legnth will usually not transmit the proper signal..

vacuum hoses  collapse sometimes inside...  limiting flow and signal...

they sell for a buck at most tranny parts stores a 90 degree molded modulator hose...  they used to include them in rebuilding kits...

straight vacuum hose bent 90 degrees will kink and close up....

plastic vacuum tees have melted and blocked vacuum  even though they look perfect...

the fittings in the intake have gotten carbon/coke  build up and blocked the proper flow...

these are all things that i have found and fixed on cars over the last 30 years.... no guess work here...

i like to pull the modulator hose off at the transmission with the engine running to check flow....     the engine speed should change when you block and free up the opening...


as for retarded cam timing.. i have seen that... too... one notch off... yep they will run...   i even fixed a chevy chevette that only had 6K miles on it...  everything was done... several times over... exhaust, feedback carb, ecm, i walked over and checked the belt and there is was... 10 years old and one tooth off...  

symptoms of modulator problems is  failure to upshift and when you take you r foot off the gas... it sort of feels like it had gone into neutral...motor just sort of freewheels...

[kb426]

My exp. with retarded cams is that the engine will sound flat. It will make excessive heat. Poor throttle response. To the best of my feeble memory, none of the 302's have retarded crank gears. That was 460 and maybe 400 stuff. My 302 at 3000' idles at around 16 inches. It has a stock cam for an explorer. I'd pick on  something else besides low vacuum but I've been wrong so much lately that you might want to do the opposite of anything I say.

[reborn55]

With the vacuum gauge installed--try advancing the timing a little at a time and see if vacuum goes up.  Could be off, bad balancer, etc.

[Crosley.In.AZ]

IF reverse works well... the direct clutch (3rd gear) should work...

I imagine the problem s inside the v-body... if the modulator is hooked up 10 -12 inches of vacuum minimum  with the pin installed in the modulator valve.