How much vacuum are you pulling with your Delta 250S cam?

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Splangy

Splangy

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How much vacuum are you pulling with your Delta 250S cam? Has anybody measured before and after installing the cam? The reason I ask is that I just got my rebuild running and found manifold vacuum to be closer to 15 than 20, but it will increase to 20 if I advance the timing well beyond the 7 degree BTDC mark.

Is this a normal amount of vacuum for this cam?

Oh, and Delta recommends a valve lash of .014" for both, intake and exhaust valves. The valvetrain seems a bit noisy. Is that typical?
 
Last edited:
Morse_FJ40 said:
Is that the better than stock re-grind??
Click to expand...

It's one of a couple regrinds that Delta offers.

Specs:

Perf 250 S grind
Duration intake 250
Duration exhaust 254
Intakes opens 17, closes 58
Exhaust opens 60 closes 14
cam rise .255 L/C 108 degrees
Lash intake .014 exhaust .014
 
I forget about the numbers, I've got an old school RV cam. pulls ab out 15 inches at idle. It's normal for this cam.
 
Same issue here

Just stumbled on this thread :eek:

I just finished my 2F rebuild ( https://forum.ih8mud.com/60-series-wagons/399712-another-2f-rebuild.html ) - with Delta 250S camshaft .

The valvetrain was very noisy when the engine fired up . So first I closed the intake valve lash from the advised 0.014" to 0.008" and that helped a bit https://forum.ih8mud.com/60-series-wagons/402996-using-valve-lash-make-valve-train-quiet.html

The noise was still very bad over 3000rpm so I fitted new valvesprings . ( see this discussion : https://forum.ih8mud.com/60-series-wagons/402283-hi-po-camshaft-valve-bounce-clearance.html )

I am picking the car up tomorrow but my mechanic says the
ticking is still there beyond 3000rpm. Not to sure what I will do next to sort the issue - maybe just run with it and and get a better stereo?

Re the vacuum - My previous stock 3F carbed engine I took out pulled 20 -21 inHG vacuum at idle . The 250s in the 2F pulls a lower vacuum 17-18 inHG ( needle jumping more - probably due to the longer duration of the cam )
 
Yspen said:
Re the vacuum - My previous stock 3F carbed engine I took out pulled 20 -21 inHG vacuum at idle . The 250s in the 2F pulls a lower vacuum 17-18 inHG ( needle jumping more - probably due to the longer duration of the cam )
Click to expand...

I'm getting a fairly steady 17-18in now. My valvetrain really seems noisiest at idle. I decreased the intake lash to .008 and noticed a little improvement, too. Did you ask the guys at Delta about it?
 
The guys at Delta advised to close the intake by 0.004" and see what happens - I set it up to stock specs .

His exact message : ( I asked whether new valve springs were required or If lash needed adjusting )
The new grind is a little more aggressive but nothing that requires more spring. try the tighter lash and see if that's better .
I would run the lash at .010 and see if that helps
 
My experience is that a stock rig runs at about 20 inches of vacuum. Our Downey Cams dropped that down to about 10 inches. Adjusting the valves might bring the 10 inches up to 11 or 12, still not enough to run TBI injection (and changing the MAP Sensor is not a legitimate remedy).
Next, your stock valve spring are only rated at 59 to 71 lbs. (too weak, can cause valve float), and they coil bind at .440. Downey sold valve springs rated at 120 lbs. that did not coil bind until .570. I may still have some of those springs left if interested!!!
 
The 250S grind is a very mild grind and according to Delta should not require more spring .
I fitted SBC springs ( VS 677 ) to replace the old tired springs - they rate at only 10lbs seat pressure more than stock and will not bind . They did the job for me in getting the valvetrain quiet - vacuum obviously unchanged .
I did not want to go to a too stiff a spring on a mild cam - did not want unnecessary excellerated wear .
 
Downey said:
My experience is that a stock rig runs at about 20 inches of vacuum. Our Downey Cams dropped that down to about 10 inches. Adjusting the valves might bring the 10 inches up to 11 or 12, still not enough to run TBI injection (and changing the MAP Sensor is not a legitimate remedy).
Next, your stock valve spring are only rated at 59 to 71 lbs. (too weak, can cause valve float), and they coil bind at .440. Downey sold valve springs rated at 120 lbs. that did not coil bind until .570. I may still have some of those springs left if interested!!!
Click to expand...
This is at sea level, yes?
 
Downey said:
Not sure, believe most specs are at sea level ??? I'm not a mechanic.
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No worries.
I am at 5000’, so the guys at Delta were interested in that when I sent my cam in.
I can report my vacuum when I get the cam back in.
 
PabloCruise said:
No worries.
I am at 5000’, so the guys at Delta were interested in that when I sent my cam in.
I can report my vacuum when I get the cam back in.
Click to expand...
I'm at 3500ft, KC grind cam, I pull about 16.
 
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