All Summit 2801 cam vacuum
 

If you have ever used a summit 2801 what kind of vacuum did you have?

I am sorting some things out and was curious what I could expect in the form of vacuum with this cam.

Thanks for your reply

Greg

Depending on your engine and static compression you should have between 16 and 17 hg maybe even a tad more

400 (040) flat top pistons
13 heads 9.5:1
pontiac 1965 tri power
2801 cam w adjustable rockers cam degreed by machine shop
Summit ready to run dist. adj vacuum can
12-13 inches of vacuum

Still sorting alot of things out

Only running center carb for start up

Greg

"2801 cam w adjustable rockers cam degreed by machine shop"

Where did they put it in at?

Ignition Timing at idle?

Deck/COmpression Ht of pistons?

Valve relief CC?

Gasket thickness?

13 are 72CC ...stock IIRC???

Calculating your CR.

The Summit 2801 is very close the the original tri power cam (Melling 068). You should have plenty of vacuum to run power brakes. The only thing I see sketchy in your combo is the Summit distributor. Never had any luck with anything except an original Pontiac dist.

I had to find a small cap distibutor for the tri power. I am looking for some one to restore a original didstributor that has had a pertronics put in it.

Greg

Suntuned might be able to help you.

I run the Summit 2801 in a 400 9.25:1 compression in an automatic with 3.08:1 gear. Heads had some work done and have headers with a stock intake. Vacuum is 17.5" and is a really good cam in a 400. Best band for your buck type of deal

Something's not right. I had 14+" vacuum in a 9.25:1 400 with a comp xe274. I would expect a minimum of 16" vacuum from that cam unless your compression is really low.

compression check

1 167 2 167

3 160 4 165

5 160 6 155

7 162 8 167

#13 heads ccd at 77 with 7cc relief

Flattop pistons

I don't know any more

Greg

Following both threads.

Is you vacuum steady at idle?
Off idle? ~ 2k RPM?

Idle 11 inches of vacuum

1400 rpm 14.5 inches

2000 rpm 16

If the needle is steady,I'd try advance the timing,
Current ignition timing? Idle RPM?
Do you have vacuum advance connected?

Some good diagnostic info:
https://www.crankshaftcoalition.com/...gine_diagnosis

Greg, My new 400 build has 9.94 to 1 compression, the 2801 cam, stock exhaust manifolds, 2.5" exhaust system, Q-jet carb on the stock iron intake.
It's a fresh build and still breaking in (maybe 10 miles on the engine since it was installed a few weeks ago). The heads are 1970 small valve #16's.

Timing is 12 degrees initial; 36 degrees total (by 3000 rpm) and has a 10 degree vacuum advance cannister for 46 degrees total for cruise.

Vacuum at 800 rpm idle (no vacuum advance) was 15.5 - 16.0 inches and we expect it to go up a couple pounds with more miles as it breaks in. The running temperature was 180 - 190 degrees on an 85 degree day.

Cylinder pressure was consistent at 175 in each cylinder. The cam was installed straight up (I don't recall the intake centerline).

Dennis

Dennis I would try removing the vacuum advance and bringing up the initial to 18 or 20..... You will need a 160 thermostat to do this... I would try 89 gas too if your using 87..

The 2801 is an excellent cam for a powerful street Pontiac motor..

Dennis

I just sent the carb to Dick Boeneske to go through, it was not idling at all. I was surprised I thought my compression test would ne higher. with almost 10:1 compression.

I have been following your build and am quite impressed. I found out my small valve 15s ccd at 90 cc which gave me about 8.1:1 compression on the previous build.

Good to hear from you.

Greg

I'm running the 068 in my 70 400. 10.13:1 compression with the original 12 heads.

I run 14 initial timing with 34 degrees total all in by 2600 rpm. I run an additional 10 degrees of vacuum advance. I installed the cam on a 108 ICL.

I have a solid 13 inches of idle vacuum at 5,000 feet elevation. At sea level it's a little over 16 inches.

Very small cam for a 400, idles smooth, very docile. The engine has been perfect on 91 octane for a few years now.

The true static compression ratio is a BIG player with engine vacuum.

Altitude is another, and of course which cam and where it is installed.

With a 2801 cam, and 9.5 to 1 compression you should see around 14" vacuum with only 10-12 degrees initial timing.

The 068 cam will make similar numbers.

Carb tuning becomes a player and this assumes that adequate idle fuel is available or you may not reach those numbers.

One can also increase initial timing and see higher numbers but I seldom use manifold vacuum to the advance as it's really not needed with the 068 and 2801 cams in 400 builds provided they have some compression in them.

Now, if we increase the static compression ratio to 10 to 1 or a tad higher the same build will make 15-16" vacuum with only 10-12 degrees initial timing.

Lower the compression ratio down to 8.5 or a little higher and you'll loose a couple inches of vacuum at idle. Even more important you also loose throttle response and power at lower RPM's, plus less efficiency for "normal" driving. This means increased fuel consumption and not enough power to do a decent burnout up against a stock converter, for example.

So choosing the cam becomes more important than just vacuum production for power brakes and accessories. A smaller cam becomes the better option when we aren't running optimal compression. This also works for us with higher compression. If I move up to 10.5 to 1 compression with my 400 build the 2801 no longer becomes the ideal cam, and one can quickly get into troubles being able to manage pump fuel with "normal" timing/fuel curves. At this point the 2802 or even better the Crower 60243 cam works better. With higher compression and larger cam we will still see good vacuum at idle, about the same off idle and low speed power, but a BUTT LOAD more upper mid-range and top end power especially if we have increased head flow to 230-240cfm or so. The higher compression engine can also manage pump fuel w/o issues with correct tuning.

This sort of throws a monkey wrench into the proverbial "brick-wall" of 9.5 compression for pump gas. That statement is one of the most inaccurate and miss-understood ever to be put in print on these Forums.

I've seen engines with as little as 9.2 to 1 compression pound the rod bearings right out of an engine on the dyno before they even reached optimum timing numbers. I've seen engines with well over 10.5 to 1 compression and iron heads manage pump fuel just fine for decades with well chose camshafts in them. I've built a handful of those here and to date zero issues anyplace, and a couple of those iron headed 400's push street driven Pontiac's well into the 11's without a lot of gear or converter.......FWIW.......Cliff

The lions share of power originates from induction efficiency (heads, intake and valve motion curve).

454 with 8.2 compression. .050 duration 236 / 242 and a mismatched Hurricane single plane intake. All gain above 3200 RPM and made 567 HP. Obviously a dual-plane intake would have improved below 3200.

As you increase compression up the scale you get less return. Moving from 8:1 to 9:1 will yield more than 10:1 to 11:1

Don't remember the numbers but the 400 low compression motor in the 81 has one. Idles like a stocker.