[455rebel]

Had a voo doo 702 cam loose a lobe and went with the summit 2801 as a cheep fix.
All went well with the install and break in, had everything dialed in with the old cam but now have to start all over again. Drove the car 400-500 miles now and been noticing light valve rattle on light thottle and light load. When climbing a hill on light throttle is when it's worse.
Backed initial timing down from 16 to 14 btdc , no change. Backed down to 12 then 10 no change. I'm running man vac to dist so I took another 4 degrees out and helped but still ping ping ping. I put stock adv springs back in dist and backed initial down to 8 btdc and finally now no rattle under light load. On paper these cams look similar but in the engine they sure act different . the 702 had more sound, it must have been bleeding some of the compression off at low rpm.
Any u all running the 2801? What is your initial timing?
Thanks
It may be scratched
It may be dented
But I drive the beast
Like it was rented

[Blued and Painted]

what type distributor?
How much mechanical advance.
What cylinder heads?

[tom s]

455?

[ta man]

What is your total mechanical timing?Was the cam degreed?Is your vacuum advance stuck on?First thing I'd do is confirm total timing and see if the vacuum advance is stuck...

[455rebel]

455, 73 bonie donar, all stock except 2801 cam. 400 6x4 heads cut .020
Cardone dist, crane vac can set to pull 10 deg. Inital was 16btdc. Now 8.
Total 30deg now.was 36.
Problem was too light springs in mechanical adv. At light throttle the vac can was engauged And the light spring gave it too much adv.before the vac signal dropped off. I think.
Now that I've got it not pinging lm going to up the initial to 10-12 deg. And test drive.
I run 93: bp has.
Stock soop bowl pistons .
With the old cam I ocasonally ran some 87 gas with no ping!
Thanks

[77 TRASHCAN]

I'm no expert, but your combo is close to the edge of octane sensitivity, requiring the modifications you've just made.
You've got nearly a 10:1 compression ratio. I'm wondering if the 2802 cam might have been a little better for you...
Keep up the good work, "Rambler Man"!

[tom s]

I did a 455 with a 2801 with 9.5 true CR and it pumped 200 and needed race gas.Would not run on our 91 CA gas.A 2802 might bleed off at idle but is designed to build more at upper RPMs.Just no free lunch.Do it right the first time or do it again later.Tom

[steve25]

Do a cranking compression test on atleast 4 cylinders ( 2 on each bank) and note them down, then get a 2 and 4 degree Cam key, pull the timing cover and try each Cam key along with a cranking compression test, whichever one gives as close to a 25 psi drop , use it and put the motor back together!
If there is one thing that I have found out over the years a Cam that size and with low compression Pontiacs is that once you get to 9 To 1 comp and if you are not going after every little scrap of power , then leave it at 9 to 1 as the will allow you to run a really good advance curve , plus add a good shot of vacuum advance and that all adds up to better overall drivability then if you had 9.8 static compression.

All of this is even more of a concideration with a 455 , its greater stroke related piston speed builds cylinder pressure far faster then the 3.750" of 4.00" stroke motors!
Note that it does not take much pinging to spin the Rod bearings out of a 455 ( don't ask me how I know this ) ,so correct this issue soon!

[Cliff R]

"455, 73 bonie donar, all stock except 2801 cam. 400 6x4 heads cut .020"

6X-4 heads untouched come in between 89 and 96cc, with the vast majority of them at 92cc.

This means close to 10 to 1 compression on a 455 build assuming standard thickness head gaskets and "normal" deck height.

The 2801 cam is better suited to a 400 engine build down around 9 to 9.5 to 1. So basically you don't have nearly enough cam in the big 455 engine and it's going to make a LOT of cylinder pressure at lower rpm's and require either high octane or less than optimal timing specs, or a little of both.....Cliff

[Blued and Painted]

I'll use the wallace sight.
6x4- I will round down to 93cc.
Mill heads .020, subtract 4cc.
Cut the valves and seats type valve job, add 2cc
Piston to deck, .010 in the hole
Piston volume- unknown
comes out to 9.74 to 1.. Not crazy out of the ball park

Yes the cam is a bit small, but still bigger than stock.
Lets check the cranking compression before deciding its un-tuneable

http://www.wallaceracing.com/headmill.htm
http://www.wallaceracing.com/head1.htm
http://www.wallaceracing.com/cr_test2.php

[grivera]

Were the heads cc'd to get an exact #?

[455rebel]

I'll play with the inital and get back. Might run a comp test this weekend.
Thanks

[455rebel]

Originally Posted by Blued and Painted

I'll use the wallace sight.
6x4- I will round down to 93cc.
Mill heads .020, subtract 4cc.
Cut the valves and seats type valve job, add 2cc
Piston to deck, .010 in the hole
Piston volume- unknown
comes out to 9.74 to 1.. Not crazy out of the ball park

Yes the cam is a bit small, but still bigger than stock.
Lets check the cranking compression before deciding its un-tuneable

http://www.wallaceracing.com/headmill.htm
http://www.wallaceracing.com/head1.htm
http://www.wallaceracing.com/cr_test2.php

What about the soup bowl pistons, they were large dish, I think the Bonnie. Was close to 7.5 to 8 to 1. I could run 87 With the old cam. Bumped the timing to 12deg btdc.no ping yet but it ant been hot yet.

[455rebel]

Originally Posted by grivera

Were the heads cc'd to get an exact #?

No.

[455rebel]

I remember doing some rough math when I put the heads on over a year ago. Think it was somewhere near 9 to 1 , or less.
This engine had like 7..8 to 1 stock if I remember right.

[455rebel]

I done some rough math when I put the heads on over a year ago. I think 9 to 1 or less was my best guess.
It would run on 87 with old cam.

[steve25]

You keep referring to Soup bowl Pistons and Pontiacs never had such, they had a chamfer around the top of there OD!
Are these 8 valve notch type pistons you have in the motor?

[Cliff R]

The only high compression 455's were in 1970 with #15 and #64 heads. In the later years the heads had HUGE chambers to reduce the compression. Most of those later engines are under 8 to 1 when you do the math on them, but they didn't lower the compression with the pistons, it was done with the combustion chambers.

In any case, the big 455 sees the 214/224/112 like a very small cam. It will make a lot of cylinder pressure early, and if the static compression is very high, it isn't going to like it......IMHO.....Cliff

[tom s]

Steve,very old info but pontiac did have dished pistons in 61-62 for sure for their economy engines.In 63 they made the diff with head CCs.Tom

[455rebel]

Bumped it to 14btdc and drove it20t-30 miles tonight, it rattled in light throttle up hill tonight.
Try to find stiffer dist springs tomorrow and back down to 12btdc and get back. Try to do a comp test if time allows. Thanks