[Cliff R]

What distributor? What has been done to it?

We use a different approach for each type of distributor when it comes to building an advance curve for them.

For the most part I do NOT use, or work on aftermarket "high performance" distributors. If/when I end up having to use one here, it will usually be the MSD ready to run unit, simply because it is very simple, and has a vacuum advance. The MSD billet distributor is a nice part, after you remove and zinc plate all the internals (they rust just looking at them), but we use and highly recommend a vacuum advance on ALL of these engines.

Anyhow, I will repeat this part, it is DIFFICULT, if not near IMPOSSIBLE with some of these aftermarket distributors, and aftermarket part (spring/weight kits) for stock distributors to get a decent advance curve.

The aftermarket stuff will more often than not use parts that increase the leverage of the weights on the center cam so the curve is much quicker, and difficult to control, plus more times than not they put some of the curve in at idle speed.

This fact makes idle tuning very difficult, and at times impossible. I'll bet that 9 out of 10 carburetor "issues" when it comes to idle tuning are actually distributor problems instead. I would also add here that currently there is some PURE JUNK available for these engines coming in from off-shore. They look like factory HEI's, but the parts are "soft", and the quality of them is simply OK to PATHETIC. I don't want any of them sent here for any reason. Until the supply of factory HEI's is completely gone, we'll keep working with stock units and continue to get the results we are looking for with minimal effort.

I'd like to have $1 for every phone call or email I get from folks who tell me that they can NOT get their engine to idle well, and it slows or stalls when the transmission (automatic) is placed in gear. They will have dozens of questions about the carburetor and setting up the idle system, when 90 percent of the time the cure is to remove the POS advance weights/springs that have been installed and put in something that does NOT allow any timing to be added below about 900-1000rpm's.

Once they do this, and the timing now becomes ROCK SOLID at idle speed, the carburetor "issues" go away more times than not........Cliff

PS: I'll add in one more thing here so I can make a few more enemies. We do NOT advocate using manifold vacuum to the advance for most of these set-ups. Despite reading the long/lengthy and heavily regurgitated information on this subject using Google searches, that information is very good, but flawed in several areas.

IF you find that you have to run the timing clear off the scale, or add 15, 20 or even 30 additional degrees of timing to make the engine happy or want to stay running, then you have fundamental issues someplace else, such as too much cam and not enough compression, your carburetor can NOT supply the needed fuel at the engines current vacuum reading at idle, or combinations of several other problems. Basically we NEVER use tons of timing to curve running issues with these engines, you have problems in other areas and more times than not that is simply a "crutch" fix instead of finding and correcting the "root" issue(s).....IMHO

Even with that said, some engine like a little more timing at idle, so we tune all of them on a case by case basis, but most of the ones we build and tune here do not want, like, or need a ton of timing at idle speed to be happy.....FWIW

[TedRamAirII]

Cliff, I have a stock GM points distributor, with a Pertronix point conversion. Could not tell you the part number off hand. It does have a vacuum advance to Manifold Vacuum. My carb 7028262 I think, does not have a ported port. Compression ratio is approx 10.5. I end up with 9 initial and 30 total, but its all in at 2500. It does idle better with more initial. I have not had time to play with the timing to see where the best inital should be. Whats the best procedure to actually determine what the best initial timing should be? Yes I do need to get the Qjet carb tuned better. I do have your book, but have not had the carb off yet. I want to have your kit on hand before I tear it apart. Thank You All. ; )

[455rebel]

Originally Posted by Cliff R

The way I tune all street set-ups here is to forget about the vacuum advance and find the ideal initial timing, then total timing the engine wants combined with the most ideal advance curve.

Once you find settings that allow for hot restarts without "bucking" the starter, and a curve that's fast enough for best power and total timing without detonation, lock the distributor down and forget it.

Then start adding in vacuum advance to improve things in the "normal" driving range.

Most very well thought out engine combinations will like about 10-14 additional degrees from the advance at cruise. This will improved off idle power, throttle response at low throttle angles, fuel economy, engine cooling and allow for a leaner mixture from the carburetor w/o negatives. This also adds up to less carbon build up in the cylinder heads and exhaust system.

With higher compression engines and relatively small camshafts you'll find 9 times out of ten ported vacuum to the advance will be the best choice. Same thing with very well thought out engine combinations making great power, there will seldom, if ever be any need to run the timing clear off the scale at idle speed to make them happy.

If you do not have an adjustable advance (for how much timing is added), there are several methods to modify them. I use the MIG here, but a screw and a washer can be made to work equally as well. Use drill bits to measure the travel of the arm so you know how much timing is being added with each modification. .120" is around 5 degrees (10 at the crankshaft).

You can also custom modify the mechanical curve in a similar manner with a positive stop for the advance. HEI's are slightly different that points distributors, but same basic concept, you need to control the amount of movement of the rotor from idle to full advance.

I attached a couple of pics showing how I set them up here. This gives you the amount of advance added, when it comes it can be verified and adjusted on the distributor machine or engine with a marked balancer and or dial back timing light.....Cliff

PS: those aftermarket advance kits are completely HOPELESS for attaining the same results, and are complete JUNK, IMHO. They move the relationship of the cam/weights and make it nearly impossible to establish a smooth advance without some of it in at idle. I just toss all that crap in the trash can when factory distributors show up here with it, and install the factory parts for perfect results every time.....

I spent weeks dialing the dist in With the 702 cam, I bought a crane adj vac can and I had springs of all asst sizes. A member Geoff I believe helped me with the dial in.
All that went out the window with the new cam.
The stiff springs , and backing the initial down to 8btdc are band aid fixes, I know , just trying to get the rattle stopped before I do some damage.
I used the 2801 on forum advice , and because budget .
Hopefully before I go 6ft under I can do a complete rebuild and do it right.
I'm in process of cam retard this weekend, hopefully that bleeds of some low end comp and I can retune my dist.
I have more fun in this old ratty 4 door, and get more attention at the gas pump than it should.
What is that dann car? What u got under hood, it sure sounds good. Most I tell 290 on fender, 455 under hood, sometimes I get that jaw drop look, and have to show them.

[Cliff R]

"I used the 2801 on forum advice"

You just plain got some BAD advice.

Using a 2801 cam in a 455 is like having a 2800 cam in a 350 build at 8 to 1 compression. It's a tiny cam and best suited for very low compression and smaller engines, and in the big 455 it's going to make a lot of cylinder pressure and raise octane requirements.

I do NOT believe that retarding that cam is the solution here, I'd rate is as more of a "crutch" fix instead.


"My carb 7028262 I think, does not have a ported port"

Most Pontiac carburetors after 1967 have ported vacuum at the front port in the main casting just to the right (as viewed from the front) of the fuel filter housing.

As with all Q-jets that had a ported source for the advance, it is very well located, and supplies FULL MANIFOLD VACUUM to the distributor with the slightest movement of the throttle.

So basically the only difference between full manifold vacuum and the correct ported port is no timing coasting and at idle with ported vacuum to the advance.

For a high compression 400 engine base timing on pump fuel will have to be pretty "low", or you may run into difficult hot restart issues. This assumes the cam is stock, and not some aftermarket cam with tight LSA and enough overlap to kill off vacuum signal at idle speed.

I have never once found that we had to run very much initial timing on an early high compression engine with a stock cam in it. Most are fine with the timing at or close to stock specs. With aftermarket cams, larger than stock and/or tight LSA, more times than not we'll have to increase timing at idle some. At the same time we'll add idle fuel as well, as the engine simply isn't pulling (vacuum) as hard on the carburetor and the stock idle system may not supply sufficient idle fuel to the engine without some help.

Anyhow, that's getting pretty off track for this thread. The easy fix here would be to install a larger cam and all the problems would go away. I've found very few of these types of issues that could be cured by retarding the camshaft, as that usually brings in negatives in other areas as well, like sluggish off idle performance and degraded idle quality, "lazy" in the mid-range and often less power at every rpm......Cliff

[KO]

I ve never seen factory 455 pistons with any type of dish. Ive seen 400s with the large chamfer

[TedRamAirII]

OK. Checked the carb 7040262. No port for vacuum on the left front corner of carb. Engine is a 428 +.30, Cam is 041 , 1.5 rockers. Stock piston Speed Pro 2882G. I'm going to drive it this weekend and see how good it starts while good and hot after a hot soak. Maybe I will revise my initial timing setting.

[Cliff R]

Correct, one of the very few factory q-jets that did not have a ported vacuum source for the advance.

1970 was an "odd-ball" year for that sort of thing, they were trying different methods to employ the advance thru "indirect" sources, switches, etc.

It didn't work out all that well, and after 1970 that port will be there on most factory q-jets.....Cliff

[tom s]

Cliff,I agree!The worst 455 I ever did was a true 9.5 engine with custom dished pistons.That engine pumped 200 with the 2801 and had to use race gas.Ran hard but just sucked as a street car.Needs more cam.Tom

[455rebel]

I'm almost ashamed to admit it(hear hold my beer) but when I installed the 2801 I put the crank gear in adv instead of straight up. The marks are really hard to see. Its straight up now and going back together tomorrow.I knew something was wrong, it ran out of steam at 47-4800 rpm.
Ran a comp test on 4 cyls , a whopping 150psi across the board.
Don't understand why u all thought it would be 200psi.
Bet I'm closer to 8.5 than 9.5
Thanks

[Cliff R]

That isn't enough camshaft to make power to 5000rpm's in a 455 build, not going to matter where you put ICL.

We have to keep in mind here that the 455 is a HUGE engine, and it will see a 214/224 as a very small camshaft, which means smooth idle, strong low end power, and power ending early in the rpm range.

Even in a 400 build with low compression, the 2801 acts like a small cam, but it is much better choice there than in the bigger 455's since it doesn't make nearly the dynamic compression as early in the rpm range in the 400's.

Some folks choose it in lieu of the factory 068 camshaft for 400 builds, and it fairs pretty well in those applications.......Cliff

[tom s]

With all due respect to the OP,there have been 50 posts and 3 pgs of people trying to help.In post 8 Steve ask cranking compression.In post 11 it was asked if the heads were CCed and on post 28 it was said to pull the cover to see where the cam was.I posted my experience with a 2801 in a TRUE 9.5 455 with the 2801 cam set straight up and although it ran great it had to have race gas because it pumped 200.The issue has been lack of correct info for people to give solid info.Tom

[455rebel]

Originally Posted by tom s

With all due respect to the OP,there have been 50 posts and 3 pgs of people trying to help.In post 8 Steve ask cranking compression.In post 11 it was asked if the heads were CCed and on post 28 it was said to pull the cover to see where the cam was.I posted my experience with a 2801 in a TRUE 9.5 455 with the 2801 cam set straight up and although it ran great it had to have race gas because it pumped 200.The issue has been lack of correct info for people to give solid info.Tom

Comp 150 psi .
Heads weren't cced.
Cam was advanced(my bad,hold my beer).
Engine came out of a 73 bonnie with 80,000 miles.
Ridge ream, file to fit rings, all stock except for cam.
Why is my comp so low with the 400 Heads?
From what I gathered on hear it should have been 200psi not 150.
With the 702 Cam it pulled from idle to 5100 rpm and would run on 87.
So what about the 2102 With my combo? Would it be the best budget cam?

[pastry_chef]

Originally Posted by 455rebel

I used the 2801 on forum advice , and because budget .

http://forums.maxperformanceinc.com/...d.php?t=787391

We can see one person mentioned 2801 but most were very different.

Originally Posted by 455rebel

So what about the 2102 With my combo? Would it be the best budget cam?

Forget budget. The cost of two Summit cams adds up to more than one Voodoo.

[STEELCITYFIREBIRD]

Run the tank down and put a few gallons of 100+ octane fuel to it, that would be very telling.
Verify you don't have a wrist pin or rod bearing knock. Valve train noise? The Summchit lifters are just that. Bottleneck studs? You may not need to adjust, just torque and go. TBD
-----------------
Think about under what conditions does it knock.
Where is the temp running, and where does it go when it knocks, if anywhere.
Does it run on when you shut it down hot?

It had a cam lobe, and an "ATF oil treatment" in it's diet not to long ago.
Base engine needs to be evaluated and considered.
Do you have blow-by from the crankcase with the PCV valve line capped and removed,with engine hot, held revved @ 2500RPM for at least a minute, from the oil fill cap?
150psi on ALL cylinders?

Honestly, any oil smoke from the exhaust?
>@ start up or on hard accel
>engine braking decel
>Any evidence of oil on the plugs
Any oil burning in the chambers will aid and abet detonation.

This is an 80K motor with a re-ring job. The condition of the guides, valve seals and ring sealing may be suspect...above and beyond the cam choice.

Were the rings file fit rings for std bore 455, or .010"+ rings you file fit?
Ridge ream, makes me cringe. If their is a lot of taper in the cylinders, your rings may have lost their tension prematurely, a leak down test is where I would be @ myself. Maybe even just an air hose connected to the compression tester if it has a quick disconnect.

------------
Garbage in , garbage out.
Let's get all the facts.

Flat top or dished pistons? Your looking @ a big swing in compression ratio.

So you have........ 6x-4 heads,cut .020", factory deck height, .040" head gaskets, stock valve springs, no shims, no valve job in your ownership.
----PREVIOUS CAM----
Lunati 10510703
Advertised Duration (Int/Exh): 268/276
Duration @ .050 (Int/Exh): 227/233
Gross Valve Lift (Int/Exh): .489/.504
LSA/ICL: 110/106

----CURRENT CAM---
2801 Summit
Adv Dur : 288/298
Dur .050 : 214/224
Valve Lift : 0.444/0.466
Lobe Separation (degrees): 112

Correct?

Hope it all comes together for you.... on the cheap!

[steve25]

Did you do the cranking compression test with the Carb wide open?

Now it may be time to rent or get a hold of a leak down tester.

Worn cast piston ring lands ( more than 002" vertice clearance) can bleed of some pressure easy as can non round tapered 80k bores and cylinder head factors !

[455rebel]

Originally Posted by STEELCITYFIREBIRD

Run the tank down and put a few gallons of 100+ octane fuel to it, that would be very telling.
Verify you don't have a wrist pin or rod bearing knock. Valve train noise? The Summchit lifters are just that. Bottleneck studs? You may not need to adjust, just torque and go. TBD
-----------------
Think about under what conditions does it knock.
Where is the temp running, and where does it go when it knocks, if anywhere.
Does it run on when you shut it down hot?

It had a cam lobe, and an "ATF oil treatment" in it's diet not to long ago.
Base engine needs to be evaluated and considered.
Do you have blow-by from the crankcase with the PCV valve line capped and removed,with engine hot, held revved @ 2500RPM for at least a minute, from the oil fill cap?
150psi on ALL cylinders?

Honestly, any oil smoke from the exhaust?
>@ start up or on hard accel
>engine braking decel
>Any evidence of oil on the plugs
Any oil burning in the chambers will aid and abet detonation.

This is an 80K motor with a re-ring job. The condition of the guides, valve seals and ring sealing may be suspect...above and beyond the cam choice.

Were the rings file fit rings for std bore 455, or .010"+ rings you file fit?
Ridge ream, makes me cringe. If their is a lot of taper in the cylinders, your rings may have lost their tension prematurely, a leak down test is where I would be @ myself. Maybe even just an air hose connected to the compression tester if it has a quick disconnect.

------------
Garbage in , garbage out.
Let's get all the facts.

Flat top or dished pistons? Your looking @ a big swing in compression ratio.

So you have........ 6x-4 heads,cut .020", factory deck height, .040" head gaskets, stock valve springs, no shims, no valve job in your ownership.
----PREVIOUS CAM----
Lunati 10510703
Advertised Duration (Int/Exh): 268/276
Duration @ .050 (Int/Exh): 227/233
Gross Valve Lift (Int/Exh): .489/.504
LSA/ICL: 110/106

----CURRENT CAM---
2801 Summit
Adv Dur : 288/298
Dur .050 : 214/224
Valve Lift : 0.444/0.466
Lobe Separation (degrees): 112

Correct?

Hope it all comes together for you.... on the cheap!

Previous cam was a 702 not 703
On very cold mornings I have piston knock for a few min till it warms some.
I have a 195 stat in so it will heat in winter(same as I have ran since engine install)
It ratteled or ping when up to temp , light to part throttle, when climbing hills, in high gear at25-40mph.
I've drove it 1500-2000miles since cam install.
Changed oil twice, filter 4 times, oil never got black.
No blowby. Added about. 1/4 qt in 2000miles.
No smoke. And I've hammered on it a lot!
Pcv works and no oil in line.
Only measured comp on 2 cyls each side, 1,3,2,4.
Plugs look clean, well orangeish from the 104 boost I added.
Valve job done on 400 Heads before install, and Teflon seals on intake guides..
Rings were 10 over and filed to fit.
Wasn't much ridge to cut out.
Dingleberry hone.
The pistons were dished, but according to post hear pontiac didn't use dish pistons.
Comp cam springs, speced for the 702 Cam.
Comp roller tip rockers.
Poly lock adjustable lock nuts.
Factory push rod guides.
As stated before with 702 cam it pulled off idle to 5100rpm.
It would run ocasonally on 87.
Inital at 15-16btdc. Man vac on crane advance can.
Putting it back together today. Will post comp after together.
I will test drive it at initial 8btdc then sneak it back up till it pings or till I get to 14-16 btdc.
Then I'll go back to softer dist springs till I get ping then back down.
Thanks all.

[lfdsteve]

Originally Posted by Cliff R

What distributor? What has been done to it?

We use a different approach for each type of distributor when it comes to building an advance curve for them.

For the most part I do NOT use, or work on aftermarket "high performance" distributors. If/when I end up having to use one here, it will usually be the MSD ready to run unit, simply because it is very simple, and has a vacuum advance. The MSD billet distributor is a nice part, after you remove and zinc plate all the internals (they rust just looking at them), but we use and highly recommend a vacuum advance on ALL of these engines.

Anyhow, I will repeat this part, it is DIFFICULT, if not near IMPOSSIBLE with some of these aftermarket distributors, and aftermarket part (spring/weight kits) for stock distributors to get a decent advance curve.

The aftermarket stuff will more often than not use parts that increase the leverage of the weights on the center cam so the curve is much quicker, and difficult to control, plus more times than not they put some of the curve in at idle speed.

This fact makes idle tuning very difficult, and at times impossible. I'll bet that 9 out of 10 carburetor "issues" when it comes to idle tuning are actually distributor problems instead. I would also add here that currently there is some PURE JUNK available for these engines coming in from off-shore. They look like factory HEI's, but the parts are "soft", and the quality of them is simply OK to PATHETIC. I don't want any of them sent here for any reason. Until the supply of factory HEI's is completely gone, we'll keep working with stock units and continue to get the results we are looking for with minimal effort.

I'd like to have $1 for every phone call or email I get from folks who tell me that they can NOT get their engine to idle well, and it slows or stalls when the transmission (automatic) is placed in gear. They will have dozens of questions about the carburetor and setting up the idle system, when 90 percent of the time the cure is to remove the POS advance weights/springs that have been installed and put in something that does NOT allow any timing to be added below about 900-1000rpm's.

Once they do this, and the timing now becomes ROCK SOLID at idle speed, the carburetor "issues" go away more times than not........Cliff

PS: I'll add in one more thing here so I can make a few more enemies. We do NOT advocate using manifold vacuum to the advance for most of these set-ups. Despite reading the long/lengthy and heavily regurgitated information on this subject using Google searches, that information is very good, but flawed in several areas.

IF you find that you have to run the timing clear off the scale, or add 15, 20 or even 30 additional degrees of timing to make the engine happy or want to stay running, then you have fundamental issues someplace else, such as too much cam and not enough compression, your carburetor can NOT supply the needed fuel at the engines current vacuum reading at idle, or combinations of several other problems. Basically we NEVER use tons of timing to curve running issues with these engines, you have problems in other areas and more times than not that is simply a "crutch" fix instead of finding and correcting the "root" issue(s).....IMHO

Even with that said, some engine like a little more timing at idle, so we tune all of them on a case by case basis, but most of the ones we build and tune here do not want, like, or need a ton of timing at idle speed to be happy.....FWIW

Always great information and advice Cliff so a question. If you prefer the original distributors over aftermarket, and the rebuild/re curve kits are "junk" Where would someone like me get parts that are appropriate to recondition an older unit? Obviously the weights dont go bad. Where would I get springs ect?
thanks as always!
Steve

[Cliff R]

Steve, good question.

Many years ago I stumbled on to a HUGE supply of distributor springs, as well as a butt-load of NOS 2GC, Monojet and Q-jet parts.

I have also purchased hundreds of distributors over the years for parts.

I'm actually starting to run a bit low on springs, and center cams/weights for HEI's. Even so we don't advertise distributor work, PLENTY busy with other things, but we still do one or two a month.

We are finding that most HEI's will have wear at the pins and weights, so we're frequently having to replace the pins and braze the weights up and re-drill them to size. I actually like doing them in that manner vs using the whimpy plastic/Teflon bushings the factory used in many of them. I haven't had a single HEI repaired in that manner wear at all as the braze provides a nice bearing surface against the hardened steel pins......Cliff

[Blued and Painted]

can you use chevy weights and flip them over?

[STEELCITYFIREBIRD]

Dished pistons.
6x-4 heads,cut .020
factory deck height
0.040" head gaskets,
comp springs
1.65 comp roller tip rockers/polylocks

----PREVIOUS CAM----
Lunati 10510702
Adv Dur : 262/268
Dur @ .050 : 219/227
Gross Valve: .468/.489
LSA/ICL: 112/108

----CURRENT CAM---
2801 Summit
Adv Dur : 288/298
Dur .050 : 214/224
Valve Lift : 0.444/0.466
LSA: 112


I Corrected data.

If cam timing adjustment does it, an interesting study on cam timing. I'd start with the dizzy set up exactly how it ran well with the previous cam, minus the vacuum advance...for now.

If adjusting cam timing doesn't eliminate detonation, adding some fuel to, or timing of the power enrichment circuit, may be a viable option.

Cheers