[AdamIsAdam]

Thanks! Yup, I see how you got that now
(http://www.wallaceracing.com/cr_test2.php)

Very cool. Thanks. I think I got that CR number from that paperwork. I can't find any email from my friend where he said it was 10.4:1. Must have been our bad for reading the paperwork from Warren.

Another branch of the family tree discovered.

[AdamIsAdam]

Just wanted to come full circle on this thread and update everyone:

Spent some time with the timing today. Results as follows:

Initial 13°
MVA connected idle = 35° (car's sweet spot is 36°, and it HATES ported vacuum advance, surges and runs hot).

Car idles good, no ping at all. Temps are way down around 175-180°, but it's very cool out tonight and I didn't drive as far as other days. Oil PSI is good too.

I am still getting a slight surge at a steady 3,000 RPM, but not as much as before (but again, it's not as hot out).

I'll wait and drive it again on a hot day before I do anything else.

WOT power seems a little down, otherwise, running well. And as stated, when it's cool, oil pressure is good.

[STEELCITYFIREBIRD]

You may be down on power, and/or surging, from amount&timing of mechanical advance -vs- vacuum advance.
Just got back from a power run myself, did some free black top work around town.

[AdamIsAdam]

My mechanical timing is: ~13* initial and 33* at 2,800. I have ~20* at 1,800.
With MVA connected I get 35* at idle and about 55* cruising at around 3,000.
(And like I said before, my car HATES ported vacuum.

Here's a picture of my distributor springs if that helps. Richie said my timing curve was good (that was last summer but nothing changed on the mechanical curve of the timing. The Qjet is new, replaced a Holley 800DP so maybe I'm just too lean at light, steady throttle).

Here are my springs:

[STEELCITYFIREBIRD]

I'd be curious to disconnect and plug the vacuum line and take it for a ride.
If it likes a bunch of initial advance,I'd take some out of the mechanical advance,or go lighter on the springs and use the vacuum can, ported, for fuel mileage at light throttle cruise.

I'm sure someone has some #'s that are a good baseline for your combination, what you have may very well be that.
Does the carb respond well to adjusting the idle mixture screws? You can stall it by closing them and make it stink fire by opening them too much?

[HWYSTR455]

I still question the timing marks on the balancer. Still say you need to verify TDC and the mark. I'm guessing an OE type balancer? Is it used?

How are you checking timing, with a dial back light? If so, brand/model?

55+ sounds like an awful lot to me, but maybe because it's a low-9 something SCR is why. And 36 at idle sounds like a lot too. Usually 20-24 is max that I've seen work well.

.

[AdamIsAdam]

All good questions. I'll insert what I hope to be good answers...

Originally Posted by HWYSTR455

I still question the timing marks on the balancer. Still say you need to verify TDC and the mark. I'm guessing an OE type balancer? Is it used?

It's an aftermarket balancer with timing marks up to 50*. I don't know the brand but it's black with white marks. I'll take a pic and look for a name but don't recall seeing a brand.
I have not yet verified the marks.

How are you checking timing, with a dial back light? If so, brand/model?

I've verified with three fixed style timing lights (no dial backs): my 30 year old Craftsman, my newer model (don't recall the brand) and one of Richie's that he believes to be accurate.

55+ sounds like an awful lot to me, but maybe because it's a low-9 something SCR is why. And 36 at idle sounds like a lot too. Usually 20-24 is max that I've seen work well.

According to the people that believe in using MVA, I followed their directions on how to establish good MVA timing. Basically, you find the sweet spot of timing that the engine likes by turning the distributer at idle with vacuum disconnected and plugged, and watch the tach for the RPM's highest point and then note that timing number. For me it was 36* (and the car liked that). So starting at 12* initial, the idea is to add back in the 24* of timing with MVA. This means your cruising timing is also higher by that 24*, hence the number in the 50's. Several books also talk about 50+ degrees as a common cruising timing figure.
And remember, I've tried ported advance it the car hates it.

Originally Posted by STEELCITYFIREBIRD

I'd be curious to disconnect and plug the vacuum line and take it for a ride.

I was too. So I did just that. Car runs fine without an vacuum advance (no ping anywhere) but is not nearly as responsive down low, it has a lumpy idle and the exhaust is smelly and MPG.

If it likes a bunch of initial advance,I'd take some out of the mechanical advance,or go lighter on the springs and use the vacuum can, ported, for fuel mileage at light throttle cruise.

Don't follow you there but I think that's what I'm basically trying to do with my vacuum advance. I can't start the car with more than about 14* advance.

Does the carb respond well to adjusting the idle mixture screws? You can stall it by closing them and make it stink fire by opening them too much?

It's a brand new Cliff Ruggles carb and I have not touched it one bit yet. He had all the specs on the engine when he built the carb this winter. I will reach out to him but was waiting for some time to pass given her personal life situation with his dad and all.

But yes, my next thought it that the car is running well at current settings except for the surging at steady part throttle, so maybe it's time to richen the idle circuits. Hopefully that's just the idle screws. I don't want to mess up this carb.

[AdamIsAdam]

Here's a pic of my balancer.

[STEELCITYFIREBIRD]

Idle mixture screw settings are specific to each vehicle. The way they came preset is just a baseline to get it started and idling. With as much timing advance as you have at idle I wouldn't expect them to do much.
I can't give you a good baseline for the engine deal your running, but I am sure someone here can.


based on your info
A 13 initial
B 20 mechanical
C 23 vacuum

36 at idle
33 at wot under load (assumed)
56 total cruise rpm/light load

I'D GO ABOUT IT A DIFFERENT WAY, see what the PONTAC experienced people have found to work with that type deal.

Do you know what you cranking compression psi is ?


Time to start a tuning thread!!

[steve25]

Go two steps up in primary jetting and the suge should bit the dust!

[Cliff R]

Couple of comments in the FWIW department.

Right to start with the cam is too small and LSA too tight for a 469cid engine with 10.4 to 1 compression. It's going to be sensitive to total timing, especially at light throttle cruising.

This will cause several things to happen. First, the engine will not like or want a lot of timing at cruise, so ignore the PM's from the "part timers" and forget the nonsense about trying to find a "sweet spot" by adding in 22 degrees of vacuum advance at idle speed then ending up with nearly 55 degrees of timing at light throttle cruising.

Second, there isn't one ounce of difference once you move the throttle an 1/8th of an inch running ported vs manifold vacuum to the advance provided you are using the ported source in the main casting. Both sources are FULLY uncovered and providing the same exact vacuum to the distributor off idle, light throttle cruising, and any heavy or full throttle.

The ONLY difference is at idle speed. If your engine wants, likes or requires a LOT of timing at idle speed then use manifold vacuum to the advance.

Most of the "quirky" symptoms you are getting from the engine combination is the cam choice. It's simply too small and LSA too tight for that much engine with that much compression. I've tuned a number of them and the symptoms you are getting are pretty much on par with what I've seen here, the XE274 camshaft is a piss-poor choice for a 455 build right to start with. It leaves too much power on the table and builds too much cylinder pressure too early in the rpm range. It might work OK at 8.5 to 9 to 1 compression, but will not work well, or at least not nearly as well as a bigger cam on a wider LSA over 10 to 1 compression.

These days I usually just sit back and watch these threads run, because telling the truth quickly gets me labeled as the Comp XE cam "basher".

Anyhow, in lieu of changing the camshaft, do the following things instead.

Unhook the vacuum advance and time the engine to where it makes absolutely the most power everyplace when you are running it hard, heavy and WOT throttle. Play with the advance curve and initial and total timing. A dyno or drag strip would be the best place to do this, but you can get close on the street. Use the fuel/octane that you plan on running all the time, nail down the mechanical curve, initial and total timing and be done with it.

Next, reduce the travel of the vacuum advance unit to about 10-15 degrees and start tuning with it. MVA or ported really doesn't matter, if it idles cleaner on MVA then that's fine, but try both places and fine tune the idle mixture screws accordingly.

Next, remove the set screw over the APT and raise it up slightly, about 1/8th turn CCW at a time and dial in the part throttle A/F for smoothest operation at light part throttle/normal driving. To really nail down the part throttle A/F and tune I would also make changes to the VA unit and vary timing added between about 10 and 15 degrees till you find the "sweet spot" for light part throttle operation. Keep in mind here that ported or MVA is exactly the same when doing this, the only difference is that MVA adds timing at idle and when coasting, otherwise no difference.

Give this stuff a try and let us know what happens. I really wished you were closer, I could nail all this down in less time than it took me to type this!.......Cliff

[AdamIsAdam]

Originally Posted by Cliff R

Couple of comments in the FWIW department.

Right to start with the cam is too small and LSA too tight for a 469cid engine with 10.4 to 1 compression. It's going to be sensitive to total timing, especially at light throttle cruising.

This will cause several things to happen. First, the engine will not like or want a lot of timing at cruise, so ignore the PM's from the "part timers" and forget the nonsense about trying to find a "sweet spot" by adding in 22 degrees of vacuum advance at idle speed then ending up with nearly 55 degrees of timing at light throttle cruising.

Second, there isn't one ounce of difference once you move the throttle an 1/8th of an inch running ported vs manifold vacuum to the advance provided you are using the ported source in the main casting. Both sources are FULLY uncovered and providing the same exact vacuum to the distributor off idle, light throttle cruising, and any heavy or full throttle.

The ONLY difference is at idle speed. If your engine wants, likes or requires a LOT of timing at idle speed then use manifold vacuum to the advance.

Most of the "quirky" symptoms you are getting from the engine combination is the cam choice. It's simply too small and LSA too tight for that much engine with that much compression. I've tuned a number of them and the symptoms you are getting are pretty much on par with what I've seen here, the XE274 camshaft is a piss-poor choice for a 455 build right to start with. It leaves too much power on the table and builds too much cylinder pressure too early in the rpm range. It might work OK at 8.5 to 9 to 1 compression, but will not work well, or at least not nearly as well as a bigger cam on a wider LSA over 10 to 1 compression.

These days I usually just sit back and watch these threads run, because telling the truth quickly gets me labeled as the Comp XE cam "basher".

Anyhow, in lieu of changing the camshaft, do the following things instead.

Unhook the vacuum advance and time the engine to where it makes absolutely the most power everyplace when you are running it hard, heavy and WOT throttle. Play with the advance curve and initial and total timing. A dyno or drag strip would be the best place to do this, but you can get close on the street. Use the fuel/octane that you plan on running all the time, nail down the mechanical curve, initial and total timing and be done with it.

Next, reduce the travel of the vacuum advance unit to about 10-15 degrees and start tuning with it. MVA or ported really doesn't matter, if it idles cleaner on MVA then that's fine, but try both places and fine tune the idle mixture screws accordingly.

Next, remove the set screw over the APT and raise it up slightly, about 1/8th turn CCW at a time and dial in the part throttle A/F for smoothest operation at light part throttle/normal driving. To really nail down the part throttle A/F and tune I would also make changes to the VA unit and vary timing added between about 10 and 15 degrees till you find the "sweet spot" for light part throttle operation. Keep in mind here that ported or MVA is exactly the same when doing this, the only difference is that MVA adds timing at idle and when coasting, otherwise no difference.

Give this stuff a try and let us know what happens. I really wished you were closer, I could nail all this down in less time than it took me to type this!.......Cliff

Thanks for jumping in Cliff. One important note: turns out I have 9.3:1 CR. The paperwork I have on the head flow sheets had some errors, but folks here helped me sort through it and determine the CR. Makes more sense than 10.4:1 considering I never get WOT ping on pump gas.

I don't mind the truth about the cam - I didn't pick it.

I'll re-read these posts and continue to try and dial this in. The car does like MVA timing, but I'm open to anything and willing to try everything to get it running its best.

PS. Cliff, my condolences. Seemed like a great man.

[Cliff R]

9.3 to 10.3, still isn't going to work well. The cam is just too small, and with the "modern" lobe profiles and short seat timing too good at cylinder filling at lower rpm's. Keep in mind as you read this that a stock replacement CS-274 camshaft from NAPA for a 350 SBC engine that works fantastic in low compression 350 engines sports 274 degrees seat timing.

Here's a case in point, as I love real-World examples, that happened recently when an engine shop attempted their first Pontiac 455 build. It is a very similar combo as yours, using a well prepared short-block and ported #96's. Instead of the XE274 they chose the similiar Comp XR276HR cam. The shop is VERY knowledgeable with race engines, and builds a lot of BBC stuff, but no experience with any Pontiac builds.

Their 455 ran poorly on the dyno and pinged enough to damage some rod bearings when they tried to throw some timing at it to make decent power.

I got involved as one of my customers did the Q-jet for it, and of course it was taking some blame for all the "issues" they were having. I talked to the shop owner and recommended that they call Comp and order a larger HR cam with 290-310 seat timing on a 114LSA, basically an "Old Faithful" clone on a 114 instead of a 112.

The XR276HR cam only made about 428hp @ 4900rpms no matter how they tuned it, and they ran into audible detonation at 30 degrees total timing on the dyno.

The new cam made 514hp @ 5800rpm's and no hint of detonation anyplace, per my recommendation, they set the total timing at 30 degrees and left it there for the entire dyno session.

The larger cam also made MORE torque at every rpm, and idled better than the smaller cam on the tighter LSA! The best they could get out of the XR276 cam was 516tq and it was clear down to 441tq @ 5000rpm's.

The new HR cam made 559 ft lbs peak torque, and still making 519 ft lbs at 5000rpm's, and 500ft lbs at 5300rpm's. (This kind of power is why the big Pontiac 455's run so well at the track and still have great street manners).

The ONLY change to this engine was the camshaft. The #96 heads were professionally ported to apprx 250cfm, for those who are taking notes.

I've been telling folks this for years, the WORST cams for these engines are short seat timing on "tight" LSA's, but for the most part it goes on deaf ears.

What these little cams also do is make tuning for "normal" driving more difficult, as they make a LOT of cylinder pressure early in the rpm range, as problem that we NEVER see with larger cams on wider LSA's. They also produce a "quirky" idle, probably from closing the intake valve so early and "tight" LSA with short seat timing, so considerable "reversion" for lack of a better description.

I've had folks drive, flat tow, roll-back and trailer Pontiac cars here for us to tune that bought into the Comp Cam XE and XR cam technology. Not in one single instance have we been overly impressed with any of those builds, and have had difficulty tuning them to run well in the "normal" driving range......FWIW......Cliff

[AdamIsAdam]

Does it make any difference that I've got 1.65 rockers?

[Cliff R]

That actually helps some, as it makes the cam act a little bigger than it really is, so you get some additional effective seat timing, etc, which reduces cylinder pressure at lower rpm's, but also degrades idle quality at the same time.

Those cams don't help these engines idle all that great right to start with. Some says it's the closing velocity and the valves are actually "bouncing" on the seats. Not sure about all that, I just know I absolutely HATE those cams, and everything that goes with them.

If I were to play around with "modern" lobe profiles, for absolutely and positively sure use some of Harold's Ultradyne lobes. They have opening/closing velocities closer to "stock" cams, then get more done before and after all that, and work like they are supposed to. This means they don't require KILLER valve springs to keep things in check, no tendencies for unstable harmonics at high rpm's, or lifter "crash", as we have and continue to see with the XE lobes in these engines.......Cliff

[STEELCITYFIREBIRD]

[AdamIsAdam]

Thanks for all the tips. Some day maybe I'll replace the cam. I'd like the car to be streetable first and foremost. Power second.

I'll work on the timing and carb tuning. Cliff, I may call you for some specific tuning tips based on how you built this carb. The surging issue started with this carb, but I also played with timing MVA about the same time, so who knows. I just don't want to screw up anything with the carb unnecessarily. It runs pretty good now, just not as good as I know it can.

My mpg is nicely up over the Holley :-)

Also, I have a full 1/2" fuel setup ready to install. RobbMc pickup and pump.

[Cliff R]

The APT system will provide full control of part throttle A/F so you can tune any "surging" out by simply adding some fuel in that range. It will still delivery better MPG's than the Holley did, even once you fatten it up a little bit.

I may also help as mentioned in my first response to play around with the vacuum advance. Few engines built with a moderate compression ratio, tight quench, etc, require nearly that much timing at idle or at light throttle cruising for best performance and fuel economy.......Cliff

[AdamIsAdam]

Thanks. Started to pull the car out after adjusting APT only to see rain drops appearing. Pulled it back into garage. Maybe later or tomorrow.

[AdamIsAdam]

Was able to spend time tuning. Here's my findings: (yes, I know I need to start a tuning thread, but everything is here so I'll just continue)

I turned the APT CCW 1/8 before setting out to drive. Cold it surges a fair amount BTW.
Once fully warmed up, the 3,000 RPM cruise still has a surge. So on my way back home, I decided to unplug the vacuum advance entirely. The surge was completely eliminated, however the temps went from 180 right up to 195 and didn't come back down until shut the car down for a bit, even after I reconnected the vacuum advance before getting home.

So per my conversation with Cliff and others here, I backed the vacuum advance down quite a bit. Initial is around 13-14*, and with MVA it's at 26* at idle, so I'll adding about 12° off vacuum advance. But I noticed as I tried to fine tune that with the allen screw that the timing was varying from 20-26* with one turn of the screw, so I decided I must be at the verge of the vacuum advance opening, so I switched to a ported pickup instead. hey, who doesn't like a lump idle, anyway?! . The idle is down a bit to about 650. But it does sound good.

WOT without vacuum advance connected and the car runs really strong. No ping ever. Once I took the vacuum advance down to adding about 12*, the part throttle feels good, the temps are still decent, maybe around 180-190* (so my oil PSI remains good),

HOWEVER...
I still get a slight surge at 3,000 RPM. So I backed the APT out another 1/8 turn, but I still get the slight surge at 3k (but not really any surge below 2,500).

So, do I keep making the APT richer so I can keep this amount of timing so my temps don't soar (will this even work)? or do I keep reducing the vacuum advance until the surge is gone, even though my temps rise?

I didn't adjust the idle mixture screws at all since it's idling fine and always has. My issue is only while cruising high at 3,000 RPM. Everywhere else it feels very good.