Engine and Transmission Tech

Don't panic yet, Rob. - my B303 cam is quite happy cruising the highways at 2200rpm (70mph).
Current distributor specs are 10* initial, and 26* centrifugal....Of course, you'd have to figure out the right spring rate combination to optimize the advance curve.
Car doesn't 'buck' until I get down close to 1500rpm

Well, our motors are pretty close to identical spec wise. I should be able to achieve the same then if I can get close to your timing curve.

Also, what carb are you running these days? If it's an Edelbrock 1405, what jets & rods are you running too?

Rob, Just checked my notes and I went 2 stages (8%) leaner on the primaries and retained the stock secondary. That makes the primary jet 0.100 (#1428) and the rod .075 x .047 (#1459).
Seems to work fine there but the engine didn't like another stage leaner.

That's very interesting Graham. You went two stages lean in both power & cruise modes. I thought I'd read that one primary cause of missing was being too lean. Going richer didn't help me & I'm now 3 stages richer in cruise than you. Our motors are similar spec although there are a few differences - but if your car isn't bucking or missing @ cruise, I think my issue is more likely to be timing related than fuel. I'm going to double check which centrifugal advance plate is in the distributor - was told it would be the 15L but didn't check it. Also need to see how much advance the vac adv. is adding in.

Update: Rich-Porter distributor advance plate isn't marked. There are two different size slots & it was on the smaller of the two. But not sure how much centrifugal that slot allows. I'm going to call them tomorrow to get the specs. But, I'm also going one to test it on the car to see how much it adds. There were different weights - light spring and a heavier one. The heavier one is a little loose; I think that's so the light one can do its work up to a point where the heavier one takes over. I'm also going to do the same with the vacuum connected to see what it adds & where.



Edited 1 time(s). Last edit at 05/02/2012 11:21PM by rficalora.

Vacuum advance is pretty well a non event other than at idle - won't affect WOT total advance condition,

I knew it doesn't affect WOT but assumed it could/does affect light throttle cruise - thought was that is a higher vacuum condition so if the centrifugal advance isn't all in by the 1800 to 2200 range I have the miss, then the vac would be adding some timing still. Is that not right?

True, Rob - there can be some vacuum advance effect under part throttle and decel but that contribution would be hard to determine - you'd almost have to have a vac gauge hooked up to get a feel for how much and when.
I also understand that there is an internal adjustment available to reduce vacuum total advance (requires an Allen key adjustment through the vac nipple) but I've never tried it.

Perhaps some wisdom from "Fred" at this point ? As I recall 'the leaner the mix, the hotter the spark' ? How many volts ? Cheers, roverman.

Yeah, I've noticed Fred's been quiet. I'm imagining he's sitting back with a good Scotch amused by the follies of this neophite!

Hi Rob,

Don't get frustrated. When I'm tracking down a bothersome problem I always try to remind myself that the internal combustion engine is a hunk of metal at war with itself, angrily trying to rip itself apart and destroy its very existence. When you think about 5,000 explosions a minute acting against little metal objects hurling themselves to the heart of the explosion it gives you pause. Then a misfire that happens every 20,000-30,000 explosions seems to come into perspective.

If you could somehow identify the cylinder it's occurring in then you've got it narrowed down. If it's a random misfire then you have to look broadly at your entire ignition. Things like swapping out the msd, different spark plugs, a different brand of diz cap, etc., and hope it's not a valve. As I'm sure you're aware, the valves rotate in their seats as they operate so a bad valve may seat 80% of the time and allow a misfire the other 20%. I had that happen on my GTO and it drove me nuts until I just yanked the engine and replaced the wear items I hadn't when I built it to begin with, even though I did the valve job myself I missed it.

Good Luck,
NCtim

Oddly enough Rob that's exactly what I'm doing!
Actually just really busy at the shop.
Race season is starting and everyone has gone mental.
There is no reason that you can't run that cam at 2200 rpm. It's an aggressive grind but it's not that big.
What happens when you drop it down a gear and get the revs up a little?

Rob, WRT your Rich-Porter distributor centrifugal plates not being identified for degree advance, I found this on the 'net that may help by measuring the slot width.

To figure approximate slot width for a given advance figure Multiply the number of desired centrifugal degrees by .013" then add .150" to account for the width of the stop pin.[/ib]

8L slot = 16 degrees centrifugal advance = .358”
9L slot = 18 degrees centrifugal advance = .384”
10L slot = 20 degrees centrifugal advance = .410”
11L slot = 22 degrees centrifugal advance = .436”
12L slot = 24 degrees centrifugal advance = .462”
13L slot = 26 degrees centrifugal advance = .488”
14L slot = 28 degrees centrifugal advance = .514”

Great info Graham. But get this... Put the dizzy back in. Fired up the car & reset initial timing. After a few minutes I started hearing a squealing. Listen around & its coming from the dizzy. Loosen the retaining bolt just a little & squeal stops. Tighten again & squeals again. This just can't get much more "fun." When I bought it O'Rieley's said they haven't had any come back... Now I; wondering how many they've actually sold. Thinking I'm going to have them get me a real duraspark.

Fred & others - if I drop to a lower gear the missing goes away. I'm not sure, but I think it has more to do with load than RPM. I'll test steady cruise at higher rpm but I have noticed that, while less pronounced, it still misses in cruise at least up in the 2400 to 2600 range. When it's missing, if I simply accelerate a little - even very little - the missing stops till speed stabilizes @ new cruise speed.

As another test, I disconnected the vacuum advance & plugged it @ the intake to see if the missing improved w/o it (I don't recall the missing being as pronounced with the MSD). Net, no change - missing @ cruise was the same.

Rob, Maybe it's time to get it to a shop to do some diagnostic/scope work.
These new scopes can run gas emission checks/AF ratio condition, check electrical firing condition, indicate a rich/lean condition, indicate engine vacuum leaks, etc.
My reason for posting this now is the fact that my car is at one of these garages right now - first indications are that the electrics are OK but there is a lean condition at idle (possibly due to a vacuum leak.
Sometimes it's less frustrating to hand over a persistent engine issue to the professionals.

I hear you Graham. What sort of scope should I verify they have? Asking because I've chatted w the owner/proprietor of a local one man shop. He's a great guy who is more than happy to help. His business is really state inspections but he's known as someone who'll sort things like I've got going between other jobs. Not sure what sort of diagnostic scope(s) he has. He does have a rolling road & AFR that's used for the inspections -- don't know how flexible the software on that is to use it for other diagnostics.

Here's a couple of good articles from the straight six forum on distributor tuning:

[classicinlines.com]

[classicinlines.com]



Edited 1 time(s). Last edit at 05/04/2012 11:27PM by mgb260.

Replaced the Rich Porter distributor with a rebuilt Ford unit. According to Cardone's web site, their 30-2831 is for an 85 mustang 5.0L 4Bbl, manual transmission, steel gear. ScotLand's computer says the same thing... But got two different ones and both had cast gears on them. Local NAPA got me a distributor for the same spec car. Box is clearly a Cardone box but has a NAPA sticker over the Cardone part # and instead it's listed as 48-2831... But it did have the the steel gear :). Aside from that, the difference was $79+30 core @ Napa vs 45+10 core @ AutoZone. So, twice the price, but the right thing.

Oh, and the NAPA one's vacuum advance is a good bit bigger diameter & it feels softer - like it will pull in with lower vac (& I compared with the adjustment on both all the way to the lightest setting). Initially I swapped it out with the rich porter one (also smaller) to get it timing set because NAPA one was hitting my A/C compressor but then I realized I could turn the oil pump rod & get the distributor to seat so the vac can is right in the middle of the compressor & thermostat housing. So, I may swap it back.

Now the good part... Car is definitely running better with the rebuilt Ford distributor. There's still some missing @ cruise, but not as bad as it was. I've decided to take it to the shop I mentioned anyway since BV8 is coming up so soon but it's definitely closer than it was.

almost forgot, pretty sure the squealing on the rich porter was coming from the bottom of the gear rubbing on the machined surface that you access the oil pump drive through. The bottom of the gear is now shiny - it was black before I installed it. That distributor is definitely going back.

Made a little progress - took my car to a shop. They were able to find a vacuum leak that I didn't. I was spraying carb cleaner at idle (about 900rpm). It didn't show up there. They found it by bringing the revs up a bit - small vacuum leak at carb to intake gasket - but enough that it kept running with idle air bleed all the way closed. Also AFR showed lean @ idle & when revved - don't know yet if that's due to the vac or if carb will need adjusting.

Your carb will need to be set up for sure Rob.
You need to nail down your timing as well.
But you must focus your efforts on one change at a time.
I generally set up the mixture first on a street motor because timing has very little effect on the mixture.
Set your total timing at 38' with the vacuum advance disconnected.
Disconnect the secondary linkage on your carb. You just want the primarys only.
Next go get or build something like this.



This is just an autometer wide band o2 meter that I built into a hard case. It has some extended leads and a lighter plug for power.
I use some stainless welding rod bent up to hold the sensor a foot or so into the tailpipe or on some cars an unused o2 bung.
Plug into the lighter and you're good to go.
It gets used every day at the shop and has been drop dead reliable.
You will need an assortment of needles and jets such as the old Carter strip kit or the Edelbrock cal kit.
Find yourself a good straight level road that you can make some hot passes on without getting into trouble.
Warm your car up and make a full throttle run in third gear with a passenger watching the o2 meter. Obviously, back off if you hear any detonation or run extremely lean.
Start changing metering rods to dial in your fuel mix. If you run out of room on the rods, then change jets. (you are concentrating on the small tip of the needle at this point). You are looking for a consistent reading around 13-1 Once you are there, write down the rod and the jet size.
Next we'll set up the cruise mix.
Pull out your metering rod springs for now. You don't want the rods lifting for this part.
Gently take your car up to it's cruise speed and swap out rods until you can consistently read 15 to 15.5 to one, which should be good with your cam.( this is the thicker part of the metering rod).
Again copy down the rod and jet sizes.
Now reassemble the carb completely using the best rods and jets from the full throttle run.
Reconnect the secondary linkage.
Do the full throttle runs again and this time change the secondary jets only, to get the 13-1 mix.
Now the hard part. You need to calculate which rod and jet combo will net you your results from the driving tests.
Edelbrock has a chart that came with your carb that will help, or you can just do the straight area calculations(PiR2) of the jets and rods and go from there. (The secondary jets won't change from your test results).
A huge variety of rods and jets exist so just about any combo is doable.
Now you can do timing.( vacuum advance is still disconnected)
Mark off a distance on your road that will accommodate a full throttle run from 2000 to red line in third gear.
With a stopwatch, start adjusting your timing to get your fastest average run between your markers. Don't be surprised if it's less than you think. (IE 34' total) Take note of the total timing.
Next is cruise.
At speed (yours is 2200 rpm I think) in 5th gear, you want to dial in as much timing as the engine will tolerate. Probably somewhere around 46-50' @ 2200 rpm. You will know when the engine is happy. Take note of this number. Take a manifold vacuum reading at this point and a ported vacuum reading as well.
Now lock down the distributor so that at max advance it reaches the reading of your best power run.
Rev the engine up to 2200 rpm and note the timing. Is it stable? Remember the smaller and larger advance springs? At 2200 rpm you want the smaller spring to be maxed out and the larger spring to be just starting to take up the slack so that the timing stays relatively stable at your target rpm. Some experimenting here with different springs will make a big difference.
Now you connect the vacuum advance.
Ported or manifold is your choice, but I have never used manifold vacuum on an engine that was tuned well.
You want to adjust the can so that it's all in at the vacuum reading that you took at cruise.
You also need to file, bend, weld, paperclip or chewing gum the vacuum stops to get the timing reading that worked best @cruise rpm.
The cruise "manifold" vacuum vacuum reading should be slightly higher than the metering rod springs rating. Your springs should be pretty close if I remember correctly.
And there you have it!
Should run nice and get decent mileage.
All in the time it takes to enjoy a good scotchy scotch.
Seriously, there is a lot more to it and you do get a feel for it after a while, but this should get you closer than you are now.

Cheers
Fred



Edited 1 time(s). Last edit at 05/12/2012 01:14PM by DiDueColpi.