Foxy Green Foxbody Build

[Badd_Dadd]

If it was fat and rattling, it may be detonation, not preignition?
Others may help determine what's what.
I'm just looking on from the cheap seats.

 

[itey]

Another 10 miles on her today. Some concerning things.

Full throttle detonation in a second gear pull. High idle at stop lights like something is hanging blades open. Can't seem to get idle air fuel mixture to lean up enough. I'm now 1 turn out after engine is hot, still low 13s afr.

Here's some cruise info:

35mph, 1500rpm, 4th gear, 19"hg, 12.5afr

40mph, 1800rpm, 4th gear, 21"hg, 13.4afr

45mph, 2100rpm, 4th gear, 22"hg, 13.5afr
45mph, 5th gear, went high 16s afr shifted back to 4th

50mph, 1800rpm, 5th gear, 22"hg, 13.0 afr

Of course, the knock must be avoided, so whatever the RPM range was when it occurred you need to retard and try again. I hope you have quiet exhaust because high RPM detonation is sometimes not easy to detect, can sound like bacon frying or a wire feed welder, a sizzling sound. Low and mid RPM knock is what it is, sounds like crushing rocks. Noisyass flomaggot mufflers will hide detonation and encourage ignorance of engine damage occurring until it is too late.

Detonation leaves tiny black specks on plug ceramic, like the tip of a pin touched the tiniest bit of india ink to the ceramic, or tiny spots of black dust. You may need magnification to see this.

The high vacuum A/F is richer than I try to achieve, but the level road high vacuum lean limit may need to be richer than stoichiometric (14.7) because of EGR dilution through valve timing overlap can funk the combustion and require slightly richer A/F at high vacuum. However, when it went to 16 what was the vacuum (load) and RPM? Part throttle, heavier mid throttle brisk acceleration load between 12" and 6" (PV opens at 6") vacuum can tolerate much leaner A/F than high vacuum because with less vacuum EGR is less and combustion is more vigorous, so as lean as doesn't misfire is sometimes OK, 16 and leaner is OK if it runs OK.

Leaner than stoichiometric is less fuel than burns all the O2, so the EGR contains hot O2 which can improve combustion, so some engines with sporty cams will run part throttle A/F with lean numbers that make some people nervous, however, the O2 sensor is also being tricked by the large overlap cams because they pass through more O2 than mild valve timing. With larger cams the oxygen sensor is seeing more unburned O2, not because of poor combustion, but because of O2 that passes through the chamber and doesn't get trapped in the combustion.

 

[itey]

Low/mid rpm, looks like I stomped it at 2000rpm up to 4000 in second gear. Heard rocks in a can. A/f dropped to 10.2, extremely rich obviously. I don't have anything connecting the vent tubes, don't know if fuel might be pissing over the top when I stomp on it.

@Badd_Dadd I took the #4 plug out. I tried fucking with the carb at idle before shutting it down so there was a little fuel on it, but otherwise it was a light tan and looked good. Wish I would have gotten a pic. Car is stored for the winter so this thread will be boring until April

Rich won't make it knock, rich will suppress knock. (up to a point)

Now you see the situation where a curve with less advance in that range could be necessary, providing it wants more advance at 6000+. I forget what the total was???? What was the advance in the range where it knocked?

I should be working on this Pontiac points distributor anyway, instead of putzing on the interbexz, so until later.

 

[Badd_Dadd]

Misunderstood Causes of Detonation in High Performance Applications

In the engine tuning world, detonation is the uncontrolled and often unwanted igntition of the air-fuel charge, which can cause significant damage.

www.enginelabs.com

 

[itey]

If it was fat and rattling, it may be detonation, not preignition?
Others may help determine what's what.
I'm just looking on from the cheap seats.

Preignition can occur without knock. Triggered by excess heat before the spark occurs, Preignition is normal combustion, but the same as if the spark timing is advanced and may or may not result in detonation.

Detonation is explosive combustion of all or a large part of the cylinder A/F charge in an instant, instead of progressive combustion like dominoes falling, one molecule triggers the next, etc, which is 'normal' combustion.

 

[BOSS#1540]

Low/mid rpm, looks like I stomped it at 2000rpm up to 4000 in second gear. Heard rocks in a can. A/f dropped to 10.2, extremely rich obviously. I don't have anything connecting the vent tubes, don't know if fuel might be pissing over the top when I stomp on it.

@Badd_Dadd I took the #4 plug out. I tried fucking with the carb at idle before shutting it down so there was a little fuel on it, but otherwise it was a light tan and looked good. Wish I would have gotten a pic. Car is stored for the winter so this thread will be boring until April

Hmmm, maybe something not right with the timing or the load it was under showed the limit of yer fuel. But you should feel that in 3rd and 4th even more than 2nd.
I don't believe an octane # can be given for a specific C.R. There are too many variables. Such as the weight of the vehicle, gearing, tranny etc and the engine design, piston speed, piston to head and valve clearances etc.
Although you being at 10.3:1 and using 93 (I assume?) sounds like it should be ok I've had 9.5:1 on 93 run backwards at shutoff and I've ran 12.8:1 on pump 93 that WOULD shut off instantly. Big clearances allow end gases to collect and ignite on the next cycle. At least you can check that by using some 110 race gas or similar.
Lock that fucker at 31° and see what it does.
At least that eliminates the springs and bushings until you figure out what's wrong. If it still rattles get some race fuel. Process of elimination.
By the way, my bronco with the 414 at 9.4:1 and baby low end tq cam (that makes 190 psi cranking) with open chamber heads will rattle if I don't use 91 or higher octane. Heavy, automatic, 3.55 gears with 40" tires, open chambers etc

 

[BOSS#1540]

You can have proper ignition, and end gases that have collected at the outside of the cylinder ignite almost instantaneously, the two flame fronts hit each other rather than a controlled burn.

 

[Mike Beck]

Don't always believe what a wide band is showing you, they can lie......

For example: Pull a spark plug wire off and watch the A/F, it will show very lean. Well, it isn't. It is just raw oxygen being passed through that cylinder, along with the fuel. But the wide band does not see/care about the raw fuel, only oxygen content.

An extremely rich A/F can actually be displayed as lean. Not typical in an non-power adder application though. Usually the engine falls on it's face if it is too rich, and the wide band will show it. Most will go down to .9.5 AFR before getting flaky. This would be on gasoline.

 

[BOSS#1540]

Low/mid rpm, looks like I stomped it at 2000rpm up to 4000 in second gear. Heard rocks in a can. A/f dropped to 10.2, extremely rich obviously. I don't have anything connecting the vent tubes, don't know if fuel might be pissing over the top when I stomp on it.

@Badd_Dadd I took the #4 plug out. I tried fucking with the carb at idle before shutting it down so there was a little fuel on it, but otherwise it was a light tan and looked good. Wish I would have gotten a pic. Car is stored for the winter so this thread will be boring until April

Do you know your piston to deck height, gasket thickness and valve clearances?
Dish in piston?

 

[89 Fox 427]

Been busy, might not get on here to answer for a couple days. Have to watch the video back from the drive to verify things.

Big thing to say, I was running 90 octane ethanol free since I'm storing the car and didn't want 93 pump winter blend shit.

 

[440roadrunner]

The mechanical curve is WOT RPM related timing. There is no (or very little) vacuum at WOT, unless the carb is too small, such as restricted circle track with a 350 or 500 2bbl or 390 4bbl.

To understand the vacuum advance, you guys need to connect a vacuum gauge to manifold vacuum and see what the vacuum does, how it varies at different RPMs when you change throttle positions, cruise, light and heavy acceleration.

This was the PM post you refer to above ^ the RPM related advance is describing the mechanical advance, the vacuum is .... the vacuum advance.

"The last 393 Ford I did wanted
18 initial, start 1200 RPM,
22 at 2000,
24 at 3000,
26 at 4500 and
28 at 6000 <--(edit-- that originally, in the PM, was 5000)
Vacuum advance 0 deg 8" Hg, start or 1 deg 9" Hg and total 12 deg 16" Hg."

The ^^ advance numbers are in crankshaft degrees.

In the case of that particular engine it was a situation of the 393 Windsor had some generic chinese aluminum head, copy of ?, that were on it because the price was right, and the chamber size was intended for a 5.0L 302 I think, and because the cam timing was conservative it had too much compression for pump gas and knocked like a bitch with the "all in at 2500" MSD distributor with the black bushing 18 degree curve.

... so ... we formed a committee of three of us, one young enough to have good ears, and went cruising around one night with a timing light messing the distributor back and forth while making short 1000 RPM "pulls" in every RPM range from idle to valve float, the purpose was to find the amount of advance which ran OK and did not knock.

It was fun, we spent two or three hours in the middle of the night giggling like it was 1966 again (engine was in a 1966 Mustang). We took notes and decided on how much timing at each point in the RPM range from idle to 6000 or so was the hot setup, then I used the distributor machine to setup a Ford Motorcraft distributor and added the vacuum advance. Ford vacuum chambers are adjustable and I think we fiddled with it after installing that distributor and driving the car some more while tuning the carb.

For a highway car you need to finalize the ignition advance scheme before tuning the carb.

I have not kept up, but something that can REALLY help with this sort of highjinks is some sort of onboard performance monitor. I used to have a couple of "G-tech"

G-TechPro

G-Tech car performance measuring devices

gtechpro.com

and even the older, more basic ones were awesome for as simple as they were to set up. They can give you "g's" of acceleration, monitor RPM and vehicle speed, so you can tell if your are really feeling something or getting tricked by engine noise.

There are even guys who experimented with DIY knock sensors with nothing more than a set of headphones. Not sure how really effective those are, as it seems reasonable to suspect that some of the engine noise is at the limits of human ears for frequency response

 

[Steve439]

Is your carb a four-corner idle, and how are you setting your mixture screws?

 

[89 Fox 427]

Of course, the knock must be avoided, so whatever the RPM range was when it occurred you need to retard and try again.

2k to 4k pull

I hope you have quiet exhaust because high RPM detonation is sometimes not easy to detect, can sound like bacon frying or a wire feed welder, a sizzling sound. Low and mid RPM knock is what it is, sounds like crushing rocks. Noisyass flomaggot mufflers will hide detonation and encourage ignorance of engine damage occurring until it is too late.

It has bullets on it, the house shakes at idle. I'm doomed.

Detonation leaves tiny black specks on plug ceramic, like the tip of a pin touched the tiniest bit of india ink to the ceramic, or tiny spots of black dust. You may need magnification to see this.

The high vacuum A/F is richer than I try to achieve, but the level road high vacuum lean limit may need to be richer than stoichiometric (14.7) because of EGR dilution through valve timing overlap can funk the combustion and require slightly richer A/F at high vacuum. However, when it went to 16 what was the vacuum (load) and RPM? Part throttle, heavier mid throttle brisk acceleration load between 12" and 6" (PV opens at 6") vacuum can tolerate much leaner A/F than high vacuum because with less vacuum EGR is less and combustion is more vigorous, so as lean as doesn't misfire is sometimes OK, 16 and leaner is OK if it runs OK.

This was before I had the camera rolling so I don't have exact numbers. It would have been cruise rpm, part throttle after letting clutch out. Between 1400 and 1600 rpm, I don't want to assume anything, but should have been 20+"hg based on the rest of my test

Leaner than stoichiometric is less fuel than burns all the O2, so the EGR contains hot O2 which can improve combustion, so some engines with sporty cams will run part throttle A/F with lean numbers that make some people nervous, however, the O2 sensor is also being tricked by the large overlap cams because they pass through more O2 than mild valve timing. With larger cams the oxygen sensor is seeing more unburned O2, not because of poor combustion, but because of O2 that passes through the chamber and doesn't get trapped in the combustion.

This makes sense. I did send you valve events, and it does have quite a bit of overlap. Thanks for that explanation

Rich won't make it knock, rich will suppress knock. (up to a point)

Now you see the situation where a curve with less advance in that range could be necessary, providing it wants more advance at 6000+. I forget what the total was???? What was the advance in the range where it knocked?

With the springs I have in it, it's all in by 2100 rpm, so the entire pull 2k to 4k was damn near total timing which is 34 degrees. Patriot has told me his 427w (very different combo but similar head chamber) wants 29-30* total by 3k but his car sees no street time if that matters

Hmmm, maybe something not right with the timing or the load it was under showed the limit of yer fuel. But you should feel that in 3rd and 4th even more than 2nd.
I don't believe an octane # can be given for a specific C.R. There are too many variables. Such as the weight of the vehicle, gearing, tranny etc and the engine design, piston speed, piston to head and valve clearances etc.
Although you being at 10.3:1 and using 93 (I assume?) sounds like it should be ok I've had 9.5:1 on 93 run backwards at shutoff and I've ran 12.8:1 on pump 93 that WOULD shut off instantly. Big clearances allow end gases to collect and ignite on the next cycle. At least you can check that by using some 110 race gas or similar.
Lock that fucker at 31° and see what it does.
At least that eliminates the springs and bushings until you figure out what's wrong. If it still rattles get some race fuel. Process of elimination.
By the way, my bronco with the 414 at 9.4:1 and baby low end tq cam (that makes 190 psi cranking) with open chamber heads will rattle if I don't use 91 or higher octane. Heavy, automatic, 3.55 gears with 40" tires, open chambers etc

I think I answered before, but it's 10.4:1 compression on 90 octane ethanol free. It will typically run 93 pump but with being in winter storage right away I used ethanol free

Do you know your piston to deck height, gasket thickness and valve clearances?
Dish in piston?

I believe deck height is .007 in the hole
.040 gasket
26cc dish piston
Shit load of valve clearance. I have it listed in either this thread or the 427w thread and I sure as fuck can't find it right now.

Edit I found them:
.215 intake
.235 exhaust
.100 radial

 

[89 Fox 427]

Is your carb a four-corner idle, and how are you setting your mixture screws?

Yes.

With a screwdriver, duh.

But really, I need to get timing right then mess with carb more. The mixture screws are only 1 turn out and still rich, does seem like vacuum is still increasing with turns in. we already discussed your thoughts on that

 

[BOSS#1540]

2k to 4k pull


It has bullets on it, the house shakes at idle. I'm doomed.


This was before I had the camera rolling so I don't have exact numbers. It would have been cruise rpm, part throttle after letting clutch out. Between 1400 and 1600 rpm, I don't want to assume anything, but should have been 20+"hg based on the rest of my test

This makes sense. I did send you valve events, and it does have quite a bit of overlap. Thanks for that explanation

With the springs I have in it, it's all in by 2100 rpm, so the entire pull 2k to 4k was damn near total timing which is 34 degrees. Patriot has told me his 427w (very different combo but similar head chamber) wants 29-30* total by 3k but his car sees no street time if that matters



I think I answered before, but it's 10.4:1 compression on 90 octane ethanol free. It will typically run 93 pump but with being in winter storage right away I used ethanol free


I believe deck height is .007 in the hole
.040 gasket
26cc dish piston
Shit load of valve clearance. I have it listed in either this thread or the 427w thread and I sure as fuck can't find it right now.

Edit I found them:
.215 intake
.235 exhaust
.100 radial

So those clearances do leave quite a bit of room for end gases to collect and being 7 thou down with a dish along with 90 octane may have been the problem.
Did it shut off immediately when you turned the key off ?

 

[89 Fox 427]

So those clearances do leave quite a bit of room for end gases to collect and being 7 thou down with a dish along with 90 octane may have been the problem.
Did it shut off immediately when you turned the key off ?

It definitely seems to have a few extra pops after key off

 

[BOSS#1540]

It definitely seems to have a few extra pops after key off

I would think thats fuel then and not a timing issue, if it's actually 34°

Did you happen to verify your timing pointer while degreeing your cam ? When you were at true tdc.

 

[Mike Beck]

If you ran it at 34* on 90, boooooooooo............

Run it at 26* on that crap. I would start at 28* on Super in the springtime. The typical SBF head does not need much timing.

 

[Steve439]

A simple way to check if your IFRs are too big is to stick a little wire in them to restrict the area.
Try something like a .015 wire, which you should able to get out of a stranded electrical cord.
Bend the wire in an "L shape so the wire sticks out of the IFR opening and sits on the surface of the metering block, where it will be trapped by the gasket.
That should change your idle AFR and place your idle screws in a more advantageous place.

Maybe just try it on the primaries to see how it works.

 

[BOSS#1540]

If you ran it at 34* on 90, boooooooooo............

Run it at 26* on that crap. I would start at 28* on Super in the springtime. The typical SBF head does not need much timing.

And timing is not the "fix all"
If it's lighting off on end gases less timing will do nothing.
There's a reason why I was able to run 12.8:1 on pump 93 while locked out at 31° with old 1982 heads