10.2 : 1 compression 360 at sea level. Options?

[nm9stheham]

But think back to olden days,lol, when a vehicle came into your shop with a dead cylinder. During the diagnoses, how many times didn't you pull the dipstick, and find the oil diluted with gas in the crankcase?
Your thoughts?

But did the excess gas kill the cylinder from a leaky carb or what? Thinking of the overall higher wear in the carbed days, I am sure you are right over the long term and when things were cold. I just think with the OP's warmed engine, it probably was not a factor in the readings. (But I think I killed some aircraft engine cylinders with too much raw fuel on a cold start once....)

 

[nm9stheham]

I wish I knew why the front lifters were bleeding down.

I think everyone wants to know why there are so many hydraulic lifters failures theses days. I've been collecting a few to diagnose some day so if you pull any, send them along. My son had one go on #4 cylinder in <1000 miles. It just got weaker and weaker, 'til eventually it stayed soft all the time. You could hear the weakness in the passenger side exhaust get more and more pronounced.

And it ain't just these... I've had them be hit-or-miss for a Dakota 4.7; fine when new but a few got weak/leaky within 5k miles.

 

[SBM4theW!n]

Just an update, 93 octane and a bottle of octane booster seems to be keeping any detonation at bay. I'm also seeing that Austin ranges from 500ft to 900ft of altitude (10.29 at 900ft is comparable to 10:1 at see level), which could be helping as well. I'm currently at 31 degrees total mechanical advance and running cooler plugs (2 steps down from stock) which might actually be too cold, but we'll see. Car runs at about 180 degrees.

The car feels quite a bit quicker down here than it did at 5000ft in Denver!

Next step is adding a hood scoop to get cooler air into the engine, which hopefully will mean I can drop the octane booster and just run 93.

 

[moper]

You shouldn't need high test for where you are and what you have. Timing is important, but timing is not just the "how much", but also the "when". So when the centrifugal starts and finishes is just as important as the amount of advance. You should also focus hard on the step up springs in the carb, and the sizes of the steps on the metering rods once you get the timing curve done. I don't think you'll need super unleaded, never mind the octane booster once the tune is right.

 

[nm9stheham]

Next step is adding a hood scoop to get cooler air into the engine, which hopefully will mean I can drop the octane booster and just run 93.

Don't let your guard down for a while if you put in the cool air. The AFR from the carb may change with a lot lower temp air..... it may get a bit richer or it may get a bit leaner....

 

[SBM4theW!n]

Don't let your guard down for a while if you put in the cool air. The AFR from the carb may change with a lot lower temp air..... it may get a bit richer or it may get a bit leaner....

I've got an afr gauge. Best 120 bucks I've spent on the car.

 

[AJ/FormS]

Don't let your guard down for a while if you put in the cool air. The AFR from the carb may change with a lot lower temp air..... it may get a bit richer or it may get a bit leaner....

It went leaner for me, I up-jetted one size front and rear.But I thought the idle was more stable, and I was able to drag the rpm down further with the clutch; 4mph @550rpm,with 3.55s,when combined with a dial-back timing device to 5* advanced, from a normal 14*. And midrange was crisper.
Speaking of timing, you guys are spot on. With my power timing delayed to 3400, I can burn 87E10 with impunity (aluminum heads), on 10.9 Scr. I know I'm leaving a bit on the table, but I don't notice it. There was a time that the difference in the cost of fuel,(over $500C per year), was very important to me on account of the car was my DD. Over the course of 100,000 plus miles, I have saved a lot of money that way, way more than the cost of the aluminum heads, which made the running of 11/1 even possible.

 

[nm9stheham]

It went leaner for me, I up-jetted one size front and rear.

THAT is what the OP needs to be concerned about. (Possibly one reason that Holley and other aftermarket carbs seem to come out of the box a tad on the rich side.)

 

[KnuckleDuster]

Hey Matthew,
You gonna bring that thing out Saturday so I can see it in the daylight?
I may have some goodies you'd be interested in, depending on what you decide to do. Don't go buying stuff until we talk. I'm on vacation this week, you are always welcome to come by the house and take the spare parts tour.

 

[MopaR&D]

THAT is what the OP needs to be concerned about. (Possibly one reason that Holley and other aftermarket carbs seem to come out of the box a tad on the rich side.)

As long as his O2 sensor and AFR readout are accurate, and the OP isn't brain dead (lol), that should become apparent pretty quickly.

I find it interesting how other factors in your local air are obviously affecting how it runs. If you took the super dry mountain air from CO and simply compressed it to sea-level pressures you'd need like 100+ octane fuel, but I'm guessing where the OP now lives the air actually has some humidity to it...?

I still want to make a water/meth injection system for my Duster at some point, my engine would be grateful for the occasional cool spray down the nose when hauling a$$ up I-70 over the Continental Divide.

 

[AJ/FormS]

That (water/meth) was my original back-up plan in 1999, when I had the Scr set at 11.3.
My local speed-shop thought I was nuts building an 11.3 engine to run pumpgas. No one around here had ever heard of Dynamic compression, or Effective compression. I had to do all the equations long hand, until I figured it out. If I'd have listened to him, Ida had a dog engine for sure at 9.5 which is what he recommended.
It turns out that at 900ft here;neither 11.3Scr nor 185psi was a big deal for aluminum heads, and 87E10.

 

[moper]

Yup - you always have to remember when these type of carbureted engines were in service they put on 4-5K miles a year, got tuned up twice a year at least, and got major engine servicing regularly.

 

[nm9stheham]

If you took the super dry mountain air from CO and simply compressed it to sea-level pressures you'd need like 100+ octane fuel, but I'm guessing where the OP now lives the air actually has some humidity to it...?

All depends on how the carb reacts to the extra air density. Austin TX (where the OP is now) is a mix of dry and humid weather. Being fall now, I would expect he is getting the worst case situation if he is running on dry days.

Interesting you mention the humidity though... one rally acquaintance had a turbo Subie motor run fine on an aggressive tune at 3-4k ft in WV in hot, humid summer weather. Fast forward 3 months to a cool, dry day in October in upstate NY at around 1k ft and.... kablooie! The engine management was right on the far edge and had no margin for the lack of humidity. It was tuned in humid NC summer weather ...

 

[SBM4theW!n]

Hey Matthew,
You gonna bring that thing out Saturday so I can see it in the daylight?
I may have some goodies you'd be interested in, depending on what you decide to do. Don't go buying stuff until we talk. I'm on vacation this week, you are always welcome to come by the house and take the spare parts tour.

Hey KnuckleDuster, what's goin

You shouldn't need high test for where you are and what you have. Timing is important, but timing is not just the "how much", but also the "when". So when the centrifugal starts and finishes is just as important as the amount of advance. You should also focus hard on the step up springs in the carb, and the sizes of the steps on the metering rods once you get the timing curve done. I don't think you'll need super unleaded, never mind the octane booster once the tune is right.

So what's the recommendation for mechanical curve timing/ what rpm should it start kicking in? I haven't personally considered that part before, but it definitely makes sense.

 

[Bill Crowell]

I don't have any answers for you but I am very interested in your thread because I'm having the same problem with a 360 that is similar to yours, except that the best gas we can easily buy around here is 91 octane, and the engine really detonates on that. Ported "J" heads. No quench, I guess. I am going to pull the heads and inspect everything to make sure I haven't damaged anything with the detonation, and then decide what to do about it.

 

[yellow rose]

I don't have any answers for you but I am very interested in your thread because I'm having the same problem with a 360 that is similar to yours, except that the best gas we can easily buy around here is 91 octane, and the engine really detonates on that. Ported "J" heads. No quench, I guess. I am going to pull the heads and inspect everything to make sure I haven't damaged anything with the detonation, and then decide what to do about it.

A simple cam change will fix it.