318 bogging at high rpm, but only in first gear?

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Señor Ding Dong

Señor Ding Dong

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I’m pretty new to this, and can’t logic myself an explanation.
1974 318, some cylinder wear, nothing terrible
1971 stock heads with a fresh valve job and springs were tested
New lifters
Double roller timing set
Unknown cam, either stock or very mild, no advance
TDC confirmed, as well as cam timing
Edelbrock performer intake and 1406 carb
Dual exhaust, 8.75 - 3:23 gears
Proform distributor and Accel coil
1977 A904 Torqueflite

First, the engine wants a ton of initial timing. Tuning by ear, with vacuum port plugged, idle keeps rising until 25° or more of advance. I dropped it back to 18°, don’t have a tach or an advanced timing light to check total timing. When I accelerate hard from a stop, it goes fine, (if a little underwhelming), until it gets to higher rpms, then it bogs right out. Doesn’t stall, but zero power, rpms drop. Then once it shifts to second, it’s fine, and doesn’t do it in second or third at high rpms.

So it doesn’t seem to be a fuel issue, since it doesn’t do it in other gears. Ditto for timing. No discernible vacuum leaks.

Any ideas? What am I missing, what should I be looking for, and has anyone else dealt with a similar issue? When I search for it here, I’ve never found a post where it was in first gear.

Thanks!
 
Could be a fuel issue... but probably something like tons of leak down. The motor goes flat in other words. Valve springs and poor ceiling Rings will do that.

How about showing us the plugs?
How's the carb setup, jets n rods?
Are these valve spring to this stock or mild cam singles or have a dampener spring or?
Whats the cranking compression and have yo done a leak down test?


Faster it can rev up in a lower gear the more it shows up? Does it blow smoke out the breathers?
 
Fuel delivery. Blocked fuel filter, faulty pump etc. The fuel in the carb gets used up very quickly at WOT in 1st gear; in the higher gears, the fuel gets used more slowly, has time to 'catch up'.

Is the comp ratio low? If the engine wants 25* of idle timing, then you should give it 25*. 25* is not a lot for a modified engine. See below.

img307.jpg
 
1) If the distributor is factory, it was likely curved for 5* initial, and 30 degrees in the flyweights. for a total of 35Degrees..
With 18* initial now, you are trying to run 53* of Power-Timing, and the engine is complaining by detonation, which kills power.

2) With hi-compression heads on a low-compression short, you get an intermediate compression engine, that may be detonation-prone. It depends on where the Quench lands.

3) With 3.23 gears, Second gear works out to possibly 4500= 68mph, and 318s with factory springs usually float the valves about there, so perhaps you have a third problem.

Numbers 1 and 3 you can fix fairly easily.
But number 2 may require better octane gas than you can get at the pump. A high stall convertor, and/or more rear gear, and/or delayed max-ignition timing, may help. But if your Quench is in the zone of 050 to 080, it may not be fixable.
Happy HotRodding

But honestly, you gotta get the Power-Timing under control before anything..
 
Last edited:
MOPAROFFICIAL said:
Could be a fuel issue... but probably something like tons of leak down. The motor goes flat in other words. Valve springs and poor ceiling Rings will do that.

How about showing us the plugs?
How's the carb setup, jets n rods?
Are these valve spring to this stock or mild cam singles or have a dampener spring or?
Whats the cranking compression and have yo done a leak down test?


Faster it can rev up in a lower gear the more it shows up? Does it blow smoke out the breathers?
Click to expand...
They weren't fresh plugs, I had run them briefly before in my old 318, I just had a look at them and re-gapped, they only had a few hundred km on them and were in good shape, so I'd have to swap in a fresh set to read them.
I don't know the carb setup, the intake and carb came with the engine.
Stock heads off my 1971 block, I had the machine shop clean them up, the valves were good after cleaning the carbon off of them, and he said he tested the springs and they were all within specs, and within 5 lbs of each other. Single spring, factory.
Cranking compression was around 120psi, I don't have a leakdown tester. No smoke blowing anywhere, exhaust is clean, no evidence of oil burning or anything

Bewy said:
Fuel delivery. Blocked fuel filter, faulty pump etc. The fuel in the carb gets used up very quickly at WOT in 1st gear; in the higher gears, the fuel gets used more slowly, has time to 'catch up'.

Is the comp ratio low? If the engine wants 25* of idle timing, then you should give it 25*. 25* is not a lot for a modified engine. See below.
Click to expand...

Compression ratio would be fairly low, standard bore 1974 318, with stock 1971 318 heads, so likely 8:1 or so? Only real mods are the 4 bbl, and the timing set. Possibly a mild cam, I think the previous owner nuked the top-end, as it had aftermarket pushrods, 360 heads, new timing set, and old valve marks on the piston tops hidden under some carbon build-up.

AJ/FormS said:
1) If the distributor is factory, it was likely curved for 5* initial, and 30 degrees in the flyweights. for a total of 35Degrees..
With 18* initial now, you are trying to run 53* of Power-Timing, and the engine is complaining by detonation, which kills power.

2) With hi-compression heads on a low-compression short, you get an intermediate compression engine, that may be detonation-prone. It depends on where the Quench lands.

3) With 3.23 gears, Second gear works out to possibly 4500= 68mph, and 318s with factory springs usually float the valves about there, so perhaps you have a third problem.

Numbers 1 and 3 you can fix fairly easily.
But number 2 may require better octane gas than you can get at the pump. A high stall convertor, and/or more rear gear, and/or delayed max-ignition timing, may help. But if your Quench is in the zone of 050 to 080, it may not be fixable.
Happy HotRodding

But honestly, you gotta get the Power-Timing under control before anything..
Click to expand...
It's not a stock distributor, it is a Proform 66991 distributor, and I am running an Accel Super Stock coil.
The heads aren't high compression, they are stock 1971 heads (2843675 casting number), with factory valves.

I haven't a clue what quench is, or how to measure it. I've only come across the term in a couple of posts here, and haven't looked into it.

I do have another fuel filter I could swap in, and a carb rebuild kit. I suppose I should go with that, and try to figure out my total timing first and see where I get? I was afraid to advance the ignition timing past 20 degrees, as I'm worried I'll get pinging at high rpms and won't hear it. The proform is easily adjustable for the advance, so if I get my hands on a timing light that can help, I'll do that. If the engine wants 20 degrees initial timing, does that change how much total timing I should be aiming for, or should I be going for that 34-36 degrees that it seems most people recommend for a 318? Is there a way to tell what the engine needs for total timing, other than backing off if there is detonation?

Thanks!
 
Señor Ding Dong said:
I’m pretty new to this, and can’t logic myself an explanation.
1974 318, some cylinder wear, nothing terrible
1971 stock heads with a fresh valve job and springs were tested
New lifters
Double roller timing set
Unknown cam, either stock or very mild, no advance
TDC confirmed, as well as cam timing
Edelbrock performer intake and 1406 carb
Dual exhaust, 8.75 - 3:23 gears
Proform distributor and Accel coil
1977 A904 Torqueflite

First, the engine wants a ton of initial timing. Tuning by ear, with vacuum port plugged, idle keeps rising until 25° or more of advance. I dropped it back to 18°, don’t have a tach or an advanced timing light to check total timing. When I accelerate hard from a stop, it goes fine, (if a little underwhelming), until it gets to higher rpms, then it bogs right out. Doesn’t stall, but zero power, rpms drop. Then once it shifts to second, it’s fine, and doesn’t do it in second or third at high rpms.

So it doesn’t seem to be a fuel issue, since it doesn’t do it in other gears. Ditto for timing. No discernible vacuum leaks.

Any ideas? What am I missing, what should I be looking for, and has anyone else dealt with a similar issue? When I search for it here, I’ve never found a post where it was in first gear.

Thanks!
Click to expand...
What rpm does it drop off at?
 
I'm not a fan of cleaning up spark plugs. I'd put in new plugs, how old are the plug wires? What's the float bowl level, fuel line size from the fuel pump to the carburetor? Is there any rubber lines between the fuel pump and carburetor? I don't mean to sound disrespectful here but I have seen people install the fuel filter backwards. At what rpm's does this happen at? Factory springs are good for around 4500 rpm's. Even though I don't think it's your problem, but 120# of cranking pressure isn't much. I'm thinking that it's more of a fuel starvation issue than anything else. You may want to check out the condition of your fuel pump as well. Good luck
 
The 8:1 CR, 120 psi cranking pressure, is why it wants a lot of timing at idle.

To get the optimum idle timing [ let us ay 25* ], you have a couple of choices:

- shorten the curve in the dist to about 11-13*. That will give 36-38* at WOT. The low comp ratio will want more timing. This much initial could be hard on the starter & starter with a higher HP rating might be needed. Another way to retain the stock starter if it cranks slow: put an on/off sw under the dash that grounds one of the dist pick up wires [ also a good theft deterrent ]; get engine cranking, & flick switch to remove the ground,

- use an adjustable vac adv unit, connected to manifold vacuum [ MVA]. Use the factory initial timing [ say 12* ] & add the difference to 25* [ 13* ] with the VA unit. You will have to fabricate a stop to limit the VA plunger travel. It is all part of tuning......
The Allen screw in the VA should be wound fully CW.
 

Bewy said:
The 8:1 CR, 120 psi cranking pressure, is why it wants a lot of timing at idle.

To get the optimum idle timing [ let us ay 25* ], you have a couple of choices:

- shorten the curve in the dist to about 11-13*. That will give 36-38* at WOT. The low comp ratio will want more timing. This much initial could be hard on the starter & starter with a higher HP rating might be needed. Another way to retain the stock starter if it cranks slow: put an on/off sw under the dash that grounds one of the dist pick up wires [ also a good theft deterrent ]; get engine cranking, & flick switch to remove the ground,

- use an adjustable vac adv unit, connected to manifold vacuum [ MVA]. Use the factory initial timing [ say 12* ] & add the difference to 25* [ 13* ] with the VA unit. You will have to fabricate a stop to limit the VA plunger travel. It is all part of tuning......
The Allen screw in the VA should be wound fully CW.
Click to expand...
I learned something new about tuning, thanks Bewy
 
You should only NEED that kind of idle timing if you don’t have enough compression or your cam is too big or you don’t have enough compression.

Very rare that I build something needing that kind of idle timing.

I just did a street BBC that made 640ish HP at about 10.25:1 and all it would take was 20 initial. It might take that or a skosh more in the car, depending on his converter.

His cam was 250/254 at .050 which is less cam than I use.

I’m not saying everyone builds their stuff wrong but when you see initial timing like that we can say they missed somewhere.

Or they have a weird combo.
 
Newbomb Turk said:
You should only NEED that kind of idle timing if you don’t have enough compression or your cam is too big or you don’t have enough compression.

Very rare that I build something needing that kind of idle timing.

I just did a street BBC that made 640ish HP at about 10.25:1 and all it would take was 20 initial. It might take that or a skosh more in the car, depending on his converter.

His cam was 250/254 at .050 which is less cam than I use.

I’m not saying everyone builds their stuff wrong but when you see initial timing like that we can say they missed somewhere.

Or they have a weird combo.
Click to expand...
Well, it’s not really a “built” engine, just a slightly tired placeholder until I build another 318 in a couple of years. It’s got some cylinder wear, so I’m guessing losing some compression there. The previous owner of the engine had everything the same, but with a set of leaky 360 heads on it, so an even lower compression ratio.
 
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