Pre-ignition question
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Tuned
Joined: Feb 2022
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From: Central Montana
Pre-ignition question
I've noticed when i drive my 84 f150 with any sort of load, or hit a hill. I get that can of gravel sound when i shift into top gear. It's a 351w with a edelbrock 650 avs2 paired to a np435. I presume it's fuel but not sure. I don't think I'm shifting at the wrong speed it'll sound like that even if i shift at 2100 and hit fourth at 1100. It does respond to pressing the throttle more if i let off it goes away till i hit the throttle again. I'm not the most confident with carb adjustment, so this is probably a stupid easy one.
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Tuned
Joined: Feb 2022
Posts: 295
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From: Central Montana
fair still seems sad. I set my base timing to 12 degrees which so i guess I'll pull it back to ten.
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From: Angier, NC
Look up the specs and see where the RPM is for HP & TQ and you will not see it that low.
Heck my 300 six is around 1800 RPM but with the long stroke mine will pull, unloaded, down at the 1000 RPM mark.
I get pinging if I run 87 octane and run a lower RPM and put a load on the motor, my timing is at 12* to 14* and should kick it back a little.
I have found when running high test I dont get pining even when I pull a 20' enclosed trailer but I also run the RPM up higher than when not.
What rear gear ratio and size tires you have on the truck?
I have 2.75 gear and 235 / 75R / 15 tires and that was what the factory set the truck up with.
Oh I also run a NP435 granny 4sp but have added over drive so 45 MPH is 1200 RPM
Dave ----
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Posts: 30,935
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From: Angier, NC
I had to ask MS Copilot the spec's
Here you go, David — the verified horsepower and torque specs for the 1984 Ford F‑150, based on the exact engine options available that year. I pulled the numbers directly from authoritative sources.
Below are the factory ratings for each engine offered in 1984.
Dave ----
Here you go, David — the verified horsepower and torque specs for the 1984 Ford F‑150, based on the exact engine options available that year. I pulled the numbers directly from authoritative sources.
Below are the factory ratings for each engine offered in 1984.
🔧 1984 Ford F‑150 — Engine HP & Torque Specs
📌 4.9L (300 cid) Inline‑6
- Horsepower: 125 hp
- Torque: 339 Nm (≈ 250 lb‑ft)
- RPM values: Not listed in the source, but these engines typically peak torque around 2000–2400 rpm.
📌 5.8L (351W) V8 — Standard 2‑bbl
- Horsepower: 150 hp
- Torque: 280 lb‑ft
- RPM values: Not listed in the source, but typical mid‑80s 351W 2‑bbl torque peaks around 2600–2800 rpm.
📌 5.8L (351W) V8 — High Output (H.O.)
This was the strongest engine available in the 1984 F‑150.- Horsepower: 210 hp @ 4000 rpm
- Torque: 305 lb‑ft @ 2800 rpm
⭐ Quick Comparison Table
Engine HP Torque Peak RPM (if known) 4.9L I‑6 (300) 125 hp ~250 lb‑ft Not listed 351W 2‑bbl 150 hp 280 lb‑ft Not listed 351W H.O. 210 hp 305 lb‑ft 4000 rpm (HP) / 2800 rpm (TQ)If you tell me which engine your ’84 F‑150 has, I can break down its real‑world performance, towing behavior, and common upgrades that actually make a difference.Dave ----
Last edited by FuzzFace2; Feb 8, 2026 at 09:01 AM.
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From: Virginia
You can also experiment, when you hear the gravel sound pulling a hill, what happens if you press the pedal all the way down not quite to the floor? Does the sound go away? If it does, that is a sign your vacuum advance is contributing to the problem. There are things you can do with that also.
Your engine has been stripped and reconfigured from what the factory had it. You will need to experiment with it to get the best tune, the factory specs are out the window now.
Thread Starter
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Tuned
Joined: Feb 2022
Posts: 295
Likes: 7
From: Central Montana
1100 RPM for a 351 with a load pulling a hill is way too low of a RPM for that motor.
Look up the specs and see where the RPM is for HP & TQ and you will not see it that low.
Heck my 300 six is around 1800 RPM but with the long stroke mine will pull, unloaded, down at the 1000 RPM mark.
I get pinging if I run 87 octane and run a lower RPM and put a load on the motor, my timing is at 12* to 14* and should kick it back a little.
I have found when running high test I dont get pining even when I pull a 20' enclosed trailer but I also run the RPM up higher than when not.
What rear gear ratio and size tires you have on the truck?
I have 2.75 gear and 235 / 75R / 15 tires and that was what the factory set the truck up with.
Oh I also run a NP435 granny 4sp but have added over drive so 45 MPH is 1200 RPM
Dave ----
Look up the specs and see where the RPM is for HP & TQ and you will not see it that low.
Heck my 300 six is around 1800 RPM but with the long stroke mine will pull, unloaded, down at the 1000 RPM mark.
I get pinging if I run 87 octane and run a lower RPM and put a load on the motor, my timing is at 12* to 14* and should kick it back a little.
I have found when running high test I dont get pining even when I pull a 20' enclosed trailer but I also run the RPM up higher than when not.
What rear gear ratio and size tires you have on the truck?
I have 2.75 gear and 235 / 75R / 15 tires and that was what the factory set the truck up with.
Oh I also run a NP435 granny 4sp but have added over drive so 45 MPH is 1200 RPM
Dave ----
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Tuned
Joined: Dec 2024
Posts: 448
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From: Texas, near Houston
I've noticed when i drive my 84 f150 with any sort of load, or hit a hill. I get that can of gravel sound when i shift into top gear. It's a 351w with a edelbrock 650 avs2 paired to a np435. I presume it's fuel but not sure. I don't think I'm shifting at the wrong speed it'll sound like that even if i shift at 2100 and hit fourth at 1100. It does respond to pressing the throttle more if i let off it goes away till i hit the throttle again. I'm not the most confident with carb adjustment, so this is probably a stupid easy one.
Last edited by Denzil B; Feb 8, 2026 at 03:10 PM.
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Joined: Nov 2015
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From: Angier, NC
I think you just need to run the RPM up a little higher.
Can do a long highway drive and then pull the plugs and give a look see but that is a art and can be hard to tell.
I run a AFR gauge and it runs between 14:1 to 16:1 with the factory Carter v1 on my 300 six motor. It is somewhat easy to adjust on mine on yours you will need to change jets.
You still running the factory MC v2 carb?
I know as I got the same transmission in my 81 F100.
Dave ----
Tuned
Joined: Dec 2024
Posts: 448
Likes: 94
From: Texas, near Houston
I think a lot of what happens is we get use to the lower RPM of the new cars & trucks and when we jump in our older trucks we think the motor is screaming when it is not.
I think you just need to run the RPM up a little higher.
Without a AFR gauge he really cant tell if he is running at the magic number of 14:1 or rich at 11:1 or lean at 17:1.
Can do a long highway drive and then pull the plugs and give a look see but that is a art and can be hard to tell.
I run a AFR gauge and it runs between 14:1 to 16:1 with the factory Carter v1 on my 300 six motor. It is somewhat easy to adjust on mine on yours you will need to change jets.
You still running the factory MC v2 carb?
He I think said he has a NP435 with the granny first and 1:1 4th and with his gear ratio and tire size should be a nice sporty truck other than that truck transmission.
I know as I got the same transmission in my 81 F100.
Dave ----
I think you just need to run the RPM up a little higher.
Without a AFR gauge he really cant tell if he is running at the magic number of 14:1 or rich at 11:1 or lean at 17:1.
Can do a long highway drive and then pull the plugs and give a look see but that is a art and can be hard to tell.
I run a AFR gauge and it runs between 14:1 to 16:1 with the factory Carter v1 on my 300 six motor. It is somewhat easy to adjust on mine on yours you will need to change jets.
You still running the factory MC v2 carb?
He I think said he has a NP435 with the granny first and 1:1 4th and with his gear ratio and tire size should be a nice sporty truck other than that truck transmission.
I know as I got the same transmission in my 81 F100.
Dave ----
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