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Help Upgrade 4jb1t pump head to 12mm

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Re: Help Upgrade 4jb1t pump head to 12mm

Postby rabidrabbit001 » Thu Aug 03, 2017 7:58 am

I am getting ready to do the pump head swap and am thinking I need to replace the shaft seal while it's out. Does anyone have a source for the seal. Is it 18mm 30mm 7mm?
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby stardog » Thu Aug 03, 2017 4:36 pm

I got mine from these guys freewai.com they sell a lot of Isuzu parts.
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby rabidrabbit001 » Sat Aug 05, 2017 5:18 am

stardog wrote:I got mine from these guys freewai.com they sell a lot of Isuzu parts.

I have purchased several items from them. There is 2 problems with that company. #1 the seal they have on their site shows 2 different sizes. I need to know which one. The shaft measures 19.96mm on the caliper. They show and 18mm and a 20mm.
#2 a $3 part cost $75 to ship to me
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby geeves » Sat Aug 05, 2017 6:30 am

If you have the old seal out you should be able to take it to a engineering shop that does seals and have them match it
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby stardog » Sat Aug 05, 2017 4:21 pm

I just bought some more stuff of them freewai.com only cost me $14 Australian dollars for postage 5-8 days delivery time but $75 us dollars for postage is a bit rich.
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby rabidrabbit001 » Wed Aug 23, 2017 11:05 am

I ordered 2 pair of seals from freewai.com and am hoping they are correct. They are labeled 4jb1 and 4ja1 pump seal.
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby rabidrabbit001 » Tue Aug 29, 2017 10:12 am

Put the 12mm pump head in today. Got it running
and fuel line developed a leak. Very irritating.
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby MISTIRIODES » Fri Jun 12, 2020 5:23 am

Hi, i was curious what did you do about 12mm head did you see any advantage? I am looking to upgrade my pumb as it is a 4jb1 on a 4jg1 custom made
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby paulthepilot5 » Tue Jun 16, 2020 7:32 pm

stardog wrote:I got mine from these guys freewai.com they sell a lot of Isuzu parts.
you can get a full seal kit for the VE4 pumps at most injection shops for like $30-$35 aud
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby Roadrunner » Sun Sep 24, 2023 6:49 pm

Hi Rapidrabbit, any updates on the engine and injection system?
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby paulthepilot5 » Sat Oct 21, 2023 11:26 pm

It’s pretty common practice running 12mm heads on these pumps. Most people chasing decent power upgrade to 12mm if rebuilding. Stock 11mm pumps are limited to approximately 140hp depending on turbocharging efficiency. 12mm will see up around 180hp. There are variations in cam plate lift that also affect this. Correct shimming and setup of the assembly is needed to get the most potential.
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2.8 4JB1T
Inline injection pump conversion
+50 injectors
Borg Warner s200 turbo
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby Roadrunner » Tue Oct 24, 2023 8:46 pm

paulthepilot5 wrote:It’s pretty common practice running 12mm heads on these pumps. Most people chasing decent power upgrade to 12mm if rebuilding. Stock 11mm pumps are limited to approximately 140hp depending on turbocharging efficiency. 12mm will see up around 180hp. There are variations in cam plate lift that also affect this. Correct shimming and setup of the assembly is needed to get the most potential.


Yeah, I'm pretty sure that my 4jg2 has the 12 mill pump as standard, and I must have been up close to 180 hp as it did the zero to 100 km/h in 19.5 seconds (weighing in at 2160 with driver) until I got sick of changing the melted glowplugs too often so had to back off on the fueling a tad. After watching your ute run the 1/4 I feel a bit inspired to wind the fuel up again, but have to find a way to pump more air through the engine first.
I'm betting that the plunger cam on the 4jb1 pump will have a better (more steep) rate shape, so maybe I should look into it further, although chances are that a direct injection rate might not be compatible with the IDI engine requirements. I was wondering what diameter exhaust manifold you run on the ute, as I'm guessing you would have to go up a few sizes to accommodate the increase in flow through the engine.

You might like this video of some diesel action at willowbank- https://youtu.be/LPpa_9mMJNw?si=ipGG7-IrJFTvKTUp
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Re: Help Upgrade 4jb1t pump head to 12mm

Postby paulthepilot5 » Wed Oct 25, 2023 10:38 am

Roadrunner wrote:
paulthepilot5 wrote:It’s pretty common practice running 12mm heads on these pumps. Most people chasing decent power upgrade to 12mm if rebuilding. Stock 11mm pumps are limited to approximately 140hp depending on turbocharging efficiency. 12mm will see up around 180hp. There are variations in cam plate lift that also affect this. Correct shimming and setup of the assembly is needed to get the most potential.


Yeah, I'm pretty sure that my 4jg2 has the 12 mill pump as standard, and I must have been up close to 180 hp as it did the zero to 100 km/h in 19.5 seconds (weighing in at 2160 with driver) until I got sick of changing the melted glowplugs too often so had to back off on the fueling a tad. After watching your ute run the 1/4 I feel a bit inspired to wind the fuel up again, but have to find a way to pump more air through the engine first.
I'm betting that the plunger cam on the 4jb1 pump will have a better (more steep) rate shape, so maybe I should look into it further, although chances are that a direct injection rate might not be compatible with the IDI engine requirements. I was wondering what diameter exhaust manifold you run on the ute, as I'm guessing you would have to go up a few sizes to accommodate the increase in flow through the engine.

You might like this video of some diesel action at willowbank- https://youtu.be/LPpa_9mMJNw?si=ipGG7-IrJFTvKTUp


I don’t think any of them came standard with the 12mm, they should be 11mm (it will be engraved on the pump model number. The 4JG2 I believe has the bigger lift cam plate, probably in the order of 150-160hp worth of fueling. The JB1 cam plates are smaller lift generally. . A 12mm JB1 pump with 2.7mm camplate is around 180hp (with efficient intercooling and turbo charging. I wouldn’t push a 4JG2 head anywhere near as far as a JB1 head.it will just be problematic.
I run a stock JB1 exhaust manifold, they are designed well and retain heat and velocity in the exhaust flow.
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Posts: 129
Joined: Thu Apr 05, 2018 8:56 pm
Age: 38
Country: Australia
City: Brisbane
Vehicle: 1995 Isuzu Rodeo 2.8d
Compound twin Turbo
12mm fuel Pump
+50 injectors
Water/meth injection

TF Rodeo ute 2WD short wheelbase
2.8 4JB1T
Inline injection pump conversion
+50 injectors
Borg Warner s200 turbo
300hp, 650nm

Re: Help Upgrade 4jb1t pump head to 12mm

Postby Roadrunner » Wed Oct 25, 2023 8:30 pm

paulthepilot5 wrote:
Roadrunner wrote:
paulthepilot5 wrote:It’s pretty common practice running 12mm heads on these pumps. Most people chasing decent power upgrade to 12mm if rebuilding. Stock 11mm pumps are limited to approximately 140hp depending on turbocharging efficiency. 12mm will see up around 180hp. There are variations in cam plate lift that also affect this. Correct shimming and setup of the assembly is needed to get the most potential.


Yeah, I'm pretty sure that my 4jg2 has the 12 mill pump as standard, and I must have been up close to 180 hp as it did the zero to 100 km/h in 19.5 seconds (weighing in at 2160 with driver) until I got sick of changing the melted glowplugs too often so had to back off on the fueling a tad. After watching your ute run the 1/4 I feel a bit inspired to wind the fuel up again, but have to find a way to pump more air through the engine first.
I'm betting that the plunger cam on the 4jb1 pump will have a better (more steep) rate shape, so maybe I should look into it further, although chances are that a direct injection rate might not be compatible with the IDI engine requirements. I was wondering what diameter exhaust manifold you run on the ute, as I'm guessing you would have to go up a few sizes to accommodate the increase in flow through the engine.

You might like this video of some diesel action at willowbank- https://youtu.be/LPpa_9mMJNw?si=ipGG7-IrJFTvKTUp


I don’t think any of them came standard with the 12mm, they should be 11mm (it will be engraved on the pump model number. The 4JG2 I believe has the bigger lift cam plate, probably in the order of 150-160hp worth of fueling. The JB1 cam plates are smaller lift generally. . A 12mm JB1 pump with 2.7mm camplate is around 180hp (with efficient intercooling and turbo charging. I wouldn’t push a 4JG2 head anywhere near as far as a JB1 head.it will just be problematic.
I run a stock JB1 exhaust manifold, they are designed well and retain heat and velocity in the exhaust flow.


Yeah it probably is an 11 mill head, it was 10 years ago that I looked it up, my memory is a bit rusty. I don't intend on pushing the 4jg too far, it needs some more low end grunt because the rhf5 doesn't give much boost at 15/17 hundred revs, and that's where a lot of my daily driving is done as in stop start traffic. I was thinking that a smaller turbo would boost better lower in the rev range, but I don't want to lose any top end, so it's either go the smaller turbo and add a second, or fit a small positive displacement blower to it and keep the original turbo for good top end power. ...or I might even try advancing the camshaft 5 ish degrees. Decisions decisions!
I didn't like the look of the log manifolds insides, so I took to it with some grinding stones and took out some bolt bosses that were sticking out into the exhaust flow, enlarged it where I could and put a divider plate in the centre to divide cylinders 1 and 2 from 3 and 4. It works well, and helps to preserve the blowdown momentum. After this mod cruising boost at 100 km/h went down from 6 to 3 pounds of boost, and the turbo spools a bit earlier too, presumably because the exhaust gas only sees around half of the manifold volume and is forced to go out through the turbo.
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