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4jg1t "franken-engine"

Share and discuss mod ideas here that make your Isuzu safer, faster, more homely, more user friendly or just crazier! The best from here will be made into a full DIY write up for the FAQ and DIY mod section.

Re: 4jg1t "franken-engine"

Postby paulthepilot5 » Thu Sep 02, 2021 6:38 pm

Definitely get an advancing of peak cylinder pressures with water meth, the more meth in the ratio the more advance. It is a bad thing if already pushing the limits, this is why I don’t have advanced timing while running water meth, also running lower comp. Not sure if you follow Gale Banks or not, have a watch of his video on water meth testing with live readings of cylinder pressures. Long video but worth a watch a few times, particularly the data on peak cylinder pressure. As far as I know no one has done anything to the same level of detail with water meth.
https://youtu.be/k0oWISH5eT8

I’ll have a look into hard anodising. I’ve not had any issues with ceramic coming off on mine nor piston melting activities :lol: , but I am planning to push things a lot harder with the inline pump and surface hardening can only help. Also good to know the cheaper pistons are holding, that’s my biggest fear of running the aftermarket pistons.
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2.8 4JB1T
Inline injection pump conversion
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Re: 4jg1t "franken-engine"

Postby handymanny01 » Fri Sep 03, 2021 10:45 am

yeah man, Gale banks is great! ill def watch anything hes done with water meth, always open for fresh perspectives! : )
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Re: 4jg1t "franken-engine"

Postby Myarmila24311 » Wed Apr 13, 2022 5:05 pm

I am interested in converting my 4jg2 EFI to Direct Injection like you did. Awesome. Need help from you, according to what you post, I just need to buy a 4jg1 piston, 4jb1 head, 4jh1 injector, right? The others all use 4jg2 such as overhaul kits, liners and others. Is it possible to maintain the use of efi pump for this
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Re: 4jg1t "franken-engine"

Postby Myarmila24311 » Wed Apr 13, 2022 5:09 pm

The main reason for this is because of the efficiency and durability of the engine. Power from the engine is not necessary, as long as it is still standard
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Re: 4jg1t "franken-engine"

Postby geeves » Thu Apr 14, 2022 5:12 pm

I know someone that put a 4jb1 into a bighorn and used the original efi pump from the 4jg2 untill he found a good manual pump and had time to sort the wiring for the taco etc. Still went better than the 4jb1 but it was torquey down low and ran to 4k fine but no more than that. Even economy was great but it ran better still on the proper pump
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4jg1t "franken-engine"

Postby Roadrunner » Sun Sep 24, 2023 10:52 pm

handymanny01 wrote:Hey Isuzu Rob! Thanks,, looks good, but not performing as I'd like just yet,,, 100kw at wheels, 360nm, both at 2700rpm, so heaps to come if we can get it to inject properly,,, There is def a compatibility issue , either with the 4jh1 injectors and 4jg1 pistons,, or possibly in the custom pump,,, What sorta pump and turbo Combo are you running?


I hope that you guys are still modding these engines, it's all very interesting!
I played around with the camshaft timing a few years ago on a 2.4 toyota IDI to see what effect it would have on the powerband. I got 2 keyways ground into the camshaft drive sprocket (belt drive), one at around 4 degrees and one around 7 degrees. The effect was pretty huge, The IDI engine had a small combustion chamber in the head which lowered the compression ratio down from the N.A. engines 22-1 to a more turbo friendly 18-1, but I went a bit further and unshrouded the valves to lower the compression a bit more. The valve to piston clearance was really good so I could actually skip a tooth on the drive belt and play around with various amounts of camshaft advance and retard without any piston to valve clearance probs. The first major change was to advance the camshaft around 7 degrees relative to it's usual position, this turned the engine into a tractor with oodles of low end torque, it was strange driving around town without having to shift out of 4th gear most of the time, where as previously I had to row the gearshift to keep up with traffic. The downside was the lack of power above 3000 revs, which was so bad that out on the hyway I couldn't pass cars anymore because there was no power left.
I then retarded the camshaft around 7 degrees from standard and lost some low end (below 3000) but gained a fair bit of top end power, which made hyway driving much better. It only cost around $100 to get the slots ground into the camshaft sprocket so it wont break the bank and should enable you to experiment to see what works for your engine (valve to piston clearance allowing). I eventually went back to around 4 degrees retard to pick up the bottom end a bit because this was my daily driver. If valve to piston clearance is a problem then maybe you could sink the valves into the head a bit. Apparently if you fly cut the piston tops for valve clearance it kills the chamber swirl resulting in more smoke according to the online diesel engine builders. Do the different engines use the same camshaft specs? I also did some mods to the standard exhaust manifold which worked well, let me know if you are interested and I'll explain what I did.
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