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Chasing EGTs: larger injector?


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Bigger injectors mean more fuel; more fuel means more heat, smoke, and power....

I'd expect that for an equal injection quantity and boost level, power should be the same and the shorter duration injection event would improve combustion, effectively advance timing, and lower EGTs. Can those who have swapped injectors around confirm this?

I'm still running the stock ISB 205 injectors with my B5.9 215 P-pump and my EGTs are not well controlled. They don't drop at higher RPMs under load - possibly in part since my wastegate is shut. I can play with the wastegate and maybe help myself out a little, but grossing at 24k through the PA hills there were places that I was pedaling myself down to 40mph to stay under 1400˚, keeping it under 1350˚ was near impossible. Flat ground cruising I'm rarely under 1000 loaded. 700˚ish at 70 flatland when empty (8500#) I read that with the higher ISB popoff pressure my timing should be retarded about 3˚ from where it's set, so my timing should be at about 15˚. It's a hard start in the winter so I'm planning to retard it about a degree from where it is when I check it next.

I also kept my mechanical fuel pump, so I'm running the 12v cam. The only consequential difference between the two is exhaust lift, I'm sure loosing exhaust lift isn't helping my pyro, but it's only a 13% difference...

12V Stock:

INT: 159° .235” Lift

EX: 204° .263” Lift

102 LDA

24V Stock

INT: 159° .235” Lift

EX: 206° .297” Lift

107.5 LDA

I'm thinking that RV275s and turning my fueling down a little should help me out the most without loss of power.

Turbo is a stock B5.9 HX35, I try to keep boost under 33-35, it'll hit 40 or so. I have a bad wastegate actuator that I haven't swapped out yet.

--- Update to the previous post...

still stock intake and air filter, by the way. Filter minder says it's about 75-80% used up right now. Exhaust wise, a 4" straight pipe from 3" straight pipe when I did the exhaust brake made essentially no change at all.

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Your making too much boost for that HX35, its pumping hot air which is increasing your EGT's. I would also guess you are running too much drive pressure, which doesn't help your already choked exhaust. I went with a Stage 1 Colt Cam and the difference was only 7% on intake and exhaust and made a difference!

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  • 1 month later...

Found I had a blown gasket on the intake plate while swapping another troublesome injection fuel line. Hard to believe a roughly 4" by 1/16" or less gap can make such a difference.I still have not replaced the wastegate actuator, and did not play with timing, star wheel, fuel plate, injectors, or anything else. Back up to the pre-24v 37-40psi max boost instead of 27ish and very similar EGTs as I used to have. Loaded and holding 75 up good hills, boost and pryo climb smoothly and at max boost EGTs will slowly climb from 1275-1300.... Next time I'm bored I'll slide the fuel plate back maybe 1/8" and see how it does. Hopefully I can get the AFC in exactly the same spot again, it's very well adjusted for smoke at the moment. Then I'd be able to let the cruise control mat it through the hills again and not need to care :thumb1:It's like a whole different truck. Amazing what some RTV can fix!

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