Thread: things to upgrade for high performance

Originally Posted by jakeslouw

Somebody mentioned an electrical lift pump to increase the fuel pressure before it reaches the IP?

Would a stock V8 carby version electrical lift pump do the job, or are we talking a 3PSI EFI jobbie?

I assume by pre-pressurizing the diesel, the IP does less work, there is less kW lost and also you get a higher nozzle pressure?

Or what?

I don't know details of either V8 electric pumps so can't comment other than to caution against their use - the Bosch mechanical lift pump on the side of the injection pump is proven and will suit most people.

Sorry, none of the last 3 assumptions are valid.

While looking for something else yesterday I found the details of the valve springs I used.

Stock 4BD1/T valve springs details are:
Free length:
inner 52.4mm (2.065")
outer 53.65mm (2.112")

Assembled spring force:
inner @ 42.0mm (1.65") 10.9 kgf (24.03 lbf)
outer @ 44.0mm (1.73") 23.0 kgf (50.72 lbf)

Crow valve springs 4843 for Chevy small block:
Outside diameter 1.250"
Inside diameter damper 0.86"
Free length 2.07"
Rate 405 lbf/inch
Installed height 1.700" 120 lbf
max lift 0.5" (1.2" height) 320 lbf

The Isuzu spring retainers need a little machined off to allow for the smaller inside diameter of the Chevy springs.

Thanks heaps John I shal see if my mate has some in his shed...so your running these on your motor At the moment? Are they worth having even without increasing max rpm ? Or is it going to help mainly when higher boost pressures are being achieved ?

Originally Posted by c.h.i.e.f

Thanks heaps John I shal see if my mate has some in his shed...so your running these on your motor At the moment? Are they worth having even without increasing max rpm ? Or is it going to help mainly when higher boost pressures are being achieved ?

I fitted them because of both higher boost pressure (compound turbos) and higher rpm (4000 +).

The stock springs were suitable for use with an exhaust brake and turbo, and I don't know of anyone having issues with stock springs, no exhaust brake and boost pressure of about 25 psi.

Remember also that Isuzu changed the cam to address wear rate when they made other upgrades sometime in 1988 - so I wouldn't use these springs with an early cam if you don't have very high boost pressure and/or run at very high rpm.

Mmmm I thought the cam change was only to do with the lift etc etc and not durability but now I know for future reference.
I am planning on between 25-30psi and standard governor settings as I am hesitant to increase rpm until I find a factory turboed late model motor and i also have a exhaust brake installed at the moment... Also will the exhaust brake cause any bad effects on turbo seals ? Or is that not feasible ?

Isuzu changed valve timing as well as addressed cam wear problem. I doubt valve lift was changed.

I don't know of any issues with turbo seals from using the exhaust brake, but you never know with the little turbo you are using.

Auh ok so it was to do with valve timing... so did they address the problem with something similar to tufftride/nitride etc etc ? That turbo is no longer existent I now have a new one I shal hopefully get a bit of a thread going on soon with a few pics of things.
I can not remember if it was the cam or crank measurements on a "t" were smaller than a NA motor but I'll try and find it.

Originally Posted by c.h.i.e.f

Auh ok so it was to do with valve timing... so did they address the problem with something similar to tufftride/nitride etc etc ? That turbo is no longer existent I now have a new one I shal hopefully get a bit of a thread going on soon with a few pics of things.
I can not remember if it was the cam or crank measurements on a "t" were smaller than a NA motor but I'll try and find it.

I can't recall what method was used to improve the camshaft wear - obviously involved hardening, but tufftride (a form of nitriding) is probably overkill.

Nitriding can only be carried out on a limited range of steel alloys. One advantage of nitriding over other methods of surface hardening is that it can be done after the part is finished machined without distortion and practically no dimension change. The other great advantage is that nitriding induces compressive stress in the surface layer, which reduces the risk of cracks starting at stress raisers such as fillets in corners.

Edit: I checked my manuals and found that camshaft journal dimensions (55.94/55.97 mm) are the same for both 4BD1 and 4BD1T. For the cranks, the nominal sizes of crank pin and main bearing journals are the same for both 4BD1 and 4BD1T, the upper limits (63.944 mm for crank pin and 79.925 mm for main) are the same for both 4BD1 and 4BD1T.

However the lower limits differ slightly between 4BD1 and 4BD1T. 63.932 mm for 4BD1 crank pin journal vs 63.924 mm for 4BD1T. 79.913 mm for 4BD1 main bearing journal vs 79.905 mm for 4BD1T. The difference of 0.008 mm is insignificant from my perspective.