I was putting together a TPI unit for a stock GM goodwrench V8 boost project the other night. I have some 24lb/hr injectors sitting around. Since this is a "cheapie" build I don't want to buy 30s or 42s. Even a cheap FMU seems expensive for this project. Anyone make their TPI FPR into an FMU by playing with spring rates?

https://www.thirdgen.org/forums/tpi/...djustable.html

 

Converting the stock FPR to adjustable isnt hard, need to hammer the cap to gain clearance, weld a nut to the top, put a bolt in there, done deal. I used a quarter across the top of the spring cap, its still in my car like that today. Been in there for almost 10 years now. Changing the spring, that may prove difficult. I never looked into getting a different spring either. I may still have my test sheet somewhere, or the data is posted up somewhere here, but I determined the spring rate of a couple stock springs. That would be helpful information to have in picking the right new spring to use. I'll see if I can find it later.

 

I took apart the FPR and got the spring off. It wasn't pretty. The diaphragm was junk on this unit so I had nothing to loose. Autozone has them for $40. The spring is held on to the diaphragm using a rod with a cap on the other end that rests on the housing. The rod comes out of the diaphragm end. It is held in by a spring clip (like on a wagon wheel axle). The spring clip is staked in place at the diaphragm housing.

It seems possible to install a new spring. I bent the spring clip back to accept the pin again. Although, I think you only get one or two different tries with new springs before the spring clip will be junk and need replacing.

The tolerances for the pressure adjust are very tight between vacuum pressure (idle/light_throttle fuel pressure) and heavier throttle fuel pressure. I am not sure I will be able to find a spring to make it work like an FMU due to the limited adjustment. That is, I am not sure it is worth messing with.

I will measure the spring rate tomorrow. The spring has a free height of 1.365" and the coil diameter is 0.115". I am going to check what mcmaster-carr has to offer for springs in that size.

If it doesn't work out then I will just make it a regular AFPR and set the fuel pressure at 55PSI to make the 24lb/hr injectors flow like 27 lb/hr injectors. Maybe activate the cold start injector under boost. I haven't measured the flow rate of the cold start injector. Anyone know the fuel lb/hr it flows?

EDIT: I have debating if I should just install a single NOS nozzle in the bottom of the plenum with a N20 fuel jet and a fuel solenoid tapped off the fuel rail shreader valve port. I could active the fuel solenoid using the ECM with a relay at 2-4 PSI of boost. I would just need to tweak the VE boost tables for the extra fuel to cut back the injector duty cycle. I think I could do that setup for less than $100 with a new solenoid.

 

Do you need one bro....?

 

Thank you for the offer. This intake is a 1986 and still has the original cold start injector installed. I am going hook it up to a fuel pump this weekend and see what the flow rate is. It would be nice if it flowed around 20 lb/hr. Between the stock 24 lb/hrs at 55 PSI making them 27 lb/hr and a 20 lb/hr cold start......it would have the equivalent of 27 + (20/8) = 27 + 2.5 = 29.5 lb/hr injectors. That is just what the build calls for. A fine hillbilly fuel setup.

 

Here's an idea, why not swap rails from another fuel rail, and run two cold start injectors at the same time. You would just need to find a second entry for the second cold start injector....

 

for 35$'s u could get an ebay afpr, u just gut the stocker and plumb it into the return line and they are boost refrenced on a 1-1 scale

 

5-lbs....

 

Yeah, I am not sure which way to go. Here are the options I thought about:

1) Get a bung from http://sdsefi.com/ for $45 and install it in the plenum with a 60 lb/hr hi-Z injector ($60). The ECM could control it and I have a TIG welder. This would be very reliable and allow for future upgrades / boost.

2) Go with the nitrous fuel solenoid and fogger nozzle on the plenum. Probably around $100 and allows for future upgrades. Not as reliable as (1) but not bad.

3) Use the cold start and AFPR. This would cost $0 and is reliable. Downfall, is no future upgrade / boost path.

4) FMU from ebay. Allows for a little bit of upgrade path.

The engine is a stock 350ci targetmaster and it is getting a T4 turbo with a 51mm compresser. Yeah, it is undersized for this engine. I am looking for bost to come in at 2000 RPM or less and probably rev no higher than 4000 - 4500 RPM. Overall, a lame build.....but it is just an old 1-ton dump truck that needs some more pulling torque. I am kind of liking (3) or (4). I don't see it making more than 350 - 400 BHP at peak boost. It is low compression (8.5:1) so I thinking of running between 8 - 12 PSI on 87 octane.

 

That injector cant flow much, based on the intended application. Make sure you post it up. I thought someone like Willie had posted the info before, but I did not find it.

I couldnt find my file either, I'm half packed and its hiding in a box somewhere. You have the spring size though so that'll probably do it.

 

THOSE BUNGS ARE FAWKING SWEET

 

Yeah they are. Reasonable price too.

I decided on just making an AFPR out of the stock TPI unit. With the 24 lb/hr injectors and 55 PSI of fuel pressure I get the following.

24 * sqrt(55/43) = 27.1 lb/hr

.9 * 27 *8 / .58 = 335 HP -> 90% duty cycle, 27 lb/hr, .58 BSFC (turbo)

The brand new EP241 TPI fuel pump (40 GPH) will probably be down to about 35 GPH at 55 PSI.

35 * 5.8 / .58 = 350 HP -> 35 gph, 5.8 lb/gal, .58 BSFC

I am going to test the cold start injector. I am hoping that it flows enough fuel for at least 20HP. 12 lb/hr would do it. I will post the results after I test the flow rate.

 

^ I was being serious, it flows 5-lbs/hr....

 

I thought you were joking. Did you find the 5 lb/hr from looking up the part number or a flow test?

 

There is a 5-lb indication on the cold start injector itself, but when I called GM parts directly yesterday they confirmed it....

 

HHHhhhmmm, I am going to check what it says on the cold start injector I have.
Thanks. That would be about 10 HP at 55 PSI.

 

^ Curious, let me know if your cold start injector's part number corresponds with mine. Mine is marked as the following (also from an '86 TPI setup)....;

Bosch #17080402, #5 on the electrical connector post, and #109 along with #0-280170-600 underneath that number on the side of the injector itself....

 

My TPI unit is 1986 and has all of the exact same part numbers as the ones you posted. I will try doing a better search later..........right now google does come up with anything useful.