Hello,

I'm new to PROM tuning, but have a question about a different throttle body I'm going to try tomorrow. I currently have a stock 350 truck TBI running at about 14.5 psi.

I recently purchased a used Holley throttle body that uses a GM injector pod and parts. The injectors are 17084304. I understand that the BPW should be the first thing I change. Any recommendations as to fuel pressure and prom changes with this setup?

 

I'd offer a reply but I am figureing out the same issues. I have a bbc tb and 90pph injectors . I found a formula somewhere on this board to figure out the bpw. I came up with 100bpw. But I haven't figured out how the fuel pressure figures in to that formula. Maybe someone can chime in here.

 

The fuel pressure figures in because the flow rating of your injectors is based on a specific pressure. If you are running more or less pressure than what the injectors were measured at, then the actual flow of your injectors will also be more or less (respectively).

For instance, I have 85 pph holley injectors in my holley TB. They're rated as 85 pph @ 20psi. However, since I'm running 15 psi, the actual fuel flow of the injectors is 73.6 pph, which is what was put into my calibration (after I converted it to a BPW, of course).

Teeleton

 

Just a little more info. I'm tuning against an aftermarket chip. The VE table is heavily stacked towards 95% in the upper rpms and the current BPW is 112.

 

http://www.fortunecity.com/rivendell...24/gm_inj.html

 

How did you come to that??

"However, since I'm running 15 psi, the actual fuel flow of the injectors is 73.6 pph, which is what was put into my calibration (after I converted it to a BPW, of course)."


I have 90pph injectors, @ 13-15 psi (gotta get a new gauge), but I haven't figured that part out yet. what are the 90pph injector rated at what psi??, ect. I just set my BPW @ 102 and left it there.

 

You mean how I arrived at 73pph?

This will make it easy.
http://www.corvetteactioncenter.com/...linjector.html

Teeleton

 

if no one helps out b4 tomorrow i will get my book out of the truck that has alot of formulas in the back of it. (eletronic fuel injection book) cause i bought it to study to prepare to tune while i collect the parts going on it.
John

 

OK. I set the BPW to 78, the fuel pressure to 11psi and drove it. It actually drove pretty decent but the BLM numbers indicated a fairly rich condition. I adjusted the VE table and drove it again. Although I know it had to be a step in the right direction, it kinda felt slower. I swapped the first chip back on the side of the road and noticed a substantial power increase.

How do I keep the power while getting the air fuel ratio in line? Some sort of power enrichment (like an accelerator pump)?

 

Trailwing- I just checked and your injectors are the 80 lb/hr TBI 454 injectors. Since you have changed your injector size and TBI bore size you have greatly changed your AE settings, as well as your VE table. You BPWC has also been changed. Based on a 355 CID V8, with 90 lb/hr injectors @ 11 PSI, I get the following.

BPWC = Scaler * (Cyl Vol /Flow Rate)
Scaler = 1461.5
Cyl Vol = displacement of 1 cylinder in Liters
Flow Rate = Grams/second for each bank of injectors
New Flow rate= Square Root (New pressure/Old pressure)x original flow rate.

Cyl Volume=0.72741 L
Flow Rate= Square Root*(12/11)*10.144 =10.595 gms/sec

1461.5*(.72741/10.144) = 104.8 which rounds to 105.

Using these calculations hasn't steere me wrong yet.

My current BPWC is.
Cylinder volume = 0.6391 L
68 lb/hr injector*0.126 = 8.568 gms/sec
Square root (35/12)*8.568 = 14.633 gms/sec

1461.5*(.6391/14.633) = 63.831 or simply 64 after rounded (this was for the WOT portion as I have a VAFPR, which lowers the pressure at idle, and drastically alters the VE table and decel enleanment) Can't wait until the Ultimate TBI code comes out, to fix this problem. Why so little pulsewidth? I can rev my engine very high like this before going static. 6,500 RPM and 300+ RWHP enough for you? Yet with the VAFPR, I have a relatively smooth idle and can PASS a dyno smog test, without a cat.

 

I spent some time yesterday tuning the VE table. It was frustrating, because it seemed like the closer the BLM numbers got to 128, the worse it ran (at WOT anyway).

While playing with vacuum lines, I unhooked the PCV line and somehow managed to blow the RTV out of the back of my intake. Now that I have to pull the intake off, I'm thinking about changing it.

Pro Jection or Performer (carbed)?

 

The WOT fuel table is a modifier to the VE table, so tune the VE table first, then tune the WOT table. Trying to do both at the same time will only frustrate you.

Teeleton

 

Where do you have you O2 sensor? In a cast iron manifold or a header? What type is it? 1 wire unheated or 3 wire heated?

The projection intake is a good intake for the money. If you want to put a 1" spacer under the TBI assembly you can provide clearance for a carbed type EGR valve and the IAC.

 

Where do you have you O2 sensor? In a cast iron manifold or a header? What type is it? 1 wire unheated or 3 wire heated?

The projection intake is a good intake for the money. If you want to put a 1" spacer under the TBI assembly you can provide clearance for a carbed type EGR valve and the IAC.

 

Edelbrock shorty headers (truck) with a 1 wire O2 sensor in the collector. I thought I'd try the larger throttle body with the Edelbrock Performer TBI that's on there now (using an adapter gasket) just to see if it would work at all.

I can probably sell the Edelbrock and recoup some of the cost of the Holley, but I don't want to go through the hassle unless it helps me.

As far as the tune goes... I was working towards getting the BLMs good across the board. Guess it will have to sit for a while. My options are:

1) Replace gasket and reinstall old TB like it was.

2) Buy Holley Pro Jection intake. This moves me a little farther from stock configuration, but I'll still have all the old stuff if I need it.

3) Buy carbed intake and adapter. Even further from stock with increased accessory mounting headaches.

It just seems like I keep pouring money into this engine, but don't get corresponding performance.

 

http://www.users.bigpond.net.au/ben_...ctorsizing.xls

this is a good tool to calc BPW as well as potential capacity of injectors vs FP.

 

If the engine is running worse the closer you get to BLM's of 128 then you need to either replace your o2 sensor or fiddle with the spark.
It's always a good idea to try out a new o2 sensor because even if it doesn't help you'll have it ready as a replacement.

 

The O2 sensor is pretty new. The engine doesn't miss or anything, it just seems to lose WOT power. I'm going to install a 2" bore intake (when it comes) and start tuning from there by getting the BLMs right and then messing with pump shot type parameters.

However... Should I continue working with the low BPW and high VE in my current chip or start over? Wondering if different injectors act differently at different duty cycles.

 

Ignoring the AE while you tune the VE might get you into trouble. AE not "close" can cause your VE table to turn out all wrong. To get your AE close do the math in your head as too how much fuel you think you need now than before (stock). Example; From stock let's say I installed a large dual plane intake and bumped my fuel pressure up by 25%. Working backwards we know that the AE is pulse width calculated meaning it doesn't take into consideration the injector size that is programmed into the calibration! So all of a sudden I've got more AE just by increasing the fuel pressure. My new fuel flow rate is about 1.12 times as much as it was before. So to get back to my original AE "close" would be scaling down all of my AE tables by 1/1.12 . AH, but we're not done. There's the larger intake that has a LOT more surface area. So we need more AE. Okay, approximate the new surface area difference and scale the AE tables again. Let's say the intake is about 1.5 times the size of old. Simply multiply the AE tables by 1.5 and the AE should be pretty close. At lot closer than if you did nothing to them and just started messing with the VE tables.

 

Performer RPM or a Weiand single plane (can't remember the number, 7525??). Use an adaptor and add a _little_ heat to the plenum.

I see in your side-bar sig a 355 with Edelbrock heads and a 2030 cam. True? If so then a stock 350 2bbl TBI will choke the engine. I've been through what you are going through (as others also have). What you need to do is to get a decent estimate of how much power the engine is expected to make.

Then calculate the required fuel and air. Set up the injector sizing (via additional fuel pressure if required) and airflow via TBI bore size, set the BPC and start tuning. It will be tough at first as there will be way too much fuel at lower RPMs and load.

First question: how much power would you expect this engine to make? Then size the injector flow and BPC to a reasonable value. With the Edelbrock heads using a BSFC of .45 may be a good value.

As far as the injectors working differently at various duty cycles, yes, they do. And this also varies upon fuel pressure. The higher the fuel pressure the longer the opening time.

RBob.

 

Yes. Small port (like 165cc) Edelbrock centerbolt heads. I think Vortecs flow a little more, but that could be hearsay. I know they need a lot of timing. I ordered a Holley intake Sunday to get the 2" bores (impatient). Do you think the carb manifold makes enough difference to justify sending it back?

To summarize the above posts... I have a Holley TB (2" bores) with GM 80lb injectors. I set the BPW at 78 (just kinda scaled down from where I was) and the fuel pressure at 11psi. It seemed to have good power, but rich BLM numbers (down low, anyway) and an idle that hunted all over the place. As I started to lower the VE values, it seemed to lose power. It also had a hesitation off idle, like a bad accelerator pump.

Now I'm waiting on parts to start over again. Since I have to go out of town next week, I can always send the intake back to Summit I guess. Or have my Edelbrock bored out?

 

Vortecs might flow more on the intake but not on the exhaust. Infact the vortec's have rather poor exhaust ports but what do you expect from a truck motor with a rev limiter around 5000 .
If the engine is hunting at idle and feels like a bad accel pump then it's probably lean. Actually I'm telling you it's lean. I'd set the BPW to 100 and do all of the fueling through the VE tables. I've rarely, even with bbc injectors, gotten enough fuel at peak hp when I set the bpw "correctly" so I think there is a flaw in the code or the way the TBI's calc the fuel. It's just been my observation. I can't see any real problem with setting the bpw higher than "actual" and it should keep you from pegging the VE tables which does happen.

 

Welp. Swapped the Holley Pro Jection on today. I started over tuning (from my old chip) and was really getting pissed. It did exactly the same thing. The more I worked the BLM numbers, the worse it ran. The idle surged all over the place, it backfired and generally sucked. As a last resort, I swapped the relatively new (maybe a few hundred miles) O2 sensor out, and it started idling normal. The BLM numbers looked better. Hmmm.

It still needs some tuning for power, but at least I can drive it now. When I get back next week, I'll fine tune the VE and then play with AE. May even go to the dragstrip to do it...