ben73

I think I am getting close to finding the true limits of the TBI system.
My 383's previous best was a 12.81 @ 107 mph with a few lame excuses like hot air and 3000ft altitude... It was running 2 x 90lb injectors at 15psi and seeing 90% duty cycle at the top end with the WBo2 showing a safe/fat 12.3-12.6 (commanded at 12.6)

I have just completed a cam swap and started tuning again. New cam is a comp 12-430-8 (280/280, 224/224, 560 lift w/1.6's and 110 LSA) I have got the VE's right again and am now working on the top end. With no changes to the fuel pressure, the WOT AFR's went to 13.0-13.3 and the injector were static, 100% + DC ! (commanded at 12.2). I was pretty happy with that as it means its breathing deeper ;-) I am putting in more fuel that before and it is STILL LEANER! Cool! ;-)

I have upped the fuel pressure from 15 to 16psi and its now showing 12.8-12.9 on the WB, still commanded at 12.2.

I will now go to 17psi and see if i can get the WOT AFR down a bit closer to the commanded AFR.

And the big question is, "is the idle suffering??"..
Not yet.. The PW's are getting short, but I think it will be ok.. The car is definately faster than when it ran the 12.8's and i will be going to the track asap.

I thought this maybe of some interest to the other guys who play with TBI.

RBob

iTrader: (1)

Nice, sounds like you having it running well. TBI isn't as bad as people make it out to be. Just can't be running stock 4.3L TBI units on a hi-po engine

With one of my setups I'm running 81.5#/hr injectors at 22 psi. Like yours the idle PW's are small, but it works. Another setup that I am aware of is running the 81.5#/hr injectors at 20 psi. Still working on taming the idle, however, the mid-range and top end is much improved.

RBob.

ben73

Hi RBob,

I just got home from the track after giving my new camshaft a run!
Results were good and bad..
The bad part is that my new tyres, or the track prep was crap! No matter now gently i launched, it just flashed to the 6k rpm limiter and smoked the rears...

The good news it that my tune was near perfect on the WB and i picked up a solid 4mph! Managed to crack just a little over 110mph!! VERY VERY happy about that! That equates to a solid 30-40hp gain. Awesome!
I ran 12.8's and 12.9's still, but my 60 foot times were a full 4 TENTHS slower than before due to the lack of traction! This, and the fact it can now run 110 mph means its got a 12.4-12.5sec ET in there if i can get it too hook up! I'll put the old tyres back on next time, they used to hook up perfectly for 1.74 sec 60's.

I now have the 90lb injectors at 18psi, and they are still at 96% duty cycle to give me 12.6:1 at ~5800rpm! It likes the fuel! Idle is still ok with PW around 1.0-1.1msec.. I believe 0.7 is the accepted low limit?

I'm pretty happy with this setup now ;-)

Dewey316

Great progress!

I'm thinking you may be the type of build-up that actualy needs a VAFPR, so you can get the idle PW long enough to contorl it.

I'm really glad to see your trap speeds up that high. Its proof, that as many of us have said before, if you can somehow get enough fuel in there, the TBI stuff can support more HP than most people think.

--John

ben73

Hey Dewey,
I played with a VAFPR some time ago (previous motor) and didn't like it.. The fuel pressure swings were too hard to tune around..
As it stands, the idle may be getting near the limit, but its still good.. And if i did need to bump the pressure again, i could always set it up to idle a little richer anyway.. At the moment it idles closed loop at 14.6-15 AFR, and its very good. No hunting at all, MAP only moves in a 2-2.5 kpa range.

BTW, I am only using 2" TB's.. This is a crossfire/x-ram setup, but its essentially the same as normal TBI.

As far as weight-shifted horsepower calcs go, it was pushing 320rwhp, now it looks like 360 according to the few online hp calculators i play with. (3400lb '84 vette)
They also guess at ~430 flywheel, up from the previous cam's 390... assuming 18% losses...

** don't flame me on the use of these calculators, i know that attempting to calc flywheel hp is a wild guess ;-)

RBob

iTrader: (1)

Shame about the tyres. However, like you said the engine is definately making more power. As for the idle one engine is running 1.0 to 1.1 msec PW. Of this 0.778 msec is the injector bias. So the actual fueling PW is closer to 0.275 msec. Not a whole lot of fuel.

RBob.

RBob

iTrader: (1)

I've tried/played with vacuum referencing the fuel pressure regulator. With the stock code it just doesn't work correctly. What I found was that the fuel pressure changes lagged the manifold pressure changes. This caused rich and lean spikes. On opening throttle the lean spikes caused surging. This made it difficult to drive the car in a smooth manner.

Another issue was the VE table. As the manifold pressure fell the VE% values needed to be increased. So much so that at low KPa the VE table was max'd out. Not enough range. That put an end to further testing.

On the other side of the coin, the code now has a table of BPC values based on manifold pressure (2d table, interpolated lookup). That should alleviate the VE% range issue. The BPC is then lag filtered. Hopefully by using the correct filter coeficient the BPC value will track the fuel pressure regulator response.

Haven't tried it yet. Maybe later this summer. As it is now by using closed loop during idle there is fairly good fuel control.

RBob.

dimented24x7

iTrader: (2)

I had a similar routine in mine as RBob talked about. BPW correction vs. vacuum with a lag filtered term. Never got to use it so I just deleted it. What would be really cool, though, is if there was a fuel pressure sensor available that could be hooked in place of one of the resistance based sensors, or even a digital one with a 0-5V output. That would really be sweet to be able to measure the instantanous fuel pressure.

Grumpy

What I did was use two Mallory Fuel Pressure regulators. One vacuum referenced, the other just open to atmosphere. It cut down on the dynamic range, and made for a small but nice WOT increase in F/P..

Good Work.

ben73

I did that at one time too Grumpy. I used a holley reg to limit the upper end of the VAFPR's pressure range.. It was better, but still a bit messy.. I probably should have narrowed the pressure range further.. Its almost impossible to get the VE's lined out when the FP moves around too much!

I'll keep that in mind as something to try again in the future. As it stands now, its working very well, and my VE's are all where they should be, so there is no reason to tamper with it ATM..

JPrevost

Cool beans! Congrats on the mph mark. I'd like to get up there with TBI but the StealthRam for votec heads is looking mighty tempting... especially when you've got two GN turbo's sitting on the desk . I might sell em off and just build up the 2 barrel TBI like you're doing. I definatly need to do some engine work because this low budget performance crate is LOW BUDGET with it's parts.
What code are you using right now? Also, mind going into more detail on the combo you've put together as it sits?
I also don't like the vac.AFPR. Like RBob said, hard to tune with the stock code and the pulse widths with these P&H injectors can get mighty small without having issues.
Another question; Do you have any datalogs of your runs? I'd like to see the MAP pressure drop.

ben73

I am running a 16168625 PCM from a '93 truck, $E6 code and ostrich. It has been one of the best mods so far. Way ahead of the 7747!
Combo is a 383, AFR195's, comp 12-430-8 (280/280, 224/224, 560 lift w/1.6's and 110 LSA, single plane weiand x-celerator manifold (x-ram/crossfire), 2" TB's, 90lb injectors at 18psi, tri-y's, ~2800stall, 700r4, 3.07 rear..

I datalog with datamaster. Here is a run showing the MAP reaching a low of 96.3.. Engine off is 102.2, so pressure drop = 5.9kpa. I do have some 2.20" TB's in the making, but they are not ready yet. Wonder how much difference they will make??
Look at the speed graph (blue line), see the wheelspin!
Also, ignore the knock counts, thats from hitting the starter motor in the staging lanes a few times.. It gets no knock counts during the run with 36.2 degs at WOT.
Also note that we figured that datamaster calcs the inj DC incorrectly and you should double the displayed number.

ben73

here is a WB snapshot also....

Grumpy

Time for a Traction Control Routine........

ben73

I was thinking along the lines of sticky tyres!

Grumpy do you think there is much to gain with bigger TB's?
5.9kpa isn't a lot, but every bit helps...

Low C1500

Nice numbers!, sounds like you could use some drag radials (not the best if your car is a daily driver).

Any drivability issues with the setup, part throttle stumbles, etc?

You got more motor than me, and I liked running my 90lb injectors @ 20+ psi

ben73

Its not a daily driver, but i am a bit concerned about running drag radials.. Common belief on corvetteforum is that a dana36 will break if the tyres are too sticky..
A replacement rear will cost a small fortune in this country!

No driveability probs at all, it has never run better.
This time i really put more effort into my VE's and it really shows. no stumbles, no popping out back, just nice smooth grunt ;-)


there are 2 vids here.. they really show the crap launches with bulk wheelspin and early change to 2nd to bog it.. turn up the volume []

http://members.***.net/desertvette/ben/newcam.wmv

http://members.***.net/desertvette/ben/newcam2.wmv

JP84Z430HP

impressive.