Go to this url and checkout this mod. https://www.corvetteforum.com/techti...=154&TopicID=2
This mod was done on a 87 vette, and I was just wondering if anyone has tried this on an lt1 or lt4, and got the same results. Did anyone?

If not I will bring my fuel pressure gauge home from work tomorrow and try it myself. Then I will post my results. This is something I will try till I get my adj. regulator in.

 

Very interesting

 

:iagree:

 

When you do that mod you are setting your fuel pressure to a constant value equal to the WOT setting (where manifold vacuum drops to near zero; the same as disconnecting the vacuum line).

At WOT performance will be the same as with the vacuum line connected.

At part throttle, in closed loop mode, the ECM will simply cut back the injector pulse width to get a stochiometric air/fuel ratio. However, higher fuel pressure often produces better atomization which increases combustion efficiency, so fuel mileage & power might go up a little. Most of that calculated mileage increase is fake since the ECM bases the calculation on injector pulse width, assuming stock fuel pressure. With increased fuel pressure the perceived fuel flow would be lower, due to decreased injector pulse width, so calculated mileage would be higher than actual.

That jump in fuel pressure of 30psi to 40psi a is rather high 33% (13% fuel flow increase); bone stock my fuel pressure would increase from about 38psi to 44psi only 10% (5% fuel flow increase). Meanwhile the stated calculated gas mileage increase is only 8%, from 26.5mpg to 28.5mpg.

For example I have increased my fuel pressure by 8% from 44psi to 48spi (4% fuel flow increase) but have a mileage increase of 7% from 29mpg to 31-32mpg, highway.

Part throttle performance may have improved a little. Also, true mileage should increase a little unless the constant increased pressure causes an injector to leak or stick open.

 

:iagree:

 

Yeah that works and has been around for a long time. Us mechanics use that with a guage hooked up to test the regulator and see if the pump will put out more pressure as a pump test. It works on other cars too........ and trucks. Want another one?........ unplug the knock sensor for a while........ but if it pungs you'll get a "check engine " light when the thing doesn't see a signal after the engine is over 194 degreesF........ You might want to leave it that way but you'll need a 160 stat and keep and eye on timing and use 93 octane. :lol:

 

Thanks for taking the liberty to explain this. I did not want to type all that... :D

 

I had my unplugged for a while now and have notice a difference. :cheers:

 

Have seen this explained (overall design) as part of the enrichment/WOT throttle strategy to insure air flow did not get ahead of fuel flow. Should this occur, likely a hesitation or other driveability problem would surface. Carbs have the accelerator pump (prevents "flat spot" during acceleration) but no such hardware noted in the ECM. As noted above, the computer is supposedly fast enough to catch this "change" and over time, trim the fuel.

dlmeyers 90 coupe zf6 3 speed shocks

 

Will this mod work on a LT-1

 

Well I thought it was a good thing to have around 40psi. I used to run around 50 on my 85 L98. So if stock is 30, and removing the vacum line will give you about 40, then why not do that till you do a few more mods, and need the fuel pre. regulator. So it sounds like a good thing to do. Anyhow here I go with my fuel pressure gauge. Time to test out what it does. I will post back later on the results.

 

stock fuel psi=38
modded fuel psi=46

The results are in. Stock fuel pressure on my lt4 was 38 psi with the vacum line connected. Now it jumped up to 46-47 psi with it removed, and blocked. Since I have increased my airflow by my A/O induction system, and my exhaust by my corsa kit. Now I will leave the vacum line off to bump up my fuel pre. This will be temporary till I get my heads cnc'ed, my cam, and my headers in. Then I will upgrade the fuel pump and regulator.
So I will have to agree, no matter L98 or LT1, and LT4, the removed vacum line will increase fuel pressure which=more performance.

 

Could someone explaine me how to do this 'simple 15 seconds mod' (assuming to have a fuel pressure gauge ) ???
step by step.... I want to try but I don't want to do a mistake....
Thanks in advance
-Beppe-