Tuning the F77 table negative from bigger inj..

[cheatham2492]

I have been tuning trucks for 5 years or so and I ran into a funny thing today. I am dealing with a stock motor,950cfm turbo and 50lb injectors.Truck would'nt run of course he had an ultimate for a stock set up.His fuel pressure was at 50psi and he doubled the injector size so you have to lower the pressure half as much with the stock chip. I told him to put the fuel pressure to around 18psi and it started right up. he drove it over and we have been working on it. The motor likes to run around 70-73 total on the VE table. Under wide open throttle its still at 73.3 and the o2's Are 1025 or so. I would like to see around 925-950. The Injector flows so much better with higher pressure "under boost" that I think I need to lower the VE table through the F77table. by using a lower figure than 1.0. For instance .9. The fuel tables are all just multiplication of them selfs including the EGR constant.I was'nt taking into account the fuel pressure rises along with the boost levels. We ran out of time before I thought about it to make the change.I ran into this before with my syclone running too rich under boost but would run great up to boost...... Wish I had thought about it a little more.I was running 12.50 at 108mph and my o2's were 1000 something. I know I could have got a lower et.Just a little food for thought.Tell me what you think.
Dan Cheatham PS.I think lowering the 1st map range of the F77 table will effect all the map ranges below it. Not sure will have to experiment.

 

[JSM]

Re: Tuning the F77 table negative from bigger inj..

I think using the stock o2 is about as accurate as a blind guy playing pool. Sure once in awhile you will get a ball in the pocket.

There are better ways to adjust for bigger injectors. 18psi base fuel pressure I hope was only used to get truck to your shop and not a permanent fix.

 

[dgoodhue]

Re: Tuning the F77 table negative from bigger inj..

I am surprised it ran. Some of the injectors I have played with have stopped firing properly at ~30 of fuel pressure.

 

[cheatham2492]

Re: Tuning the F77 table negative from bigger inj..

Yea, It was just to avoid the tow truck. O2's are defiantly for ball park but better than nothing I suppose. As far as the injectors I have run 25psi no problems...
DC