Fuel Pressure in Tuning
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Cadillac Powertrain Control Module (PCM) Tuning Discussion, Fuel Pressure in Tuning in Cadillac Engine Technical Discussion; I didn't know where to post this, so here goes. Can you change the computer to read a different fuel ...
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    Fuel Pressure in Tuning

    I didn't know where to post this, so here goes. Can you change the computer to read a different fuel pressure? I read on a website that a person lowered his fuel pressure in his car and gained 14 DYNO PROVEN horsepower. Now the main question is, he lowered his pressure to 36 PSI and that brought his Air to Fuel ratio in the "normal" range. He didn't state what the normal range is supposedly, however the computer saw that (that he lowered the fuel pressure and the Air to Fuel ratio changed) and it corrected it back to factory stock programming. I want to know what he REALLY did. I mean, by lowering the fuel pressure, he corrected the Air to Fuel ratio mechanically. Can you do this with tuning? If so, it must gain you power. He also mentioned what n0dih mentions in his tuning by going MAFless. He talked about getting his blm's (Block Learn Memory?) as close to 0% as possible. Now, being a novice tuner (just got my computer, cable, and tunercat software with $EE definition file), I want to know if gaining this much power is possible with a MAF sensor. If not, I can go MAFless and do it. Changing BLM's sounds pretty involved in tuning the fuel maps, but I want to gain as much power as possible. Please help a novice tuner out!! Thanks! I will have my cable next week, so let me know sometime. Thanks!

    Here is the link where I found it: http://www.ws6.com/mod-7.htm (This was a 1996 WS6 OBDII TA)

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    Re: Fuel Pressure in Tuning

    You do have to watch going too low in pressure, as the spray pattern will get weak and you won't get good atomization.

    But yes, leaner is most often more powerful. In the $EE you can change WOT fuel mixture and lean it out. But you need to do it with a WB02 and not get too lean, as it could cause engine damage.

    Losing the MAF wasn't really my goal, but it proved interesting to lean to tune without it. I didn't do it because it is a restriction to my max hp. It IS a restriction, but how much is a question. And probably will be argued to the end of time. But my thoughts are it IS in the way, regardless it IS in the way to airflow, no matter what it WILL oppose airflow. As to if it hurts power is very very hard, if not impossible to quantify.

    The key is tuning to get the BLM's in line. You can reduce fuel pressure, or update the VE table. The VE table is the right way, the fuel pressure may work, but the VE table is the base of all fueling in the engine.

    You can't deviate from stochiometric, on gas that is 14.67:1, as the O2's are lamba type O2's and they will always force it, doesn't even matter what sort of fuel you are running, E85, gas, E10, E20, etc. It will always maintain stochiometric A/F.

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    Re: Fuel Pressure in Tuning

    Thanks for replying. I have been waiting to see what someone thought on this. If going through the VE tables is the right way to go, then that is the way I want to do it. Question on the wide band O2. If I can get two of them, where do I put them in relation to the cats, after or before? I want to keep my stock ones don't I? I was just doing a little thinking on this, if I can put the WB O2 sensors in the exhaust and keep the factory ones, couldn't I theoretically hook up a cheap voltmeter and read the volts and convert that to fuel air mixture? Or do I not understand how WB O2 sensors work... I may be able to come up with a gauge with a few LED's to read the Fueal Air mixture. Just wondering on how to hook it up and what o2 sensors to use. Oh, by the way, found a website to get LT4 springs, caps, and retainers for $50 plus shipping. All brand new GM parts! Just thought you might be interested. My brother-in-law can get full roller 1.6 ratio stainless steel rockers for $130 also. THey come from a place in Brookings, SD. He lives there and comes home every so often on the weekends. They are self-aligning and fit under center bolt valve covers. I am going to do that upgrade before I go to Des Moines in the Spring. Just an FYI... Thanks again!

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    Re: Fuel Pressure in Tuning

    WBO2's always before cats. I hope to get one, I think I finally found someone who will let me borrow one. I just need bungs installed now.

    I have been thinking the same thing, WBO2's are $79 each, so they aren't terribly expensive at all.

    I expect that WB02's will be standard on all cars come 2010, as next level OBD hits....

    1.6s will need different springs for sure. And make sure the rockers are self aligning, else you will need guideplates. That price seems very low cost for rollers and self aligning.

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    Re: Fuel Pressure in Tuning

    There is a guy in Brookings that has a shop and if you live close and can pick them up, you can avoid $30 shipping and handling. Cheap, but strong and warrantied!

    I will let you know when I am ordering if you want to get some, I will send them to you, or bring them to Des Moines if you are going!

    BBB

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    Re: Fuel Pressure in Tuning

    Quote Originally Posted by bigbluebrougham View Post
    Oh, by the way, found a website to get LT4 springs, caps, and retainers for $50 plus shipping. All brand new GM parts!
    LT4 springs will not fit the cast iron LT1 heads, I'm pretty sure. Even the aluminum LT1 heads use a different spring pocket size, so I'm pretty confident the LT4 heads use a different size spring.

    You will need to purchase springs specific for the iron LT1 heads. These are necessary if running 1.6 rockers since the stock springs are marginal at best for stock 1.5 rockers.

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    Re: Fuel Pressure in Tuning

    Yeah, I looked at the specs for the stock springs, pretty weak if you ask me. 84 lbs at open and 200 something for closing, pretty weak. I thought there was extra room on the heads for LT4 springs...if you can put a hot cam kit in there, it comes withthe LT4 springs and they fit without modification, AFAIK anyway. Let me know if I am correct in stating this, but I think I am.

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    Re: Fuel Pressure in Tuning

    Quote Originally Posted by bigbluebrougham View Post
    Yeah, I looked at the specs for the stock springs, pretty weak if you ask me. 84 lbs at open and 200 something for closing, pretty weak. I thought there was extra room on the heads for LT4 springs...if you can put a hot cam kit in there, it comes withthe LT4 springs and they fit without modification, AFAIK anyway. Let me know if I am correct in stating this, but I think I am.
    LT4 HOTcam kit was intended for the vette (car with aluminum heads). B and D bodies have different heads with diff head pocket sizes.

    You are better off ordering the HOTcam seperately (or buying used for dirt cheap) and then quality springs good for .525/.525 lift. I like EX Components springs sold through Combination Motorsports. But beehive springs are all the rage know.

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    Re: Fuel Pressure in Tuning

    I have been thinking of one for my ride.... With the 3.42 gears I really honestly still insist the factory B/D cam is too small. In the old days, ALWAYS GM put a larger cam in the cars with steeper gearing.

    Look at a (some) 350 4BBL, all 400 4BBL and 455 Pontiac all got the 067 cam, which was 200/213 @ 0.050 duration. The 2BBL's got 200/210 @ 0.050 duration, this was the common cam with 2.56 to 2.73 gears. So my thoughts are that my cam is waay to small for this engine.

    The stickshift cam (370hp 455 HO, 366 hp 400, etc) got the 212/225 degrees @ 0.050. Which is on par with the HOT cam.

    Here is some good reading on camshafts: http://www.classicfirebird.com/hand/jhand5.html

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    Re: Fuel Pressure in Tuning

    Quote Originally Posted by N0DIH View Post
    I have been thinking of one for my ride.... With the 3.42 gears I really honestly still insist the factory B/D cam is too small. In the old days, ALWAYS GM put a larger cam in the cars with steeper gearing.
    The gearing is one thing, but the low stall of our cars coupled with its weight is a detriment. To take full advantage of the HOTCAM it would help to have a higher stall plus gears.
    Even the stock B/D cam can benefit with a higher stall TC in the 2000-2500 range.

    ^^^Performance wise, anyway. Anything that helps you get close to peak torque @2400rpms will help out. Gas mileage around town will likely suffer, though.

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    Re: Fuel Pressure in Tuning

    I had the stock 301 torque converter in my 80 T/A and I put in a mild 455 and it stalled in the 2400-2500 rpm range. It was perfectly drivable and still tight enough that you didn't notice it. But it was looser. Not near as loose as my 4.0L Aerostar I put in a 3L converter. That was loose, probably closer to 3000 rpm stall. NICE!

    I am miffed, I had a 2000 rpm stall converter from a mid to late 80's THM200 4R (according to the broadcast code it is ok for a 700R4/4L60/4L60E), but I sold it before I realized what stall it was (darn!). Oh well, I know what to get one from now. I still wonder if a 3.1L V6 truck converter from a S10 with a 4L60 will work with an even higher stall? Or is the 4.3L V6 full size truck converter better?

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    Re: Fuel Pressure in Tuning

    Quote Originally Posted by N0DIH View Post
    I still wonder if a 3.1L V6 truck converter from a S10 with a 4L60 will work with an even higher stall? Or is the 4.3L V6 full size truck converter better?

    To be honest, from what I have read countless times on the forums and from local buddies in the club who have 'been there and done that', the difference between a super-quality converter from places like Edge and Vigilante are NIGHT and DAY from mediocre converters from GM and aftermarket companies. Not to mention the smaller diameter quality converters (9.5") greatly reduce rotational mass alone.

    FOr these big heavy cars I would shy away from a converter meant for a small engine, light-weight truck when planning to put it in a heavy heavy car meant to tow and do some spirited or performance driving.

    Downside to quality converters is that they cost $550(Edge) - $800(Vig). But they will most often rebuild it under warranty if tranny fails, flushing out old crud and even re-stalling it if your drivetrain changes. So all in all money well spent although hard to part with initially.

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    Re: Fuel Pressure in Tuning

    Yeah, the cost of them... Sheesh....

    The factory converters are at least designed to meet factory requirements.

    I will look into it, but for now, I don't have that much $$ to drop into it. Wish I did....

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