I have a turbo master and an a-1 customs fuel controller, and I'm looking for information about the function of aftermarket chips for my 95 tahoe. Since I'm in control of the boost and the fuel what advantages can chips provide on top of this. Do they have a modified fuel acceleration curve which would allow the rpm's to ramp up faster or do they trick input to and from the engine for advantages beyond factory parameters. Has anyone out there dyno'd before and after to verify any results, and are there recomendations for one chip over another. Thanks.

Unfortunately, and contrary to what has been hyped, the PCM reads the FSD resistor only at start-up, stores and uses the value it reads at that time.


If the value changes, the PCM can adjust to the new value over several start-stop cycles. It is not an instant thing, and total variation is less than 5%.


The quote-unquote 'fuel control' is a variable FSD resistor substitue. It will cause Cal Resistor DTC's for too great change over preceding value.


The GM scanner Tech-II can alter the stored value instantaneously, as required for an inj pump changeout.


FSD resistor compesates for mechanical variations in the inj pump. If your pump required a factory value of 8, the max resistor is 9 - minimal fuel rate change would be effected for increase from 8 to 9.


You could hope that your pump required a 1, to effect maximum change at 9, which is still minimal fuel rate improvement.


Max oem stock fuel rate out is 63cmm for your truck, so increasing Boost to 12-14psi is advantageous, if the exhaust system has been upgraded. More boost = more oxygen.


Increasing Boost lowers Exhaust Gas Temperatures under load, as in towing.


Anything over 14psi, exhaust back-pressure increases above 20psi rapidly, raising EGT and Engine Coolant Temperature, and preventing any further power increase. The GM turbo is the 12psi bottleneck.


If you do a lot of towing, you will see just as much gain from a charge-air cooler, as it lowers Intake Air Temperatures from ~200deg to near ambient.


Cool air contains more oxygen per volume than same volume of hot air. More oxygen = more power.


The 'hot chips' alter timing and fuel to ~78 - 80cmm. Check with John Kennedy for real hotrod chips, check with Bill Heath for towing chips. Hypertech may be emissions-limited.


These require engine cooling system upgrades, exhaust upgrade from stock, and a charge-air cooler.


If you have not, read TurbineDoc's post on upgrading the 6.5L - ups the HP from 190 to about 240.


He's running what he's preaching.


Any further hp increase requires lower compression ratio, to 18:1, new turbocharger(s).Edited by: gmctd

The chip should change your shift points as well have more agressive maps. TDC off set could be programmed in.


So, how much tweaking can you do to the valve train. Has there ever been a cam offered with short duration intense lift peaks or split durations. Is it possible to alter the lift ratio with longer push rods and higher ratio rocker arms?

Crane offered a re-grind with higher lift for the non-turbo versions to improve flow-thru.


A turbocharged engine with 3500rpm limit would benefit little from timing and lift alterations - increased intake pressure, Boost, increases flow-thru. Intake-exhaust overlap allows boost pressure to blow previous combustion residuals from the cylinders, cooling the valves, allowing completely fresh charge air for the next combustion event. More oxygen = more power.


Gasser engines benefit from cam changes because fuel and oxygen mix is taken into the cylinder on the intake stroke. Alterations in timing and lift allow more fuel\air mix for more power.


Boost a Diesel and increase injected fuel rate for more power.


The L56 1500 engines are factory set to -1.5deg TDC Offset, very close to maximum performance advance at -1.9deg.


Compensates for EGR scheme.Edited by: gmctd

I disagree,


More lift would allow greater volumes of intake and exhaust to transfer. As is, the 6.5's overlap coupled with the stock exhaust manifold restrictions mean that the exhaust back pressure is re-entering on the intake stroke. This would decrease efficiency by increasing combustion tempatures, it's the reverse of intercooling, you're interheating. More flow = more go, with less energy consumed to go there. If you want to drive your 6.5 with this factory engineering fiasco till you break down and get a duramax, go ahead. I will follow another path. My intuition tells me the 6.5 is superior for the least of which it has Grey cast iron heads, instead of white aluminum. Aluminum is soft as lead, with nearly as low a melting point. I'd go cast iron anyday. That is, unless you want to tell us about how the roswell crash has changed the auto industry.Edited by: quantum mechanic

Would not , then, greater lift also allow even more back pressure to 're-enter' the cylinder even quicker, preventing even more flow?


Exhaust-intake overlap is important to producing power in a turbocharged Diesel engine. Proven, inalterable fact.


The GM-X T-3 turbine is configured for a 250 - 300cuin displacement engine - this allows quick spool-up at low rpm, but quickly becomes a bottleneck as exhaust volume, velocity, and heat increase from increasing engine rpm.


Now, you've got 400cubic inch exhaust trying to get out of a 300 cuin area, and getting worse by the rpm.


Therein lies the answer to cause and effect regarding exhaust backpressure in the 6.5L, not the exhaust manifolds.


Put a T-4 turbo on, and no power, black smoke off-idle, but works great at high rpm, with low backpressure. (But, then, we sorta liked the initial kick with that GM turbo, didn't we? Decisions, decisions.)


You can hang 5" tubing headers off the heads, hoping for some improvement, but once you see the physical size of the eight exhaust ports (those are ports? they look like EGR taps!), then comes the question - "But, why?"


Check out HMMWV - that's Hummer, for us rednecks - headers for appropriately sized and shaped stainless steel tubing headers. Oem factory stock.


And don't forget - tuned exhaust is detrimental to turbocharging, where the powerband must be spread across 'street-use' rpm ranges.


But, try out your ideas - experimenting is fun. Always is for me.Edited by: gmctd

That's why a forge and casting parts is on my list.


I wonder how much change I can affect by porting and polishing my heads when they come off? What's the possability of oversized valves?

First, I forgot to mention that you are correct - high exhaust backpressure is a big part of the stock 6.5L turbomotor problems. It does increase EGT, ECT, and limit power. While I was just being facetious with that 'higher lift' reply, increasing 6.5 output does not require any camshaft changes.


Other changes, yes.


Port matching and polishing works, intake and exhaust.


But, GM reduced '82 valve size for the '83-up heads, because of head-cracking between the valves.


Indirect injection requires a pre-combustion chamber, where injector and glow plug is, made of some super heat-resistant alloy, inserted into the head to the outside of and centered between the valves. This requires a 'special' coolant passage to remove the added concentrated heat. The passages are visible, where the cap plugs are under the intake ports.


This area is noted for cracking in the 6.2L, with even greater incidence in the 6.5L turbo engine, caused by poor coolant flow thru heads from block.


Note:GM put some patches in for this with '97\98 cooling upgrades - dual t-stats, hi output HD waterpump, hi flow fan, orange coolant. But it does not appear as though anything was done with the block and head water jackets. The upgrade patches greatly reduced complaints of over-heating.


So - 300hp streetable work truck?


Portmatch\polish, lower comp ratio to 18:1, balance rotating assembly, larger turbo, increase boost, increase fuel rate, and charge air cooler is the proven way to go. Many of these are in daily use even as we type, from towing to hotrod trucks.


Lowering compression ratio is important, allowing 50% more boost at same cylinder pressure as the stock high compression version. More oxygen = more power, 20psi vs 15psi.


450hp? Same modifications as 300hp, add twin turbos, increase fuel rate. Increase engine cooling.


And, for no leaks, ever - use the Fel-Pro super orange sticky head gaskets any time you've got the heads off. Works for me.


Edited by: gmctd

GmcTD,


You're a virtual archive.


I am thinking more and more about the cooling upgrades. I want to open this engine up as much for flow as the abality to transfer heat( bigger exhaust minifolds, twinturbos) so that I can use multifuels. I want to use 20% diesel, 80% propane, with compressed O2 on demand. This is either going to blow or melt the heads, piston, cylinder or find itself exhausted.


What do you think of tunning down the diesel response with programming to run more propane? I can see a propane intercooler that also feeds the intake. Propane boils at -44 deg. so i'm talking liquid to gass conversion and the associated heat transfer inside the intake manifold. Precombustion worries?


most super heat resistant casts are white cast.

That's a little too exotic, for me, QM.


That big hawg I drive is meant to pull defunct tractors across open farmland on a gooseneck flatbed, and return reasonable fuel mileage, to and from.


But, your '93 has the mechanical inj pump with adjustble fuel rate, and it has the mechanical wastegate control, so all tweaks and adjustments are within your reach, so to speak (type?). You might use it for a testbed - you don't need 'chips' or boost foolers, or any of the gadgets designed for the EFI truck.


Same engines, different technology, but the engine doesn't care what technology is feeding it. Just improve the exhaust over factory equip.


HowieE has indicated that he uses propane, with info on his website - if you have not, you might check that out.


Banks has a "Banks talks tech" page, covering all aspects of Diesel hotrodding, mostly Cummins and Power Stroke, but the concepts are all-Diesel applicable.


Bill Heath Diesel offers water mist injection, for those who don't want a heat exchanger at the front of their truck. Put a block of ice in an insulated water tank, and IAT, ECT, and EGT would all drop, for more power.

Matt,


Out of curiosity can you answer a few questions on your fuel control, I'm not 100% sure you have as much control over fuel delivery as you were told. From my experience once the PCM has stored a value it's there until a learn is enabled with a T2 or proper application of APP to floor and key on key off sequence, at least that is true for OBD 2, not sure for OBD 1, also resistor changes only net incrimental gains, in actuality my #5 resistor vs a #9 is more a mental change( I think it so I must be faster) not a seat of pant that I can actually discern any gain..


Does the "fuel controller" have you remove the existing resistor from the FSD connector socket, & does the fuel control spice into the harness or does it sandwich into the existing socket, and are you still pump mounted or on a cooler remote mount.


What is your goal in your quest for more power, to make a tow machine or a go fast machine, it's important to define this so you can know what your expectations are or should be and what mods do you need to make. My journey was/is for towing power I've done just about all the bolt on stuff, will go into the engine once my extended warranty runs out.


Here are some thoughts I jotted down GMCTD was directing you to check out; I might do some things a little differently since I posted it but most of what you can do to a 6.5 is here


http://dieselplace.com/forum/forum_posts.asp?TID=1138&KW

My truck is a 95 Tahoe that I flew half way across the country to buy for four wheeling. It never has or will tow anything. It never overheats. It runs great! I haven't driven with the fuel controller long enough to get a feel for what its doing for me (as I'm still playing with it). I replaced the lower intake with an "F" model and fabricated a new upper as I felt the factory upper one was lame. I extended the wiring on the fuel controller and moved the FSD into the grill where its been staying nice and cool. I have my turbo master cranked up about as high as it can go and have been looking at the garrett gt-30r ball bearing turbo to give me the boost I'm looking for. I'm working with a local shop on a 4" exhaust which seems pretty easy as I have installed a 3" body lift. Back to the questions you asked the factory resistor was removed, and I'm not looking to race or tow. I want enough power to turn 40"tire's and not be a road slug. So is a chip going to help me and if so from who.

First, you'll need a Boost gage, and an EGT gage.


Once you have those installed, then all advice given above will make sense.


Putting 40" hawgs on sets you up with same conditions as towing and racing, except absolutely full-time, no pit stops, no unhooking the trailer, no unloading.


Crank the engine, put it in gear, and you're heavily loaded.


A chip from John Kennedy will firm-up the transmission, but you'll still need the coolant upgrades, and a charge-air cooler, for the required and included power increase.


The Boost and EGT gages will tell you that, as will your Engine Coolant gage.


The 21.5:1 compresion ratio limits max safe Boost to 14 - 15psi - any higher than that requires lowering the c.r.


And, if you had a Transmission Temperature gage, it would likely scare you into parking the thing, for a while.


Making power requires heat, putting it to the ground makes heat - and it all adds up. You'll need some preparation to help dissipate it, safely.


Talk to John at Kennedy Diesel- tell him where you're at, where you want to go.Edited by: gmctd

Matt,


If you're at all serious about turning big tires off road you'll need a hydrolic ram instead of the weak, over linked system you have now. I keep three k3500 going and alot of the investment is in keeping the front end in working order. The brakes also use the powersteering hydrolics so with the addition of the high volume pump to feed the ram, your breaking will improve (it will help stop those big tires from moving when they don't want to). Even if you switch to a solid front driveaxle.


gmctd,


The '93 has been my daily driver for a few years 'till just recently when a hurt back and the choice between my wife's automatic and my manual transmission forced me to find this place to learn the EFI problems and solutions. Hard to believe that's five months ago. Now I have a tool box in the '94 and the '93 hasn't started since easter.


What happens when you raise boost to 20 psi with stock ratio? Is this the same on a highly modified intake/ehaust intercooled L65. Exoticly modified (twin turbo, big exhaust, customcast heads)?Edited by: quantum mechanic

I have been looking at the ram steering booster and I like it. I have built a Tahoe for off-roading before and loved it. Problem with my last gas one was the 4l60e(junk). The 4680e and the high torque in the low rpm of the diesel were main reasons for this build. The 8 mile per gallon improvement over the 97 vortec 350 doesn't hurt either. IFS works for me and I wouldn't have it any other way.

I was wondering what they built the drive line with on the k1500. 6.5 to 4L80e is a good start. Do you have the corporate 14 bolt in the rear and 9 1/4" ring gear IFS?

The 1500 pickups recieved the 9.5 rear axle and 8.25 front. But the tahoes and yukons only got the 8.5 rear and 8.25 front. I have not hear much good about these axles. but my rear in my other tahoe never gave me any problems w/35" tires. so as to keep the project cost low I'm not replacing any thing on the drive train unless it breaks then I will replace the broken part with something stouter.

I got stuck in the mud and shortly after blew the corprate 14 bolt rear axle in the '93. I swapped in a '79 14 bolt but I had to reweld the spring perches and shockmounts to make it work.

Which corporate 14 did you blow the 9.5 inch ring(semi float) or the 10.5(full float).

10.5 " 4.10 gears. I heard a humming sound and then snap! and I was on three wheels.














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