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Old 05-02-2005, 08:04 PM
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Tbi Mods

I am building a TBI truck engine for a friend of mine. He has a 1/2 ton 4wd Chevy and it's a 1988 model.

I've done a little research, but I get conflicting views from different folks as to what modifications to make concerning the TBI unit, intake manifold and ecm prom upgrades.

The engine is close to stock with a smooth idling, computer compatible cam, 9.5:1 compression, and a set of world products S/R heads with a street port job for increased torque and midrange. It will also sport headers and dual exhaust.

Turbo City said it was a must that I go with 67 lb injectors, a modified TBI unit to flow 620 CFM, a TBI spacer, adjustable fuel pressure regulator and a custom chip. All for the low, low price of $950.00 bucks. The guy pissed me off, because he basically tried to blow a bunch of smoke , and expected me to buy it. I don't think I'll be calling him back anytime soon.

I called Jet Performance, and their tech told me my combination would run fine with the stock intake and TBi unit, but to add an adjustable fuel pressure regulator, and run the engine as-is.

He said it should run well, but if it doesn't he could make a custom chip for it for $395.00---ouch!!!!

I see other guys boring the original intakes and using the 454 TBI unit, but I don't think that's necessary for 300 gross horsepower.

Being that I'm not really EFI saavy when it comes to hotrods, I'm looking for some good advice from some of you guys who have done it.

My thoughts are to run as-is and try to shop for a little cheaper prom upgrade if necessary.

Brian

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Old 05-02-2005, 09:14 PM
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Most of my FI experience is with multiport setups. That said, an adjustable fuel pressure regulator has been a valuable tuning device for me. I dont know how much variety in tuning you can do via fuel pressure with a TBI unit so that is better left answered to TBI experts.

Even given your better flowing heads, I dont think the stock intake and cam warrant bigger injectors OR a larger throttle body. A custom chip might help a bit, but again, with a tame cam and stock intake your flow characteristics probably aren't going to change enough that the base parameters of the computer will need changing.
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Old 05-02-2005, 09:15 PM
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Quote:
Originally Posted by NAIRB
I called Jet Performance, and their tech told me my combination would run fine with the stock intake and TBi unit, but to add an adjustable fuel pressure regulator, and run the engine as-is ...

My thoughts are to run as-is and try to shop for a little cheaper prom upgrade if necessary.

Brian
My advice is to run an AFPR and do your own programming. DIY-PROM is not hard and there is a ton of support at www.thirdgen.org.

I did the DIY route and all told, the equipment and software was well under $300, depending on what options you want to get. I am not sure what ECM and mask the 88' TBI unit uses, but like I said, answers can be found at TGO. If you decided to go that route, contact Craig Moates at www.moates.net. He can tell you exactly what is needed for that year as far as hardware goes. The program I use to read, change and burn data is TunerPro RT and is free (suggested donation of $30). There are plenty of bins for free download and ECU files are also available for a large number of masks. I am sure the 88' TBI ECU and mask are supported. You can also read the original bin.

Here's how I did it. Don't let anyone fool you into the "custom" chip myth. My custom chip from Street & Performance was a stock F-body binary file with a few modifications to the upper spark tables, fan on-off and EGR.

EDIT: For the 88' TBI ECM, I am almost positive it is a Service #1227747 and you will have to solder in an adapter for the flash chip. Here is a page showing how it is done. But for $25, Moates can do it for you. The benefit to DIY is that for the intial cost, you can burn onto flash chips hundreds and hundreds of times. Erase and burn again, however long it takes to dial in a perfect tune.

Also, for TBI spacers, AFPR, etc, check out www.cfm-tech.com. Best of luck, Ed

Last edited by edge; 05-02-2005 at 09:48 PM.
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Old 05-02-2005, 09:18 PM
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A good while back (around 1998) I took a 1994 Chevy 1/2 ton ext cab (my old boss`s truck) and with his money ordered a 300hp crate motor from GM... I took the cam out and replaced it with the largest computer friendly cam that Crane had at the time... Then added an Edelbrock performer intake (with EGR) and used the adapter from a 90 model 1 ton with a 454 and the larger TBI unit also (the adapter fits on a Q-jet or spread bore base) and used the 5.7 injectors in the larger BBC unit and added an adjustable fuel pressure reg. also added a set of Edelbrock headers and a custom exhaust... This all worked great with the cheap version hypertech chip and a 160 degree thermostat...

Then we put the 300hp cam back in and put a part number 7777 custom hypertech chip in and also a TCI streetfighter 700R4 with 2400 stall and a 3.73 rearend (from an SS454 truck) and the silly thing ran 14.0`s in the 1/4 on street tires... Wasnt to bad for a heavy ext cab truck...

Oh and about the custom chip (which it was) the truck also got 20+ mpg... When we went to sell the truck about 2 years later I de-tuned everything and put a reg TBI manifold and unit on it and a stock cam and chip also the 4L60 back in as well... The chip I gave to a good friend that did my trans work and he put it in his completely stock 94 Chevy and was amazed with the 22-23mpg and his 350... Not sure what they did to that chip but it was different to say the least... Yes I know the 93-94 computers are different...

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Old 05-02-2005, 10:53 PM
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Other than spark timing, a lot of what these custom chips do is interperate the info from the ECT sensor. You can fool the stock computer into giving you more fuel by adding resistance to the ECT circut, it is a voltage drop reading circut, and runs on a 5 volt reference. If hot resistance is, say, 150 ohms, and dead cold is 17000 ohms, adding an external resistance and making the full warm to say 2500 ohms will fool the computer into thinking the engine is not hot yet, and deliver more pulse width to the injectors. This is kind of a trial and error way, but really cheap.

The adjustable regulator is a good idea, but I don't think it is an absolute must. These run at an almost fixed pressure, as the injectors are not subjected to drastic instantaneous changes in atomospheric pressure. The pressure differential at the injector tip is almost constant at atmospheric pressure, so the only real reason is incresed tunability for differing atmospheric conditions.

BTW, I think those guys are hosing you on the chip programming. I had a custom PROM built for a 1994 K1500, and the whole thing, including shipping, cost less than $375.00 CAD. I'll see if I can find the recipts tomorrow at work so I can find the name of the place that did it for me.
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Old 05-02-2005, 11:58 PM
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Quote:
Originally Posted by sbchevfreak
BTW, I think those guys are hosing you on the chip programming. I had a custom PROM built for a 1994 K1500, and the whole thing, including shipping, cost less than $375.00 CAD. I'll see if I can find the recipts tomorrow at work so I can find the name of the place that did it for me.
I think you got hosed too . Prices like those are the reason (as well as Edge's encouragement) that I got into custom tuning/chip burning.
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Old 05-03-2005, 06:16 AM
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At the time, the exchange was not so good as it is now, it worked out to about $285 US. Around 375 was with with all taxes in(GST, PST, both at 7%). I didn't think this was too bad, was it still too high?
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Old 05-03-2005, 06:40 AM
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Well this thread has me thinking about one of my ideas again! The idea is to take a complete TBI setup from a donor truck and find another with the same TBI and bolt all this onto a schoshty 350 with one Edelbrocks Low Rise 2-4 intakes{the stock height kind}.

It seems like the right chip would allow 600HP and let it idle like a stocker for mere pennies on the dollar when compared to an equivalent aftermarket fuel-injection system. (not highjacking the thread..just thinking out loud!)
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Old 05-03-2005, 06:50 AM
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Quote:
Originally Posted by sbchevfreak
BTW, I think those guys are hosing you on the chip programming. I had a custom PROM built for a 1994 K1500, and the whole thing, including shipping, cost less than $375.00 CAD.
LOL! The only way to do a "custom" binary file is to tune the engine on a chassis dyno and/or run it on a street with real-time datalogging. No two engines and cars are the same. If you knew what you really bought for $375, steam would be coming out of your ears.

I realize that everyone has their own opinion on something like this, but I know first hand that the "custom" chip I bought from Street & Performance for like $300 was nothing more than a stock F-body binary file. I compared the two and they were nearly identical. Is adding 3*-4* of spark advance to a few 95-100 kPa RPM areas custom? See for yourself, the numbers shown are degrees added over a stock F-body binary file:



I have heard similar stories with "custom" stuff from TPIS, Hypertech, etc. It makes no difference. Their business is based on the ignorance of their customers. Afterall, how many people will actually check to see what they are buying? People buy into the idea of a mailorder "custom" chip hook, line and sinker.

The best part of DIY is you can make countless changes for a one time investment. You can also use the equipment and software for more than one vehicle. Examples: if you datalog and find a high number of knock counts in a certain RPM and load range, you can take it out gradually until the spark table is smooth and correct. The same goes with changes to the VE table. More examples: want to change the lockup speed on your converter or raise your idle speed, do it yourself and save the costs of shipping your "custom" chip back and paying more $$$ for the changes. I have a 94' Suburban that I converted to TPI. But is still uses the 4L60E transmission. I was never happy with the shift points in stock form. All I had to do was buy one additional MEMCAL adapter and flash chip and use the same hardware and software to read the original parameters, and then I can change stuff in small increments and dial in what I want. That is my idea of "custom".

Don't believe what I am saying? Do yourself a favor, go over to www.thirdgen.org and see what I am talking about. NAIRB - If you decide to try the DIY route, there is one member at TGO whose username is "JPrevost" who seems to be one of the more knowledgeable on the TBI ECM and masks. If you had any questions, I am sure he would be willing to help out if you sent him a PM.

Ed.
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