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TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

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Old 10-13-2006, 05:43 PM   #1
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Car: Chevy Caprice
Engine: 350 TBI LO5
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350 TBI Tachometer

Hello guys! I'm new to the forums, but I've been trolling (in a good way.) And yes, I am only 17. I have a question about my 350 TBI. My car did not come with a tach, but do Camaro's and FireBirds of the same year have a tach? If I wanted a tach, could I just get one for a Camaro of the same year / engine? And is there a tach available that doesn't go up to 10k RPM and isn't *****? BTW, I've searched and couldn't find anything helpful, thanks!
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Old 10-14-2006, 06:57 AM   #2
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What year is your car? You didn't provide it.

Copcar TBI Caprices with the 350 5.7 engine (for 1991-1993) all got a digital speedo and an analog tach. Civvy Caprice with the 350, only offered in 1993 as the LTZ Caprice, got the same instrument cluster. The only other 350 TBI Caprices were the 1989-1990 copcars, and they had a large analog speedo with no tach. So that leads me to think you have an 89-90 model, or you have a 91-93 model with an LO3.

I can provide more info but I need to know more about the car.
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Old 10-14-2006, 08:59 AM   #3
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Yeah, you got it. It's a 1989 Caprice, huge analog speedo. Previous owner said it's got the 9C1 police package, although I have no idea what that exactly includes.
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Old 10-14-2006, 06:21 PM   #4
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Bump!
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Old 10-15-2006, 01:02 PM   #5
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That's what I thought.

OK the copcar option code is 9C1. You'll find that, plus other codes, on the sticker affixed to the underside of your trunk lid. You should also see LO5 (your engine) and GU6 (3.42 rear end), and possibly 7X6 (driver's side spotlamp).

For general 9C1 info this will be a useful link:

* The Caprice 9C1 Information Source

and then follow though the pages within.

Tach install is fairly easy on your car. My NH neighbor did one in his '89 LO5 (same car as yours). He mounted his atop the dash pad on the right side of the steering wheel, with the tach turned slightly twds the driver's location. He pirated the illumination lamp from the ashtray to use for the dimmer-controlled lamp on the tach.

IIRC there are only four wires needed on most tachs: a wire feed from the engine coil (white wire on GM models) which gives the engine speed, a switched power wire to power the tach, a dimmer controlled lighting wire (to illuminate the tach face plate) and a ground wire to complete the circuits. You'll have two options on the main tach signal feed, either from the coil directly or from the ECM.

For the coil directly you need to fish a wire through the firewall to get to the coil, and a good place for this is the oval-shaped plug on the driver's side, visible with the hood open and looking down past the left front fender twds the firewall. If you remove the plug, the rubber can be pierced with a knife, and then a wire fed through it. Make sure the wire is longer than you really need so you can route the wire along the firewall inside some split loom tubing, or along side an existing wire. Routing the wire isn't difficult, just time consuming.

If you'd rather source the signal feed from the ECM, read this post:

Impala SS Forum: Tachometer is off

So I think the only wire that presents a challenge is tying into a switched power source (ON only when the ignition is ON). In past installs, I've used unused (but powered) fuse box slots and fused them with 2A minifuses, but you could alternately splice into a wire that's HOT-IN-RUN.

The other thing worth reading here on TGO is your search results for "tach install" because the wiring issues are much the same for both the 3rd gen Fcar and the Bcar (Caprice).

If you go to the Impala SS // fullsize GM web sites, there are 89-93 Caprice owners that have installed aftermarket tachs, and the install procedure they used will be identical for you. The light truck people, FullSizeChevy, also fall into the same group, because they had TBI engines in the late 80s to mid 90s light trucks. HTH.

Last edited by kdrolt; 10-15-2006 at 01:20 PM.
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Old 10-15-2006, 01:34 PM   #6
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Thank you! I probably look stupid, but hey, I'm 17 and it's my first car. And yes, my car is an automatic. I just feel that I need to know what RPM the engine is at, and I also want to get a more accurate speedo. I'm pretty sure the limiter is @ 115 mph, but the car maxes out the speedo at 125.
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Old 10-15-2006, 01:37 PM   #7
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Quote:
Originally Posted by capRICEyay View Post
Thank you! I probably look stupid, but hey, I'm 17 and it's my first car. And yes, my car is an automatic. I just feel that I need to know what RPM the engine is at, and I also want to get a more accurate speedo. I'm pretty sure the limiter is @ 115 mph, but the car maxes out the speedo at 125.
Civilian model B-Bodies had a governor at 108. That is ECM provided fuel-shut-off. The only 9C1 package that had a speed limiter was the 350 with P225/70/R15 tires, it was set at 130 mph.
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Old 10-15-2006, 01:49 PM   #8
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Oh, haha. Still, could a stock 350 TBI really push a 4000lb car to 125+mph? Not that I'm complaining, thanks for the info!
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Old 10-15-2006, 01:56 PM   #9
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Oh, haha. Still, could a stock 350 TBI really push a 4000lb car to 125+mph? Not that I'm complaining, thanks for the info!
I am thinking that it could. A stock TBI 305 will push a 5,500lbs G-Van to about 110 MPH.
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Old 10-15-2006, 02:26 PM   #10
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In that Turbos&TBIs thread, you said that you have a supercharged 350 at 7 PSI, what kind of HP / TQ gains did you see? I realize you have many other mods, I'm just kinda looking for an estimate.
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Old 10-15-2006, 02:29 PM   #11
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Quote:
Originally Posted by capRICEyay View Post
In that Turbos&TBIs thread, you said that you have a supercharged 350 at 7 PSI, what kind of HP / TQ gains did you see? I realize you have many other mods, I'm just kinda looking for an estimate.
75-100 FWHP/ 125-150 FWTQ

It actually had a Weiand Blower on it. Mods in sig. I pulled the blower off, waiting for a 4L80E buildup and swap.
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Old 10-15-2006, 02:40 PM   #12
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Dang, those numbers look nice. Did you have any clearance problems with the hood and the blower? Where did you get the blower kit from? Probably Weiand.com or something, but just wondering.
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Old 10-16-2006, 07:56 AM   #13
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Quote:
Originally Posted by capRICEyay View Post
... I just feel that I need to know what RPM the engine is at, and I also want to get a more accurate speedo. I'm pretty sure the limiter is @ 115 mph, but the car maxes out the speedo at 125.
You probably have 3.42 rear end (GU6 on the trunk Service Parts Identification sticker) given that you have an 89 w/LO5. You also have a certified speedo (it's a copcar, remember?). That means it's supposed to be accurate to within 2 mph at all speeds, IIRC.

In 4th gear (overdrive), the trans ratio is 0.70. The 13.5 number, below, is the approx rolling radius in inches of a rear tire (225/70R15 size). The numbers 60, 6.2832, 12, and 5280 are all constants needed to make the units of rpm convert correctly to mph. So if you have tires a different size than 225/70R15 then you'll need to measure the rolling radius (in inches), and use a different number other than the 13.5 inches I used. If you have a different rear end, say 3.08 rather than 3.42, again use the correct number.

mph = engineRpm*60*6.2832*13.5/(12*5280*3.42*0.70)

Example: 4th gear on my old 94 9C1 at 1700 rpm in 4th with a GU4 3.08 rear end

mph = 1700*60*6.2832*13.5/(12*5280*3.08*0.70)
mph = 63.3


I think what you mean is that you would like to delete, or change, the speed limiter. Fast355 is correct that the civilian cars were limited to 108 mph, largely due to the S speed rating of the factory issued tires (see the sticker in the driver's side door jamb).

I don't know for a fact what the electronic limiter (in the ECM chip) were for 91-93 copcars because those models were tested at 130, 133, and 132 mph during the annual Michigan State Police tests of cop cars.... so the limiter on those models, if there were one, would have to be above 133... not that it mattered because the cars were drag limited with only 195 to 205 fwhp.

The 94-96 copcars got a set of different speed limiters: 120 mph for the L99, 130 for the LT1 with H-rated tires like my old car, and approx 147 mph for the LT1 with V-rated tires.

The 89-90 TBI models topped out at 120-122 mph during Michigan State Police tests, and that's about where the brick car body would be aero drag limited with the 190 fwhp of the 89-90 TBI LO5 engine. So that means in good condition and tune, the car could reach that speed with a long enough flat road. So GM probably had a limiter set to something just above 120-122 mph.

You mentioned stupid & age 17 above. A fast car, especially an ex cop car, is a good way to meet the police... or much much worse. Don't add to the statistics for male driver's under age 21. FWIW, HTH.

Last edited by kdrolt; 10-16-2006 at 08:01 AM.
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Old 10-17-2006, 03:30 PM   #14
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Thank you guys, and don't worry. I'm 17 but I'm no idiot. Besides, the US 131 Speedway is only around 45-60 minutes away, so there's no reason for me to do anything overly illegal on the streets.
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Old 10-17-2006, 03:38 PM   #15
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I've been toying with those numbers, at 5000 rpm my car is geared to go 165+! Damn, that's way too fast for this car.
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Old 10-17-2006, 05:06 PM   #16
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LOL you'll be lucky to hit 130....little somthin called aero drag.
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Old 10-18-2006, 08:16 AM   #17
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Bone stock, the 89-90 LO5 9C1 will do 120-122. The same engine installed into a whale body (1991) will go 130 mph. The aero drag on the bricks (1990 and earlier) is more than on the whales (1991-1996). Proven by the Michigan State Police in their tests.
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Old 10-18-2006, 03:11 PM   #18
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Silly, I said geared!
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Old 10-18-2006, 03:11 PM
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