Can anyone recommend some mild mods for a 5.7 1993 Z71 Chevy truck - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-19-2004, 10:16 AM
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Can anyone recommend some mild mods for a 5.7 1993 Z71 Chevy truck

Gentlemen, I just bought a really nice 1993 Silverado Z71. It has the 5.7-litre engine with two-unit throttle body fuel injection. The stock specs are 210-hp @ 4,000 rpm, and 300 lbs-ft. torque @ 2,800 rpm. The tranny is the four-speed automatic-overdrive with lockup torque converter. I think the rear-end ratio is a stock 3.73.

The truck is very clean and has never been used for work or for towing. The engine has always had regular oil changes (5k) with Castrol synthetic oil. It has 86k miles.

I had it thoroughly inspected by the Chevrolet dealer before I made the deal. They found some engine fluid leaks, (intake manifold, oil pan, and (1) valve cover). They also said the PCV valve had some carbon build up and recommended a tune up. The rest of the truck checked out okay with just a couple of drivetrain gaskets and seals needed. The electronic diagnostics all checked out and I didn't have a compression check done. The truck runs out very well on the road.

I was thinking that since the oil pan gasket and manifold gasket needs to be replaced it wouldn't be that much more of a stretch to do a cam swap. I don't want to get crazy here, after all it is an 86k mile engine. Most of my driving will be on the street and very occasionally it will be used for towing. This is what I was thinking: I'd like to get an improvement in Torque/HP of maybe 10-20%, getting close to the 300 gross range, without a give up in mileage or drivability. Would a mild cam swap, KN filter system or the equivalent, and a efficient exhaust system get me there?

I'd like to avoid changing the intake manifold and throttle body. I also want to use the stock cast iron manifolds. I don't want to do any head work, if at all possible. I will do a compression check before hand. I'm not familiar with throttle body systems but I've heard these can be "blueprinted". What about the stock electronics for this engine? Can they be reprogrammed or "chipped" or will they even need to be with the mods I'm thinking about?

Thanks to all in advance for sharing your knowledge.

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Last edited by Axelrod; 02-19-2004 at 10:53 AM.
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Old 02-19-2004, 11:09 AM
STUPID is as STUPID does...
 
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Jacobs Pro-Street ignition.
Edelbrock Jet-Hot coated mid-length headers and big "Y" pipe.
Deleted converter and added 3"single in dual 2 1/2 out muffler.
Trans-Dapt "smooth bore" TBI spacer.
Hyper-Tech Thermomaster chip
Open element 14"x4" air cleaner.
These mods woke up my '95... and helped the mileage.
Biggest improvements? Ignition and headers.
Talk to Comp Cams about their computer grind for these trucks. You will need some chip work to make it work affectively.
Mark
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Old 02-19-2004, 01:29 PM
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Astro, I don't want to install headers. I'm not looking to make it hot, just 30-50 more ponies and the equivalent increase in torque. I'd like to get there with no more than a cam, throttle body mods, a less restrictive air filter and exhaust system, and tuning components, ignition, chip work, etc., if possible. Can this be done with what I'm considering or do I need to lower my expectations?

By the way, nice looking bumper you fabbed up for your truck. Cool to see a one off unit.
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Old 02-19-2004, 07:10 PM
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I have a GMC Sierra SLE short bed reg. cab 2WD with 5.7/4L60E and a 3.42 Traction Loc rear. I installed the Hypertech Thermomaster chip, 160 degree themostat, power pulleys, accel super coil, K&N air filter, 1" helix bore tbi spacer, Flowmaster 40 series muffler with 2.5" duals out the back, and I also removed the air cleaner silencer and replaced it with a strait piece of flex tube. The flex tube is better than a open air cleaner because you get cool outside air to the engine. This helped the truck a great deal. The biggest things holding the truck back now are the swirl port heads, weak cam that gives out at about 4500 RPM, and the stock TBI unit that is rated at about 500 CFM. But if you change any of these items, you will need a custom chip.
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Old 02-19-2004, 07:39 PM
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Thanks for the kudo's on the bumper... I appreciate it.
If you don't want to go to headers then you are limiting anything else you do. A cam change to a mild computer grind is a step in the right direction of course but headers are a proven performance gain and will really allow any mods you make to the rest of the system come alive. You will see better gains if you open up the exhaust as soon as you can and then build on that... Just my opinion.
Mark
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Old 06-29-2004, 01:09 AM
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Thanks for the kudo's on the bumper... I appreciate it.


I have always been a fan of frontage.

Nice opts you offered, with an emphasis on headers "to grow on".

Headers, chip, and some clean air will get all you will need for common street driving, and weekend power displays. You won't blow em' away, but will hold your own.

I have a 1993 Chevy Z71 stock cab, stock motor (210 hp), but with the 3 aformentioned components, hmmm, aint had a dyno, but 300 hp isn't a laugh. My opinion? Blow off the cam........
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Old 06-29-2004, 08:42 AM
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Well it's been a few months since I first posted this question. I've learned alot about this engine and it's limitations. My goal was to bump up the HP/TQ and hopefully get this TBI motor closer to the Vortec range. I'm trying to keep costs within reason and I want to stay with the TBI system.

I've changed my mind on headers. No doubt well designed headers free up HP the engine already makes and makes it available for the rear wheels. I've decided to go with Doug Thorley long tube Tri-Y headers. What I like about the Doug Thorley headers are the Tri-Y design and the extra thick flange and overall quality. I've also acquired a set of L98 heads and an Edlebrock TBI performer intake manifold. Not sure what cam I'll be choosing yet but it will be matched to the components and designed for a truck. Of course, I'll need to get a custom chip programmed too. I've already done a chassis dyno beforehand and will do one after to verify the results. I'm guessing the above mods to get me somewhere around 50 HP at the rear wheels.
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Old 07-01-2004, 03:03 PM
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L98 heads leave a lot to be desired. They weren't anything that were known for above average performance.
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Old 07-02-2004, 09:25 AM
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Quote:
Originally posted by Siggy_Freud
L98 heads leave a lot to be desired. They weren't anything that were known for above average performance.
Thanks for your input BUT L98 heads are a BIG improvement over the stock swirl port heads on the Chevy truck 350 TBI motor. That's what I'm modding and it's a truck. All I'm looking to do, is too enhance what I've got and increase the performance where I can use it, down low and in the mid range. MATCHED components are the key and I believe these heads will suit my application very nicely and do it at a very affordable price.

FYI: You might think a set of Dart sportsman II's would be a better choice to make power since they are intended to run up to 7000 rpm, over a set of mildly ported and polished L98's, good for maybe 6000 rpms. However , the Dart heads sacrifice air velocity at low rpms and suffer the resulting loss of torque at low rpms, not good for a street car or especially a truck. Also, in my case, the TBI unit and my cam choice would never support where the Dart heads are designed to flow. Again, it's matching components to achieve the intended result that is the key to success. I can't think of a better head for what I'm doing.

If anyone thinks otherwise and can support it with something other than an opinion, feel free to post.

By the way, the late John Lingenfelder achieved HUGE HP and performance gains with his L98 Camaro and Corvette mods, and using the L98 heads, ported and polished to his specification.
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