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Need help figuring out exact specs. on '90 Jimmy 1500

Yeah, old gas is useless for just about anything now. Lawnmowers won't run on it. It's probably so nasty now if you did use it to wash parts you play like hell to get the stink out of your hands. Not sure it would be very effective.

The L05 TBI's weren't known for brute strength by any means, but they were pretty darn reliable. Gearing would make a difference with the tires. Even with stock sized tires 3.73's would have at least multiplied the L05's torque a little better. It would have made the engine feel a little more powerful. Now as far as the oil drainback was concerned I haven't heard that that era of small block was any worse or better that previous versions. Larry's Polar bear burb with it's original L05 TBI 350 was a gutless wonder too. I think he had 3.42's to start with too. In his words "it wouldn't pull a greasy string out of a Coke bottle" it was so weak. He stuffed his extra 14bff and 8 lug d44 with 4.10s under it and it felt better, but gutless still. He swapped out the 465 4 speed for a Nv4500 5 speed and at least he had overdrive. Biggest difference he made on it before the 8.1 swap he did was the gearing.

I went the same route as Trusty. I'm running a 5.3 Vortec out of a 2001 Silverado which makes a ton more power than the tbi 350 ever did. Been driving it for a few months now and LOVE it. I'm running 35" tires with 4.10 gears with the stock 700r4. It's a pretty good combo.

Now if you want to hear it run, use ether or carb cleaner. I'm not too keen on doing that, but if you must go with moderation.
 
Hello all, recent member and first post. I'm nowhere near expert but will add what I hope might help. Sorry post is back & forth.
I own an engine & trans distribution shop since early '03; don't do any building on site. Also own an '89 k5 that I bought from a potential customer who declined replacement of its bad engine w/ a reman longblock. Knew I was also buying a 31', 5550lb dry, bumper pull camper and thought I'd use it as a tow vehicle. So I had our engine reman company build me a long block for it. It had a factory oil cooler so I added a stand alone trans cooler, trailer receiver and brake controller and air bags to tow.
First off, what I've found and learned- all 1/2t 6 lug trucks came w/ 2 bolt main blocks. Light 3/4t w/ 6 lug axle, 2 bolt. 8 lug 3/4t and 1t, 4 bolt mains. Exceptions abound I'm sure. But that's the 1st easy identifier.
All '87-95 vin K engines are 350tbi and have 1pc rear main seals and center bolt valve covers. Cast numbers might vary but the same specs were used internally and won't make a difference you'd care about or realize. Builder also told me so little difference that they use them interchangeably with same performance. They were never power houses but I think your compression #s are lofty. When building for said camper, I got input from my builder and the first things we did were upgraded from stock to 9:1 flat top pistons, high volume oil pump and roller lifters. Both upgrades were over stock and essentially made it the same tbi 350 from the Caprice cop cars and Camero and Firebird. You're more likely in the 8.2-8.5:1 range, stock.
They warned me about making changes to the cam as OBD1 computers were archaic and didn't like a lick of change on the vacuum side which is an issue w/non stock cams. I didn't listen and upgraded the cam for better low end power.
Add one tbi edelbrock performer intake, headers, tbi spacer, 3" single exhaust through a non legal cat and rebuilt injectors and it's at 16.0mpg on the highway, but 5.22 to 7.0mpg pulling that camper from CO to IL and back.
Ran so rich we could not roll the back window down for air and nothing I did changed that till I ordered a custom PROM from a shop down S after sending me a 40? form asking all sorts of details of my build to customize the fuel and timing curves. That worked wonders and I now know to leave fuel injected engines alone unless you plan to do computer changes, too.
Mine has stock 31" tread and 3.73:1 gears and runs sweet for the size and weight; fast as hell as per my shop techs. To the member w/ the VIN and full RPO code breakdown, kudos. Nice moves.
Your crap mileage points to other issues that need addressed. Taller tires would also hurt if you had too little power to turn them easily.
Also from experience, don't use anything from the existing fuel system until cleaned thoroughly. Disconnect fuel feed side into the engine and run cleaner through all lines and ports; not into the engine obviously. Boil out the tank. Gas is a joke these days and breaks down so fast that adding gas to the tank and using it as normal will cause regret and possibly damage. Saw that first hand from doing so. Better off using squirt bottle to mist gas down the throttle body before ether or carb cleaner, w/ fuel pump relay pulled. Let the starter turn the engine over for you if fluids are good.
Thx for reading my rant. Mines been sitting for years as I knew my camper was pushing my Blazer around and trashed tires quick. Too much weight. So went diesel and it sits neglected. Good luck.
 
tRusty, It sounds like you are going to have a nice rig. How much more do you have to do? Bear in mind that other than watching TV and the occasional look under a hood that I don't know anything about the new series of small blocks. I don't think/remember this truck has ever gotten the gas mileage that it should have, under any conditions. It's always been very reliable. Since it was carrying my wife and 2 girls, I was able to live with that and them being in a full size truck didn't hurt my feelings either. Pam really liked being able to see over most traffic and acting accordingly.

This project is showing me just how little I know about today's stuff. If a buddy of mine would sell it, I'd quit worrying about keeping this thing original. He has one of the registered (?) 427's in the crate from a few years back. I've seen the crate and the registration certificate.

I watch TV and see them sticking these new motors in everything but a shopping cart. They make them look like a piece of cake to work on once you know a little about it. The electronics seem to be the worst thing most of the time.

Once I get it running, hopefully with this engine, I'll probably try to give it a little more bottom end, up to around 3500. I think that was the normal rpm range when it was running.

First thing, I've got to see if it's seized and if so get some oil down in the cylinders. It shouldn't be too bad. It hasn't been partially disassembled and left to sit, It's just like it was when I parked it.

I guess that I'll try the starter first, then the harmonic balancer bolt. I'm not going to get stupid with it. There isn't any reason that I shouldn't use the balancer bolt, is there? Do you know what size socket it takes it, do you?

If it's not seized, I plan on doing an oil /filter change and spin the oil pump to get everything oiled. Any particular oil that you would suggest for the first oil? Pull the fuel pump fuse and try to see if it will fire not start. Can I pour a little gas through the TBI and try to get it to fire that way? Seem OK so far? Any suggestions or warnings?

Paul
 
cfdawg, What you said about the compression ratio probably being more like 8.2 to 8.5 is more like I was expecting. Somewhere in all of this, I've made the statement that 9.25 to 9.5 was alot more than I was expecting. I found those specs on a engine/head rebuilders site. The same one that I got the head casting numbers 191, 193, and 810.

I keep hearing about the PROM in the computer. Is getting another one or getting mine reprogrammed that hard or expensive? Is a chip out of some higher performance set-up not possible or are there so many variables that I'd never find the right one? I'm pretty patient, I recently finished building a wildcat rifle and cartridge that only took 2 1/2 years, so if time or money is the problem, I'll go as slowly as necessary. I'm not rich, I'm on S.S. disability, so I have to be patient.

What would be ideal is if a set of headers, preferably shorty, an intake, and possibly a few other simple tweaks will do what I want. Can't I change the exhaust and intake and not have too much trouble as long as they have the provisions for the sensors?

How about a list of fairly simple things that I can do without causing problems or changing the appearance drastically. The gears will probably have come later, at least until I understand exactly what I need and have the axle(s) in my possession.
Can the stock TBI be tweaked without a real problem since the computer controls it.

I'm just trying to get a game plan until I get the minor body stuff done and I really check the motor and see exactly what I've got. I don't want to just throw good money away.

Thanks, Paul
 
scpaul said:
cfdawg, What you said about the compression ratio probably being more like 8.2 to 8.5 is more like I was expecting. Somewhere in all of this, I've made the statement that 9.25 to 9.5 was alot more than I was expecting. I found those specs on a engine/head rebuilders site. The same one that I got the head casting numbers 191, 193, and 810.

I keep hearing about the PROM in the computer. Is getting another one or getting mine reprogrammed that hard or expensive? Is a chip out of some higher performance set-up not possible or are there so many variables that I'd never find the right one? I'm pretty patient, I recently finished building a wildcat rifle and cartridge that only took 2 1/2 years, so if time or money is the problem, I'll go as slowly as necessary. I'm not rich, I'm on S.S. disability, so I have to be patient.

What would be ideal is if a set of headers, preferably shorty, an intake, and possibly a few other simple tweaks will do what I want. Can't I change the exhaust and intake and not have too much trouble as long as they have the provisions for the sensors?

How about a list of fairly simple things that I can do without causing problems or changing the appearance drastically. The gears will probably have come later, at least until I understand exactly what I need and have the axle(s) in my possession.
Can the stock TBI be tweaked without a real problem since the computer controls it.

I'm just trying to get a game plan until I get the minor body stuff done and I really check the motor and see exactly what I've got. I don't want to just throw good money away.

Thanks, Paul
Click to expand...

I haven't heard of exhaust changes messing with the stock TBI control system, but I'll leave the actual list-writing to folks with more experience. Gearing is one thing that I guarantee you can change without messing with engine control logic. Newer injection systems can be pretty easy to reprogram (plug cable into your computer and start tweaking), but this one requires writing instructions directly to the Programmable Read-Only Memory chip. Most folks don't have the ability to do this, so they wind up working with someone who has the right equipment. Find a programmer who has experience with this system, tell him what you have, and he'll send you a PROM set up for your configuration. If it's not quite right, it may take a couple iterations to find the magic recipie. This is what folks mean when they complain about how long it takes to set up a system, if your programmer is in Idaho you might spend a bunch of time waiting for a chip to come in the mail only to find that it's not quite right either, and you spend weeks before it's running just right.

@EagleMark used to be the designated PROM guy around here, but he died last year. Not sure who to talk to anymore. Maybe @208motorsports?

Again, I'm not convinced that you need a bunch of mods to get it running better than it has been. 6MPG definitely isn't right, something is broken.
 
Ok, It looks like I can get rid of the exhaust with no problems and add a true dual exhaust system (X pipe?), how about an intake and I've heard some pretty hard to believe statements about spacers? What kind of dealings have y'all had with them?
 
scpaul said:
add a true dual exhaust system (X pipe?)
Click to expand...

Why would you do this? Go with single 3", you will make as much or more power. If I'm not mistaken, your truck already has this.

Headers are going to be the next major power producer in terms of sheer HP numbers, but you will want/need a tune of the PROM if you go that route.
 
It's been so long that I had to go look.

The exhaust system on mine is 100% stock. The passenger side exhaust crosses over to the driver side just in front of the transfer case and joints the other pipe at an almost perfect 90*, from there it goes through the converter, muffler then exits behind the drivers rear tire. The exhaust pipe is 2 3/4" measured. The passenger side exhaust manifold exits at the very rear, so it's pretty normal. The driver side exhaust exits the manifold about 2/3 to the rear at 90* too. The only halfway streamlined connection in the whole system is where it exits the passenger side manifold and it's really just a std. manifold.

I think that I just found some of the missing performance/horsepower/gas mileage. Very seldom have I ever seen an exhaust system so restrictive. If it weren't for everything that I've read and have been told saying that it was a 350, I'd wonder if it was a 307. I think that a 307 would be restricted with this system. It's hard for me to believe that where the two exhaust pipes come together that they aren't at any angle. Has anyone else seen this type of exhaust system on a Blazer/Jimmy?

A possibly happier; we'll see, Paul
 
IMO the manifolds are the real problem. You are dumping 4 cylinders into one "log", all exiting towards the rear, so there is zero scavenging. As bad as the manifolds are, short of a physical failure further down in the system, anything done after the manifolds, with them still in place, is a waste of time. If the converter or muffler is plugged that could be a hindrance.

2.75" exhaust, probably even 2.5" is not going to cost any power on a stock TBI truck motor. Manifolds need to go, then I'd worry about the angles in the pipes. Or not, as they aren't going to make much difference in terms of actual power gained. Typically long tube headers are tested around +15-25HP on a bone stock motor, which is nothing to sneeze at.

Does that have the old style "pancake" (large/flat) converter? Those things don't flow well either. Again, worth replacing just for power gain? Probably not. But if it's plugged up, a modern high flow converter is only going to help.
 
dyeager, Everything that I've been reading and watching on TV is saying that an x pipe increases the horsepower. I don't know. By my old standards, I'd want an exhaust pipe that would do like a header pipe and help scavenge the pipe like a header tube. They are using rear wheel dynos to check the results. They're even comparing x pipes to pipes that are a 90* cross and the x pipe almost always wins. I don't know, somebody explain it to me.

I don't know how much difference it would make, but I know some guys that are running gutted converters since we don't even have vehicle inspection any more. They said the big thing is how much cheaper they are gutted. The converter is so far back that I don't see how it would get hot enough to work and not clog up.

If I can get it running fairly easy and change the exhaust, that might be all I'm looking for, well, maybe a little more.

Thanks for getting me to look at it, Paul
 
Paul.. Every stock Blazer or Jimmy equipped with a cat converter came with a similar exhaust routing and manifolds. Part of the issue on the drivers side manifold is shifter or clutch clearance. It's not ideal, but it is what fits. Those units only ran one cat so they joined the two banks together in front of the cat. Blazers weren't alone in this system, all the trucks of the era were set up that way. Even the next generation of trucks after the Squarebodies. It's not to say you can't go duals. There is no standard kit for these so you need an exhaust guy that can route the pipe with clearance to the trans shifter and all the other goodies down that side.

Even the newer engine's like the 4.8, 5.3 and 6.0 have a similar setup where the pass side is swept back and the drivers side dumps straight down. I say this because the changes you make to the exhaust on this engine are not going to net giant horsepower gains. At least not like back in the day where a switch to headers and duals pumped up the power greatly. I don't mean to say this to discourage you, but just to set your expectations for what the real world gains would be. Anytime you can make the exhaust breathe better helps, but being the intake side is going to be restrictive.
 
dyeager, I was saying the same thing. That's why I described the manifolds like I did. The one on the drivers side looks like it was on a 60 model motor, it's that bad. If I'm going to do the manifolds, I might as well do the whole system. It does have the flat style converter on it, and like I said it's too far from the manifolds to have gotten hot enough unless you were on a long trip. It's probably half if not completely clogged. I don't remember it making the blowing noise like they used to when clogged, but I wasn't listening for it. I had the windows up with the AC and stereo on.

The only reason that I'm saying shorty headers is because I figure that they would go on easier and the collector flanges not get caught on stuff.

OK, I'm getting an idea how this thing is going to go. Get the motor running and as right as I can then put a good exhaust system on it.

I still haven't heard anyone say anything about an intake.

Paul
 
X-pipes make power, but look at the exhaust as any other fluid: It will only flow as much as the most restrictive area allows. The manifolds are the most restrictive portion of the exhaust system (ignoring the heads, which also don't flow well) so anything you do after the manifolds is going to be very unlikely to net noticeable gains. Most if not all the testing you see with x- or h-pipes is done with headers or more modern manifolds which generally act like shorty headers, and the more power the engine makes in the first place, the better the gains will be when you start modifying the exhaust side smartly, so dyno tests will generally make it look like huge power is to be made. I can't recall what the TBI 350 made for HP (195? 215?) but exhaust modifications to a 215HP 350, will have far smaller gains than the same mods on a 300HP 350. Hedman 69830 are somewhat of a mid-length header, but they clear pretty much every conceivable drivetrain with a SBC for an engine in these trucks.

I'd be willing to speculate that with *long tube* headers, high flow cat, mandrel bent exhaust, you'd see at best 45HP. And that is being optimistic, 30 is probably more realistic. You'd still need a PROM tuned for those mods, which might give you a bit more power.

As to the converter. If it's in the OEM position, and is an OEM converter, you can guarantee it got hot enough. Flowmaster told me the below when I inquired about converter temps so I was able to determine proper placement.

"Desired “light off” temperature is 400°C (750F). This remains pretty constant throughout all converter applications and refers to the temperature of the gas as it flows through the center of the converter. Typically we will measure 250 – 350F on the inlet pipe not the converter body."

Google "ultimate TBI mods" and I think you'll find some info on what all can be done to make power with TBI. I don't recall if an intake swap is recommended. The heads just don't flow much, so an intake swap isn't likely to do much with the head bottleneck. The TBI heads have good velocity at low RPM's, and the swirl ramp, but limit power as the RPM's climb. Too much on the intake or exhaust (without changing the heads) is going to tend to make the engine "lazy".
 
ZooMad, I just posted re: the exhaust, converter, well the system in general. I know that it's not going to be doing wheel stands, but it was so bad when parked that I really didn't care and I used to love it. I've also asked about the intake and a spacer if they do what I've been lead to believe.

The fact that the oil returns in the heads were clogging up still has me wondering. If it had only happened once it would be different, but it happened twice that I remember so it probably happened more. You can bet at some point it's going to get new valve cover gaskets so that I can get a look at the heads. It's the only small block that was even half way maintained that the head oil returns clogged up.

This has the valve covers with the center bolts which I've never messed with at all. Do the cork, rubber or other (synthetic?) material gaskets work best or does it matter?

Thanks, Paul
 
Rubber/silicone gaskets are far better than cork. From what I've seen lately, the OEM (GM) ones are the best out there.
 
I haven't talked to him in a long time, but I think that I've got the exhaust system covered. I figure that this is going to be a low to mid rpm motor. I know that the heads are going to be a limiting factor. Just doing a little port matching would probably help. I had thought about if I seperate the 2 cylinder banks completely that I might get better scavaging by going to a slightly smaller pipe, like 2 or 2 1/4". High flow converters are going to be a must. We used to use mufflers for big cars like a Lincoln or Chrysler to keep them reasonably quiet with low back pressure. The best that I ever had was for a hot factory Corvair of all things. I bought a pair of "Hush Thrush" mufflers when they first came out. I finally gave or threw them away. They were mufflers not glass packs or straight through.

I understand that I'm going to be good to get 30 HP, but that's probably close to 20%, maybe a little more. That would be noticeable. Then a low rpm intake. If I don't get into higher rpm's the heads aren't going to hurt me as much as if I were trying to turn 5 to 6000 rpm's. Somebody mentioned the Vortex heads the other day. They aren't a bolt on, are they? I still have enough contacts, most of them are my old hot rod buddies kids. I say kids, most are getting close to 40. I could probably have them find some things for me if they don't already have some of them.

I'm going to start looking at some places like Summit and the others that I can't remember right now to see if they have some of the stuff that I'm going to need eventually. I don't want to go too far, I want to have a reliable, reasonable 4 wd. I don't want a vehicle that can't pull a greasy string out of a "coke bottle", I've always heard it a little different, but at least the first letter is right.

Thanks again y'all, it's almost my bedtime, have a good safe night, Paul
 
You want a stock looking head and intake setup you should upgrade to the vortec heads. Also known by L31 option code. These came out in 1996 on the trucks when gm moved away from TBI and a multi-port injection setup. The heads borrowed port designs from the Corvette gen II LT1 engine. A high swirl design with 64cc chambers they out flow the old Camel back heads by a good margin. They have center bolt valve covers so they would look stock. They do require a vortec specific intake since the vortec heads use 8 bolts to attach instead of the 12 the originals had.

That combo would boost the power over stock TBI parts but will require programming to the ecm.
 
Again, separating the banks is inconsequential when you aren't getting any meaningful exhaust flow in the first place. Scavenging relies on velocity, upsizing pipe hurts velocity, as do the manifolds. GM ran duals back when they didn't make pipe large enough to run singles. They've long ago solved that problem with 3" tubing being almost the norm anymore.

Running two sets of anything under these trucks is a complete PITA. If you look under the truck, should be a heat shield above the converter. You'd need to add another one if dual w/cat. Then look at your crossmember/transfercase on the passenger side, and see what kind of clearance is in there, what kind of access you'll have if the crossmember has to come down, plus access to the front driveshaft flange, etc. I "had" to have duals when I put the truck together (factory 6.2L exhaust), and after having to deal with that setup 3 or 4 times for other issues, decided quite easily that running twice as many components wasn't worth the pain. When I went to single over dual, there was zero noticeable increase or decrease in power.

Everything in the TBI system is designed for low RPM power. The heads, the intake, throttle body, arguably the exhaust. Just about anything you do is going to move the point at which it makes power higher in the RPM range, short of 1-1/2" primary long tube headers (almost all are 1-5/8").

As suggested above, Vortec heads may be a decent swap to consider, but I'm not entirely sure they make more low-end than the '193's. They are a good head design unquestionably, I run them, but they introduce a whole host of their own peculiarities. If considering Vortecs, it's time to start considering aftermarket heads, of which there are a plethora, for prices/performance that best, equal or rival the Vortecs.
 
I was thinking that since separating the exhaust from each bank would reduce the volume of gas through everything from the converter back and slow it down in pipe of 2 3/4 inchs. Duals with a slightly smaller diameter (about 2 inchs) would reduce backpressure and increase gas flow speed which would help scavange each side, wouldn't it?

One thing that hasn't been brought up: is the reduction in back pressure going to be a problem?

Talking about the exaust being like this on so many years and models, it looks like that they could have atleast joinded the two exhaust pipes at an angle. Nothing fancy, just an angle so the exhaust would at least be pointed in the right direction.

I'm planning on getting the prom done, but shouldn't I wait until I get close to the final configuration? I know a guy that I used to work with that can write the chips, he just doesn't know cars at all and he's a real jerk and that's being nice. I probably know some others, but there again, they don't know anything about cars.

I want to make sure that I'm understanding: I can put the Vortec heads on this block, but it takes an intake spacifically for that combination, If I'm right on that, what is the situation with the exhaust ports, are they the same shape as the original heads or does it take special headers for the exhaust ports on the Vortec heads? Later I might consider after market heads if I think I need them. Just getting this motor where it should be and add a little more, I may be happy. I said it earlier, I'm not looking for wheelies, it would be nice to be able to get out of the way.

As always, Thank y'all very much, Paul
 
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