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  #1  
Old 03-21-2009, 11:27 PM
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Default info on the 4.3 CPI engines

Has anybody done something like this: http://www.jeep4.0performance.4mg.com/ for the CPI 4.3 guys? I've been looking and haven't found anything that comes close. If you look around that site, there is an amazing amount of info. Just trying to find something similar for a CPI 95 Blazer. I'd like to get it down to a 16 flat in the quarter as cheaply as possible and with no loss in fuel economy. For example, I saw where a guy freed up some power by disconnecting the balance shaft (but leaving it in place). What's the best/easiest way to do this? Any other slick mods like this? Did the 95s still use an E-PROM chip? I saw a thread where they said 95s aren't programable. Are they chipable? I thought all PCMs are one or the other? Just mostly finding threads were the guys are arguing over what works and what doesn't. I want to keep my 3.42 gears and present fuel econ. This is my first Chevy since 1985! I hope this one works out better than the last one! Thanks to all who help. Regards, Eric

Last edited by holaman; 03-22-2009 at 02:50 AM. Reason: change "were" to "where"
  #2  
Old 03-22-2009, 09:36 AM
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95's are a messed up year. Some very early models were completely OBD-1 while after the brief starting up period, they transitioned to a part OBD-1 and part OBD-2 system. This makes these PCM's very difficult to program for any added.

That and the CPI engine is quite restrictive on the fuel supply side as well. With the specialized fuel system, your options are non-existent for upgrades.

What are you running in the 1/4 now?
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Old 03-22-2009, 12:15 PM
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95's are not programmable.... most use a ODB 1.5 system so like a swartlkk said they are hard if not nearly impossible to program. I would say as a 95 owner that they are a good truck, I've had mine for a little over a year and have had very little problems with it so i hope there's a bonus for you to think about lol.

You can try some other things like ignition ugrades (plugs wires coil) and a cold air intake that could help a little.

Oh.. if you look for a Cold air intake on eBay then look it up for a 94 S10 .. it probably won't list any for a 95 Blazer as 96+ actually have a different version of the Vortec
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  #4  
Old 03-22-2009, 07:14 PM
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Thanks guys. Haven't run it yet in the quarter but Car and Driver got a corrected 17.0 out of a 95 in Feb. 95.: "In every acceleration and passing test, the Blazer dusts the Jeep [Grand Cherokee] and Explorer---and it beat them in observed fuel economy by 1 mpg." Through the years I have found C & D to be very accurate.
Unfortunatly, in today's world, a 17.0 is an also ran. I just want the truck to be able to hold it's own in traffic. I know it can be done. I have a MB 400E that I just ran a 14.72 (14.44 corrected) on 03/07/09 that everybody said I wouldn't be able to get much improvement out of (15.3 corrected stock C & D 3/93) read about it here: http://www.500ecstasy.com/forums/showthread.php?t=5998 That thread has recieved over 4000 hits BTW which is alot for that highly specialized site. Now here I go again with this one.
Are there any links to any sites like that Jeep guy did?
Why did the 92 Bravada have 200hp even though the 94-95 CPI has better heads?
If I replace the muffler with a straight pipe and free up the intake breathing somehow will the PCM be able to compensate even without a reprogram? I've read that some of the systems from that time period are actually in "open loop" mode during WOT just relying on the pre-programed program in the computer and that's why mods often don't work until the PCM is addressed. Is that the case here? How hard would it be to make this truck think it's a true OBD I? The Jeep 4.0 guys have found the OBD Is much more receptive to mods than the OBD IIs are but it seems you guys think it's the other way around? Is that true? Thanks again to all who help. Regards, Eric
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Old 03-22-2009, 07:37 PM
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The OBD1 vs OBD2 debate centers around how easy things are to modify. OBD1 computers can easily be editted with some relatively cheap software. OBD2 computers are more sophisticated and thereby more difficult to get to know. Once you know how to program one for the highest potential for your motor though, they are much better at maintaining that potential as they adapt much more than and OBD1 computer can.

As far as sites like the Jeep one you listed, I looked a bit and could not find anything. I could not even find anything even related to CPI performance and that is a topic that many others have broached as well.

I am in no way saying that you cannot get to the 16s, but I doubt you will be doing it through PCM programming. I would look into internal engine modifications (cam and possibly head work) along with a true CAI and a free flowing exhaust (headers, high flow cat, free flowing mufflers). The PCM can handle quite a bit of changes. So long as you do not go too radical with the cam, you should be good.

What is your source on the HP levels for the 92 Bravada? It should be the exact same CPI motor found in the Blazer of the same year.
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Old 03-22-2009, 09:06 PM
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05/92 Car and Driver. That CPI powered rig also was the fastest in the comparison and also got the best observed fuel economy. Those 2 CPI rigs (92 and 95) really shined.
How is that balance shaft disconnect done?
Can I fool this 95 OBD I.5 into thinking it's a 94 OBD I?
All V-6 vehicles on this platform have the 8.5 rear-end not the 7.5 right? That's really a big deal to me because even the V-8 Grand Cherokees of this time period only had a 7 9/16s rear unless you spent extra money and few people did. That rear isn't even strong enough for the 4.0 much less the 5.2.
Why is the 96 and later 4.3 5hp and 10ft lbs weaker (190 and 250 vs. 195 and 260) than the 95 despite having much better heads? In the 04/96 C & D a one year newer Bravada (1 year newer than the 02/95 Blazer) sank from that 17.0 to a 17.8 and it's observed econ. slipped from 19 to 15 (still 2nd best). It was 130lbs heavier bit still that doesn't account for 8/10s. I chose this 95 cause it seemed like the peak year for that body style. I understand the limitations but it also seems like there should be some potential as well. I didn't get into my 400E's eng. at all. All changes were external. And when it comes right down to it, I didn't really do that much. Again, I appreciate all help. Regards, Eric

Last edited by holaman; 03-23-2009 at 02:56 AM. Reason: fix 05/02 to 05/92 and add more info
  #7  
Old 03-23-2009, 07:41 AM
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You are not getting the whole picture from those reviews. You would love to believe that they are comparing like vehicles (gear ratio, tire size, drivetrain configuration, etc). They do not tell you that and a gear ratio difference alone can account for a lot of that difference.

For actual numbers:
1992-94 - CPI L35
HP = 200 hp (150 kW) @ 4500 rpm
TQ = 260 lbft (353 Nm) @ 3600 RPM
Compression Ratio = 9.1:1

1995 - CPI L35
HP = 195 hp (150 kW) @ 4500 rpm
TQ = 260 lbft (353 Nm) @ 3600 RPM
Compression Ratio = 9.1:1

1996-2002 - SCFI L35
HP = 190 hp (140 kW) @ 4400 rpm
TQ = 250 lbft (339 Nm) @ 2800 RPM
Compression Ratio = 9.2:1

As you can see, the torque peak dropped in RPM considerably with the SCFI motor. Just looking at the HP/TQ numbers alone can be a dangerous way to qualify motor strength.

1995 was the first year of this body style, but I am not sure I would classify it as the peak year. Reliability concerns with the CPI motor take away that hope IMO (FPR failures taking the top spot there).

As far as the rear axle goes, unless you have a 2dr 5spd and got lucky enough to get the 8-1/2" rear or you have a ZR2 Blazer (which also had the 8-1/2" rear stock), you have the 7-5/8" rear end. But there are people putting some impressive numbers down using this rear. It all depends on what you are trying to accomplish.

As far as tricking the PCM into thinking it is an OBD1 only... Not going to happen. You would likely have to swap entire wiring harnesses out to revert back to the older style and that would also extend into the cab. That is A LOT of work just to get back to OBD1.
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Old 03-23-2009, 07:36 PM
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Quote:
Originally Posted by swartlkk View Post
You are not getting the whole picture from those reviews. You would love to believe that they are comparing like vehicles (gear ratio, tire size, drivetrain configuration, etc). They do not tell you that and a gear ratio difference alone can account for a lot of that difference.

For actual numbers:
1992-94 - CPI L35
HP = 200 hp (150 kW) @ 4500 rpm
TQ = 260 lbft (353 Nm) @ 3600 RPM
Compression Ratio = 9.1:1

1995 - CPI L35
HP = 195 hp (150 kW) @ 4500 rpm
TQ = 260 lbft (353 Nm) @ 3600 RPM
Compression Ratio = 9.1:1

1996-2002 - SCFI L35
HP = 190 hp (140 kW) @ 4400 rpm
TQ = 250 lbft (339 Nm) @ 2800 RPM
Compression Ratio = 9.2:1

As you can see, the torque peak dropped in RPM considerably with the SCFI motor. Just looking at the HP/TQ numbers alone can be a dangerous way to qualify motor strength.

1995 was the first year of this body style, but I am not sure I would classify it as the peak year. Reliability concerns with the CPI motor take away that hope IMO (FPR failures taking the top spot there).

As far as the rear axle goes, unless you have a 2dr 5spd and got lucky enough to get the 8-1/2" rear or you have a ZR2 Blazer (which also had the 8-1/2" rear stock), you have the 7-5/8" rear end. But there are people putting some impressive numbers down using this rear. It all depends on what you are trying to accomplish.

As far as tricking the PCM into thinking it is an OBD1 only... Not going to happen. You would likely have to swap entire wiring harnesses out to revert back to the older style and that would also extend into the cab. That is A LOT of work just to get back to OBD1.
That's another reason why I like C & D is because they do usually provide that info and they usually do try to get similarly equipped vehicles. The 96 test was an exception because there were so many vehicles in that test but it's a 98% probability that it had 3.42s or 3.73s right? Also they didn't list the transfer case in that article but all Bravadas of that era were full time right? The 92 Bravada was also a F/T case, only had 3.42 gears and still ran a 16.7 quarter. That's why I didn't doubt the 200hp rating. So why is it stronger than the 94-95? The info I have shows the power and torque numbers being the same for 94-95. 94-95 heads flow 10% better and 96 and later heads flow tons better right? The 95 Blazer had 3.73s and had a P/T case. The new body was about 100 pounds heavier but with less drag from the P/T case and better gearing, it should have been able to run the same as the 92. I'm not just going by power ratings I'm also going by the fact that the 96 was 8/10s slower and the 95 was 3/10s slower. And in other articles the later rigs are slower as well. I'm thinking maybe it was because the 96 and later eng. doesn't have an "active" intake manifold? But I can't account for why the 92 is so strong. Tire size in all cases was P235/75-15.
Very disappointed about the rear-end. Does what you say also apply to the later rear-ends in this body style that had disc brakes?
So I go out of my way to get a 95 only to find I'm SOL?
Can I get more timing the old fashioned way? Can I rotate that distributor a little? (I have a good timing light.) If I open up the intake a bit (keeping it cold air), replace the muffler with a staight pipe, and put a little more timing in, what kind of Q/M E/T can I expect? A 16.4? I could live with that. I can't live with a 17.0. Thanks again. Regards, Eric

Last edited by holaman; 03-23-2009 at 07:49 PM.
  #9  
Old 03-23-2009, 08:53 PM
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Honestly, to debate about C/D results seems pointless to me. If you look hard enough, you can poke holes in many of their "tests" and "comparisons". I have ridden in and driven many s-series 4.3L equipped vehicles and they all excel in their own way.

You are going to find it difficult to set timing on a computer controlled distributor. Too far out of whack and the PCM will complain.

I doubt you will see much gain from straight piping the muffler. The restriction is in the manifolds and y-pipe.
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Old 03-23-2009, 09:12 PM
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I didn't mean for it to seem like a debate. I was just filling in the blanks to present all the info. and answer the questions you raised. I do appreciate all your help. Could you please address all the questions in my last post? I understand that I can't get too crazy with the distributor but I can't even see back there---is that thing rotatable? Regards, Eric
Old 03-23-2009, 09:12 PM
 
 
 
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1995, 43, 95, adjusting, blazer, chevy, computer, cpi, ignition, l35, modify, obd1, start, timing, v6, wont


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