I rewired a 1998 C1500 L31 "Black Box" harness identical to the 2002 Express Van L31 wiring schematic. The stock Express Van tune is a good starting point. I use EFI Live to to tune the '0411.
I rewired a 1998 C1500 L31 "Black Box" harness identical to the 2002 Express Van L31 wiring schematic. The stock Express Van tune is a good starting point. I use EFI Live to to tune the '0411.
How was the LT1 performance improvement with the base Express Van tune?Originally Posted by dave w
I did the conversion on a TBI 350 engine, NOT a LT1.
dave w
Well, I've made the decision to go ahead with the Opti delete on the 94 Lt1 and am starting to pick up the necessary parts.
Will be doing the 4x (using a 96-97 4x reluctor wheel, timing cover, and CKP sensor - getting a great deal on this) and using a 96-99 Vortec dizzy for the 1x CMP signal and spark distribution.
Have a few questions (going with the 02 Express Van calibration) re what to use for O2 sensors, and what KS's to use?
Will the 94 Lt1 O2 sensors be compatible, and if not, what are my options (96-97 Lt1 O2's, L31 or LS or 01 and newer Vortec).
Can I run the 96-97 KS (as they will fit the LT1 KS thread), and do I need 2 KS's, or be ok with 1?
Can I retain the LT1 ICM and dual connector coil, or do I need a L31 ICM and coil?
Am assuming all the other 94 Lt1 sensors (IAT, MAP, MAF, TPS, ECT) will be compatible?
Advise/previous experience re this is greatly appreciated. Thanks
If your running headers and not manifolds, run 01 corvette secondar o2 sensors in the normal, primary position you need them in and repin your vehicle side harness not the sensor side of the harness to make them work. search ls1 tech for reasons why.
Switch to the l31 coil/ign module. knock sensors whould be from the 02 g3500 with 5.7 the original lt1 sensors are most likely worn out at this point and you need to flush the block properly anyway. Use liquid pipe sealer not tape if there is no preapplied sealer on the threads. use 2 sensors.
The rest of the sensors should be GTG. There will be area scalers and values to change before first fireup. We'll cross that bridge then. Idle air handling is no where near what your used to seeing on the lt1.
Fuel pressure for the injector constant is 4 bar not 3 bar like the lt1.
Lots more.
Get to work, we need pics..
Chris
I'm running headers and will be using the 94 LT1 harness and re pinning it at the PCM connector side with the LS PCM (blue/red) connectors. Will add wires for the CKP (the 94 LT1 does not have the CKP) and changing other pigtails as necessary.
Did some research on part numbers and the 94 LT1 ICM and coil, and the numbers are different from the 96-97 Lt1, however the 96-97 Lt1 and L31 share the same ICM and coil numbers. The difference is a change from a dual connector (94 Lt1) to a single connector (96-97 Lt1 & L31). Outside of the connector, I'm not sure there's a change in the coil (given I'm re PIN'ing the 94 LT1 engine harness, I should be ok with the 94 LT1 coil, or NOT)? With the ICM, I've read where there are guys saying there's a difference between the 94 Lt1 ICM's and the 96-97 ICM, and then there are guys that say there's really no difference and they're interchangeable.
Anyone know for sure? Is the difference in the sensors/parts something that can be dealt with when doing the PCM re-flash (ie give the info to the programmer, and he'll know what to do)? That's the thing I'm finding - the more research/opinions I find, the more certain things are clearer, and there's also more differring opinions/experiences on other parts compatibility questions.
As for the KS, I'll go with the L31 KS. There was no correlation between the any of the LT1 KS part numbers, and the L31 KS part #.
Also re the CKP sensor, the 96-97 Lt1 and the L#1 share the same 4x reluctor wheel, but the crank sensor part # for the Lt1 CKP sensor and the L31 are different. However the L31 share the CKP sensor part # with the LS1, but the LS1 is a 24x, not a 4x. From what I've read, a 4x sensor will not work for a 24X system, and visa versa?
Re fuel injectors, am I ok to stay with the 94 Lt1's (they also share the same part # thru to the 97 Lt1) but I've not found anything re if the 411 PCM will require a different injector?
I've collected some of the parts, and still trying to clarify some of the parts I should go with. Doing this in a tight budget, so hoping to get the parts right the 1st go around.
I'll get some pics up as soon as I start the dis-assembly, but that's probably going to be a couple weeks yet. I did manage to score a damaged SBC Edelbrock Performer 2101 intake (for $0) which I'm going to use as a making a template for the Vortec dizzy hole for the LT1 intake. Once the template is ready, am going to cut out a portion of the Edelbrock rear section where the dizzy hole is, and cut out the correlating section in the LT1 intake, and weld the Edelbrock section in.
It sounds like you've experience with this, and I appreciate your feedback. btw is there anyone on this forum that would be able to flash a base tune that I could run with until have the $ to get it on a dyno?
Last edited by pather; 01-01-2016 at 08:15 AM.
While I’m waiting to pick up the parts, I’ve had some time to go back and re-read some earlier posts on this forum and a few other forums, and some of what didn’t make a lot of sense, makes more sense now. I’m still pretty new to this but have been on a pretty good learning curve.
I’m picking up the 96-97 LT1 timing cover and 4x reluctor in a few days, and might also be able to get my hands on a used L21 24x reluctor for $10. The possibility of the L21 reluctor got me thinking about the decision of a “4x or 24x system” again, as the major reason earlier for leaning to the 4x was the part(s) were already available on the 96-97 LT1 (and putting this on a 94 Lt1 was relatively a bolt on).
I went back to the earlier post by Sandrock and Eaglemark re the L21 reluctor, and now understand what he was trying to do, but the focus on that discussion got to a point, and then dropped off.
I want to take one last look at whether a 24x may be do-able on a tight budget. I can get a set of 8 coils for under $50 (and I understand the L21 wheel must go with the L21 CKP sensor), so my budget shouldn’t take a huge hit. The only other variable is the tuning and whether there is much difference in cost between a 4x and 24 to base tune and or dyno?
The questions with the L21 reluctor are (1) the ID is 1.6” whereas the SBC/LT1 is approx. 1.25” (2) the thickness of the L21 (from what I’ve read) is thicker than the Lt1 4x reluctor and (3) is the OD of the LT1 4x and L21 4x reluctors the same?
Sandrock had looked at fab’ing a centering tool and bolting the L21 reluctor to the crank gear, but there were concerns whether the bolts might interfere with the gear operation, and it wasn’t clear if the alignment and clearance of the reluctor inside the timing cover would be ok – both due to the extra thickness of the L21 reluctor. Then there is the final issue of the orientation/placement of the sensor. I had asked the sensor placement/orientation question earlier in this thread, but being a newbie still, can’t say I 100% understand how to do that properly (yet).
The idea of trial and error and what is entailed with “re and re” to do a trial and error, was the reason for leaning to the 4x. I don’t have the equipment to do a bench test to see if the sensor orientation/placement on the reluctor is correct before installing it. If somehow I can figure that out definitively, then this is what I’m considering with the L21…
Take the Lt1 reluctor and turn it down to 1.6” OD and press the L21 reluctor onto the Lt1 reluctor base and tack weld it in place. This would be done on a lathe to ensure run out and concentricity. But before tacking it in place (as long as the thickness and OD issues were ok/resolved) I’m back at sensor orientation/placement question. The LT1 timing cover having the sensor boss at the 7:30 location, I would have to make sure the L21 reluctor was properly oriented before tack welding it in place (ie using the keyway on the 2 reluctors as a guide apparently is not 100% accurate or right).
What do you guys think, or has this been thought out before, and is not do-able?
Last edited by pather; 01-03-2016 at 12:06 AM.
Considering the steep learning curve (first time challenge with this type of conversion), I think using the 4x system would provide a more affordable and simple path to success.
How much will you have invested by the time you buy the L21 reluctor wheel and sensor and do the machining work? Also consider how much you have to spend again to get a working setup if it doesn't work. $150 gets you a working 24x wheel that simply replaces the 4X LT1 wheel.
Tuning would cost the same either way.
I have no idea if you could make the L21 wheel fit and work on the LT1 engine. If you try the machining work, you would probably want to machine out the L21 wheel to have a larger ID before trying to mate it to the center of the 4X wheel. Otherwise, you're talking about cutting the center of the 4X wheel down to 0.175" thick and I'd think that thin a piece could easily distort or break at the keyway. The orientation would require careful measurement but isn't that difficult. The TDC on cylinder #1 should correspond to one of the tooth edges on the 4X wheel. So, align the TDC #1 tooth of the 24X wheel at the same spot. A picture was already posted with the TDC #1 cylinder tooth edge on the 24x wheel. You do it all relative to the keyway slot of the 4X wheel so the new wheel tooth is in the same location as the old wheel.
As I posted before, I wouldn't do the swap unless it included CNP. Going as far as you're going, I'd just spend the extra $150 to do the 24x setup.
You're 100% right about the cost. I wouldn't be considering this if I wasn't on a tight budget, and the fact that the machining etc. is a zero cost thing for me.
I've got the parts (timing cover, 4x reluctor, 24 reluctor, vortec dizzy, L21 CKP sensor, LT1 CKP sensor,) for just under $125. Am expecting to get a used the 8 coil pack for $60 - $70. Would re-PIN the Lt1 harness with LS PCM connectors. Have somebody welding the Lt1 intake for the Vortec Dizzy for $40, so all in, I'm hoping to be done (before tuning) for about $325 for parts, gaskets, etc.
Was thinking about opening up the L21 reluctor for the very reason you mentioned. Once I get the parts, then it just waiting for my buddy to have time on the lathe.
I just figured given I would have to open up the 94 Lt1 for the 4x reluctor install, I would give this 24x reluctor idea another shot. Be a shame to go in that deep, and then decide the 24x is the way to go.
It might be a few weeks, but I'll update etc. when I get into this (waiting for my buddy's schedule is the unknown). Thanks for the input re the reluctor/sensor orientation. That was my last "what to do about that" question before changing back to the 24x system.
I’ve almost all the parts for the 24x conversion now. Besides finding time to work on this, I’ve a question re the positioning of a LS2 CMP sensor before starting the teardown.
Am designing my own 1x CMP signal using a LS2 Cam Gear concept (details of unit etc to come). My question is where/how to position the CMP Sensor (part # 12591720) in relation to the raised portion of the Cam Gear trigger.
Have attached a pic with 2 drawings. The green section is the raised trigger on the Cam Gear, and the pink circle is the CMP sensor. Drawing “A” has the trigger leading edge at edge of the CMP sensor at TDC 1, and Drawing “B” has the leading edge at the center of the CMP sensor at TDC1.
Which is the correct positioning?
Attachment 10199
Just checking in to let you guys know that the plan is still going ahead with the 24x conversion. Between work, and life in general, its been hard to find the time. Have assembled most of the parts (just a few connectors/pigtails, and the coil pack left), and waiting until I've the budget for the tuning software before starting into the conversion.
Will update...
Doing the same retrofit. Has anyone figured out the BBC 24x reluctor wheel phasing to the SBC?
I've completed the fabrication and machining for a DIY CMP, and a L21 24x reluctor. As soon as I have time to install (hopefully between now and Xmas), I'll report back.
Please keep me posted!
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