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L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Lsx/4+3 swap

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Old 05-14-2017, 01:16 PM   #61
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I fired up my LQ9 yesterday, wow that engine sounds awesome. The 3in exhaust sounds great.

What a long journey to get to that point. Just waiting on a few pieces, and see what I can break.

Its gonna be awesome to see what your set-up looks like with the turbo installed.
I noticed you mentioned cutting the c-beam in half and welding an extension in the middle-did you take any pics? I might have to do this if I can't get my bolts in. They're only about an inch or two off as of now though.
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Old 05-14-2017, 01:36 PM   #62
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No pictures, simple crude fix. I just cut the beam in half,near the transimission end. Added two 1/4in thick 6060 aluminum flat bar top and added some 1/4in thick 6060 aluminum plate to the outside of the c-beam. Re-forced the ends of the c-beam, as the factory stuff is pretty wimpy. I had to weld up the beam twice, as I can't measure
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Old 05-14-2017, 03:07 PM   #63
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No pictures, simple crude fix. I just cut the beam in half,near the transimission end. Added two 1/4in thick 6060 aluminum flat bar top and added some 1/4in thick 6060 aluminum plate to the outside of the c-beam. Re-forced the ends of the c-beam, as the factory stuff is pretty wimpy. I had to weld up the beam twice, as I can't measure

how is far off were you're holes? I'm not too far off so I'm hoping I can get them in the stock location with a little massaging.
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Old 05-14-2017, 09:15 PM   #64
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I was 1.5 inches off from the c-beam factory holes. Curious on where did you put your engine at vs. the factory position? I was 0.625in ahead of factory 350 position.
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Old 05-15-2017, 07:44 AM   #65
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I was 1.5 inches off from the c-beam factory holes. Curious on where did you put your engine at vs. the factory position? I was 0.625in ahead of factory 350 position.
I haven't taken any measurements. Am I missing something about removing the harness behind the battery? I've taken the nuts off and undone the clips. This harness is for the guages and the one that goes through the firewall is for the actual engine sensors/ecm?
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Old 05-15-2017, 06:06 PM   #66
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I haven't taken any measurements. Am I missing something about removing the harness behind the battery? I've taken the nuts off and undone the clips. This harness is for the guages and the one that goes through the firewall is for the actual engine sensors/ecm?
I'm reusing the factory sensors that come off the L98 engine. My dash is burnt out so I'm not sure on what's going on. My fast digital dash been working like a champ. The stock LQ9 has a nice rumble with my custom cheap skate home made 3in exhaust system I built

My factory harness is just laying off to the side, unused. I don't even have a check engine light on yet.

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Old 05-15-2017, 07:31 PM   #67
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I'm reusing the factory sensors that come off the L98 engine. My dash is burnt out so I'm not sure on what's going on. My fast digital dash been working like a champ. The stock LQ9 has a nice rumble with my custom cheap skate home made 3in exhaust system I built

My factory harness is just laying off to the side, unused. I don't even have a check engine light on yet.
I'm going to be using the c4 sensors as well for my digidash. What did you do for a harness again? I'm just trying to figure out how to go about merging the truck harness with the c4 harness.
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Old 05-15-2017, 08:09 PM   #68
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So far I'm running the FAST efi ez 2.0, using the factory wiring harness where ever I can, really so far its just the power to the factory distributor. Autometer oil/coolant temp gauges for back-up, but way better than any factory gauge.

Stock temp gauge is in my rad return hose. The fast efi is right cylinder head, autometer is left cylinder head. Oil pressure is from factory location and autometer at the where the oil cooler hookups go.

Not sure on the alternator right now. Thinking about converting my alternator four pin to two pin. I'm not sure if that will work.

Stock L98 fuel pump and ebay special fuel regulator. Right now its a on/off switch, at some point I will hook it up to the key on/off. My pump is only drawing around 7 amps for 60psi. I have replacement unit and aftermarket 80psi 355lph pump. Curious on how good the 30 year pump is prior to switching out.

exhaust is cheap skate ls swap shorty headers, attached to home made 3in custom.

Intake typhoon ebay special, fast ev6 injectors, 102mm throttle body, aluminum rad, AFE C6 cold air.

Still about a month out from my first drive. I have to work out of town for the next two weeks.I'm waiting on my Lokar cables for my throttle/cruise.

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Old 05-16-2017, 06:42 PM   #69
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Harness I can't get to come out..



@Mike-did you just remove all of the C4 engine harness or are you saying you left it in the car unhooked?
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Old 05-16-2017, 06:44 PM   #70
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Harness I can't get to come out..



@Mike-did you just remove all of the C4 engine harness or are you saying you left it in the car unhooked?

after being sent the wrong adapters for my injectors I noticed the stock L98 injector plugs fit the ls1 injectors. Woo hoo

does anyone know if I can just remove the whole L98 harness and add in the stripped down truck lsx harness? I found and posted a link to what chaos did as far as the wires he reused to am I correct in thinking I just add those into the truck harness?

Last edited by armybyrd; 05-16-2017 at 06:54 PM.
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Old 05-16-2017, 09:49 PM   #71
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The original vehicle wire harness (stuff for the engine), is just laying on my firewall for now. I'm reusing the factory oil/temp pressure (using the L98 sensors for that), alternator harness, the relay for the radiator pusher fan. As soon as I happy with everything I will cut the factory harness out. Originally I was going to take apart my dash and make everything pruddy, but that's over rated.

The original L98 coolant sensor will be plugged into an adapter I purchased to joint two rad hoses together and to hook in my head coolant drip line.

I have way less wiring than you. My car is a 85 and has a very simple wiring system.

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Old 05-17-2017, 10:03 AM   #72
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The original vehicle wire harness (stuff for the engine), is just laying on my firewall for now. I'm reusing the factory oil/temp pressure (using the L98 sensors for that), alternator harness, the relay for the radiator pusher fan. As soon as I happy with everything I will cut the factory harness out. Originally I was going to take apart my dash and make everything pruddy, but that's over rated.

The original L98 coolant sensor will be plugged into an adapter I purchased to joint two rad hoses together and to hook in my head coolant drip line.

I have way less wiring than you. My car is a 85 and has a very simple wiring system.
mines an 88 so I wouldn't think it would have much more wiring. Happen to know if the harness behind the battery is all the dash/gauges?
does it matter if I use the factory oil pressure gauge? Is it needed to be able to start the engine? I've got an adapter for using an auto meter gauge for the spot on the rear valley.
Need to find my '88 electrical book or google the schematics of the car. That and I think I'm overthinking the wiring aspect.

for the alternator did you just switch the plugs or are you using the L98 alt on your lsx?

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Old 05-17-2017, 05:55 PM   #73
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I didn't touch my wiring harness behind the battery, so I can't answer that one. I removed the LQ9 oil pressure sensor and installed the 1985 corvette L98 engine fitting with the 85 vette oil pressure/oil temp sensors. The LQ9 oil pressure sensor looks similar, but I'm unsure if it would work as I the LQ9 oil pressure sensor has a different connector on it. You could try installing the LQ9 connector onto the stock vette wiring harness. I took the easy way out.

As for alternator, I'm still figuring this out. I have the newer 4 wire style alternator (really only two wires are being used any ways). A bunch of LS forums say you can use a resistor on the one of the wires. I purchased an ac delco adapter that converter from four wire to two wire. Of course the connector on the adapter is different than my alternator. I bought a replacement connector for my 05 alternator and I'm going to tie the wires from the adapter into the replacement connector.

I'm just using the L98 vette distributor power for the switchable power on for my fast ez power on. There is one wire output from fast ez to the tach. There are two wires (power/negative) direct to the battery.

The stock oil pressure/temp sensors are the stock 85 vette, so the stock wiring harness from the car plugs into it.

I'm going to make my own relays for the fuel pump, rad cooler fan #1 (the stock pusher fan), and another relay for the aftermarket rad fans.

Hopefully that makes some sense. Buying an already done harness makes it alot simpler. I would get a more weather proof system, than what I got, as it is very crude. So I may have to rebuild the entire system at some point.
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Old 05-17-2017, 06:14 PM   #74
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Did you also leave the harness on the pass side firewall attached? I've already sold my ecm so I might as well remove the engine harness.
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Old 05-17-2017, 08:36 PM   #75
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You can't compare the removal/rewire of an '85 and an '88 other than just very "general references". The '85 @Mike doesn't have the battery jump-block behind the battery. His fusible links are all either from the battery or the starter motor originally.

The PCM "run harness" I'd think is very straight forward and the use of various gauge senders in the engine for cluster shouldn't present many issues.

There's a point where you need to determine what you actually would like functional in the OE cluster.

With the FSM of the correct year I'd think most could be sorted!
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Old 05-17-2017, 10:13 PM   #76
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Yes all the wires are still attached, you can see in one of my posted pictures. I will clean up everything next time I tear everything apart. The only wires I'm going to reuse is the wires for the AC stuff, as I'm want AC down the road.

I plan to just cut and shrink wrap the unused wires. I have my LQ9 ecm still, not sure on my plans.

I'm hoping I can get to drive the car in a few weeks. If something break, o-well, I know I'm cutting corners. Worst case its just a matter of calling a flat deck truck to pick-up the car.

Comes down to me on how I baby the car for the next few months.
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Old 05-18-2017, 07:25 AM   #77
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What we've generally done on any project is inventoried the C100 connector at the firewall/dash panel for desired circuits and worked from there. Never done a C4 though. A couple times we've bought the mating connectors and created our own. Very clean results.

The FSM @ 8A-202-0 for the '88 seems to be quite complete with appropriate circuits. The '85 FSM format is differently arranged but the information seems to follow the ground distribution section. Looking at the FSM seems to be somewhat more challenging but doable. I didn't study the FSM at length.
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Old 05-19-2017, 11:38 PM   #78
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You can't compare the removal/rewire of an '85 and an '88 other than just very "general references". The '85 @Mike doesn't have the battery jump-block behind the battery. His fusible links are all either from the battery or the starter motor originally.

The PCM "run harness" I'd think is very straight forward and the use of various gauge senders in the engine for cluster shouldn't present many issues.

There's a point where you need to determine what you actually would like functional in the OE cluster.

With the FSM of the correct year I'd think most could be sorted!

my digidash works fine so I would like to use everything. Can anyone answer in simplified terms whether I can remove the L98 harness or the harness behind the battery? I don't have my ecm anymore so I'm assuming keeping the harness is pointless.
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Old 05-21-2017, 05:33 PM   #79
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Is the truck alternator bracket too high? Interfere with the hood; I see you have the alternator mounted lower now. Also are you still using the truck crank pulley and water pump?
Thanks.
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Old 05-21-2017, 08:15 PM   #80
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Is the truck alternator bracket too high? Interfere with the hood; I see you have the alternator mounted lower now. Also are you still using the truck crank pulley and water pump?
Thanks.
Joenova uses the truck brackets but has a small case alternator. I want to use my large case alt and would rather not cut into the hood so it makes sense to mount it lower. Plus no sense
in using the huge truck bracket just to mount the alt.
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