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3.4 DOHC to L26 Swap - OBDI to OBD II


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Ok, Everyone. For those who wonder what would be involved in doing L26/L36 Swap here Is what is involved. This is what I've learned. Some of you might know this, but any who might wonder here it is....


1995 Cutlass DOHC, Swapped out and installed L26 with OBDII upgrade.


Basic Parts Installed/Used:

1995 DOHC 4T60e 3:43 Ratiio

2008 L26

1997 Grand Prix GT Flywheel

1997 Grand Prix PCM (Miltzy Motor Programmed) / optional 96 Regal PCM (Stock)

1996 Buick Regal Engine Harness

1996 Buick Regal A/C Compressor and Lines

1995 Cutlass A/C Accumulator

1996 Trans Mount GM #9521522 (Only Year can use)

3.8 L 4T60E Trans Dip Stick

Down Pipe (1998-2000 Z34 down pipe or DOHC Down Pipe w/ 96 3.8 Manifolds)

1998 Monte Carlo Z34 Throttle Cables

1998 Monte Carlo Z34 Upper Engine Mounts

L26 TB adaptor (ZZP)

1996 regal/1998,99 monte-Lumina power steer press hose

1996 Regal/1998,1999 Z34 Radiator Hoses and Heater Hoses


DOHC to L26



First are some differences/Changes you will have to do to keep the original 4T60E trans.

The Trans Sticks are different. THe 3.4 DOHC dip stick is angles sharper and will hit the 3.8L exhaust manifold. Grab one out of a 3.8L 4T60E trans.



Second: PRNDL Switch 1996 / 1995- OBDII/OBDI: You can use same trans. You will need to use the OBDII PRNDL Switch, OBDI switch has intregral harness.



Third: Throttle cables from the 3.4 DOHC are shorter than 3.8 Monte Carlo/Regal




Fourth: Down Pipes. You can use the original Down pipe from DOHC engine IF you use the 1996 Exhaust manifolds. he 1996 3.8L manifolds bolt directly to DOHC exhaust. Notice the difference in down pipes. First is the 1997-current 3.8. The 1996 3.8 is Second. If you use Exhaust manifolds from 1997- then you will need to get an aftermarket down pipe or one from Monte/Lumina.

1997-Newer Downpip and L26 Exhaust Manifold


1996 3.8L Exhaust and DOHC Down Pipe





Fuel Lines. Used Fuel rails off of 1998-2000 Monte Carlo/1996 Buick regal. Cut them off from the frame rail and then used high compression fitting to attach.

. post-5429-14368911503_thumb.jpg

Used Pipe cutter to cut and splice fuel lines


More To come.....


1996 Regal/1998 Z34 Heater Hoses with N/A Alternator bracket. If you use the L26 Alternator bracket you will need 2000 Monte Carlo Heater hoses and Alternator from S/C 3800- The nipples are different angles and alternator is completely different.


N/A Bracket 98-99 Z34/96 Regal


L26 Alternator Bracket



Intake Manifold L26: You can use either the plastic manifold with no mods, or L26 aluminum intake. With the L26 Manifold you will need Throttle body adaptor, and swap out the rear Vacuum Nipple for brake booster.


Nipple with red cap would need swapped for Evap Small line


Installed 98 Supercharged throttle body with 98 MAF. The TB just clears the Master Brake cylinder. Had to notch out the intake hose. only about 1/2. Using a CAI would avoid this, I suspect that the 2 door might have little more room here.



Also, While front suspension picked up 96 Regal strut assembly to give front ride height with correct spring rate. DOHC engine is almost 100#'s heavier than the 3800. Running correct springs gives better ride height and was able to up grade to 96+ brakes




Hope this helps those considering a swap from DOHC to 3800 and helps keep cost down from adding trans and c/v joints.


There is more down below in follow up discussions.






Edited by pshojo
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post-5429-143689115165_thumb.jpgTrans Swap Details:

To bolt a 4t60 to a 3800 you will need trans bracket that is unique for 1996 Regal Only. Gm still has the part avail for $20, or use the one in the junk yard. The reason is the motor mount set up on the pre-96 is different and 97 post 3800 uses 4T65E.





Installed Power Steering hose while Trans was out. Also cradle is the same. the 1996-up motor mount utilizes section on the K-Frame/Cradle



After pulling the engine, I would used the old bracket from the 3.4 DOHC to just hold the transmission in place so I don't have to hold trans with jack. Took the old bracket and cut it so there is no interference with 3800 when installing.




While Intake was off, Decided to install intake insert and Rockers with Springs.






Edited by pshojo
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L26 Swap Electrical portion

C100 Connector, 96 Harness on left side, 95 Body harness on right side. Directions follows for harness changes:

Cut E1 wire, reposition into A3 Connector. Run wire through fire wall and through A1 Port after disconnecting J2. Disconnect K1 and isolate.


For K1, Battery Fused wire will need to be fused. I Spliced into the 60 Amp Maxi fuse circuit for the 3.4L Air pump circuit. Pump consumes 25Amp (No longer used). Spliced into a circuit requiring 15 amps for Sund Roof/power windows/locks/Digital Temp Control.

post-5429-143689115274_thumb.jpgWire pulled from K1 DOHC Harness and reconnected into 1996 Regal harness circuit.



Also Trans wiring. Verify Which harness you have on the 1996 trans.




OBDII Conversion: Cut off OBDI Connector, Cut off OBDII connector from junkyard. Match up all colors the same. Orange to orange (needs to be fused into B+) Both Black wires spliced into OBDII Black wire, Tan to Tan.



Note the purple wire is spliced into my Serial Data wire I fed through C100 connector from A1.





Edited by pshojo
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Well, I have to say that I just piggy backed off your Thunder. You were my inspiration. :) Still wished i would've bought the Vert you did. Instead of going with 4t65, I wanted to something different. By the way I love the 3:43 FDR with the engine. Next time I think i'd do a cam though.

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Nice write up Paul.

I didn't know the 96 Regal exhaust would bolt up (using the Regal manifold).

Sure would save some cash not having to buy the 98-9 Monte downpipe.


Question though. You mention the trans bracket being unique to the 96 Regal.

I was looking at the pics and that looks like a generic 3800/4t60(e)(hd) bracket to me.

Are the bolt holes offset from later ones or something like that?

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4T60e(HD)? I didn't think the 4t60 came HD? That would've been in Riveria's? (Still learning)


(Disclaimer): this is mostly just by observation of Regals/Olds 88's that i noticed.... In the 95 and older 3800, there are two motor mounts, one in the front of the engine and one in the back that attaches to the transmission which is a two piece. The 96 & newer have one engine mount under the center of the engine and this bracket that is one piece that attaches the trans end to the back of the block. I had GM dealer run a 'where used', this part number and they said this bracket is only used in 96 Buick regal. Not saying their book is correct.


Now i'm looking through my pics from junkyard. Looks like where the bracket attaches is different, but would've worked?

96 Regal Bracket



Pre 96 4t60e



Looks like they attach to different holes on the trans, one is between trans and block the other is above the trans (96). The 96 really made it difficult to get the the last bolt on the trans/block. Dont know if the others would be easier? I went with the 96 because I knew it would work from SeriesII and I was able to buy it.



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Looking at the pictures. i do remember the holes that the Pre 96 bracket used where taken with the new 96- newer motor mount. So, it would be the correct bracket with the corrent motor mount set up...

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Ok. I'm used to the newer 3800 stuff. Haven't messed with a DOHC since I did my Vert swap a few years ago. I don't even remember a motor to trans bracket that looks like that (the old one).

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  • 1 month later...

Well I've been driving the L26 with DOHC 3:43 trans a while. In town gas mileage ranges from 16-19 mpg pending how I drive. I've taken two trips and figured 25-27.5 MPG.

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  • 9 years later...

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