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Old 08-08-2015, 12:03 AM   #1
Albegro
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Default 1999 sl1 swap to DOHC

So I am ready to gather what I need for a DOHC swap for my 99. I think I understand what parts I need but I would like it if I can get a once over on it to make this as smooth as possible.

As far as I can gather, since I have a manual trans, I need to find a 1996-2002 DOHC engine and manifolds, a 1999 DOHC PCM, and a DOHC instrument panel. What I am not 100% on is what's the best year to swap for simplicity? Any difference between DOHC and SOHC flywheel? Do I need the airbox? Is an abs PCM ok to use in a non abs car?

It will be a junkyard motor and rebuilt .020" over if needed. Ill be grabbing everything from the valve cover to the oil pan, sensors and all, minus accessories. Anything else I should grab? Im skipping on the trans swap, I dont think Ill be too bothered by the difference.

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Old 08-08-2015, 06:55 AM   #2
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Default Re: 1999 sl1 swap to DOHC

If you don't have inspections you can use an ABS PCM in a non ABS car but the idiot light will be on.

Your best bet is getting a '98-'99 DOHC; if you get a '00-'02 DOHC you'll have to grab the intake tube from the airbox to IM and either block off the air pump port in the exhaust manifold or find a '00 without the air pump. With a '96-'97 the "off throttle" tuning will be different as the earlier years use a returnless fuel system (a fix for that is to pull the fuel rail from both, and put the DOHC injectors on the '99 SOHC rail).

Flywheel is the the same '91-'02 SOHC & DOHC.
The clutch disc, pressure plate and hydraulic's are compatible '91-'02 but keep them for the same year (ie: get a '95 clutch kit and '95 hydraulics).

If you want to pull the engine wire harness the easy way, pull the UHJB off and unplug the engine/PCM harness from it (1 of the 3 plugs), then unplug the harness at the PCM and shove it into the fender well (the engine harness isn't the one that goes through the firewall by the brake booster) then pull it through the fender at the headlight end and toss it on the engine. Yes it sounds like more work than unplugging everything but it's actually easier.

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Old 08-08-2015, 11:58 AM   #3
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Default Re: 1999 sl1 swap to DOHC

Quote:
Originally Posted by fetchitfido View Post
If you don't have inspections you can use an ABS PCM in a non ABS car but the idiot light will be on.

Your best bet is getting a '98-'99 DOHC; if you get a '00-'02 DOHC you'll have to grab the intake tube from the airbox to IM and either block off the air pump port in the exhaust manifold or find a '00 without the air pump. With a '96-'97 the "off throttle" tuning will be different as the earlier years use a returnless fuel system (a fix for that is to pull the fuel rail from both, and put the DOHC injectors on the '99 SOHC rail).

Flywheel is the the same '91-'02 SOHC & DOHC.
The clutch disc, pressure plate and hydraulic's are compatible '91-'02 but keep them for the same year (ie: get a '95 clutch kit and '95 hydraulics).

If you want to pull the engine wire harness the easy way, pull the UHJB off and unplug the engine/PCM harness from it (1 of the 3 plugs), then unplug the harness at the PCM and shove it into the fender well (the engine harness isn't the one that goes through the firewall by the brake booster) then pull it through the fender at the headlight end and toss it on the engine. Yes it sounds like more work than unplugging everything but it's actually easier.
So 98-99 is the best option but back to 96 will work by just swapping the fuel rail and will give me the option for the 92 header. Is the header worth swapping the fuel rail?

And I do need to remove the harness from the donor? I was under the impression that I could use the original Harness for the SOHC.

Thanks for the help, this is my first major Saturn surgery and every bit is appreciated!

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Old 08-08-2015, 12:15 PM   #4
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Default Re: 1999 sl1 swap to DOHC

You can use the same harness (trim the locating tabs so it'll plug into the DOHC PCM), it's just faster to take the harness with the engine. I found it to be far easier than unplugging the various sensors and trying to wiggle it out of the engine. Downside is it'd have to be from the same year & door count.

If you got a '98 you could use a '92 header and not have to swap the fuel rail, if you go '99 you'd have to get an OBX/Pacesetter aftermarket header just like '00-'02's.

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