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Old 02-16-2007, 02:30 AM   #1
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Default My L36 LIM Porting (with pics)...NOW WITH DATA!

Decided to go ahead and port a LIM for my '98 LeSabre.

Obtained an L36 LIM from Morad Auto Parts on EBAY (about $45 delivered). It had "98 GT" marked on it with a paint marker.

Boy was it filthy (forgot the "before" photo); here'* how it looks after soaking in a 5-gallon bucket full of gasoline for two full days:



Still not really clean, but good enough to start working on. Some very slight pitting, but no cracks or warpage.
(Luckily, I have an ancient British Seagull kicker to burn the nasty soak gas in--that motor would run on liquid pig turds.)

Here'* a close up of one of the funky-looking ports on the L36 LIM:


You know, I swear this port is not as small as the ports I saw on the LIM on my Mother-in-Law'* '98 Oldsmobile 88. Maybe differences in casting numbers? Maybe Pontiac LIM'* are lot-selected?

In any case, there is room for improvement; here is a port where the LIM gasket has been overlayed, and the space between the port and the gasket hole marked with a Sharpie:


To match this up to the head port, I calculate that the upper right, upper left, and lower left corners need to be reamed out, and about 1/16" removed from the upper and lower sections of the left side, and about 1/32" removed from the upper right side section ("left" "right" "up" and "down" relative to the photo, not the installed LIM ) I plan not to do any reaming on the lower right corner, where the injector fits into the intake. Then the whole port perimeter needs a slight chamfer. At that point I'll have a roughly rectangular port (except for that semi-circle near the injector port), about 1-7/8" high by 7/8" wide, with a "ledge" about 1/16" wide all the way around inside the gasket hole, with no rough edges or burrs.

Practicing with various Dremel bits on a hunk of cast aluminum I found out in the shed, I found that this carbide bit should do a good job of removing material while being controllable at 15k rpm:


To be continued...
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Old 02-16-2007, 06:43 AM   #2
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Andy... try the standard sanding drums as well. They are easy to control and remove material nicely.
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Old 02-16-2007, 09:14 AM   #3
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Use the carbide bits with the rounded (raduised) ends. They're less prone to gouging.

Don't get greedy on the L36 manifold. Port no larger than the head port size (0.9 x 1.9), and don't change the shape of the inside of the injector boss.

Don't modify the size of the INLET to the runner from the UIM either. The UIM actually rests down INSIDE the inlet to each runner.

Results have been good so far on this, but haven't been tested beyond the 'butt dyno'.
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Old 02-16-2007, 11:38 AM   #4
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I will take the advice about the rounded end bits...I was playing on the scrap hunk of aluminum last night and found out what a slip can do...

I don't plan to do anything with the injector boss, or the inlet from the UIM. I won't go more than about 1/4" into the port, because of the way the water jackets butt up against the runners. I also don't plan to polish or smooth out the insides of the runners...in fact, I plan to go over the ground away areas inside the runner with a sanding drum so as to purposely "rough up" the surface.

As for testing, I got a GTech RR. I know it'* not a dyno, but it should certainly be more quantified than the "butt dyno." And, it'* cheaper than dozens of runs on a real dyno. And, if I find that it simply doesn't give reproducible results, I can sell it on EBAY.

I plan to do the LIM gaskets (GM aluminums) on the 98 LeSabre this weekend. I will be reinstalling my original unmodified LIM, so that I can get some fair and honest baseline GTech data. A few weeks down the road I'll swap in the ported LIM and compare.
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Old 02-16-2007, 11:57 AM   #5
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Quote:
Originally Posted by agrazela
I also don't plan to polish or smooth out the insides of the runners...in fact, I plan to go over the ground away areas inside the runner with a sanding drum so as to purposely "rough up" the surface.
Roughing up isn't necessary. In a carb'd or TBI engine yes, but in a MPFI or SFI engine, the fuel is atomized close enough to the valve that you don't need to induce turbulance for mixing purposes.
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Old 02-16-2007, 01:11 PM   #6
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Forget the Gtech. I've owned two (including the current RR, and a Gtech Pro Comp that I used for 2 years than flashed to the RR code) and used 3.

Your inconsistency from run to run will tell you absolutely nothing about the performance of your car, even with 100 runs averaged.

The only useful data you can get from your Gtech RR is at what rpm'* your car shifts, and at what rpm'* your torque and horsepower PEAK at. NOT the actual value of hp and torque.

My advice to you is to not even attempt to characterize your results with a Gtech, as it'll more than likely skew your results far negative or positive from your expected results.
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Old 02-16-2007, 01:47 PM   #7
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Quote:
Originally Posted by willwren
Your inconsistency from run to run will tell you absolutely nothing about the performance of your car, even with 100 runs averaged.
When you say "your" inconsistency...do you mean the driver'* inconsistency, the inconsistency of the test environment, or the GTech'* inconsistency?

Quote:
Originally Posted by willwren
The only useful data you can get from your Gtech RR is at what rpm'* your car shifts, and at what rpm'* your torque and horsepower PEAK at. NOT the actual value of hp and torque.
I don't expect actual crank or wheel hp and torque values, and the GTech doesn't promise such.
All I hope to be able to do is quantify differences in torque values and torque peak rpms "before" and "after" mods--even if the units for the data are "Gtech ft/lbs" rather than "Wheel ft/lbs" or "Crank ft/lbs". I expect that'* better than "butt dyno ft/lbs," which is what 99.999% of the "data" I see on forums is measured in

Short of shelling out for actual dynos, what would you all rather read in a thread regarding a performance mod: "it felt more powerful," or "it felt more powerful AND a few dozen before after runs on the GTech show me an average of X+/-Y higher ft lbs, peaking at XXXXrpm rather than YYYYrpm."?

Bear in mind, I'm no GTech fanboy...I've never even used one before. If the reproducibility of the data isn't good enough for me, then to EBAY it goes without qualm!

Quote:
Originally Posted by willwren
My advice to you is to not even attempt to characterize your results with a Gtech, as it'll more than likely skew your results far negative or positive from your expected results.
Please explain further...
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Old 02-16-2007, 02:07 PM   #8
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I am also very interested in this. So pretty much all that is happening is you are gasket matching the gaskets to the ports on the LIM. Also i am going to be putting a HV3 in soon, how much more work would it be to get the LIM off? Once i have the UIM off, all i do is unscrew the lim and it pulls off correct? And all i would need is the ported LIM and just LIM gaskets?
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Old 02-16-2007, 02:22 PM   #9
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TJ, I don't think he'* actually gasket matching. IIRC from the previous threads, you shouldn't exactly gasket match the LIM ports to the gasket, as the head intake ports are smaller than the gasket openings and you don't want inversion.

I'm sure someone will chime in to correct me if I'm wrong, but all I've read has lead me to this understanding.
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Old 02-16-2007, 02:23 PM   #10
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very good pict thank you im following this also i have a new doorman intake a need to change the lower gasket also and tell us how much time it take to change LIM thank you
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