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LN3 vs Series I


Guest ensign83
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Guest ensign83

Are '91 pilots getting significantly better performance and MPG with a Series I 3800 than we older year LN3 pre-series motors, or is the difference negligible?

Also, if an LN3 dies, is it worth inserting a Series I, or does the electronic tranny make it not worth the effort?

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If you look at the specs, the 1991 should be a better performer, but I have never seen any actual comparison (drag strip?) I have owned both and I can tell you that some of the 1990's I have owned seemed to be better than others. My personal input is the 1991 does not get quite the mileage as the earlier cars. This may be just the final drive ratio. 88-90 cars have a 2.97 final drive and the 1991 has a 3.33 which should be a noticeable difference but the only thing I noticed the 91 tach is over 2000 rpm at 70 and the earlier car it is under.

The Reatta was not built as a "hot rod" so it was never called a sports car. I have read that the transmission was calibrated for smooth "luxury car" shifts and that may be one reason there are seldom transmission problems. There are "tweeks" that can make the Reatta preform better but most owners are quite happy with the cars "as is"

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Performance wise, I actually think the 88 feels "hotter". This can be ascribed to the more aggressive cam profile on the 88 engine. The 91 should be better (and appears that way on paper) as it has a few more HP and an improved intake manifold and exhaust. While the 91 is certainly not weak, it doesn't seem to jump off the line the way both my 88's do. I have two 91's and two 88's so making a subjective comparison is easy. Seems Buick chose to take the edge off after 88 in favor of making it more of a highway cruiser, and there's nothing wrong with that. Just different. I like both but seem to prefer slightly the 88's better acceleration from a dead stop or from lower speed (e.g. highway on ramp).

The 88's just have hotter acceleration. I say that based on feel, not on any real logged performance numbers. To me, peception from the from the drivers seat is what matters as I'm clearly not racing these cars.

I've test driven one 89 briefly, and it was a poorly running beater so not worthy of making a comparison. Never drove a 90 yet. Drove one car with a series one SC 3800 belonging to an associate and was noticeably diffferent from any year Reatta as would be expected.

As to fuel economy, again my 88's seem to win out. MPG's are marginally better than on either 91. All four of mine are well maintained drivers so condition shouldn't be a factor. All see the same general type of driving as well (heavy on city, minimal highaway miles).

Guess my general advice if changing the engine on an 88-90 model would be to source a good used or rebuilt 88 engine just for the more aggressive camshaft. For 91 stick with the stock powertrain unless you want to deal with PCM and tuning mods.

KDirk

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Guest ensign83

Thanks for the input.

I am a HUGE fan of the Series II 3800, but that is moot without the surgery that I've read about on here, and you may as well go SC then...

I like my LN3 fine, and i like soft, smooth shift patterns too. Had a '90 Trofeo with the LN3 and my Reatta seems faster seat-of-the-pants-wise. Just passed 150k miles, and I sure hope she runs a few more years of 370 mile per week commuting.

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I found the related engine power curves for the four years involved. Pretty easy to see why they feel different. There is no doubt in my mind that the identical curves for the 88-90 cannot be correct, but the 2000 rpm torque peak indicated matches what the FSM says for the '90. It would appear the '91 gearing was likely changed to better match the higher rpm torque band. From other information that I have seen posted by Padgett, the '91 cam is even milder that the '89/'90, maybe why the max hp.post-31580-143142913124_thumb.png rpm is higher for the early engines?

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Well now, that certainly puts the proof in the pudding. The difference 88 vs. 91 is quite remarkable when seen in graph form. It is clearly evident why the 88 feels so much more powerful in the lower end of the powerband.

I agree the 89 and 90 graphs cannot be correct, they are virtually identical to the obe presented for 88 and it is known that 88 was a one year only design on the cam shaft.

KDirk

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Yes, I thought the same thing. I want to do a little more research to find some evidence of difference between the first and second year availability. I know I installed an '88 cam in my '90 engine and it definitely pulls to a higher rpm. I know the heads will flow more at higher lift, like the '88 cam, by testing on my flow bench. Everywhere I have looked and posted on engine forums have come up empty. It is simply not possible that the two cams produce the same engine output. From evidence I have seen comparing acceleration rate vs power curve, maximum accel. rate is at the torque peak in any curve. Interesting that the 2000 rpm torque peak on the early graphs also coincides approx. with a 70ish mph cruise, but it is unclear if that is where the engine is most efficient under partial throttle, ie. vacuum.

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Need to look when home but think the cam profile was different for 88 but the area under the curve did not change much. The biggest difference this century is DOHC which allows VVTi&e. This permits really fat torque curves. (e.g. 90% of peak from 1600 to 6400 rpm and HP still climbing at redline.

What is just coming online is direct injection which allows near boosted diesel operation on 87 PON.

So while the 3800 in my Reattae is wonderful for eating long distances economically at a 2000 rpm/70 mph cruise (torque peak and amazing since the National Speed Limit was still 55 then), it is still a cam in block iron engine.

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I'm glad you chimed in Padgett. The curves for the early years shouldn't all match and I hope your resources are better than mine. Unless I have the only '88 cam with more lift and duration, especially at higher lifts, something is incorrect. I looked at the '87 LG3, which is the direct predecessor to the LN3, old style intake and heads, but roller cammed etc.. The curve looks essentially identical to the '88-'90 ones presented, but at a lower level, 150hp and 200 lb/ft.

I certainly agree that more modern tech. feels quite a bit different, but that old low rpm cruise is hard to beat for soothing, although lazy feeling by comparison.

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