Hello everybody,

I have a 1990 Bonneville I have had for about a year now, I bought it with only 50,000 miles on it put on by an old man, I have put on 20,000 miles. The car has performed flawlessly, and I use all sythetic fluids. But now I am looking to get a little more pep out of the engine. I put on a new oxygen sensor, cat. convertor, and the spark plugs still look new but are nothing fancy. I hope to get about 150,000 MORE miles out of this car, so I don't want to do anything that will hurt the durability of the engine. Is there any intake work, different heads, or other swaps from newer 3800 engines that would help? I am not looking to spend as much as it would take to add a supercharger and make all the necessary changes. I just want my engine to be closer to my girlfriend'* series II engine if possible.

Thanks!

Been said before but the "C" engine is pretty much optomised the way it is - no one thing is going to make a big gain. The major limit is the cam which is pretty ded in keeping with a national 55 mph speed limit when new: is designed for max torque between about 1800 and 2200 rpm. This means that even though the car is quite quick (my '88 "C" 3800 turns 0-60 in 8.4 seconds according to the G-Tech Pro), it does not feel like it - acceleration is constant rather than increasing with RPM and is quite deceptive.

That said the air cleaner is marginal for the engine so there can be some gain there and many of the rear exhaust manifolds (where it connects to the head pipe at the O2 sensor) have a really ragged and restrictive opening.

The Magnavox ignition (single coilpack) is also not as strong as the later Delco triple coil for the "L" 3800 is also a bolt-in.

The next step is really a 1991-1994 "L" 3800 which is a simple swap (can use the stock ECM) and though only rated at 5 hp more has both the intake and exhaust opened up considerably. Cam is still quite mild and shouldn't overstress the stock transmission.

"I think as far as the Vin C engine goes it makes all of its 165 HP at 4400 Rpms, where as the Vin K makes all of its 205 HP at 5200 rpms"

This is purely a function of the torque curve - the "C" is producing 196 lb-ft of torque at 4400 rpm while the "K" is producing 207 lb-ft at 5200. That is only 11 lb-ft more (~5%) but at 800 higher RPM. (HP=Torque*RPM/5252). Usually the price of a higher torque peak (before VVT) is less on the bottom end.

Occasionally Avis gives me a LeSabre and the new ones at 3567 lbs are about the same as the '90 Bonne. While the N/A LeSabre seems to give better MPG than our '90 SE, it does not feel as quick by my perception.

I find both old (Vin C) and newer (Series II) NA 3800'* to be lacking on the top end. You start out rather nicely until past 3000, and then its like you hit a brick wall

Especially on the butt-dyno, but that can lie

I find all three of mine (88 C, 90 C, 92 L) are strong to about 4500 and strain after that. This fits with the N/A 3800 really being a torque engine rather than a winder.

Torque peaks in the normal driving speed range of 1600-2200 rpm and is very falt out to about 4000 rpm but there is a price to be paid for smooth running in o/d lockup at 1300 rpm/45 mph and that is in the (lack of a) top end.

To accomplish this, the 3800 has a very mild cam with less than 200 degrees duration on the intake. Of course one side effect of a very mild cam is extreme logetivity, particularly after the oil pump and flow were "improved" for the "L" engine.

The "L" engine really has a lot more to work with, probably in anticipation of the */C version, the "C" is pretty much limited by its intake and exhaust.

It'* the gearing, guys. My car pulls the same at 4500rpm in 1st, as it does at 2000rpm. But in second there is a noticable difference from 2000rpm to 4500rpm. But repin, that is a perfect explaination.. "it'* like you hit a brick wall."


-justin

Thanks for the input. I will have to check on my gearing, I know that it won't handle a hill at 55mph because the rpms are just at 1500. I just got back from a long trip, did 80 mph the whole way and the car loved it, finally kept it speed on all the hills at around 2100 rpm and it also gets the best gas mileage there, around 30 compared to only about 28 if I do 70 mph. I guess the biggest reason the car feels slow is because it doesn't really like to rev compared to the series II 3800. Speed limits around here are 55, so with the rpm so low, my car feels really slow, I need to push it a bit and get it to downshift if I want to pass or anything.

I really got used to having a chevy 350, add a cam and a carb with some decent exahust and pick up some HP relatively easy. I can see it isn't the same game with a V6 car, thats ok, it has been super dependable!

An L67 swap of course!

Honestly I wouln't really touch the engine. Maybe an intake and a tune up, and possible open the exhaust A LITTLE, but really in the long run I don't think you're gonna add a lot of power unless you do a lot of work, so I would just keep it in good running order and drive it until it dies (which should be a LONG LONG time).

Shawn

Just for fun I ordered an extra throttle body (I think thats what it should be called). I figured the extra sensors and everything on there had to be worth the $5 the auction ended for. Is there any kind of trick I can do with this, porting it out some, working with some of the ports on there, anything like that? If nothing will add power I may just polish the outside for the fun of it and throw it on there, but if I can do anything on the inside of it to add a little performance, that would be great.

Thanks!

There is the TPS sensor mod, where you adjust the TPS sensor so it has 4.35 volts [no more] at WOT, and .70 [is that correct?] at idle. Helps with throttle response and such. I did it to my car, and I brake torqued to 3k, let off the brake, and did a nice two wheel peel out after that [with the upgraded ignition too]. So, it'* a great improvement IMO. There is a thread here, on how to do it, search around for "TPS sensor mod" or "TPS Sensor"


-justin