Hi! New to the site and the GMs in general.

I have a 91 Brougham Caddy and a 95 Bonneville SSEI.

I was wondering why is the Bonneville lacking power over 5200 rpm ; it feels like it sputters until the shift point at 5800 rpm. Is it some kind of fuel pre-cutoff or theres something I should check out?

Car really doesn't lack power in general, has huge torque and all but doesn't like being over 5200 rpm. ( I just noticed it because I hardly ever kick it. Actually I never kickdown in first gear because with the smaller pulley it feels like everythings ripping off and you have to actually go somewhat fast to be over 5200 rpm in 2nd gear (yes, I'm not a car beater!))

I'm sure this question has been debated over and over but like I said, I'm new here!

Thanks a lot!

From what you've said, putting a smaller pulley on the supercharger without supporting mods is going to give you troubles. And did.

This is a typical characteristic of this engine. Long intake runners provide lots of velocity and as a result, lots of torque at low RPMs. However, those long runners are also smaller in diamter so that affects the overall flow, so your top end will suffer. That'* just how the engine is made. Its made to be a torquester, not a high revving screamer.

You can improve top end power with this motor, and believe me I went through every single possible way to get it done and only two things ever made a massive difference. First, porting the LIM to match the heads (did it with a dremel and cutting bit. Quick and dirty job but made a big difference), and second, porting the heads. I didn't really port so much as I just smoothed off casting imperfections that would cause turbulence and reduce flow. This was done with a dremel and grinding stones. I opened up the exhaust by a significant amount but kept the ports D-shaped. I have pictures of the work I did if you're interested.

It was such an improvement that my wife got in the car and said "wow, this feels just like the Bonneville." referring to the Bonneville GXP we had at the time with the 4.6 Northstar V8. That added airflow pushed me over to 92% injector duty. Big, big improvement. The engine grenaded shortly after from having overheated it 3 times in a California summer while chasing coolant leaks with 217k miles, and I had an L67 swapped in.

Previously, I had tried opening up the exhaust, cold air intake, roller rockers, and absolutely nothing made as much of a difference as porting the heads did. Anything else would be cost prohibitive as you'd be getting into engine swap costs that would allow you to drop in a Series 2 L67.

Like I said, I'm hardly EVER stepping on it, and never in first gear, and also, the smaller pulley doesn't bring me to the "danger" zone in the boost gauge, I didn't go monkey on the pulley size. Also, engine starts cold within 2 starter turns (generally 1) so I don't think somethings broken.

This however makes LOTS of sense! Also, could it be possible that I'm feeling some valve "float" at these RPMs?

OH and I said "'everythings ripping off" in the sense of "it just pulls too much and I believe it'* not good for any mechanical part to do it".

My suggestion to you: go back to the stock pulley size, pull the heads and port them. Yes you will need new head gaskets, bolts, LIM gaskets, and valve cover gaskets, but it will give you more reliable power. Don't put the smaller pulley back on till you've done this. The M62 is just a heat factory and boost is nothing but pressurized air not going anywhere. We have guys here putting down 400whp on 3800'* and getting less than 10psi of boost, while my stock L67 with nothing but headers and a few supporting mods pulls 12-14psi depending on the air. Its not about pressure, its about getting air moving, and the greater the pressure is, the greater the heat is, and the greater your chance of doing some bottom end damage.

Like I said, I have pictures if you want to see them. Its really not that complicated; there'* just two things you have to look out for.

1. Don't touch the valve seat.
2. Don't touch the inside of the valve guide.

All you're doing is smoothing imperfections on the intake ports and enlarging the exhaust ports a bit. You will feel the difference.

Dayum, and I threw the old pulley in the trash like a newb telling myself I'd never use it again XD

Anyhow, I know how we guys care about engines like if they were people and had emotions and you're probably somehow worried I'll kill it by abuse but don't worry, I hardly ever floor it and I drive like a real old man ( like really, really old man : I really appreciate my ride and try to make it as long as possible! Never go in the city as well ; I live in a rural area so I can be as slow as I want ).

I'm actually more worried I'll build up carbon than blow the engine by abuse :p

But for now, I'll never go past 5k and when I'll have some loose time I'll take out the head and port it. Is there anything I should do while the head is off? Originally, I'm a VW guy so I know general mechanic, but GM product is new to me ( and I bought 2 in a matter of months, strange how things are sometimes! )... but I'll have to say they're generally much easier to work on!

Also, I'll take pictures if you have em' ste_gars_la@hotmail.com

And for what it'* worth, thanks a lot my friend, I really appreciate your fast and knowledgeable answering!

Semi-related : Is this engine a real solid piece from which I can expect an excellent lifetime considering I take real good care of it and hardly ever beat it or I might consider swapping a northstar or a series II or III? I'm an electrotechnician so the electronical part of the swaps don't scare me much.

Replace any gaskets along the way. Supercharger gasket, lower intake manifold gasket, head gasket, head bolts (these are a must since they're TTY bolds). You'll be porting the heads, and you will also be porting the lower intake manifolds to match the heads. Do not gasket match as that will be too wide and you'll get some turbulence.

Once you pull the heads, check the pushrods for wear on each end. If there is wear, you'll know it. They aren't very expensive to replace. When you pull the lifters out, let them sit in kerosene. Take them apart piece by piece. Its very easy to do, and if they're stuck, then they're probably caught up with some carbon build up. Let me know when you're at that point and I can walk you through it. Check for any scratches on the roller of the lifter, and check for the spring pressure. They should all be the same. You'll be cleaning these before they go back in. This will ensure a noise-free valvetrain for many miles to come.

You'll also want to soak the rockers in kerosene. This will dissolve any carbon buildup. I recommend kerosene because its cheap, and its available at many gas stations at a separate pump off to the side somewhere.

Let me know when you're ready for this and I'll walk you through it. Its a pretty simple job though, the 3800 is extremely easy to work on.

With regard to longevity, we have a guy here (I forget the handle) who sent his bonneville to the junkyard last year because the subframe mount rusted out from under it. It was a 94 year I believe with the Series 1 3800. Engine had 454k miles last I remembered and ran perfectly. Don't over heat the engine, use a quality oil and more importantly a quality oil filter, and you should have no problems getting 500k miles out of it.

I'll send you the album that I have online with the pictures when I get home. My engine wasn't supercharged but the differences are very, very minor once you get the upper intake/supercharger off.

That'* some heavy info, thanks a lot pal!

I'll probably be doing this during my summer vacations so to have time to gather parts and knowledge ( and use my Caddy as the daily driver for that week! )

This obviously goes in a saved word file.

Good.

If you have any doubts, ask. I didn't have time to get you the pictures last night but I'll shoot you the album tonight if I can remember about it.