1998 Cadillac STS

[Jason15036]

Hey guys, hope all is well. I seem to have a little issue with my Caddy. I have noticed lately that if i put the shifter in 1st and floor it and then let off before it shifts that I feel a clunk in the front end. It feels like the motor has play with heavy amonts of torque. Also if im cruising at highway speeds and I give it a little load that the car vibrates, and when I let off the gas it goes away. Do you think this could be a bad motormount. I noticed that when I was changing my passenger side cv joint that the rubber on the mount was falling out and gone. Could this be the culprit. I haven't checked the other ones. Also where are all the motor mounts located because unlike my old Caddy this one doesn't have the dogbones (torque braces) in the front. So what stops the motor from shifting back underload. Do you think the mounts could be the problem or is it something else. Any help would be grealty appreciated.

Also I have another topic. I love my CADDY alot but I just want to make it faster and then I would be really satisfied. Do you think if I had the heads pulled and had them ported and polished and put a bigger throttle body on and put the corsa exhaust on that I would be looking at any effecient gains. How much extra horsepower would this give me. Any knowledge would be great. What do you think Scotty would it give me more power on a Northstar.

Thanks Guys, Jason

[KHE]

You may have a failed motor mount. Have someone watch the engine while you crowd the throttle in fowrard and reverse and see if the engine moves excessively. If it does, a motor mount has failed.

To comment on your question about gaining more HP from the Northstar, it is already producing over 1 HP per cubic inch. All the easy methods to gain horsepower were done at the factory. A larger throttle body won't make any difference so I'd save your money. Two things that will make additional HP are exhaust and a higher stall torque converter.

[Jason15036]

does anyone have anymore info on the play I have in the motor.

[jhall]

Jason,

Been down this same road with my '97 Deville (and also a '95). Sounds like the front mount pooped.

If it's a hydraulic mount and the fluid is gone, it will still hold the engine at torque, but will flop back into place (no dampening from the fluid) and cause the "clunk" you describe. It can also allow vibration to be transmitted from the motor to the body which may be what you're feeling when you add a little more throttle while cruising.

The dogbones will help hold the engine in place, but loosing the stiffness of the main mount adds pressure to the dog bones and they will eventually loose their bushings.

[Scotty]

As Kevin noted:

The NS is already producing over 1 HP per cubic inch. Two things that will make additional HP are exhaust and a higher stall torque converter.

See posts by MARK99STS. He has put a lot of time, effort and money into developing his NS. He made a statement that he is getting about 350 HP.

Here are a few links:

http://caddyinfo.ipbhost.com/index.php?showuser=158

http://www.markonemtg.com/marks99sts/index.html

[MARK 99STS]

Jason,

See my post I just put up on the dyno results.

The best bang for the buck is:

1) open exhaust(Corsa adds 20 Hp)

2) cold air induction (a lot of controversy on this but works very well in conjuction with the Corsa)

3) high stall torque converter. This really dosen't add HP, but puts you into the power band quicker which is just like adding HP

4) Limited slip differential to reduce wheel spin. If you go for the converter, you might as well put in the LSD while you have the tranny out.

I also have an 80mm TB and had the exhaust side of the heads ported.

Don't waste your time or money on the heads or TB unless you plan on gettig rid of the crossover pipe as this is the choke point of the motor.

I will not realize my 30HP gain from the heads until I turbo charge it and replace the existing exhaust from the CAT forward.

[Jason15036]

Thanks for the info everyone, Hey mark did you really feel a differance from the corsa exhaust, and do you think it would help more if I removed the cat or put a highflow one in.

Jason

[MARK 99STS]

Jason,

I could definetly feel the difference when I put the Corsa on. 20 HP is something you can feel, not just measure. Regarding a high flow cat, I'm not sure about that. It should flow better, but it would probably be louder. The real restriction after you put the Corsa on is the crossover pipe that runs from the front bank under the motor and over the tranny.

[CadiKing]

Hey Mark,

I am on my Second motor mount going for Three.

BBob always recommended WOT's to keep things well.

Well, what I found is, the front motor mount cannot take repeated

WOT's. What did you use for a front mount? I thought you mentioned

a billet mount...I need to order third mount, don't want to have to d it

again...It's a PIA job!

nive job on your Caddy,

thanks

[MARK 99STS]

Cadiking,

Man, I don't know what to tell you. I can't believe you are going thru motor mounts. I drive mine WOT every time I get behind the wheel to the point of abuse and no problems with motor mounts. I have the stock mount in mine. I do only have 56,000 miles on my car, so that may make a difference, but if the mount is new it should last a long time unless there is something else wrong putting extra stress on that mount. Have you checked the tranny brackets that connect to the motor to make sure all are tight and not broken?