Has anyone actually installed stiffer valve springs in the 4.5/4.9?
I saw fastjeff used the hi-po 2.8 V6 springs, but has anything else been tried?

How much work was it to get those springs in jeff?

Rockcrawl has some information on this topic at his site: http://www.fieroaddiction.com/caddy49h.html

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FierOmar

could you add shims to the bottom of the springs to increase the pressure?

I don't mean to step on your toes just want to give you some first hand advise.

When Becks car was completely stock with the turbo we would rev it up to 6000 rpm with out any valve float or complaints at all from the engine. The problem was that the car felt like it was slowing down, once it shifted we started accellerating. It all has to do with keeping the engine RPM within the productive torque and horsepower band. I changed the transmission shift govenor to shift at 5500 rpm gained just OVER 1/2 a sec in the 1/4. It does not pay to shift late with all engines. Now with all of our valve train modifications and porting we do shift it over 6200 rpm. We now have a 4T60 and I can adjust shift timing easily with the TV cable. IF I set up Becks car to shift at 4000 rpm with the turbo and everything she will run only 2 or 3 tenths slower. What I am saying is increasing your revs is not going to increase your overall performance. Bang for your buck would be porting the intake and head, there is days and days, I mean LONG days of porting required. Before you could begin benifit from higher rpm shifts. But maybe you already have and that is why you are asking these questions. Next I would go with the cam regrind and valve spring change but that is still not "easy" depending on how much lift. Ours has now a .500 lift with valve guide modifiaction, sbc duel coil springs, steel rocker support and roller rocker pedistals with modified rockers.

I hope this rambling helps.

Pete

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thanks for ANY info!

I am still learning a lot!

I will be using an allante lower intake manifold, and my custom upper intake which will be aimed toward mid-high rpm horsepower.
I was just wondering what else I could do without pulling the heads off. I am not ready for that yet. I will be getting plenty of air. I don't plan on messing with the exhaust manifolds much, except switching to some stainless ones I have to lose some weight. Will be using allante throttle body.

I read you can advance the timing 1-3 degrees to gain some hp without any harm. People on the caddy forums swear that this will give a more significant increase than bolt on intakes, or exhaust mods. What do you think? Somebody must have messed with this? 5-10 hp? Would you have to run higher octane fuel?

You'll have a hard time finding a spring with decent pressures that will fit without cutting the seats. Cutting the spring seats requires the heads come off. If you upgrade the springs you need to upgrade the rocker supports for strength. When you increase spring pressure you also increase friction on the rocker pivots, and increased friction equals lost power. How far do you want to go?

The stainless manifolds are not much lighter that the cast iron ones. I don't think I'd change them just for weight savings. They may have a performance advantage, but that's questionable, especially since they are from a smaller engine. I guess if you already have them in hand you can make your own decision.

You can advance the spark timing. More will require better fuel. You need to be careful because there is no knock sensor or spark retard to save your engine. You're not going to get 10 hp out of it unless it was set wrong from the beginning and you just switched to jet fuel. The things are pretty much on the edge from the factory, hence the service bulletin to retard the timing to compensate for poor fuel quality.