My 4.9 already runs good but I would like suggestions to improve its performance without opening it up.

Should I get new spark plug wires? AC Delco, Bosch? Which brand of spark plugs are best for this motor? I'm open to all suggestions.

Personally I would recommend sticking with the original equipment plugs and wires if you haven't modified the heck out of the engine. Unless your running a turbo, NOS or something that changes the operating parameters of the engine, the factory specified plugs will work best.

Not much you can do to a 4.9 without getting into major bucks. Rockcrawl and the guys on the 4.9 yahoo list might have some input for you.

If you have a couple hundred bucks lying around you could always put a small dose of nitrous on it. Nothing crazy, maybe a 50 shot. Should liven it up alittle.

There is basically no aftermarket for this motor. A tune up will make it run better, better fuel economy but no noticable hp increace.

If you were willing to pull the heads, thats where the hp bottleneck lies. Small valves, especially the exhaust, weak springs, small ports, small manifold. Not the best for hp performance. And not to mention a desil like cam.

So the easiest most noticable hp increace is nitrous or you will need to spend alot of money porting stuff out.

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86SE 5 speed
85GT 4.9 isuzu 5 speed
https://www.fiero.nl/forum/Forum1/HTML/027839.html

Check the HER86GT string on General Chat.

Pete is really building a 4.9 and if he can't help you, nobody can.

Unless it runs poorly now, you won't notice any performance gains by replacing plugs and wires. If it's '93 or newer it should have AC Delco 41-902 double platinum plugs in it, they are good for 100k miles or so. They are like $6-8 each but you will probably never need to replace them. If you want a little more power I can bump up the spark advance at WOT. You can try advancing the distributor a few degrees, but you'll likely get spark knock around 2000 rpm if you go above the factory setting of 10 degrees at the distributor. It depends on the fuel you use and the condition of the engine. You should be running 91 octane or greater, but some 4.9s will settle for 87 or 89 depending on conditions.

We found an off the line torque increase with an upper intake change/extention like this. Made by Rockcrawl, we tested it for him.

Thanks guys for the suggestions. However, I'm not opening the engine to massage the internals , nor am I going to use N2O. I just want to do things that will give me the optimal perfprmance from a stock setup. I mentioned spark plugs and wires because the engine is from a 92 Deville and even though it runs great I have no way of knowing when the plugs and/or wires were last changed.

So I want to be sure everything operating correctly.

For about $200. you can put on an Alante intake. It's good for 20HP. For $30. you can change the valve springs to the Fiero 2.8 springs. That will give you a little more revs. For $395. you can get an aluminum flywheel. It will let the car pull through the RPM's much quicker.

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Captain Midnight

Maybe this is more like what you have in mind:

Summit # PNX-D800
Black Cap (Red & Blue avail)
Pertonix Flame Thrower tuneup kit
50,000 volt coil & module
alkyd cap & rotot
adjustable vacum advance cannister
high performance advance kit
wiring harness
capacitor
hardware
#PNX-D800 Chevy/Cadillac v8 $119.95

quote you can change the valve springs to the Fiero 2.8 springs.

Well you can but that's not the full story. The recommended springs are not stock 2.8 springs. They are GM Performance Parts replacement springs for a small block Chevy. They just happen to be listed in the 60* V6 section of the catalog also. They are available in a set of 16, pn 12495495 or individually, pn 330585.

PNX-D800 won't fit a 4.9. The cap will have the wrong screws, module won't fit, and the rest of the stuff is just unusable. About the only part of the kit that would work is the coil, and they sell that for $40.

Rockcrawl, do you think I will see a noticeable improvement in performance by changing to that coil with everything else being stock?

In other words is it worth it by itself?

nope. I put one in my Formula along with a Holley module. Noticed no difference at all.

Thanks Rockcrawl. I changed my O2 sensor and the car got stronger pulling noticebly harder than before.
I also changed the oil and filter using Mobile 1 so that could be why it's running stronger.

[This message has been edited by Mastermind (edited 10-05-2003).]

Will a flowmaster muffler and or a true dual setup give me noticeable improvement in performance?

Will I see noticeable performance improvement if I get rid of the stock air filter setup and go with a K&N ran to the side scoop?

take out the air filter :-) thats good for a few horsies. if you really want the hp numbers get some yellow stickers and some 8-inch folger cans. lol j/k.

quote Originally posted by TaurusThug: take out the air filter :-) thats good for a few horsies. if you really want the hp numbers get some yellow stickers and some 8-inch folger cans. lol j/k.

Yeah, I was thinking of using panty hose in place of the air filter.

do they make better headers for the 4.9?

I usually go intake, exhaust, headers, and maybe a bigger throttle body if there is one, with whatever car it is.

how bout performance chips?

hey rockcrawl, how much were those valve springs you listed, do you remember? also what machining needs to be done to make them fit?