CenturyUltra

I have an 89 Century Ultra I with a 454 MAG and Bravo I. I just bought stainless marine headers for it. I'm considering a Dart aluminum intake manifold and Holley 750 carb. What is the cfm of the stock carb.? Are these good/worthwhile modifications? Any estimates on speed/hp increase with these mods and the right prop? Any prop suggestions? Thanks.

ThirdBird

How coincidental, I'm thinking of trashing my '89 454 mag Rochesters for something new and I also don't know the original cfm numbers.

Any help out there?????????????

blue thunder

I believe the stock qjets were in the range of 750cfm.

No, the dart single plane won't help you in fact it will probably hurt. You need to be spinning above 5500rpm to get to that power. Your best bet would be an rpm performer or airgap intake. The holley 750 is a good choice.

I have a dart and 2 performer intakes to get rid of if you are interested. I thought the darts would work better, I was wrong.

bcfountain

my old 330 had a q-jet on it.750 or 780 i belive.still have it.as far as a econo carb goes,it is good.better than a holey.but the holley will make more power and is a hell of alot easy to work on,cheaper too.

Griff

The original Q jets are 750cfm. I highly doubt you will see any real increase in performance by changing intakes and carbs. If you also do a cam change, it would help a lot more.

ThirdBird

Thanks for the replies, 750 it is.

Ghostrider

If you've got an exhaust (stainless high-flow) such as CMI or even just a decent Stainless Marine Manifold set with good risers, you WILL benefit from a change and upgrade to a better intake package. Go for te Edelbrock Performer RPM Air-Gap intake manifold, anything else is just pissing into the wind. You will deffinately see benfits over the stock carb if you run and properly tune a Holley 750 DP Marine carb. To make the most of your changes, ideally you'd want to look at an upgraded cam package but in the mean time, check and make sure your ignition is up to scratch. Run a set of MSD 8.5mm wires and a Blaster 2 / 3 coil, check and confirm you actual timing and you will Feel the difference.

Don't bother with the Dart manifold or Standard Performer manifold. Make sure you get your carb properly set up to match your new intake and exhaust.

I suppose the question of Speed increase expected and Prop selection is rather dependant on which package you choose but without getting a cam to make the most of your changes, I'll say around + 3 - 5mph at best, but it will be faster and more fun getting there!

Good luck!

Griff

1-3mph with the intake, carb, exhaust.
4-6mph with the cam change plus above.