Better performance : Differential or new carburator?

Hi, I need your advice! I've got a 351W in my 89 Crown Victoria (police). I find the accelerating too slow from a stop, but there is a lot of power at
high speeds. At 140KM/h (85mph?), the RPM is only at 2000. I tought about changing the differential ratio (3.75), sacrifying speed for performance. Of course, the differential locking mechanism would be rebuilt (clutches and discs) because it slips too much on winter.
The second option would be to replace my stock carb for a 4 barrels & intake. So, the RPM will stay low on Overdrive at higher speeds. I sometimes go on the highway, but more city driving. For the same price, wich one of the 2 modifications would give me the best performance from a complete stop, thinking about gaz mileage.
I already changed my exhaust system for 2.5" in dual exaust with headers, so this should not be restricting performance.
-- Jérémie Bédard Come see my car! http://www.cardomain.com/id/korn_ice
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You hit the nail in the sentence, "I find the accelerating too slow from a stop, but there is a lot of power at high speeds... " That's the tipoff for need for gears... of course, then you'll want the 4 bbl anyway.. but the increase in CFM <potential> will make no difference until you get the rpm's up. If you dont have the intake cycles resulting from RPM, the air doesnt flow. But if I were you, I'd go for something around 3.3:1, becuase you are now a lot lower than that .. I bet your current ratio is around 2.7 something. The higher the rpm, lower the gas economy.
Remember it's a combination of rear gears, lower trans gears and converter stall speed.

about
and
so
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In city driving, the motor will force less from a stop, so the fuel economy should be better?
The ideal would be to change the overdrive gear in the trans, but it's too complicated!

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I wouldn't expect much increase in fuel mileage from the gear swap. 3.50:1 is a nice all around ratio, you will feel it more than 3.23:1 from what you're at now. The overdrive trans ought to keep your mileage good on the highway (still ought to be better than if you had no overdrive).
A carb and intake upgrade _could_ increase fuel mileage over a 2 barrel. If the new carbs primaries are smaller than the 2 barrel or you get a spreadbore (like the old QuadraJets) and you keep the CFM fairly low you could increase mileage all around. It must be a vacuum secondary carb though (you know that), as a double pumper will just kill mileage. A new intake is likely be more efficient than the stock one as well.
Either way, gears are always the best *bang* for the buck. Don't go too high though or you'll regret it, especially if that 351 you've got is tame and doesn't rev real high. That's where you're new carb and intake may help. :)
Jérémie Bédard wrote:

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.