Dellortoes on 1776 flat spot, help!

Olson · Post by **Olson** » Tue May 13, 2008 2:18 am

Thanks for your help guys.

I'll try and get hold of some 30 or 32mm chokes and take it from there.

fortyeye · Post by **fortyeye** » Tue May 13, 2008 7:35 am

Bruce2 wrote:
Olson wrote:Heads are ported and polished CB performance heads with 44 and 38mm inlets and outlets, ....
This as your problem.
Whoever designed your combination didn't know what they were doing.

Good catch. The smaller venturis will get your airspeed up through the carbs and into the manifolds ... the charge will get lazy from that point on. Those valve sizes on anything but an all out engine of that size turning lots of rpms will tend to slow the intake charge. You have your work cut out for you in an attempt to reclaim low end response and tune out your flat spot.

Olson · Post by **Olson** » Tue May 13, 2008 8:27 am

So what size valves would be suit it better then?

fortyeye · Post by **fortyeye** » Tue May 13, 2008 9:11 am

Contact Darren at DRD [email protected]

http://www.drdracingheads.com/index.php

He can make some great combo recommendations.

Post by **FJCamper** » Tue May 13, 2008 9:46 am

Hi Olsen,

The rule of thumb is your venturi should be 2mm or so smaller than your intake valve on most race engine configurations.

Street use is more complex. The best arrangment is a planned size and smooth path from the car, through the manifold, to the head with no big changes anywhere along the way to upset the flow and velocity.

If smaller vents, 32's I'd say, don't tune you out right, you'll need heads with smaller intake valves.

I'd read your valve sizes earlier, and didn't say anything because I realize you have your heads in place, and you probably want to try the venturis (the easy change) first.

Good luck -- FJC

Bruce2 · Post by **Bruce2** » Tue May 13, 2008 11:38 pm

Olson wrote:So what size valves would be suit it better then?

40x35. Valves that size can produce up to 180hp. Your 1776 will never be close to that potential, so why go with valves that can make even more?
You can play around all you want with venturis, you will never get it to run well. Like Dave said, you can increase the air speed in the carb by using a smaller vent, but that won't help the air speed in the port and through the valve.

Olson · Post by **Olson** » Wed May 14, 2008 8:59 am

Thanks, I really appreciate all your advice, but the fact is I can't afford to shell out on new heads for this motor, so I am going to have to jet my way around the problem as much as possible.

Will keep you posted how I go.