Carb Sizing

[onefastmustang]

So I got a 770 carb for free today.. A guy I know has a bunch of old crap lying about his garage and there was one on the shelf. Funny thing about is the surface is really bumpy.. Is that a sign of something bad happened to it??

[mrmustang]

Originally Posted by onefastmustang

So I got a 770 carb for free today.. A guy I know has a bunch of old crap lying about his garage and there was one on the shelf. Funny thing about is the surface is really bumpy.. Is that a sign of something bad happened to it??

Forget the freebie as it's worth as much as you have into it. I suggest a Holley 04777C 650cfm DB. I further suggest a Moroso 1:1 secondary linkage kit followed by some time on a chassis dyno to propery tune and jet it for your engine. When it comes to carbs bigger is not always better. Enough said.

Bill S.

[jwd]

Originally Posted by mrmustang

Forget the freebie as it's worth as much as you have into it. I suggest a Holley 04777C 650cfm DB. I further suggest a Moroso 1:1 secondary linkage kit followed by some time on a chassis dyno to propery tune and jet it for your engine. When it comes to carbs bigger is not always better. Enough said.

Bill S.

While the Holley double pumpers make great HP at the track and on the dyno., they really suck on the street because of their air bleeds and PVCR's. Without MAJOR mods., they run too rich. A 770 SA is a much better street carb. and with vac. secondaries, it's not too large and very easy to tune correctly. But, I only have 40 years tuning Holley's. Enough said!

[mrmustang]

Originally Posted by jwd

But, I only have 40 years tuning Holley's. Enough said!

I had 20+ years of personal Holley tuning and thought I knew it all. Of course that was before I got unlimited access to a computerized chassis dyno that not only gave me air/fuel ratio, but access to real world rear wheel data across the RPM spectrum. Not only wide open throttle tuning and at idle, but a way to access a specific rpm and allow the dyno to hold that rpm for any given amount of time to get a fell for each engine and it's inherent quirks. The chassis dyno really gave me a wake up call and made me change the way I tuned a carb for street, track, or a mixture of the two. Feel free to come to NJ and I'll give you a chance to tune any carb on a specific engine (say a 351W/392hp Ford Crate engine) your way. Then I'll put the car on the dyno and tune it my way and we'll see who has better performance and driveability across the entire spectrum.....Again, without the experience of using the dyno, my eyes would not have been opened to just how wrong 70% of the carb tuners were at that time.

Bill S.

[jwd]

Originally Posted by mrmustang

I had 20+ years of personal Holley tuning and thought I knew it all. Of course that was before I got unlimited access to a computerized chassis dyno that not only gave me air/fuel ratio, but access to real world rear wheel data across the RPM spectrum. Not only wide open throttle tuning and at idle, but a way to access a specific rpm and allow the dyno to hold that rpm for any given amount of time to get a fell for each engine and it's inherent quirks. The chassis dyno really gave me a wake up call and made me change the way I tuned a carb for street, track, or a mixture of the two. Feel free to come to NJ and I'll give you a chance to tune any carb on a specific engine (say a 351W/392hp Ford Crate engine) your way. Then I'll put the car on the dyno and tune it my way and we'll see who has better performance and driveability across the entire spectrum.....Again, without the experience of using the dyno, my eyes would not have been opened to just how wrong 70% of the carb tuners were at that time.

Bill S.

With all that knowledge, how can you possibly recommend a DP for a street driven car. I too use real time info. (through a wide band reader ,on the street, under real life conditions). I hate to get into these threads as everyone is a know-it-all. My suggestion is to get an Innovate reader and go for a ride on the street where the real world is, not on a chassis dyno. Do whatever you want and I'll do the same.

[mrmustang]

Originally Posted by jwd

With all that knowledge, how can you possibly recommend a DP for a street driven car. I too use real time info. (through a wide band reader ,on the street, under real life conditions). I hate to get into these threads as everyone is a know-it-all. Do whatever you want and I'll do the same.

That works for me. Again, feel free to take any one of your cars to a shop with a computerized chassis dyno and your eyes will also be opened (I'm telling you as a guy who fought the results for over a year before taking the same challenge I posted to you). As for a DB on the street, when jetted and tuned properly, I actually get better gas mileage, crispness of throttle, and performance out of the (current offered and not 10 year old) "Double Pumper" vs the "Street Avenger" series carbs. Again the trick is to properly tune it using the best available methods out there.

Bill S.