Holley Carbs - some thought..

[mike@thenook]

Bored with the rain today I started thinking again about the Holley and decided to read up heaps of information on the Holley website about Holley's tuning and so on plus some other stuff on u-tube. This isn't incidentally because my Stromberg's don't work properly, they do but I guess there's always this desire to fiddle with the car and see if it can be improved.

The one thing that has confused me a little is that my Holley and I think most people that have them fitted to the Stag is a 390 CFM (originally bought from Tony) but inputting the various elements of Stag engine size (3000cc or 184 cubic inch) and max revs they come up with a 570 CFM carb, which is a deal bigger than the 390.

Just wondering then if anyone has ever fitted a 570 CFM?

See this link:

https://www.holley.com/products/fuel.../parts/0-85570

My initial thoughts was it may be just a bit too big but it is what Holley seem to think is right..

Any ideas..?

[flying farmer]

I think the sizing is based on 100% volumetric efficiency.

2 valve per cylinder engines struggle to make 100bhp per litre even in race tune. I read somewhere that the Cosworth DFV ran at 125%, but that gave about 200bhp/litre.

I doubt the standard Stag engine makes more than 50% which means the required carb size would be nearer 300cfm, meaning even a 390 is nearly a third too big.

[trunt]

And if you find a calculator that is not trying to sell you something.. it comes out a lot lower!!

http://4secondsflat.com/Carb_CFM_Calculator.html

is one, but I tried 3 and they all came out under 300 for a stock type engine.

[mike@thenook]

Thanks for that guys and yes, I remember Neil you coming up with some similar figures before in your past work;
Hows the lastest project coming along by the way, have I missed anything - hope not.....
Interesting link Trunt, glad I didn’t pitch in for another and bigger Holley!

[flying farmer]

Hopefully I will have it on the rolling road within the next month.

I had a bit of a set back with several scuffed cam buckets in the left head, so i have had to fit a new set and run it in again. Existing air filter and inlet pipe needs to be enlarged as I am dropping to 96% of atmospheric pressure by peak torque revs.
Neil

[Phil S]

Mike,
years ago I fitted a holly to my 3.5 range rover, at the time holly had just released a 350cfm carb and this was apparently designed for the rover.
possibly worth a look.
Phil

[mike@thenook]

Hopefully I will have it on the rolling road within the next month.

I had a bit of a set back with several scuffed cam buckets in the left head, so i have had to fit a new set and run it in again. Existing air filter and inlet pipe needs to be enlarged as I am dropping to 96% of atmospheric pressure by peak torque revs.
Neil

Bad luck on that Neil,

Looking forward to seeing the results of the finished job!

[mike@thenook]

Mike,
years ago I fitted a holly to my 3.5 range rover, at the time holly had just released a 350cfm carb and this was apparently designed for the rover.
possibly worth a look.
Phil

Thanks for that Phil;

The smallest they do now is the 390 (which mine is) 350 would be the same as the stromberg's in any case.....

Cheers