What should I do about Darwin's Carb?

Darwinskeeper

Frequent Racer
Sep 18, 2005
586
0
16
Wichita, Kansas
I'm planning to take Darwin off the road pretty soon to swap the current cam with a milder one -- Either a Comp 240H (192/200 [email protected]; .390/.390 lift; 108 sep) or a Crower Level 1 (182/190 [email protected]; .386/.387 lift; 114 sep) along with a few other things. Since I'll have to retun the carb anyways, I'm wondering if I should just go ahead and swap the current 465cfm 4160 with a smaller 390cfm carb.

My understanding is that the traditional cfm calculations yield the following:

Needed CFM = (262cuin X 5500rpm)/3456 = 417cfm

%Eff = 390/417 = .935 = 93.5%

I have been told that a mildly warmed over engine (like Darwin's) should have an efficiency in the 85-90% range, thus a 390cfm 4160 would be perfect. Is there anything I'm missing?

What should I expect to gain by going down from a 465cfm Holley to a 390cfm Holley?

Thanks,

Darwin's Keeper
 

80ECLT

MalibuRacing Junkie
Nov 21, 2006
3,927
0
0
Sheboygan Falls, Wisconsin
You know what I am going to say about that!










390.
 

guitargoalie

Amateur Racer
Nov 15, 2005
299
0
0
Central Mass
I would honestly go with a Q-jet.

When I went from the 390CFM holley to a stock Q-jet of a 79 305 I gained 5 miles to the gallon on a 267 I had in my Monte Carlo.

A q-jet really is poor mans fuel injection, just a much finer fuel metering system.
 

Darwinskeeper

Frequent Racer
Thread starter
Sep 18, 2005
586
0
16
Wichita, Kansas
guitargoalie,

Thanks for the suggestion. While the Q-jet would be the hot setup for an mpg motor the problem I have a healthy fear of the Quadrajet's complexity. Lets face it, its several orders of magnitude more difficult to tune than a Holley.

Also, we six cylinder types have a harder time finding Q-jet friendly manifolds. Where variety of aftermarket spread bore manifolds exist for most of GM's V8 offerings, I have only found 2 spread bore manifolds for the 4.3, the GM factory manifold used on early Chevy truck 4.3 instls (in '85 & '86) and a pair of marine manifolds (one for pre 96 non Vortec heads & one for 96 & later Vortecs). Unfortunately both of them are cast iron, which I'd rather avoid. I'm using a Flaming River 20:1 manual box and would rather avoid adding weight to the nose when possible.
 
A

Anonymous

Guest
What was the smallest q-jet available?

I know the one from 85 86 is for the ccc.

Trickbu
 

T5MalibuWagon

Dragway Regular
Sep 27, 2004
1,386
0
0
Fort Worthless TEXAS!
What about one of the holley q-jet replacements?
 

Darwinskeeper

Frequent Racer
Thread starter
Sep 18, 2005
586
0
16
Wichita, Kansas
T5MalibuWagon

Are you talking about the 4165/4175 spread bore series or the 4360 Economaster? Unfortunately, they are both spread bore carburetors and the only spread bore manifolds I can find are cast iron. One of the main reasons that I'm running a six is that I'm using manual steering and I wanted as little weight on the nose as possible.
 

T5MalibuWagon

Dragway Regular
Sep 27, 2004
1,386
0
0
Fort Worthless TEXAS!
Darwinskeeper said:
T5MalibuWagon

Are you talking about the 4165/4175 spread bore series or the 4360 Economaster? Unfortunately, they are both spread bore carburetors and the only spread bore manifolds I can find are cast iron. One of the main reasons that I'm running a six is that I'm using manual steering and I wanted as little weight on the nose as possible.

Ya I am going to run a 4165 so I know that they are spread bore, but I was thinking that all you would have to do is get an adapter. If you want the small primaries of a q-jet and the simplicity of a holley you might think about one?
 

Darwinskeeper

Frequent Racer
Thread starter
Sep 18, 2005
586
0
16
Wichita, Kansas
The problem with an adapter is that it must be a minimum of 1.50in thick to work and I'm not sure I could continue running a flat hood with that.
 

Jordan81

Pro Stocker
Feb 10, 2004
1,774
0
0
wichita, ks
what side of town do you live on? i'm trying to think if i have ever seen your car... i just now noticed your from wichita so i thought i would ask. also, are you on WR?
 

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