Page 1 of 1 1
Topic Options
Rate This Topic
#46805 - 01/14/09 02:06 PM Why isn't a 390cfm carb good for a 250 motor?
Freds Garage Offline
Active BB Member


Registered: 03/14/06
Posts: 164
Loc: San Leandro, Ca.
Just got my 12 Port News and I read that the Holley 390cfm is NOT the good choice for my inline 250 Late Chevy? huh? Instead it suggest that a 600/650 is a better choice. What?

Everything I have read says do not overcarburate your motor unless it is pure race.

My street 250 will have mild cam, offy four barrel manifold and some sort of headers, coupled with an HEI ignition. Do I need more carb for this?
CAN Somebody please SPLAIN to me why this carb is not recommended for this engine?
_________________________
James
Fred's Garage, Bay Area, California
65 Nova Coupe 250-Four speed

Top
#46806 - 01/14/09 05:30 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Freds Garage]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
I personally liked an old 400 CFM Carter AFB carb I ran for a while.

Does the 12 port news state why a 390 Holley it is not a good choice? If not,why? Look into where they got there info from.
Maybe it's something new? New findings?

I ran 3 48 MM side draft Webers (3 two barrels)approx 1100 CFM,you would think it was over carbed, but it ran great!

4 BBL is a different animal,I never got good results w/a 600 vacuum Holley,ran better w/a 600 DP.

I ran both 625 AVS & 625 AFB Carter 4 bbl carbs & not w/great results.

I also ran a 800 CFM Quadrajet spreadbore & also a 1000 CFM Thermoquad AKA "Thermobog",Too big to run those carbs on a mild 250.

The best bang & not too much power on top or mid range was when I ran a Holley 350 CFM 2 bbl.

I would think a 500 CFM Holley 2 BBL would work good also.


MBHD
_________________________
12 port SDS EFI

Top
#46823 - 01/15/09 12:29 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
Which issue is that? I don't recall the last one I got saying that, but I could have missed it (I thought I read it cover to cover ).

Are you sure they didn't mean an air valve secodary type carb like the Carter / Edelbrock? I've seen the 500 CFM EPS Edelbrock recommended for the 250s, but not the Holley type (Holley, BG, Quick Fuel, etc).

As I understand it the 500 Edelbrock / Carter, with the secondary air valve and the enhanced boosters on the primary side (compared to the 600) is supposed to be the hot setup (for a street 4 bbl).
_________________________
My, what a steep learning curve. Erik II#5155

Top
#46842 - 01/15/09 10:55 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Nexxussian]
Freds Garage Offline
Active BB Member


Registered: 03/14/06
Posts: 164
Loc: San Leandro, Ca.
Nov/Dec 2008 issue, page 21 Tech Question.
The engine is a 1954 Chevy 6. So I can guess it's a 235 or 261? Okay so similar to my 250. The gent has 10.25 pistons, 3/4 cam, Mallory Dual pointy dizzy and a Clifford 4 barrel manifold with the Holley 390 on top.
Pat (Six Fiend) Smith says, "As far as the carb goes, this should be the perfect carb for 6 cyl" and is not. Actually guys are running a 600/650 carb with better results."....

While I am inclined to believe this is a street driven car, the results this writer may be asking about are more race oriented?

Still my question is, does this particular Holley 390cfm have a bad Rap or is it not flexible for the engine I am putting together..Mild Street.??


Edited by Freds Garage (01/15/09 03:17 PM)
Edit Reason: (sp)
_________________________
James
Fred's Garage, Bay Area, California
65 Nova Coupe 250-Four speed

Top
#46853 - 01/15/09 02:57 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Freds Garage]
jalopy45 #4899 Offline
Active BB Member
*****

Registered: 04/09/06
Posts: 726
Loc: Oregon Outback
When I talked to Tom Langdon he said the 390 was not really 390cfm and you would wind up running on the rich side all the time and a better choice would be the Edelbrock 500 cfm, which is what I did. Hope to have it running soon and can give a report and some pictures. You might give Tom a phone call and he may be able to clear it up for you.
_________________________
'45 Ford PU
'63 Nova Wagon 250 4 spd.
'52 GMC PU

Top
#46858 - 01/15/09 03:20 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: jalopy45 #4899]
Freds Garage Offline
Active BB Member


Registered: 03/14/06
Posts: 164
Loc: San Leandro, Ca.
Nexxussian says "As I understand it the 500 Edelbrock / Carter, with the secondary air valve and the enhanced boosters on the primary side (compared to the 600) is supposed to be the hot setup (for a street 4 bbl)."

So what carb is this actually?
_________________________
James
Fred's Garage, Bay Area, California
65 Nova Coupe 250-Four speed

Top
#46873 - 01/15/09 05:56 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Freds Garage]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
It's the Edelbrock 500 EPS (500 CFM, Edelbrock Performer Series) Best I recall in the owners manual for my 600 (it's on a bent 8) it calls the only difference between the two (in the air flow path) is the booster cluster on the primary side of the carb. Having seen both, the 500's boosters definetly appear to be larger and I would expect a larger vacuum signal fom them (seems a mite excesive to drop 100 cfm that way, but they manufacure it).

You can download the manual for free here:
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

In it are specifications which incled the bore sizes of each carb, what the stock jetting is (was) and a graph the tells you which jets / springs / rods you need to chage to get a desired effect.

For 600 CFM you are looking at the 1405/1406 that's manual/electric choke respectivly (calibrated for performance/economy respectivly).

I can't seem to lay my hands uppon my Nov/Dec '08 issue at the moment (Sept/Oct '08, but not the next one).

600 seems kind of large for a 250, if you are driving it on the street. Of course you could probably make the case to match the carb to the manifold, ie a 600 with the Clifford and a 500 with the Offy (maybe, just speculating there so it's a guess on my part).

Hope something in there helps.
_________________________
My, what a steep learning curve. Erik II#5155

Top
#46884 - 01/15/09 07:04 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Nexxussian]
tlowe #1716 Offline
Active BB Member
****

Registered: 04/01/04
Posts: 2467
Loc: Dysart, Iowa
years ago there was a issue of inliners that had a great artical on how to tune the 390 for proper operation. the artical covered the rich problem and other problems to get it right. it was a great technical read. i still have it . copies can also be purchased from the club. if i remember correct 1991 was the year (yeah i've been a member for a while). tom
_________________________
12 PORT ADVERTISER
Information and parts http://www.12bolt.com


Top
#46920 - 01/16/09 01:35 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: tlowe #1716]
Freds Garage Offline
Active BB Member


Registered: 03/14/06
Posts: 164
Loc: San Leandro, Ca.
Come on Tom, dig out that issue. 12 Port News made me want to sell this carb before I ever put it on and its BRAND new!

I have got about two months before i install the 250 in the Nova so I want to be ready.
_________________________
James
Fred's Garage, Bay Area, California
65 Nova Coupe 250-Four speed

Top
#46925 - 01/16/09 04:27 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Freds Garage]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
I suggest a wide band O2 reader for tunning.

MBHD
_________________________
12 port SDS EFI

Top
#46934 - 01/17/09 12:17 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
Yeah, those are real nice, especially one like the LM-1 from Innovative, now that it will record some (so you aren't trying to read and drive at the same time, like some of the setups I have seen \:o ).
_________________________
My, what a steep learning curve. Erik II#5155

Top
#46948 - 01/17/09 09:57 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Nexxussian]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
The LM-1 is what I use,it works great.


MBHD
_________________________
12 port SDS EFI

Top
#46963 - 01/17/09 08:09 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
tlowe #1716 Offline
Active BB Member
****

Registered: 04/01/04
Posts: 2467
Loc: Dysart, Iowa
found the 12 port issue that has the article. great technical read. it is nov/dec 1992 pages 14 and 15. sorry i cannot post a copy of the article w/o permission. but the article can be purchased from bob corbett as he has the back issues. look for him in the club stuff at the left. tom
_________________________
12 PORT ADVERTISER
Information and parts http://www.12bolt.com


Top
#47057 - 01/19/09 08:18 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Freds Garage Offline
Active BB Member


Registered: 03/14/06
Posts: 164
Loc: San Leandro, Ca.
Here we go. New Age tuning tricks. Guess I will try that after all. It's the mist accurate way to get Air to Fuel ratio right.
What is the best way to reAd it OBD hand held unit?
_________________________
James
Fred's Garage, Bay Area, California
65 Nova Coupe 250-Four speed

Top
#47059 - 01/19/09 08:58 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Freds Garage]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
http://www.innovatemotorsports.com/products/lm1.php
It can record as you cruise,, floor it & so-on.

MBHD
_________________________
12 port SDS EFI

Top
#47063 - 01/20/09 01:05 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
The LM1 from Innovative is the industry standard for the home/ hobbyist/ amature 'tuner'.

You can add all sorts of data acquisition with it, but they aren't necessary.

I have read plugs before, with leaded fuels it's easy enough, but by the time the new unleaded (especially this new 'reformulated' gasoline that's out there) by the time it's colored the porcelin, if it was going to do damage, it already has.

Of course if it were off far enough to hurt itself, you would expect other symptoms as well.

Check Fleabay and Craigslist, there isn't much that can go wrong with them, except for the leads (ie right at the O2 probe).
_________________________
My, what a steep learning curve. Erik II#5155

Top
#47091 - 01/20/09 05:08 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Nexxussian]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
The LM1 from Innovative is the industry standard for the home/ hobbyist/ amature 'tuner'.

Forgot about the professional also. ;-)
_________________________
12 port SDS EFI

Top
#47094 - 01/20/09 06:22 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
strummin67 I.I. Offline
Active BB Member


Registered: 10/07/05
Posts: 509
Loc: Santa Clara, CA
So is the 390cfm ok on a 194?
_________________________
Martin
'64 Nova wagon

Top
#47095 - 01/20/09 06:26 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: strummin67 I.I.]
Kerry Pinkerton Offline
Active BB Member
**

Registered: 01/04/08
Posts: 123
Loc: Near Huntsville, Alabama
Doesn't the O2 sensor send out an analog voltage that can be read with a voltmeter? I realize it wouldn't be as good as something that stores data but I'd think a bung in the exhaust pipe, an O2 sensor and a voltmeter, along with a buddy recording readings at various speeds and loads would give you a fairly decent shadetree idea of what needs to be changed.

I've been full of crap before today...is this one viable?
_________________________
Kerry Pinkerton
http://wheelingmachines.com

Top
#47098 - 01/20/09 06:56 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Kerry Pinkerton]
tlowe #1716 Offline
Active BB Member
****

Registered: 04/01/04
Posts: 2467
Loc: Dysart, Iowa
a wide band O2 needs more to get it to work, but yes that is a crude way to do it. better than having your buddy sniffing the pipe as you drive though. tom
_________________________
12 PORT ADVERTISER
Information and parts http://www.12bolt.com


Top
#47099 - 01/20/09 07:14 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
 Originally Posted By: Mean buzzen half dozen A.K.A. Hank
The LM1 from Innovative is the industry standard for the home/ hobbyist/ amature 'tuner'.

Forgot about the professional also. ;-)


I figured a professional would likely have a LM-2 or one of the many stacked data acquisition packages they and many others offer (at that point its deductable).

Anything from 1 O2 sensor per exhaust pipe, all the way up to a wideband for each exhaust port (tempreatures, pressures, engine speed, trans speed,volts, amps, throttle position, what would you like to know, for enough $$$ they can record it for ya).

Although, a wideband for each exhaust port on a 6 cyl engine w/ 4 exhuast ports looses a touch of accuracy in the 'translation'. ;\)

That all assumes you want onboard equipment, as opposed to stationary for a dyno (there's lots for that too). \:\)
_________________________
My, what a steep learning curve. Erik II#5155

Top
#47102 - 01/20/09 07:45 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Kerry Pinkerton]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
 Originally Posted By: Kerry Pinkerton
Doesn't the O2 sensor send out an analog voltage that can be read with a voltmeter? I realize it wouldn't be as good as something that stores data but I'd think a bung in the exhaust pipe, an O2 sensor and a voltmeter, along with a buddy recording readings at various speeds and loads would give you a fairly decent shadetree idea of what needs to be changed.

I've been full of crap before today...is this one viable?


A regular 'O2' (Lambda) sensor only varies about 1 volt from as lean as it can measure to as rich as it can measure. It's at it's most accurate right at stoichiometric, 14.7 parts of air per 1 part of fuel, and reads about 1/2 ratio to either side. Or that's what I read anyway (various texts, I don't rely on the 'data' about other's products from a .com website that's trying to sell you a compteing product). Not saying I couldn't be wrong, but it's in all the print I have read about it.

A wideband (depending on whoose setup you're running) is quite a bit broader in it's sensitivity (from the single digits up to the high teens on A/F). But it takes a controller and the way you describe would require either a video camera or someone you trust to be accurate to watch it, so you can drive. Yes you have to watch it that close, if you're not recording it, as it has a tendency to vary alot, especially in initial testing.

FWIW, I haven't checked in a while but the sensor itself was over $100 + a bung to put it in with (not much) + a controller was over $100 (I hope they've come down, or maybe the Megasquirt crowd has sorted something out for that, haven't looked there for that). So to that you would add, whtever display you have / want (one of those jumpy LED things, or a nice twitchy analog needle). I won't say it's cheap to buy the whole setup that can record, but they don't usually break, you could get one used (it's consumer electronics, should cost between 15-50% of 'new') or if nothing else your local car club might be able to afford one (get the clamp on tailpipe adapter, no welding or drilling).

Not trying to be snide, or nit pic, just throwing out what I've seen. I've had the racing habbit for all my adult life (so far) and caught it before I could drive so I've always tried to find a more cost effective way to do things, cause you can't afford much speed equipment mowing lawns. \:D

FWIW JC Whitney used to sell a tailpipe sniffer for $100 ish. I ordered one years ago, they were on permanent back order and I haven't seen them in the catalog since. Anybody know how accurate they were?
_________________________
My, what a steep learning curve. Erik II#5155

Top
#47107 - 01/20/09 08:18 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Nexxussian]
speedhammer Offline
Active BB Member


Registered: 01/11/09
Posts: 21
Loc: md
Just a suggestion but have you looked into the ability of any of your local repair shops to help you? Any shop that has a L1 certified tech will likely have a gas analyzer and one of the best values on the market for a shop today is the OTC Genysis scan tool with the gas pack which has a 5 gas anylizer, calculates air fuel ratio, and displays exhaust temp, which that combination is going to actually tell you WAY more than any wide band on the market IF your operator knows how to read the data. Because it is a portable scan tool based unit you can actually put the probe in the tail pipe and take the car for a test drive (I do it all the time) and it records the data which can even be printed as a graph. May be worth a shot. I even have one and my shop sells tires (which not trying to plug Firestone, but most Firestone stores should now have these kits and someone who knows how to use them if that helps you any and the $100.00 or less that they charge you to get you that data is a lot less than a wideband setup).
Top
#47113 - 01/20/09 11:16 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: speedhammer]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
If you shop around there are wide band units that can be purchased for around $150 new.

I personnaly like to own one so I can use it my my cars as well as others for tunning & not worry about borrowing one or to pay someone for there equipment use & time.


MBHD
_________________________
12 port SDS EFI

Top
#47117 - 01/21/09 04:36 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Tony P Offline
Active BB Member
*****

Registered: 04/30/00
Posts: 514
Loc: Western New Yak state
I wrote an article for the Inliner's magazine about 8 years ago about my carburetor experiments on a 261 Chevy engine.This engine had the usual modification;M4F cam, Fenton exhaust,848 head with some milling on the block to give a measured 9-1 static actual compression ,and upgraded ignition.The engine was in a 3000 pound 37 Chevy pu truck ,3 speed manual,3,36 gears.This was a strong running engine according to several Inliners who drive it .Nothing hi tech about about the testing,full throttle acceleration in second gear from 2000 -4500 rpm using a marked distance to measure acceleration on a back road.
I tried a variety of carbs on a Clifford 4 bbl intake,time was spent to jet the carbs for best acceleration and part throttle driveability.Carbs used were:390 Holley 4bbl,500 2 bbl,400 cfm Carter AFB,500 cfm Edelbrock 4 bbl and a Holley 600 4 bbl.I bought the carbs on Ebay used,rebuilt them,then sold them after the tests,Cost me a summer of messing around and about 300 bucks.
The best results? The Carter 400 cfm AFB and the Holley 390 4 bbl.Larger cfm carbs offered no increase in performance in my tests.I also found while jetting these carbs for my modified 261 that the proper full throttle mixture for power when the throttle was opened full at 2500 rpm became over rich at over 4000 rpm. And of course when it was jetted properly redline power,the midrange went a little lean.So compromise jetting was used.It's my opinion that the power valve port channels on a 390 Holley were too small to deliver adequate fuel at wide open throttle in mid speed ranges.I believe an engine requires the richest mixture at maximum torque,which was about 2500-3000 rpm on my engine.The 500 cfm Edelbrock 4 bbl had a slight bog when the throttle was fully opened at 2500 rpm.No amount of jet tuning solved this problem completley.My conclusion was the 261 engine I had only needed a 400 cfm rated 4 bbl for best acceleration.
A few years later I built a GMC 302 about in the same state of tune as the 261 Chevy.For sure the 302 had a lot power,but I got the same results from messing with several four barrel carbs.400 CFM AFB ran as good as a larger carb.On the 302 I drilled out the power valve channels in the metering block from a .038 to .045 and that helped the midrange lean out.I think part of this was the Clifford intake port runners are too large for some engines.


Of course,your engine may be different,your seat of the pants judgements may differ than mine.

Top
#47119 - 01/21/09 05:32 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: speedhammer]
Nexxussian Offline
Active BB Member
*****

Registered: 06/12/07
Posts: 1411
Loc: Anchorage
 Originally Posted By: speedhammer
OTC Genysis scan tool with the gas pack which has a 5 gas anylizer,


Good to know, I'd love to have something 'inexpensive' that would tell me CO2 readings as well (5 gas should).

Thanks.
_________________________
My, what a steep learning curve. Erik II#5155

Top
#47131 - 01/21/09 10:31 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Nexxussian]
panic Offline
Active BB Member
**

Registered: 01/11/05
Posts: 1400
Loc: Hempstead, Long Island, NY
I'm not surprised at "mixed reviews" for carb size.
Anything that puts the fuel curve out of whack (not an error, bad adjustment or broken part - just the way the circuits operate) will effectively put that carb on the back burner as to choice, in favor of a smaller one with a fuel curve better suited to the engine's demand requirements.
These change, especially, with more displacement, cam, head work, so even a fairly similar engine may not give results you can use.
In the common Holley the air bleeds in the plate have to be drilled to change this - not fun, and very few guides.

Top
#47133 - 01/21/09 10:37 AM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: panic]
panic Offline
Active BB Member
**

Registered: 01/11/05
Posts: 1400
Loc: Hempstead, Long Island, NY
As GM proved many years ago, a good starting point for a non-traditional motor (where you can't just start with "what always worked before"): the Sprint OHC 230/250.
1. enough CFM to provide any power level the stock motor can produce without pumping loss (over 200 hp)
2. big vacuum secondary, adjustable in total air-flow, opening point, and secondary mixture
3. small primaries for good response and mileage

It's called a "QuadraJet"...!

Downside:
- it's got to turn sideways (from the V8 position) to put the primaries facing the intake ports on an L6 (linkage = fun)
- it won't fit the common Clifford etc. 4 bbl. manifolds without an adapter, and adapters may not provide the flow pattern you want
- because the secondaries are so big, the plenum is also big, which damps response somewhat

Top
#47139 - 01/21/09 05:37 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: panic]
Mean buzzen half dozen A.K.A. Hank Offline
Active BB Member
***

Registered: 09/23/04
Posts: 4895
Loc: Ca
The quadraject carb can be mounted anyway you want to mount it,except upside down. LOL

You need an adaptor plate regardless of what carb you run on either manifold.

The standard 4 BBL adaptor plates on both intake manifolds need work/porting/blending. Not so much if you are useing the 2 bbl to 4 bbl adaptor.

I used the Quadrajet carb for a Sprint 250 engine also,did not like the results

I used the Quadrajet carb & Thermalquad carb on both the Clifford & Offy intake,yes, both were speard bore patterns.


MBHD
_________________________
12 port SDS EFI

Top
#47185 - 01/23/09 02:32 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Mean buzzen half dozen A.K.A. Hank]
Freds Garage Offline
Active BB Member


Registered: 03/14/06
Posts: 164
Loc: San Leandro, Ca.
Really Lovin what I set off here. I have have learned alot at the same time i don't feel stuck with my 390. But I know I will have to work it out somewhat to be compatible with my set up.
Right now my 1974 250 Chevy is stock except for headers, Offy intake and HEI . Later with the 194 head (higher compression) and Lump POrting planned, plus a mild cam i am sure to have to mess with the Holley some. Who knows down the road I may wander off into insanity and finally and Turbo the thing just to make life more fun.

So I think i will stick with the 390 cfm for now, because as i see there will always be better set up. Its called "tweakin it" and thats what we do.
Now if someone would please locate me that 12 Port article on these carbs i could at least learn a few tricks?
_________________________
James
Fred's Garage, Bay Area, California
65 Nova Coupe 250-Four speed

Top
#47190 - 01/23/09 07:08 PM Re: Why isn't a 390cfm carb good for a 250 motor? [Re: Freds Garage]
panic Offline
Active BB Member
**

Registered: 01/11/05
Posts: 1400
Loc: Hempstead, Long Island, NY
The Sprint is a 12 port motor with quite a bit of cam timing, fairly good iron exhaust, and over 10:1 compression.
I would guess that the primary jetting is too lean for the primary metering rod cruise step, the air valve tension is too low, and the secondary rod is too rich.
Easy to play with, just do one circuit at a time.

Top
Page 1 of 1 1


Moderator:  Webmaster 
Hop to:
Who's Online
3 registered (Drew, II # 4211, tlowe #1716, littlejeep2) and 59 anonymous users online.
Newest Members
Crow, drgoetz, ulfy5082, richard owens, adamohlmeier
5681 Registered Users

Generated in 0.098 seconds in which 0.033 seconds were spent on a total of 15 queries. Zlib compression unavailable.