HELP Carb Selection

[73383]

Just got my engine back and installed in the chassis. I can't make up my mind on carb selection. Engine specs below
SB 383 9.8 comp. 6inch rods
Ported Sportsman II heads, Comp Cams Magnum 1.5 rockers
Comp cam 280H Hyd
Edelbrock PreformerRPM intake
MSD 6A, Mallory HEI Dist.

I would like to run a Holley DP. or a Speed Demon.

Vacuum secondaries???
Mech Secondaries???

Dennis

Also does anyone have a desktop dyno? Can you tell me the HP and Torq figures on this engine.

GREAT SITE
Dennis

 

[GerryLP]

This chart I added is straight from the Holley Carburator, Manifolds & Fuel Injection Book by Mike Ulrich and Bill Fisher.

The theory behind this figure (and it only applies to mechanical double pumpers) is that the lowest WOT rpm must be considered. In auto trannys, the torque converter stall speed is used. On manual trannys the WOT rpm is going to be relatively lower (i.e. 1,350 rpm or so). Vaccum secondaries, since they are based on engine load, can only self adjust to the volume being pumped by the engine.

So on column "A" select the WOT rpm, and then cross a straight line towards the engine size (column "B"), and the follow the line to suggested mechanical secondaries carburator CFM capacity at column "C".

Generally speaking, a lighter vehicle can function well with larger CFM carburators. The heavier the vehicle, the more important it is to select the appropiate carburator. Also, consider that no matter what, the most top end horse power can be attained with a relatively larger carburator. The most torque with a relatively smaller one. Check out Super Chevy Magazine(April 2003 edition, page 60) for a comparison on Holley carbs sizes. They only used 4150's and 4160's for this test to keep changes to a minimal.

I am sure that someone will disagree with the chart;nevertheless, it is one more piece of information for you to consider.

p.s. by the way...I have found this book very usefull ...:L

 

[Mako]

This chart I added is straight from the Holley Carburator, Manifolds & Fuel Injection Book by Mike Ulrich and Bill Fisher.

I don't suppose I could twist your arm for a larger scan of that chart, say ~3-4x larger in fact? The eyes are the first thing to go...

Thanks!
Mako

 

[WayneLBurnham]

There's a CFM formula right here on this 'site

I think under "tools"...."automotive math"....

I would always go with the Demon over the plain Holley.

The Demon basically is a fixed-up Holley design. I didn't run the numbers, but I'm thinking 750-780 CFM range.

OK, I lied and DID use it: with a 6500 redline for 80% volumetric efficiency it says 692-864, for 90%, 778-972. Your engine is medium compression but longer stroked, I'd guess the latter.

So pick an 800 CFM model. If you overcarburate, it bogs and acts wrong. If you undercarburate, you cut your engine's potential power terribly. 800 seems in the middle of all selection ranges.

Mechanicals react quite a bit faster, especially with decreased vacuum. You used a 280 Series cam which it says reduces manifold vacuum in the PAW cam section. That would seem to make up your mind there. I got away from this hard choice with the AFB's and now Edelbrock improved even that with their new AVS.

As on all Holley designs, try to go with the larger acceleration pumps, whichever of the Demon series offer them. Chokes seemed more necessary on Holleys than on the AFB designs I favor now, so you may consider an electric choke.

My DD is on my other machine. I'd have to sit up to use it.
As your engine is at least twice as powerful as mine I hate you anyhow and so won't do this... at least now...

Good luck on the carb!!!

 

[Mako]

Re: There's a CFM formula right here on this 'site

I think under "tools"...."automotive math"....

I would always go with the Demon over the plain Holley.

I cannot in good faith recommend Demon carbs to anyone yet.

The dyno testing I've seen always has the Demons coming in second fiddle to the 4150's.

Off idle flat spots that won't go away and general tuning and drivability woes seems to be a common complaint as well. I'm sure there are success stories out there, but I've not seen any first hand yet, perhaps my sample size is too small though. A pro engine builder with a dyno in house would be a wise person to consult.

For street rods, I've been recommending Holley Street Avengers, and so far no one has told me I bum doped them. The vacuum secondaries mean good MPG, while still delivering plenty of get up 'n go. They also are very affordable.

I personally use a Davinci tweaked 4150 DP on my 383, iirc it flows ~820CFM. The engine has knife edge throttle response and put out 487HP/485#/Ft on the engine dyno. The car runs 119MPH in the quarter, so I'm pretty darn happy with the setup. It also cost a pretty penny for the priviledge.

CYa!
Mako

 

[73383]

The engine I used as a guide to build mine used a vacuum secondaries Holley 750 reworked to flow 820cfm. However, he used a smaller cam (270H), Performer manifold, and reworked 186 head flowing 240cfm.

I built this engine to try to have my cake and eat it too. The stroker for low end torque and the cam, head, and intake for top end. I am not a drag racer, but I would not mind spanking a stang or a ricer now and then.

The car is a 4spd running a 3.36 rear end. Wanted a six speed but not in the budget at this time. Maybe in a couple of years. I still have to redo the firewall, interior, put the body on the frame, hang a front end, and paint.

Back to Carbs, can't decide on Mech or Vacuum secondaries for this engine. I would prefer Vacuum for street ability, however when I put the pedal to the metal I want it to go go go.

Wayne; Please, Please, Please

 

[73383]

Mako

I have been leaning towards the 750 Avenger, as I said earlier I have a line on one at a good price. I wish I could say money is no object, but I can't. Can it be reworked to flow more? I plan on buying David Vizards book on carbs.

Dennis

 

[Mako]

Mako

I have been leaning towards the 750 Avenger, as I said earlier I have a line on one at a good price. I wish I could say money is no object, but I can't. Can it be reworked to flow more? I plan on buying David Vizards book on carbs.

Dennis

The 383 occupies a curious place in Carb sizing. It really wants something around 800CFM above 6000RPM depending on the engine combination. In carb land, too big is too bad far a street rod. Your much better off going down one size.

Given your dual plane intake, plus the mildish cam you have, I'd recommend a 750 Street Avenger. You'll possibly be a bit under carb'ed at the 6000RPM+ should you ever go to a single plane + hotter cam setup, but it'll have excellent throttle response and make great power with your current combination.

Holley's own web page at: http://www.holley.com/HiOctn/TechServ/TechInfo/FMCTech3.html
and http://www.holley.com/HiOctn/TechServ/TechInfo/TI-224.html backs my opinion up as well.

Stick with the 750 Avenger for this revision. When your rich and famous and have $ to burn for a roller cam and single plane intake, then go to a reworked 5150 DP from Braswell or Davinci etc...

CYa!
Mako

 

[73383]

MAKO

Thanks, great web site. I printed out your cam/dyno section for future reference. I wish I had found the forum when I was planing this.

Yes, roller cam was not in the budget, maybe in the future. I started out with a Comp 292H, but got cold feet and backed up to the the 280H. After I get this thing running I may go to 1.6 rockers, we'll see.

dennis

 

[Mako]

MAKO

Thanks, great web site. I printed out your cam/dyno section for future reference. I wish I had found the forum when I was planing this.

Yes, roller cam was not in the budget, maybe in the future. I started out with a Comp 292H, but got cold feet and backed up to the the 280H. After I get this thing running I may go to 1.6 rockers, we'll see.

dennis

Thanks for the compliment, I'm glad you found my web page useful. I've tried to distill as much information as I can on the site. It could be better organized, but it's all mostly there if you click around enough

Here's an idea for when you have just a little bit of cash but want another +10 of everything anyways:

Just install the 1.6:1 rockers on your intake valves. Leave the 1.5:1's on the exhaust. I think you'll be pleased with the results. This assumes your valve springs won't go into coil bind of course...

If you can find a friend who also has a 383 or 396, you can split the cost of a set of 16, then sell the 1.5's on E-Bay. I love cheap HP

CYa!
Mako

 

[73383]

MAKO

How, did you get the Victor Jr. under the hood.

Dennis

 

[Mako]

MAKO

How, did you get the Victor Jr. under the hood.

Dennis

It's actually a Super Victor #2925 ( think I muffed up on the web page somewhere and called it a Vic Jr. by mistake) with a 1" phenolic spacer. I replaced the stock hood with a knock off el cheapo L88 type hood and have a drop base LT1 style air cleaner.

See the BIGMOUS 383 gallery for a couple of pictures.

That gave me .25" of clearance between the hood and the top of the air cleaner. That's why the car has a white hood in all the photos. That's the natural color of the gel-coat I never bothered to paint it knowing that it was a temporary fix.

I have a new long style L88 hood on the car now (click on the shark gill pic on the main page) which will also have the cowl induction air box glassed onto the underside of it with an L88 foam filter and screen on the carb.

Old timers swear that setup is worth at least tenth and +1MPH in the quarter. It also looks bad ass, so who am I to argue? I need some chromed 3 8 3 numbers to attach to the side of the cowl. I wonder if people will think I have a Mopar wedge motor under the hood if I do that?

The car is now primered and going to Dave Herlinger's shop for some header fun and an M22 install. I hope to have it back in Late March +-.

CYa!
Mako

 

[GerryLP]

I don't suppose I could twist your arm for a larger scan of that chart, say ~3-4x larger in fact? The eyes are the first thing to go...

Sure Mako, but I'll have to do it from home. I don't have the file handy in my puter at work. ...

I have been leaning towards the 750 Avenger, as I said earlier I have a line on one at a good price.

Dennis...I currently have an avenger on my engine, and after having had to change the jets for 5,000' altitude, I have tune it to make the most power possible (388 peak hp at the wheels - I only look at average power at the wheels though); however, my engine is only bored 0.030 over, and probably would not make a very good comparison to your stroker...:duh ; however, I feel that the only way my engine will make more power is if I install a double-pumper 750 or 700 at the least. Maybe larger by the looks of the chart I posted (2,400 stall converter). Right now I have purchased a 4777-2 carb, and I plan to use a 4778-2 main body for it to make it a 700 cfm carb.

I wish I could say money is no object, but I can't. Can it be reworked to flow more?

Dennis...Proform has a main body in Jeg's catalog for about $100 that will increase the flow in an existing carb.

I'll have to say that Mako has a point on Holley carbs. The 4150 and 4160's have been tried and trued at the track for many years, and of course there are exception to this, but by and large, one can be very satisfied with Holley carburators performance.

One thing to consider is that double-pumpers do not steal vaccum signal from the primary venturies. Vaccum secondaries will reduce the pressure drop across the carb. This helps to explain why they tend to bog-down when opened. Another advantage is that the pump shooters can help in acceleration. Where as in the vaccum secondary carbs that funtion is only performed by the primary venturi. Double-pumpers, on the other hand, are not calibrated to save you gas. Therefore, if one wants to maintain a little confort at the gas pump, then vaccum secondaries offer an excellent compromise.

p.s.
One problem with volumetric efficiency in some of those charts is that it is so darn hard to measure in one's engine.

 

[73383]

Thanks for all the great imput, just ordered a 770 Street Avenger. It may be a month before I fire this thing up. I am waiting on alum rad. and fans, clutch, preasure plate and flyweel, headers etc.
I' let you know when I do.

Dennis

 

[Mako]

Thanks for all the great imput, just ordered a 770 Street Avenger. It may be a month before I fire this thing up. I am waiting on alum rad. and fans, clutch, preasure plate and flyweel, headers etc.
I' let you know when I do.

Dennis

Excellent, the 770 will serve you well. Can I ask where you bought if from and for how much?

I'm helping on a Bowtie head 357 build right now and the carb will of course be a new Street Avenger.

CYa!
Mako

 

[WayneLBurnham]

onGood input on the Dem

I cannot in good faith recommend Demon carbs to anyone yet.

The dyno testing I've seen always has the Demons coming in second fiddle to the 4150's.

Off idle flat spots that won't go away and general tuning and drivability woes seems to be a common complaint as well. I'm sure there are success stories out there, but I've not seen any first hand yet, perhaps my sample size is too small though. A pro engine builder with a dyno in house would be a wise person to consult.

For street rods, I've been recommending Holley Street Avengers, and so far no one has told me I bum doped them. The vacuum secondaries mean good MPG, while still delivering plenty of get up 'n go. They also are very affordable.

I personally use a Davinci tweaked 4150 DP on my 383, iirc it flows ~820CFM. The engine has knife edge throttle response and put out 487HP/485#/Ft on the engine dyno. The car runs 119MPH in the quarter, so I'm pretty darn happy with the setup. It also cost a pretty penny for the priviledge.

CYa!
Mako

 

[73383]

I bought it from a local supplier. I paid 330.00. His cost was 300.00. I believe Summit sells for 380.00

 

[73383]

I bought it from a local supplier. I paid 330.00, he gives me a discount, his cost was 300.00. Summit sells for 380.00

 

[Mako]

I bought it from a local supplier. I paid 330.00. His cost was 300.00. I believe Summit sells for 380.00

Any chance he'd be willing to sell and ship another one?

Tnx!
Mako

 

[73383]

I don't know. I'm to pick mine up at 4:00 today. I'll see what I can do. I've spent over 5000.00 with the dude