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Need header advice #1298391 Sun Feb 10 2019 10:31 PM
Joined: Nov 2017
Posts: 18
F
floaterboy Offline OP
New Guy
Hello, I'm new to the forum so bear with me! I'm looking for help with selecting headers for my '56 3100. I'm dropping in a 230 backed with a 2004r. My buddy has a similar setup with a set of full length Hedman's and they hang really low. I going to run an Offy intake. Any reasonably priced shorty headers out there?

Thanks,
Len

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Re: Need header advice [Re: floaterboy] #1298465 Mon Feb 11 2019 04:12 AM
Joined: Feb 2004
Posts: 19,687
H
Hotrod Lincoln Offline
Boltergeist
Go on Ebay and buy a new 292 Chevy exhaust manifold for a Massey-Ferguson combine or other piece of farm equipment. Then run a mid-1970's Cadillac muffler with 2 1/2" pipes on both ends. You'll end up with an exhaust system capable of handling 500 cubic inches, without going to some outrageously expensive Mickey Mouse header system. You'll also reduce the under hood temperature dramatically with the cast iron exhaust manifold. If you want some eye candy, have a good welder split the manifold and run two of those pipes and mufflers. Then you can run 1,000 cubic inches.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Need header advice [Re: floaterboy] #1298472 Mon Feb 11 2019 05:15 AM
Joined: Apr 2002
Posts: 1,575
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Fox Offline
Shop Shark
Just a question for you Floaterboy: Is your rack and pinion rubber boot going to clear the frame gusset you have in place when the suspension is under compression? I know many IFS kits need a relief cut into the frame in order to clear that boot.

Last edited by Fox; Mon Feb 11 2019 05:15 AM.

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1951 GMC 9430 1 ton dually—-Shiny!

1970 Chevrolet C10 - Grandpa’s- My first truck.—in progress to shiny
1972 Chevrolet C20- rusted
1970 Chevrolet K20 Suburban—rusted.
1950 Chevrolet 1300- in progress to shiny.

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1951 GMC 9300
1951-GMC 9430
1951- Chevrolet 1300
Re: Need header advice [Re: floaterboy] #1298509 Mon Feb 11 2019 04:50 PM
Joined: Feb 2000
Posts: 4,054
J
Joe H Offline
Shop Shark
Shorty type headers are no better then the larger outlet 292 manifold, so run the manifold, you will still have the heat under the intake, and a lot less gasket sealing problem. Long tubes would be a better option if you really want headers, just make sure the primary tubes are really small. You will gain some low to mid range torque with very long, small diameter tubes.

No matter what you choose, without head modifications ( porting ), camshaft change, and much higher rpm, the engine is going to use the same amount of air no matter what intake and carburetors you install, so headers will have very little effect on performance. The stock manifold is not restrictive enough for headers to make much improvement.

I have run a header with three carburetor intake on an other wise stock 250. I made three passes at the local 1/4 mile drag strip, the next week I went back and made three more passes with stock intake, mono-jet carburetor and stock exhaust system, weather was same. All six passes were identical, 17.90 at 79 mph. Since the engine was stock and I was shifting at 4500 rpm, the intake and exhaust make no difference as there was no need for more air flow in or out.

Re: Need header advice [Re: Fox] #1298553 Mon Feb 11 2019 10:32 PM
Joined: Nov 2017
Posts: 18
F
floaterboy Offline OP
New Guy
Good call! I’ll take a hard look at it!

Re: Need header advice [Re: floaterboy] #1298583 Tue Feb 12 2019 01:14 AM
Joined: Mar 2010
Posts: 862
Y
yar Offline
Shop Shark
"I have run a header with three carburetor intake on an other wise stock 250. I made three passes at the local 1/4 mile drag strip, the next week I went back and made three more passes with stock intake, mono-jet carburetor and stock exhaust system, weather was same. All six passes were identical, 17.90 at 79 mph. Since the engine was stock and I was shifting at 4500 rpm, the intake and exhaust make no difference as there was no need for more air flow in or out."

Joe,

I had a long time friend who campaigned an early 1930s era 4 cylinder Model A Ford powered Model A roadster in one of the Street Roadster classes at Bonneville. Over the years he inched the class record to over 125 MPH with a small displacement flathead engine that is approaching 90 years old. So there is potential in the unlikeliest of engines. What modifications would your engine need to allow it to take advantage of the headers and multiple carb setups you fabricated?

My friend exploded a lot of those Model A engines along the way before finally adding extra main bearing webs to the block and running a custom 5-main bearing crankshaft.


Ray
Re: Need header advice [Re: floaterboy] #1298584 Tue Feb 12 2019 01:18 AM
Joined: Dec 2008
Posts: 1,362
P
panic Online
Shop Shark
the engine is going to use the same amount of air no matter what intake and carburetors you install
Not true, by definition the OEM 1 bbl. is sized to operate at (about) 3" Hg @ WOT. Reducing the vacuum load to 1.5" Hg increases VE and reduces pumping loss, even with a completely stock engine.

Missing from these comments?
Pressure at the header pipe outlet is related to displacement vs. pipe area.
However, the pressure at each exhaust port is greatly affected by how closely it's connected to another port, the entire manifold casting becomes pressurized as each port cracks open, and the local port pressure is much higher than the system pressure as an average. With mild cams, this is not of great significance, but as overlap increases pressure at the exhaust port begins to back up into that chamber, which affects idle quality, etc. Keeping the exhaust separated as long as possible helps, including siamese pairs which experience twice as many pressure spikes (and only 240° intervals alternately in the #2-3 and #4-5 ports).

Re: Need header advice [Re: Fox] #1299131 Fri Feb 15 2019 11:18 PM
Joined: Nov 2017
Posts: 18
F
floaterboy Offline OP
New Guy
It should be ok. The pic doesn’t give the true perspective.

Re: Need header advice [Re: floaterboy] #1299241 Sat Feb 16 2019 05:52 PM
Joined: Feb 2000
Posts: 4,054
J
Joe H Offline
Shop Shark
In my engine, the ports in the head and the valve opening is what controls air flow in and out of the engine. Shifting at the same rpm, the flow in and out didn't change since the ports were the restriction point. To gain power, the engine cylinders have to increase air and fuel quantities, this could be by adding more valve lift, higher rpm, or better flow through the ports. Fuel will increase with air flow, so even a small carb can add power if the air flow is increased. I now run a dual Carter W-1 intake and carb system. The carbs are sized right for the stock engine, performance is better and mileage is better, not because there or two carburetors, but because the distribution is evened out across the 6 cylinders.

A well designed header can add power even with a crappy head. The very long, small diameter tubes, can pull fresh air/fuel into an engine during valve overlap by using the exhaust pulses. As the exhaust pulse leaves the head, it creates a vacuum behind it, this vacuum is what pulls the air/fuel into the cylinders while the two valves are overlapping ( exhaust closing, intake opening). The trick is the design the header so the pulses don't run into each other and jam up the flow.
This is how some race engines can be over 100% Volumetric Efficient without added supercharging or turbo charging. It's not easy!

On a side note, I ported a 250 head and gained about 18% air flow both intake and exhaust side. I have a Super Flow 110 air flow bench to check heads on, so this was a true 18% increase! On the truck, normal driving was fine, wide open was also pretty good, felt faster, but had no data to back it up, our local track closed down. Where the problem showed up was at part throttle, climbing hills. The exhaust flowed close to 95% of what the intake flowed, this created a terrible lean condition. Under the part throttle, hill pulling, accelerating, the exhaust actually pulled the fuel out of the cylinders, creating a lean condition. I could see the temperature climb and the engine would buck something terrible. Go full throttle and the problem would go away, let off and the problem went away. If I had my wideband air/fuel ratio gauge at that time, I could have seen right away what was happening. The head is now setting on the shelf waiting to be looked some more, it will need the intake side opened up to get the exhaust to intake ratio back down to 75-80%, not the 95% it has now. Its very easy to port a head, whats hard is doing it correctly.

My engine makes a true 125 hp at the flywheel and 105 hp or so at the tires, depends on which calculator is used, ( going off weight, ET & MPH ). I am not willing to give up mileage, idle quality, and clean running to gain 15 or 20 hp. There is always a trade off for more power.

Re: Need header advice [Re: floaterboy] #1299284 Sat Feb 16 2019 09:26 PM
Joined: Dec 2008
Posts: 1,362
P
panic Online
Shop Shark
Almost every GM, Ford and Chrysler V8 in the 1950s and 60s was made in the same displacement (same heads, same cam, same exhaust) with both a 2 bbl and a 4 bbl, with a significant advantage only through more venturi area.
Examples: polyspheric 318: 2 bbl. 230 hp, 4 bbl. 260 hp; MoPar 361 2 bbl. 265 hp, 4 bbl. 305 hp; Olds 394 2 bbl. 280 hp, 4 bbl. 315 hp; SBC 283 2 bbl. 195 hp, 4 bbl. 220 hp. It's a long list.
More carburetor = more peak power (but may have other evil symptoms).
When is it not true? When the laws of physics are suspended, all the way down to WOT vacuum below 1.5" Hg.

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