The Stovebolt Site Forums The Shop Area Engine Shop Gmc 302

For a mild gmc on the street which would be better a long tube header or short tube header ?

"None of the above"
Jerry

if you are using the 2.5 inch outlet manifold, there is no reason to use headers for the street

Joe

Ok, smart guys -- Why not use headers?

OP asked a reasonable question -- educate us.

Installing headers, or more carburetion on an otherwise stock vehicle without also doing major modifications to the cylinder head, such as porting, polishing, and/or installing bigger valves is like joining two pieces of log chain with a paper clip. The stock GMC exhaust manifold is capable of handling all the volume a stock cylinder head can flow, and then some. The only other reason to install headers would be to impress the mouth breathers at a "show and shine".

Assuming the engine builder has done his homework properly and spent a bushel of money in the process, short headers increase top end horsepower. Long ones boost low end torque. The selection of the camshaft and a bunch of other nitpicking details will have a huge effect on header length and other modifications. Either one is a compromise that lowers, not raises the numbers an original equipment manifold will make over the full range of performance. The builder will be trading off performance at one end of the spectrum to increase the other. The guys who designed the engine didn't fall off the turnip truck and end up in a research lab by accident.
Jerry

That turnip truck has changed in the last 70 years...........so just maybe there room for discussion and changes ?

OK- - - -show me your own dyno figures, not something somebody dug up with an internet search engine, and let's discuss the "changes". I suppose there might have been some sort of earth-shattering new technology developed that repeals the laws of physics since I quit dyno testing every engine I built in the late 1990's. I started watching my father's 34 Ford 3-window coupe running on alcohol being tuned on a chassis dyno in the early 1950's, so I'm not exactly a newcomer to backing up one's "fertilizer" with facts and figures.
Jerry

Agree with Jerry. Unless there is changes made to get more air IN then the factory manifold is capable of getting all the exhaust out with some to spare. The siamesed port stovebolt head is just not a performance piece. If you come up with a 12 port head then the story changes but not much with just a four main bearing cap block. GM stalled for 30+ years after Ford and Chrysler had a good head before finally coming out with the Atlas engine. The Stovebolt engine is EXCELLENT for what it was designed---a low rpm engine with very good torque but some insist on entering their plow horse into the Kentucky Derby. If your honest and call it eye candy then that's acceptable.

Here is the thing the only way to learn is ask a question. I didn't ask to start a fight! That is why I use this form so little or ask a question here is there are a few here that come running to the cliff and jump.

I do know the head is the bad part of the gmc 302s and I know about the 4 mains I know its a truck motor. I understand all the short comings of the gmc.

The head is being done by sissel to help flow. I have Un ground cams shafts that will ground by Jimmy Elgin. It will have a holley efi with a tom London HEI with a msd 6 it will have a balanced crank shaft and rods with arias 9 to 1 pistons.

All I did was ask long or short tube headers.

I understand it's probably a waste but it's a one time build that I have been gathering parts for years. Just wanted to learn! So I asked

Gmc101, yes the collective is decidedly slanted towards stock on the site. In the future if you will post your performance questions in The HiPo Forum the Moderators can run interference with the purists who invade your territory. More than one member has had their wrists slapped for expressing non-performance ideals in the HiPo Forum. Good luck with your build, it sounds like it’s going to be a hoot to drive.

As the cam events become longer (especially overlap) benefits begin to appear for separating the exhaust ports, and separating the front cylinders from the rear.
What has Elgin offered you as a cam?

Perhaps if you had started your first post with these specifics, you could have gotten better responses. As was shown, just asking whether short or long tube headers was better with no other tidbits about your engine mods seemed to indicate the engine was in stock trim, and got the answers accordingly.

Gmc101 Good shot there-run to the cliff and jump. LOL LOL it's your truck do whatever you want to it!! It will all unbolt !!!

I run real tube headers on my 261. If mike Kirby is giving your head the once over, that head will flow probably as good as it will ever flow. For a street motor, I like long tube headers. I think they do a better job at scavenging at lower rpm and as noted above, better for low end torque. Clifford use to make headers for the 302 gmc but after jack clifford died, his header jigs were either destroyed or disposed of so there is no chance in getting a Clifford header unless you can fined a nos version. So if you want a real tube header, you will have to fold a race car shop who will build you a set. Also, bigger is not better with these motors so resist the urge to build a set of large tube headers. Probably 1 1/2 or 1 5/8 would be about right.

They sound great by the way when they are open.