Split manifold question

[Don Coatney]

Contrary to the misconceptions that most people have about split manifolds and/or headers, the truth of the matter is that generally they clean your wallet of money and do nothing for the general improvement of an engines performance.

Headers are meant to be ran as an open exhaust on race engines, generally they do not start to do their intended job until the engine is running above 3,000 rpm's.

Split manifolds are nothing more than an attention getter... Hey look at me, I have bigger "gonads" than you do. People generally think that noise equates to power.... Not so.

All things being equal, if the engine is stock the split manifold will do nothing and in many cases the engine will run poorly because the heat riser has been eliminated, which causes raw fuel to enter the engine.

In some cases larger pipe size and a truck type muffler can improve exhaust flow, thereby allowing the engine to perform better.

The addition of dual exhaust with an equalizer tube can improve the performance of some engines in trucks and RV's, however, addition of headers to the same vehicle will not provide any additional improvements and in many cases a reduction in power will result.

Several years ago a friend of mine that owned a muffler shop for many years told me that he had found that many customers complained about poor fuel mileage after he installed headers and/or dual exhausts on their cars.. He reinstalled the stock systems and the fuel mileage improved... He told me that he felt the poor mileage was a result of the driver sticking his foot into the engine to hear the noise that the pipes emitted...

Many years ago I ran a muffler/performance shop...

Just curious, do you actually have a flathead engine in your car or did you do some shade tree engineering, turn it into a hot rod, and stuff a modern V-8 in it?

[blucarsdn]

Just curious, do you actually have a flathead engine in your car or did you do some shade tree engineering, turn it into a hot rod, and stuff a modern V-8 in it?

My '39 Plym conv cpe has a late model V8, AT, PS, AC, & PB... I like reliability and safety while cruising in the fast lane.. My car also has more NOS and/or original parts used in it's restoration than the average car.

I have a '48 Dodge 4dr that is dead stock, paint, etc.. It was pulled out of a shed where it had sat since 1968. Unfortunately the engine and trans had been removed for some unknown reason so I re-powered the car with a nice running '48 Chrysler Spitefire eng/trans that I had... A bolt together application.

A discussion about the pro/cons of performance improvements on engines is another topic like women, politics, and religion that can never be won because everyone have their own ideas about what works for them..

The original question was regarding the application of a split manifold to an engine to improve performance.... Without other extensive modifications to the engine, the spitting of a manifold provides very little if any improvement to the performance, aside from the perceived increase that the sound emits.

[albolton]

here are the headers i ran on my flathead...phillips performance, fit well, didnt leak and sound really cool, ...not much fun adjusting the valves

hard to find ....i dont know how others feel, but i struggled alot with the trottle linkage using the OFFY dual intake...throw away the stuff from them, and make your own, you will be much happier...my opinion

[40plyrod]

sound really cool, ...not much fun adjusting the valves

hard to find ...

I never thought of that. How hard is it to adjust the valves with a split manifold and how often do you need to? I plan on splitting the manifold on my 40 the same as I did to my 51 chevy pickup but in that case the valves are overhead and the lifters are on the other side. Is that something to take into consideration or is it like going to the trouble to fit a remote master cylinder fill for the brakes only to realize for the amount of times you have to fill it is pretty rare.