Split manifold question

[Uncle-Pekka]

This may be a stupid question, but I need to ask because I do not know/understand the reason

why the factory manifolds are being split to two?

I understand the reason for pipe headers and custom made manifolds such as Fentons is improved "breathing" through better flow in smooth and larger channels.

However, by splitting a factory manifold you still end up with original size and square corners - Is there some advantange I missed to understand?

Can one measure the improved performance in case there is any?

Sincerely,

Unkka-Pekka

[Andydodge]

Peka, in the US and with other LHD cars I would assume the only reason to just split the exhaust manifold would be cost as there are both Fenton castiron headers and tube steel headers available............BUT......here in Oz where the steering box is on the same side as the intake/exhaust manifolds there is a small problem of clearance........the RHD steering box takes up the space where the front headers would have dumped.......and the clutch & brake pedals swing thru where the rear header dumps.......so I got a pair of plymouth exhaust manifolds that dump front and middle and had whats pictured done.......cut the front & back of 2 manifolds and had a blacksmith weld them up.......should work fine........regards......andyd

[Plymouthy Adams]

availibilty...cost...richer sound, improved gas flow...richer sound and did I mention it sounds a lot better..on a engine that also gets the intake split and along with a bit of a deeper breathing cam..you will need the increased ability to exhaust freely.

Idealy you would want to open the match the ports in the block and the exhaust manifold and polish these real smooth at the same time. If for example you have a have some 300 cu ft of air to move through a 1.750 pipe it only stands to reason that if you double the size of the pipe you have a less restricted flow of hot gases..thus the split. So now you have three ports into one pipe and the other three in the other..and with the firing order such as it is..you also have a balanced exhaust thus the very rich tone that goes with it. The improvement is there, it is real and also the sound is fantastic if you have the proper deep breathing cam to go with it and mufflers that will accent the manifold..I have heard a number of these engine running through dual pipes on a split and they are impressive. Ideally you want the length of both exhaust pipe equal for max performance and balance..but often time you are not afforded that luxury on these rolling elephants.

[Cpt.Fred]

these rolling elephants.

Haha, that hit the nail on the head!

you forgot to mention that it sounds a lot better.

[Niel Hoback]

Yeah, but how does it sound?

[greg g]

ever heard a big austin healy with duals or any of the 6 cylinder Jaguars with dual exhaust? They sound very similar.

The engine is an airpump. Anything you do to increase the and or ease the flow through it is better for performance.

[Rusty O'Toole]

This was originally done on what were late model cars, in order to install dual exhausts.

Dual exhausts were supposed to decrease back pressure and increase horsepower.

This was before exhaust headers were readily available.

Today there are better ways of improving performance, such as buying a newer car.

But, if you want to build up an old car in an old style, that is one of the old tricks.

[meadowbrook]

Folks, I noticed just about every dual carb Flathead 6 seems to have downdraft carbs. Has anyone ever used a side draft carb on these engines? They would seem better since it's a straight shot to the engine instead of a 90 degree bend.

[greg g]

I think a couple of folks have used SU or solex carbs like from triumph, healeys jags etc.

A weber or two would be interesting but probably over kill.

The SU type is very adaptable because of the adjustable main jet. Also there have bee som pis=cs around of folks using multiple Motorcycle carbs.

[yourpc48]

Uncle-Pekka. If you think about it. You are increasing the flow by splitting the manifold regardless of the bends and such. you now have 3 cylinders per pipe instead of 6 in one pipe. Did I mention it sounds good too?

The manifold split is an old school way of doing this and yes a header would do a more efficient job of this but the cast headers are expensive and tube type can leak like any other tube header. If you can weld cast or know someone who can then you get a fair result from the split.

[Mark D]

I've been meaning to ask that for myself. Searching the internet recently and came up with the following link... seems reasonably priced when I think about the labor costs for splitting a stock header, might as well buy new... I am on the verge of ordering an offenhauser dual carb kit and a pair of the following headers for my winter project...

http://reds-headers.net/index.php?main_page=product_info&cPath=2&products_id=818

Anybody bought these yet?

[Plymouthy Adams]

those headers as pictured have been on here a couple of times..I think they are V8 setup modified to fit the flat six by lobbing an end runner and blanking..not quite equal length but for all practical purposes and the given low RPM these engines are limited to by 98% of the owners..they will do all you need them to do..the do look quite spiffy..I think you may need to look close at these..not sure if it was these or another brand that sometimes shows up here that has som interference at the oil and fuel pump..

[hkestes41]

those headers as pictured have been on here a couple of times..I think they are V8 setup modified to fit the flat six by lobbing an end runner and blanking..not quite equal length but for all practical purposes and the given low RPM these engines are limited to by 98% of the owners..they will do all you need them to do..the do look quite spiffy..I think you may need to look close at these..not sure if it was these or another brand that sometimes shows up here that has som interference at the oil and fuel pump..

Tim I seem to remember Pete having issues with a set of the modified small block Chevy headers. Don't recall who he purchased from or what the outcome was. The Langdon's Fenton repops are about 50% more than the modified small block headers but I have been very happy with mine. And, did I mention it sounds good?

[Uncle-Pekka]

I am glad to see the lively conversation that my (stupid) question aroused!

I picked up two most important reasonings:

1) THE SOUND

2) "The manifold split is an old school way" ...of souping up the 230

Mark surprised me with his perfect finnish language and also the product by "Red's headers", which makes sense also performance vice.

I need to consider seriously the twin exhaust system for by baby as well...

[greg g]

If you are handy, you could probably modify some swap meet small block chevy headers to the same effect as the redheaders ones. As Tim mentioned, there was a set very similar posted years ago that were obviously SBC tube headers with one of the tubes cut off and flattened and welded closed. I have seen these at swap meets for as little as 25 bucks a set. You would need two sets as you need to have 2 right side sets to work with.

As an aside I believe Mark mentioned to me that his wife has family in your neck of the woods.

[Mark D]

I thought everyone spoke Finn..!?! Well at least that was what I thought when I was growing up. We had Finnish neighbors on all sides of our home, heck we even spoke to our dog in Finnish at home... so it was easy to find a Finnish blooded wife as well. We travel to Finland every other year to visit her family in Raahe, Oulunsalo, & Lappeenranta. Next time Pekka you and Fireball are on my list of people to visit! We are thinking about a Christmas visit this winter... Not sure about that yet.

As for the headers, I can certainly appreciate the alternate methods presented for modifying stock parts, but for the money, the unrestricted exhaust gas flow just seems better from my less than expert perspective. And I always have the stock stuff in my parts inventory just in case I need it.

[Uncle-Pekka]

Mark,

As you see in my member profile, I am currently living in Jyväskylä, central Finland.

However, I will most probably spend the Christmas in Kokkola, west coast, where all my & my wife's family are still living.

Kokkola is 100 miles south from Raahe.

Also my Dodge is currently in Kokkola as I have been preparing for a paint job using my fathers large garage/work shop.

It would be really great to meet you during the holidays!

Be sure to let me know if you come up North.

Br.,

Pekka

[blucarsdn]

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...

Edited September 5, 2011 by blucarsdn

[Plymouthy Adams]

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.

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

Excuse me..but if I am not mistaken, these old flat heads operate above the 3000 RPM range at speed...so even in your own words..they benefit..

I do agree with the most part of your statement that often too much added value is stated in the given mod than actually netted..and that 80% or higher usually overbuild their car for the street and will not seen the improvement they are seeking due to the blue light cruisers..

There is no exact method for cold and hot running (tunning) as to performance and economy in these older cars like we do have that with the computer controlled engines..

A header properly designed is of equal length, meets the collector at the proper angle to ensure flow out through the collector and not in any manner swirl or eddy to conflict with another incoming pipe etc..and properly matched to the correct sized pipe and muffler..will give added performance..even if it is only slight..as the reason to exhaust is only as important as you ability to breath..it is not the best bang for the buck if running stock intake and cam..

I am sure that it was good for your business to pass this along to your customer and show them the folly of wasting their money on your services..everything ingood measure..everything..

[greg g]

Hmm............ so the chassis dyno pull on my engine that showed a 20% increase at the rear wheels compared to the factory flywheel rating is what then? total fantasy.

Perhaps the dual carbs, increase in bore and increase in compression ratio had absolutly no effect on the way the engine runs, and I am just imagining the way it pulls hills, and has passing power from 40 to 70 mph that is quite satisfying. Fuel economy improved from 17 to 19 over the smaller lower compression single carb engine.

Perhaps the 4 Tops were right..........Well its just my imagination runnin away with me..

[Cpt.Fred]

the mods we did to my engine, including the 3 carb setup and equal length headers

as well as a slight raise of compression and reground valves and seats

resulted in better gas mileage and a 1/8 mile time 1 second lower than last year

when i ran a stock setup.

so now i know officially that it is at least a little more than just pissing in a wet suit:rolleyes:

[hkestes41]

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.

So, increasing exhaust flow and reducing back pressure through larger exhaust pipe diameter, "truck muffler", dual exhaust and equalizer tube to a stock 6 into 1 exhaust manifold will increase performance. Yet, increasing exhaust flow and reducing back pressure by splitting the manifold into 3 into 1 and adding dual exhaust will do nothing to improve performance and most likely reduce power?

If nothing else in an exhaust all paths from each cylinder should be equal length to optimize exhaust impulse and reduce reflected waves within the header/maifold. With the stock manifold which dumps near one end of the other, exhaust gasses must flow much further coming from the opposite end of the manifold resulting in reflected waves interfering with the scavenging of adjacent cylinders. The best way to avoid this is with individual equal length tube headers, to a lesser extent the same can be accomplished with the spitting of the stock manifold and the addition of a second dump. This will help to equalize exhaust path lengths and help offset reflected wave interference.

If you want to do some indepth reading try this link. While I agree it is applied to performance exhaust systems the general technical basics apply to any exhaust system. http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm

Edited September 5, 2011 by hkestes41

[Andydodge]

Well, I dunno about your side of the pond but I have a V8 with duals & turbo style mufflers on the 1940 Dodge and will eventually have split manifolds & a dual system on the 1941 plymouth.........noise, yep, sound, yep, more go, yep................bigger gonads?..........lol..............not since I last looked.........lol..........a less restrictive exhaust system of any sort has to be more efficent...........and if not.....so what, its MY hobby and I'll go varoom any way i want.................lol............now......where did I put those gonads again?..........andyd

[Plymouthy Adams]

check Mrs. Andydoge's purse or shoebox in her closet..may find them there..I understand by law you can petition for visiting rights with them if you are on good terms..

[Andydodge]

Tim.........your right......just looked.........she's wearing them as earings............lol............and I can walk much better without them things getting in my way now............lol..........varoom!!!!.........andyd