Future magazine article
 

This is a future article for FAMILY AND PERFORMANCE BOATING MAGAZINE, please read it and give me some feedback before I turn it in.
Dennis Moore


THE HIGH PERFORMANCE V8 EXHAUST SYSTEM
By Dennis Moore

Improving the exhaust system on an engine is one of the best ways to increase engine performance. Most people assume that an increase in performance through the exhaust will always come with an increase in the noise level of the engine. This may be true in some instances but not always. By understanding the nature of the exhaust system a boat owner can increase the performance without increasing the noise level. An exhaust system on a V8 engine is different than the exhaust system on a four or six cylinder engine. A four cylinder engine will have an exhaust pulse discharging into the exhaust pipe every 180 degrees of crankshaft rotation. A six cylinder engine will have an exhaust pulse discharging into the exhaust pipe every 120 degrees of crankshaft rotation and an eight cylinder engine will have an exhaust pulse discharging into the exhaust pipe every 90 degrees of rotation. At 4,500 rpm the four cylinders exhaust system has only 9,000 exhaust pulses per minute. A six cylinders exhaust system has 13,500 exhaust pulses per minute and an eight cylinder has 18,000 exhaust pulses per minute. With 180 degrees of engine crankshaft rotation between exhaust pulses (on a four cylinder engine) the exhaust pulse will have traveled down the exhaust pipe a considerable distance before the next exhaust pulse enters the pipe. With an exhaust pulse entering into the exhaust pipe every 90 degrees of crankshaft rotation (on an eight cylinder engine) the exhaust pulse will have barely started its travel down the pipe when another exhaust pulse is released right behind it. If there is any restriction in the pipe (that slows down the speed of the exhaust pulse, such as a small exhaust pipe or muffler) the exhaust gases can back-up inside the exhaust pipe (and the engines cylinders). This is known as back pressure and can prevent the engine from making maximum horsepower. A simple solution (it would appear) for reducing back pressure is to divide a V8 engine into two separate exhaust systems, one for each bank of four cylinders. Some less informed people (not readers of FAMILY AND PERFORMANCE BOATING) think that this solves our problems of exhaust pulses stacking up in the exhaust pipe. They think that instead of having an exhaust pulse dumping into one exhaust pipe every 90 degrees we now have two four cylinder engines with each engine having an exhaust pulse dumping into its own exhaust pipe every 180 degrees. If the exhaust pulses dumped into each exhaust pipe alternately, an exhaust pulse on the left side of the engine and then an exhaust pulse on the right side of the engine (back and forth), we would have an exhaust pulse entering each exhaust pipe every 180 degrees of crankshaft rotation. Unfortunately this is not the case because a V8 engine can not simply be divided into a left side four cylinder engine and a right side four cylinder engine. In any V8 engine we have two cylinders on each side that discharge an exhaust pulse into the exhaust pipe in succession (only 90 degrees of crankshaft rotation separates the pulses). On the left side (port) we have cylinders 5 and 7 discharging exhaust pulses within 90 degrees (of crankshaft rotation) of each other and on the right side (starboard) we have cylinders 8 and 4 discharging exhaust pulses within 90 degrees (of crankshaft rotation) of each other. When the two cylinders on each side fire in succession they will temporarily overwhelm each exhaust pipe with exhaust gases creating a restriction to exhaust flow. This sharp spike in increased exhaust pressure (inside the exhaust system) may not only create a restriction to exhaust flow but may cause some exhaust gases to reenter another exhaust port/cylinder through a (still open) exhaust valve. For example let’s look at the left side of the engine; when the #5 cylinder has expelled all of the exhaust gas from the #5 exhaust port/cylinder, the #7 exhaust valve will just be opening with high pressure exhaust gas shooting out from the #7 exhaust port/cylinder. Because the exhaust pipe is overwhelmed with exhaust gas (because the cylinders fired in succession) some of the gas from #7 may enter into the #5 exhaust port/cylinder. The exhaust gases will contaminate the fresh air/fuel mixture and hurt the production of horsepower in the #5 cylinder. As mentioned earlier both sides of the engine have this problem with cylinders #8 and #4 on the starboard side (the #4 cylinder will contaminate the #8 cylinder with exhaust gases).
An easy solution to this problem would be to install an exhaust pipe that is so large that there is no restriction to exhaust flow. This solution is also a very noisy solution; a larger exhaust pipe will definitely be much louder. A quieter solution would be to isolate the cylinders that will pass exhaust gases between themselves. Keeping the #5 and #7 cylinders exhaust pulses separated (as much as possible) on the port side and #8 and #4 cylinders exhaust pulses separated on the starboard side will help power production by reducing exhaust gas contamination. An exhaust manifold that is manufactured with separate passages, in an attempt to separate the cylinders that fire in succession, will increase performance without increasing the noise level.

it sounds good
 

I think it needs some cut away pictures to help some of the readers that do not have a good imagination. Charlie

Dennis, it`s a very informative article and you do a great job of explaining the theory. As a reader, the first thing that popped into my mind was: "where do I get this manifold?" And "Who makes a manifold designed to do this?" You may want to touch on that information as well.

Are you saying that header style, such as elbow top CMI's would be quieter than a big log type manifold?

Mag article
 

There will be photos and captions but I didn't include them in the thread. There will also be an article in the same mag about different brands of manifolds. It is going to be an exhaust manifold edition (Feb 2003).
Dennis

Sounds Great Dennis,, I am very curious about this subject as I posted previously noise restrictions are coming/here in many places. Mainly what are the benefits power wise of going to seperated exhaust pasages in a header or manifold like gils or imco's for thru prop (quiet) or a well muffled exhaust. How much power/torque gain can you expect without going to stright thru hulls as well ? The #5 cylinder will no doubt run cooler at a minimum. The #4 and 8 don't seem to interfere as much with each other perhaps sine they are further apart in the log, at least on my engine 502 mag i can see the dif on the #5 plug versus the rest, its a lighter shade of tan

Any dyno test/comparison between the manifolds?

Good question Cobra Marty. I've often wondered that myself.
There has to be way to rig up marine manifolds when the engine is on the dyno so we can get a realistic look at how the engine will perform as a package. Those long tube dyno headers can make a difference.

I read you proposed article and enjoyed it.
It reads very close to parts of the chapter on exhaust maifolds in your SBC Marine Performance book.

You didn't mention any scavenging effect the pulses create, if any, of an idividual runner type manifold vs an open chamber type production manifold.

You talked about how the exhaust pulses can stack up and possibly dilute the incoming fuel/air charge but not how a properly functioning system can help draw the fresh charge into a cylinder.

In the part about how high pressure exhaust gasses flowing from one cylinder to another could happen and that "an easy solution would be to install an exhaust pipe so large that there is no restriction", but you didn't mention how a pipe (collector) that large would actually hurt performance by reducing exhaust gas velocity and increasing the likelyhood of the pulses stacking then diluting the incoming fuel/air charge.

Very good though.

Some headders are quieter
 

Dennis,

Good points made and I agree. For instance the open style of a Gill Offshore manifold does not take into effect the separation of those cyclinders (#5, #7). On the other hand the high end "Stainless Marine" system does. It divides #1 and #3 together, and number #5 and #7 into separate collecters then discharges them later down the line when the pulses equalize. I remeber learning about this scavenging effect on Turbo Charged Engines. The reason why the Grand National was such a good turbo Car. A motor with multiple of 3 cyl has matched exhaust pulses and can actually make more power, where a V8 does not.

Also, I agree that a headder system may actually be quiter than a manifold type of system. I believe it is due to resinace inside the manifold? Last winter a buddy of mine installed CMI elbo tops in place of his gill offshores. The motors were quiter at idle and at cruise.

Keep it simple
 

Thanks Iggy!
It is obvious that you are quite a bit more knowledgeable than the average reader. As I am sure you are aware, we have to keep it as simple as possible or we will lose the readers attention. You know us boaters, we usually are reading this stuff with a beer in our hand!
Sincerely
Dennis Moore

Thanks Panther!
 

Panther, I appreciate the feedback! I was a little afraid that the people on this forum are a little more knowledgeable about exhaust systems than the average reader and I am proven right!
Dennis

Re: Keep it simple
 

I thought we were supposed to read in the crapper:confused:

Have I been doing it wrong all these years:p

Re: Re: Keep it simple
 

your confuser isn't in the crapper? I thought that is why it was called the throne:D

That is a very informative article and I liked it. My only comment would be one to aid in ease of reading. Being more of your average type boater, I was distracted by the switching from "left side, right side" to port - starboard. The article would have been easier to follow using just "port bank" and "starboard bank" consistently.

BTW... where might I find this magazine? I ordered the BBC Marine book yesterday and am looking forward to that.

Good luck with the article,

BT :cool:

Thanks
 

Blue Thunder

Thanks for the input, I think you are right and I will change it.
www.familyandperformanceboating.com

Dennis Moore

Thanks Dennis,

You have any books on sterndrives?

BT :cool:

Dennis,

Good job on the Magazine. We finally got our subscription worked out, and were sent the issues we missed. Thanks for the help you gave my other 1/2 on the phone with our problem.

I would recommend this magazine to those that heve not read it.

Dennis
 

That will make A nice article in your magizine.I think anybody who will purchase that magizine will enjoy reading it.Very easy to follow .Now if you could tell us what manifolds work the best:D .
Dave

Crossover pipes...
 

Dennis,

I guess it's time to ask my wife for a subscription to that magazine for my birthday! I think the set of Merlin heads that I wanted are out of reach financially right now anyway. :(

Is there any way that I can get some of the back-issues of the magazine? I know that there were some interesting tech articles that I missed out on in the past.

My question: What effect would a crossover (or "H") pipe have on this situation? I have seen this setup on boats before, although not frequently. It has been used in automotive applications to boost low and mid-range torque. Would this help to alleviate the contiguous cylinder issue?

I have now read all 3 articles and I think you did a great job. A lot of the guys, as you have noticed are very knowledgeable. I however am not when it comes to engines. After reading your SBC book cover to cover 10 times I think I have a good idea! :D I found your articles easy to read and understand even if you are a motor moron like myself. Good job and keep up the good work, the magazine is my favorite of the boating magazines.

Very good article, I think that if you have the cut away pictures of a manifold (such as those in your book) it will help everyone understand the need to seperate cylinders and how some manufactures did not do a very good job at that.

BTW, I love your book! I call it my BIBLE.

Bob

Budman, Milord + Bob
 

Budman
Yes you can get back issues. Give them a call. I don't know about H pipes. The Mercruiser through the transom exhaust with Silent Choice running through the Y pipe (prop) would have to be considered an H pipe setup.
We are going to test the FPB Magazines 500HP Baja this winter with a Corsa's Captains Call. We will find out then!

Milord
Thanks for taking the time to respond!

Bob
I had to leave something out so you would buy the magazine! The article has good photos including excellent cutaways of some exhaust manifolds (including the GLM).

Thanks
Dennis

First rate as always !

Sam;)

Dennis: I have seen lot's of stuff written about installing new exhaust manifolds/risers. BUT I have never seen a comparison of different systems/manufactures with a price/performance comparison....If you really want to do something that would be usefull and different a test on exhaust silencers would be GREAT! I have never seen one before that lists price/performance (HP/SPEED) AND Sound level reduction.....The cost here is monumental and the issue of quality of consruction is usually not. ALSO how about doing the articles with some basic motors and listing results....Like a Stock 350 and a mild to hot 350 (325-400hp). Then do the same with a 454/502 stock and mild. Doing this would be more real world. Alot of stuff really isn't "Bang for the buck" if your stock or mild. What will help a worked over motor and what will help a stock motor is different. And on a stock motor a $1500-2000 exhaust system may yield only small results where as a worked over motor may really wake up with the same system..... Some real tests and comparisons (similar to Hot Rod or Car Craft) would be a HUGE upgrade over articles written to a small group of people. This would GREATLY enhance your Magizine AND set it apart from the rest.....

Bad-Habit

Exhaust tips
 

Dear Bad Habit'

This winter we are going to set up our Baja to test different exhaust tips.

I don't think anyone will ever do a direct comparison between the horsepower differences of different aftermarket exhaust manifolds. We can only test aftermarket manifolds against the stock manifolds.

There is so much brand loyalty (and emotions) between boaters and the products (that they install on their boats) that the results would be too controversial to print!

We can always be sure that a low life attorney will cause all sorts of problems for the magazine if a manufacturer doesn't like the outcome of the tests.

Life with litigation, thank you attorneys!

Dennis Moore

Here's and idea?
 

What about propositioning the manufacturers to test their products against one another? I bet they will run away with their tales between their legs. Now this would put them to the test, and would make them stand behind their product, cause some competition, and maybe even make them go back to the drawing board to improve designs. It may also keep cost's competitve. If the cheaper manifold is proven to make more power then why not buy it. The only time I have seen comparisions like this done was at one of my local dyno shops.

I know what you're saying about loyalty, and lawsuits and what not. But can't it be done somehow? I mean consumer reports does it all the time. Even companies crash cars to see how well they fair. Guarantee that if a so called power making manifold or headder does not prove itself on the dyno compared to other brands there will be some redesign. For the prices that we are paying for these darn things we should be entitled to compare?

What do you all think?

Dennis,

Speaking of an actual test boat, I was very interested in the articles that Family Performance Boating did on the 65 hp 500EFI kit and the Vortech Supercharger but there was no before and after results.

Any chance of following up with the results like on the Baja? The MSD article was great.

envision

Dennis,

Great artical! As you know, you have some very good cut-away examples of stock manifolds as well as high performance manifolds in your BBC book that work very well in visualizing your points. You also show a photo of a manifold that would appear to be a high performance manifold but has a insuffiecient length divider fin between 5 & 7 as compared to the photo of the Gil which does not have the same problem. I guess the answer to the consumer considering purchasing "high performance" manifolds is to study a cut-away of the product prior to ordering.

Got cutaways (got milk?)
 

Dear Playn
The magazine article will have some cutaways and other photos. I had to leave something out or you guys wouldn't buy the mag!
Dennis

Manifolds
 

The point I was trying to make in the book was that if you are buying exhaust MANIFOLDS then you should buy a design that has the 5+7 and 8+4 cylinders separated as well as possible.

I think that any attempt to separate the cylinders will show that the designer of the manifolds had some idea of what he was trying to accomplish and understood the theory behind exhaust systems.

If you are going to spend the extra money for exhaust HEADERS like the excellent CMI or KE systems you don't need to worry about it. I guess it is all about your boating budget.

Sincerely
Dennis Moore

A few years ago another mag (I think it was HB) did a comparison test ..and I belive they used a dyno on several of the popular manifolds and headers. I cant remember all the stats but the Lightning tube headers came out on top..and I bought em. Traded off my Imcos that were on and did notice a big difference in mid range.
A real world comparison ...possibly on your Baja test boat would be a good article...or you could use my Warlock :)

Dan

Dennis,

The pictures of the cut-away exhaust manifolds in your book; "BBC marine Performance" were very beneficial and knowledgable----wished you had more cut-aways of more manifolds brands so we could see who's who in the exhaust manifold world.------I know----it's the attorney thing. :rolleyes:

But hey Dennis, we (the consumer) will tell them that we're all on YOUR side! :)

Kaama
 

Hey Kaama,

The new 496 Mercruiser has a *****in aluminum exhaust manifold! It looks like a high performance manifold with separate exhaust passages. If you ever get a chance check one out, I am going to get one of those and cut it away for a magazine article. Maybe Mercruiser will be a player in the performance manifold game!

Sincerely
Dennis

In reference to the H-pipe. There was a company in Longbeach, Ca. I believe who manufactured an H-pipe setup and some other interesting pieces. They were called Fast Motorsports and had a web site. But I just tried calling it up and it doesn't appear to work anymore. www.fastmotorsports.com Did they go out of business? Anyone know? I was interested in their A-R Planes.

Interesting article Dennis. One of the reasons that Familiy & Performance Boating has been my favorite for a couple of years!

Really do wish you wouldn't be so P.C. though. It's dissappinting when compared to the cylinder head database noted in another thread by High Performance Chevy magazine. If they can do it, why can't someone in marine publishing do it? This industry needs some shaking up. Too stagnant in technology and pricing is rediculous. For those on the lower end and or new to boating especially, many of the parts are just pipe dreams because of cost. If it was more realistic, the sales/production volume would go up. Last time I checked... That means higher profits to the manufaturers.

Just a pea-brained thought,
Scott

Pea brained? I don't think so!
 

Excellent points! Before I started writing for FPB I would seldom read a boating magazine because the projects and advice were out of my budget, totally unrealistic for the average boater. I think that FPB magazine is unlike any other boating magazine and we are feeling our way through, not knowing how far to push conventional thinking. The Ford thing will be unique, along with the small block Chevy buildup we are doing over the next few months (everybody does Big Blocks!). Technical articles are what we are going to live (or die) by. Check out the prices on the GLM exhaust manifolds that increased performance, good values there. If you want to see how far we go out on the limb check out the rather brutal article we did on the MSD in the Sept 2002.

If you only knew me you would know that I am very opinionated and I am doing my best to shake up the industry! I really have to hold back at times!
The industry is stagnant and won't change until Mercruiser gets a little competition. I believe that the Japanese outboard manufacturers will (unfortunately) blow Mercury outboards out of the water. It's a shame that Mercury OB engineers can't build something a little more innovative!

Sincerely
Dennis Moore
Politically Correct?

Perhaps Bombadier (spelling?) will shake things up with competition with Mercury since they took over OMC or whoever it was (can't remember now). Anyway, I heard those boys don't mess around. That will get Merc off their higher than mighty arse! :)

Kamma,
You're right, Bombardier is a leader in everything they do. so let's see the new outboards and sterndrives. An industry without any real competition in it is blah. Same goes for Yamaha, step-up and race those things!

Bombardier, Yeh!
 

I think you are both right, when Bombardier gets going it will be looking backwards at everyone else. If they hand the engineers a clean sheet of paper to design new engines they will be very hard to compete with!
Dennis
PS sounds like you guys are snomobilers, me too!

Microsoft their A$$
 

I think Merc. needs a little taste of Microsoft. Does anyone spell monopoly? Lets see, you have Mercruiser, Mercury, Force, Baja, Searay just to name a few. They are all owned by the same damn company (Brunswick Corp). Part of the reason that Baja SeaRay, and Bayline all come with Merc Power. I wonder what kind of deals are going on there?