High Performance Exhaust

[jw454]

I have a 1989 Mercruiser for Cruiser 7.4 330HP that I am building this winter. It starts out with forged 30 over pistons Edelbrock rpm intake manifold and matching cam shaft, double roller timing chain. I swaped peanut heads and fitted it with GM large ovalport heads, roller rockers, and some more goddies here and there. However, I am not a millionaire and figured I could save for an exhaust over time. It has come to my attention that from the aggressive profile of the camshaft.... .570 lift at valve and 240 duration at .050 I might have a problem with reversion. Currently, the engine has stock exhaust manifolds with 4 inch elbows, and 4 inch through transome exhaust. Any technical help or advice on this situation would be greatly appreciated. Also, does anyone think that this was a good edging combination? Also, I forgot to mention the forged pistons are 10.5 to 1 comp.ratio. Thank you much!!!!

 

[Walt T]

Re: High Performance Exhaust

Lightning manufacturing. (909) 678-5631<br /><br />They make stainless water jacketed headers.

 

[jw454]

Re: High Performance Exhaust

Hello DieselWalt, Apparantly I can not run boat with engine cover if I want to go with headers. This would be the best choice for horsepower, but I take my 7 year old out water tubing and would not want him or the wife to slip or fall on hot engine. do you know anyone who uses headers?

 

[Walt T]

Re: High Performance Exhaust

Well that's why those are water jacketed headers. Since I didnt know what kind of boat you had if the engine was open or not I recommended Lightning. Those headers have water flowing through them and are not great big ol headers. They are actually quite small. But if they wont work for you try Imco. They're on the web at www.imcomarine.com They have performance manifolds that will replace the current ones without a problem.<br />With that cam you need to realize you may have water getting in your engine. Generally I don't run overlap like that with a wet exhaust system.<br />However it's your boat and it sounds like you've put some thought into it. You'll find out soon enough how well it all works.

 

[jw454]

Re: High Performance Exhaust

Helo again DieselWalt, Thanks again for your response. My boat is a 20FT Celebrity ,Model 208 Bowrider with a deep V hull. Not a race boat , but not a candyass either. I am not shure of its weight. Had no problem hitting consistent 65MPH across lake last summer. Would like to see 75-80 next year. That isnt bad for a tame 330. Do you think mods will get me there? Also it didnt get on plane as fast as I would like. Hope mods help that too. I am going to try running the thru-transom exhaust at a steeper downgrade to also lessen the possibility of reversion. Do you think it is safe to run headers with engine cover on? Even though water jacketed , every ad Ihave seen says only use with open engine. Any ideas or advise is much appreciated.

 

[BRIAN03]

Re: High Performance Exhaust

Thru hull exhaust or run Gil exhaust. Gil exhaust has a long run of dry exhaust and puts the water in at the end of there pipes. Mercruiser has used them for years. You need to figure out the exhaust befor you build your engine or your wasting you time and money. There is nothing worse than a new engine full of water. I have fill many of them over the years putting too big of a cam in them. They always ran great till you shut them down. You would be on the lake with your friends badest boat on the lake and shut it down and hydro the engine. I always ran thru hull exhaust after I learned about cams and water injestion.

 

[Walt T]

Re: High Performance Exhaust

I agree with Brian. Anyway, to achieve your goals, I need more information such as drive and gear ratio and prop information. 10 mph is a pretty lofty goal, but is achievable.

 

[Doug Durako]

Re: High Performance Exhaust

As Diesel says, give us a little more info. Weight of the boat, year it was made, degree of deadrise at the stern, drive you are running, and props you have tried.<br /><br />What is your rpm at wide open throttle?<br /><br />Sounds like you might be a bit overpropped---that boat should jump out of the water. At the top end, I would think you could hit 70 mph fairly easily with just a prop change.

 

[jw454]

Re: High Performance Exhaust

Dear Diesel Walt and friends:<br />I have put most of the information of boat specs on a previous post to Diesel Walt. Maybe I forgot to include it has a bravo 1 with 1.5 gear ratio and came with 21 pitch 5 blade prop. I borrowed my friends' Bravo 1 4 blade 23 pitch prop motor ran at 4500 RPM 65 miles per hour. With 5 blade engine runs too fast 5100 RPM and only 57 miles per hour. Boat gets out of the hole just as fast with 23 pitch. Hoping with new horse power I can spin maybe 26 pitch bravo 1. Let me know your feelings on this. ( Should get me 70 plus MPH!!!) Thanks JW454

 

[BRIAN03]

Re: High Performance Exhaust

After 50 miles per hour on the water. It takes 10 hp for every mile an hour you want to go. 20 miles an hour faster you need to add 200 horsepower to the base engine. Its Math and Money. A boat is a dyno. Turning the prop faster doesnt make you faster. The engine has to make more power to over come the load put apon it. Its making usable horsepower and then putting the correct prop on for the load apply.

 

[jw454]

Re: High Performance Exhaust

My thoughts exactly Briano3, that is why with a 24 or 26 pitch as opposed to the 21 and 23 I have used,( my hopefuly ) new bigger horsepower engine will turn a larger prop within the proper rpm range. Factory says 4400-4600 (I think Ican get away with 4800). Like Ihave said before, the boat already has thru-hull 4 in exhaust. Unfortunatly, I only have crap factory cast iron manifolds and risers. The Gil system is out of my price range for the moment, but I have been in touch with Todd from Revolution Marine. Sounds like a nice affordable system (aluminum manifolds with tuned exhaust runners, and aluminum risers with reversion damms.) Have you ever heard of, or had experience with these? Todd says they flow great, and says many out there with my cam specs. and larger, have no problem with reversion. My favorite part is they only weigh 38 pounds per side. Cast, 100 plus per side. Let me know what you think. JW454. .030 JW461.

 

[Doug Durako]

Re: High Performance Exhaust

You are not transferring all your horsepower to the water with a four-blade prop. Those are designed to get bigger, heavier boats out of the water and you don't need one. At high rpms, they create more drag and lose efficiency.<br /><br />Try a quality three-blade stainless from Merc. at 23 or 24 pitch. If you go up to higher pitch, you will be even slower out of the hole, but you probably already know that.

 

[jw454]

Re: High Performance Exhaust

Hey guys I also have a Lunati cam .540in .550ex 114LS 112CL 225in 235ex @.050. Does this sound like a better choice than the EdelbrockRPM? Probabaly better to avoid reversion. But afraid it is to tame. Dont want engine to be a dog like was before. Stock cam only .271in -.282ex @ cam, must outperform that junk.

 

[Walt T]

Re: High Performance Exhaust

Changing cams does not guarantee more power. <br />The whole idea behind changing cams is to make the engine perform better at high rpms. You will not be running above 5000 so any performance gain you get will be minimal with the specs you gave. By bumping up compression you have improved hole shot pretty well. I suggest using a mild cam that gives performance up to 5000 rpm with most improvement below 3000. <br />In my own opinion the cam specs you mentioned earlier will over cam your engine having the same effect as over carbureting. It will still be a dog.<br />My recommendation is to stay with hydraulic rockers - here again you're not doing excessive rpms so rollers arent needed, see if you can get your money back for the rollers and cam-<br /> Duration of 210 intake 218 exh @ .050 and .505 and .515 lift respectively. Just a good performance cam that will give you power below 5000. Get the entire cam and lifter kit. I also suggest new or performance valve springs.<br />You will also have to check piston-valve clearance. This is an involved procedure and you will have to get the specs from the cam or piston manufacturer, because stock specs are gone. You must also check all your bearing clearances very carefully and the critical spec is going to be differences between the rods. New rod bolts are a must of course. New cam bearings are a must, have the machine shop install them for you.<br />An Edlebrock torker manifiold with a 650 or 700 vaccuum secondary carb should work perfect. I think you'll be very happy with that. The only other change I would make is to put the compression at no more than 9.5. Mostly because I dont want to have to keep a case of 104 booster in the boat. I do like high compression though, it really wakes up an engine. I prefer to keep my performance engines that are not being raced manageable. Going above 10.0 compression will shorten the life of your engine. It will definetly give you power, but rings, bearings, rods, and the crank will pay the price. <br />You should have the rods peened and carefully inspected. I would most likely not use stock rods for that compression.<br />You must also be sure the oil passages in the crank are perfectly clear. The stock oil system works perfect, in fact Chevy's system begs to be left alone. I would consider using maybe some Clevite 77 bearings. Thats a big load to be putting on stock rod bearings.<br />After all what fun is building an engine if you're afraid to put the hammer down? <br />Above all have fun and ask a lot of questions.

 

[jw454]

Re: High Performance Exhaust

Thanks for the reply, DieselWalt. I have already purchased Clevite 77 H series rod and main bearings. New cam bearings were installed. I will buy 9.5-1 Speed Pro pistons after I cc the heads. I will be running the stock rods that were reconditioned and ARP 3/8 Waveloc rod bolts. Engine is 4 bolt main, so not to worried about things coming apart. As far as oil system goes, I am going to run a Speed Pro HV oil pump. Crank was just polished and has to be sent out along with pistons, balancer,flexplate ect. to get balanced. Was highly advised to have this done. Forged pistons much heavier than cast. I already have Edelbrock RPM AIR-GAP that I will use, it is daul plane and theoreticaly should provide more torque than single plane Torker? I know what you are saying about cam RPM range and have to make choice. What is the deal with losing the ex. rotators i HAVE HEARD SO MUCH ABOUT. Seems to me valve and seat would run cooler. Original peanut heads had rotators on ex- in valves ,new heads only have ex. JW454.

 

[Walt T]

Re: High Performance Exhaust

The intakes run cool enough, the exhaust still use the rotators.<br />You'll be fine, I wouldnt bother with the oil pump just use the stock pump it will work fine.<br /><br />You know a supercharger would work really really well....... But you'd have to drop compression to 8 or so.

 

[jw454]

Re: High Performance Exhaust

Just bought NY state lottery ticket today. If I win , I will consult on your opinion for good blower. Wish me luck. JW454.

 

[Walt T]

Re: High Performance Exhaust

Nah, they're only about 3 grand. Then you get a Projection fuel injection set up for it at another 1500. Spin that prop right around.