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Discussion Starter #1
Hi Guys,

I've been a member of this forum for a few years now but more a reader than contributor and I think the time has finally come to reach out :)
I currently have a 2000 29 Scarab which I love but its time to upgrade things a bit and rather than learn from my own money eating mistakes I thought
It best to seek some advice from the knowledge full.

I am based in Ireland and familiar with european cars but American Marine stuff is completely forgien to me.

My Scarab was running a single 7.4 MPI 310hp which pained me as my previous boat had two 5.7 twin turbo motors and wanted to go down a similar
route so when I saw some value in the form of a low hour Mercruiser (Forged pistons, steel crank and low compression)502 Carb engine 415hp
which had been fitted with a Cutler EFI system 1000CFM (similar to Holley), MSD 6M-2, Mercruiser Thunderbolt IV Distributor and a set of exhaust headers I took a punt.

I then acquired an old school Gale Banks Stage Three Twin Turbo Setup. which consisted of 2 Gale Banks Exhaust Manifolds,2 Water Cooled Turbos and 2 Intercoolers.
There currently isn't the ability to control boost as it simply is preset via a hole in the exhaust side that allows gasses to bypass the turbo. From what I can find
out the system runs about 8psi stock and some people have restricted the bypass to increase up to 12psi. I can block these off and weld in some external wastegates if need be.

Here are two links to similar set ups:
http://www.performanceboats.com/part...turbo-kit.html
https://www.flickr.com/photos/menard...7616396786774/
https://www.flickr.com/photos/menard...7619340912710/

My current thoughts are to ditch the outdated Cutler EFI ECU and replace it with Holleys HP EFI (550-604) and run some bigger injectors and to remove the throttle
body and mount the intercooler on top of the inlet manifold and fit the throttle body where the carb would sit?

Is this a set up that would work anyway well? I really need to know what approximate power level these engines can run safely in stock form so that I can match the correct
injectors and to get the correct GPH fuel pump etc. I estimate a figure of about 700hp would that be a fair assumption?
Again I have no idea about American products and don't know if my existing Distributor and MSD ignition box me up to the job? are they standard
block connections that are plug and play with the Holley 550-604 kit?
Would I have a worthwhile benefit from sticking in a set of cams and rockers while the engine is out of the boat?
I know I'm probably going to be told to ditch the old kit and get a procharger but I just like the turbo idea.

Any advice or guidance as to how I would best set this up to maximize its potential on a reasonable budget would be greatly appreciated.

Many thanks from the Land of Eire!

Jay
 

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Youve been watchin for a loooong time:thumb:
Great first post, welcome.

Be safe, schick
 

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The first question, which will be extremely important in determining what boost you may be able to safely run is what fuel are you using? What's the compression ratio on that engine? I think maybe 8.75-1?

These kits were state of the art when I worked for Banks, but that was around 35 years ago. At that time they were selling a "crate" 454 with the turbo kit added on and rating it at 650 HP. However, that was making around 10 psi boost, and higher octane gasoline was still readily available at gas stations. There were several different size bypass holes drilled in the housings, and boost varied from a low of around 5psi to perhaps 15psi depending on which intercooler and engine combination was being used.

Next, low end performance would benefit greatly using some type of waste gate arrangement if you want to take the time to engineer it.

I don't have experience with either of those injection systems, so won't be able to help with that. I would suggest a cam ground for your specific application.

Adequate fuel supply and correct ignition timing will be critical for any forced induction engine.

Back to your question about horsepower capability of that engine, I blueprinted a stock 502 that got an 8-71 blower set on top of it, and has been running for about 6 years now in a jet boat application, with mild boost and pump gas.

You will probably want to stay conservative with boost since you are talking about pushing a big heavy boat putting a constant load on the engine.
 

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Discussion Starter #5
The first question, which will be extremely important in determining what boost you may be able to safely run is what fuel are you using? What's the compression ratio on that engine? I think maybe 8.75-1?

These kits were state of the art when I worked for Banks, but that was around 35 years ago. At that time they were selling a "crate" 454 with the turbo kit added on and rating it at 650 HP. However, that was making around 10 psi boost, and higher octane gasoline was still readily available at gas stations. There were several different size bypass holes drilled in the housings, and boost varied from a low of around 5psi to perhaps 15psi depending on which intercooler and engine combination was being used.

Next, low end performance would benefit greatly using some type of waste gate arrangement if you want to take the time to engineer it.

I don't have experience with either of those injection systems, so won't be able to help with that. I would suggest a cam ground for your specific application.

Adequate fuel supply and correct ignition timing will be critical for any forced induction engine.

Back to your question about horsepower capability of that engine, I blueprinted a stock 502 that got an 8-71 blower set on top of it, and has been running for about 6 years now in a jet boat application, with mild boost and pump gas.

You will probably want to stay conservative with boost since you are talking about pushing a big heavy boat putting a constant load on the engine.

Yes my engine has the lower 8.75 C/R, my banks kit is a stage 3 kit if that sheds any light on what boost it is set at? the bypass hole is 14mm (9/16th) the fuel rating in Ireland is rated differently and we have 95/98 which is equivalent to 91/93 in the US, that said I run various fuels in my cars and have drums of 107 octane fuel to hand but will run this on pump fuel as It will drink it at a rapid rate.

I suppose what I need to find out is what the stock engine can take and conservatively set the boost levels accordingly. I think I'll be happy with a 650-700 bhp 75mph boat (for the minute)

Having no major boat modifying experience would it be a good investment fitting a boosted cam for drive ability or would i just be wasting my time and money only wanting to run 700bhp?
 

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Some guy
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Yes my engine has the lower 8.75 C/R, my banks kit is a stage 3 kit if that sheds any light on what boost it is set at? the bypass hole is 14mm (9/16th) the fuel rating in Ireland is rated differently and we have 95/98 which is equivalent to 91/93 in the US, that said I run various fuels in my cars and have drums of 107 octane fuel to hand but will run this on pump fuel as It will drink it at a rapid rate.

I suppose what I need to find out is what the stock engine can take and conservatively set the boost levels accordingly. I think I'll be happy with a 650-700 bhp 75mph boat (for the minute)

Having no major boat modifying experience would it be a good investment fitting a boosted cam for drive ability or would i just be wasting my time and money only wanting to run 700bhp?
A 9/16" bypass ( 1/2" or 5/8" would have been more common coming from Banks) should keep the engine in the pump gas range (maybe 6-8 psi?), and you could even try it that way and later remove and restrict the hole if you wanted more boost. I understand some people tap the housing for a 1/2" pipe plug with a hole drilled in the middle to accomplish that.

Some years ago I put together a 588 inch single carbureted engine for a 29' Scarab. I tested the boat with the owner and would guess it ran about 75 mph. The heads were rebuilt by someone else at customer's request and after the boat sat over the winter the customer went out and ran the boat with the old fuel, probably flat out across the lake, and a valve broke. Moral of the story is the same thing I suggested in the previous post, it's a big heavy boat, you don't want your tune up to be too much "on the edge" in case of a bad load of fuel.

Cam selection is one of the most important things of any engine build, but I have a local cam grinder I deal with who can regrind the stock camshaft for me without too much trouble. I suspect that's more difficult to find in Ireland?
 

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Discussion Starter #7
A 9/16" bypass ( 1/2" or 5/8" would have been more common coming from Banks) should keep the engine in the pump gas range (maybe 6-8 psi?), and you could even try it that way and later remove and restrict the hole if you wanted more boost. I understand some people tap the housing for a 1/2" pipe plug with a hole drilled in the middle to accomplish that.

Some years ago I put together a 588 inch single carbureted engine for a 29' Scarab. I tested the boat with the owner and would guess it ran about 75 mph. The heads were rebuilt by someone else at customer's request and after the boat sat over the winter the customer went out and ran the boat with the old fuel, probably flat out across the lake, and a valve broke. Moral of the story is the same thing I suggested in the previous post, it's a big heavy boat, you don't want your tune up to be too much "on the edge" in case of a bad load of fuel.

Cam selection is one of the most important things of any engine build, but I have a local cam grinder I deal with who can regrind the stock camshaft for me without too much trouble. I suspect that's more difficult to find in Ireland?
Very hard to get an exact measurement of the hole TBH, I'm going to weld them up anyway and run one or 2 wastgates. its defo a lot harder doing stuff on boats as everything has to be cooled in the engine compartment.

I push the envelope on a lot of my tuned cars (1048 bhp from 3.6 turbo'd M5 engine) I will be running knock sensors, EGT anf AFR gauges permanently to help keep her safe.

I would say that the cost of Cams for this engine are relatively cheap for these engines and don't mind buying new, can you recommend a good off the shelf cam for this set up?

what spark plug would you recommend?
 

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Are you running the stock iron heads on that engine? I would run an NGK, probably in an "8" heat range for recreational use. The camshafts that were used in the Banks engines originally were very mild by today's standards. The TCS 7 Engle was the cam put in most of them when I was there, but I suspect you want something that will make more power. I can have something ground for you, possibly get get someone to hand carry to the UK if you are not in a hurry,, friends from Scotland come back and forth for water ski racing here in the US.
 

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Hi Guys,

I've been a member of this forum for a few years now but more a reader than contributor and I think the time has finally come to reach out :)
I currently have a 2000 29 Scarab which I love but its time to upgrade things a bit and rather than learn from my own money eating mistakes I thought
It best to seek some advice from the knowledge full.

I am based in Ireland and familiar with european cars but American Marine stuff is completely forgien to me.

My Scarab was running a single 7.4 MPI 310hp which pained me as my previous boat had two 5.7 twin turbo motors and wanted to go down a similar
route so when I saw some value in the form of a low hour Mercruiser (Forged pistons, steel crank and low compression)502 Carb engine 415hp
which had been fitted with a Cutler EFI system 1000CFM (similar to Holley), MSD 6M-2, Mercruiser Thunderbolt IV Distributor and a set of exhaust headers I took a punt.

I then acquired an old school Gale Banks Stage Three Twin Turbo Setup. which consisted of 2 Gale Banks Exhaust Manifolds,2 Water Cooled Turbos and 2 Intercoolers.
There currently isn't the ability to control boost as it simply is preset via a hole in the exhaust side that allows gasses to bypass the turbo. From what I can find
out the system runs about 8psi stock and some people have restricted the bypass to increase up to 12psi. I can block these off and weld in some external wastegates if need be.

Here are two links to similar set ups:
http://www.performanceboats.com/part...turbo-kit.html
https://www.flickr.com/photos/menard...7616396786774/
https://www.flickr.com/photos/menard...7619340912710/

My current thoughts are to ditch the outdated Cutler EFI ECU and replace it with Holleys HP EFI (550-604) and run some bigger injectors and to remove the throttle
body and mount the intercooler on top of the inlet manifold and fit the throttle body where the carb would sit?

Is this a set up that would work anyway well? I really need to know what approximate power level these engines can run safely in stock form so that I can match the correct
injectors and to get the correct GPH fuel pump etc. I estimate a figure of about 700hp would that be a fair assumption?
Again I have no idea about American products and don't know if my existing Distributor and MSD ignition box me up to the job? are they standard
block connections that are plug and play with the Holley 550-604 kit?
Would I have a worthwhile benefit from sticking in a set of cams and rockers while the engine is out of the boat?
I know I'm probably going to be told to ditch the old kit and get a procharger but I just like the turbo idea.

Any advice or guidance as to how I would best set this up to maximize its potential on a reasonable budget would be greatly appreciated.

Many thanks from the Land of Eire!

Jay
I know the guy in those pictures! :)

At 12lbs of boost on my 468, I was right around 800hp. It ran great for quite sometime. Obnoxious forgot more about these things than I will ever know...but I think you have the makings of a nice engine. I powered mine draw through with a slightly worked Holley 850. If you stick with those older turbos (providing they are in good shape) since they have carbon seals in them, you could put a 4150 style throttle body between them and not have to worry about a blow off valve. As far as the fuel injection part of it though...way beyond my paygrade.
 

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Discussion Starter #10
Are you running the stock iron heads on that engine? I would run an NGK, probably in an "8" heat range for recreational use. The camshafts that were used in the Banks engines originally were very mild by today's standards. The TCS 7 Engle was the cam put in most of them when I was there, but I suspect you want something that will make more power. I can have something ground for you, possibly get get someone to hand carry to the UK if you are not in a hurry,, friends from Scotland come back and forth for water ski racing here in the US.

Thanks for your offer and again for your knowledge.I am running completely stock engine internals and from what I am reading I thing for the moment I will just leave it that way, I am using Bravo 1 and have another 2 other spare ones so I think at 700bhp which is realistic for my set up I might just see how it holds up. I also have a second banks kit and second 502 engine so might build that as a 1000bhp motor and work towards a different outdrive to drop in after that.
 

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Discussion Starter #11
I know the guy in those pictures! :)

At 12lbs of boost on my 468, I was right around 800hp. It ran great for quite sometime. Obnoxious forgot more about these things than I will ever know...but I think you have the makings of a nice engine. I powered mine draw through with a slightly worked Holley 850. If you stick with those older turbos (providing they are in good shape) since they have carbon seals in them, you could put a 4150 style throttle body between them and not have to worry about a blow off valve. As far as the fuel injection part of it though...way beyond my paygrade.

Hey :) I like your set up, its what kinda kicked me off again on the idea! my Cutler EFI set up has the same set up as the 4150 and I'm thinking of re-positioning it from the inlet manifold to where your carb is pre turbos and draw through it. the system just bolts together that way and I don't see it being a problem. I was going to sit the inter cooler on top of it but decided against that for two reasons, firstly I it wasn't designed for that second I didn't know if it would cause problems with blowing out of linkage seals and secondly I would have to make up an adapter plate(not a big deal but why bother if it will work the other way) Maybe Obnoxious has experience in this field and knows of some issues that I have not foreseen?

I din't think there would be any need for blow off valves on marine engines? they only really stop turbo stall when throttle is closed but compared to a car with multiply gear changes a boat would rarely be in that situation? perhaps the definition of blow off valves are something different in the USA compared to Europe?
 

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Discussion Starter #12
Are you running the stock iron heads on that engine? I would run an NGK, probably in an "8" heat range for recreational use. The camshafts that were used in the Banks engines originally were very mild by today's standards. The TCS 7 Engle was the cam put in most of them when I was there, but I suspect you want something that will make more power. I can have something ground for you, possibly get get someone to hand carry to the UK if you are not in a hurry,, friends from Scotland come back and forth for water ski racing here in the US.

Yes Obnoxious001 I am using stock iron heads, my engine is completely standard. I'm really trying to decide on cams now. I was going to just run standard cams as it will still exceed the the power limitations of my Bravo one but now I'm thinking I might put one in now that the engine is out and easy to do. I'm sure after I blow up the bravo one I will upgrade it and then will ultimately want to run more power so a bit of forward planning :)
What should I run in your opinion? Do I go all out hydraulic roller cam with roller rockers with girdle or am I wasting my money and just stick in a mid range cam and nothing more? as this is a boat and will probably max out at 5200-5500 rpm I'm thinking the latter? Your experience/guidance would be greatly appreciated. Should I be doing anything else while I am at it? ARP bolts/studs?If you had my box of bits what else would you do? I don't mind spending a few $000 but I really don't know about these American engines and don't know their weaknesses and as such want to spend the money in the right places.:)Unsure I have mocked everything up today and have opted to fit the throttle body after the intercooler, a little bit of minor fabrication and she will be good to go.:)
 

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Ya might want to put a good set of rocker arms on it while you got it opened... Hard to see but it looks like stock stamped GM rockers in the pictures...

Steve
 

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Ya might want to put a good set of rocker arms on it while you got it opened... Hard to see but it looks like stock stamped GM rockers in the pictures...

Steve

Yeah Steve, I'm defo going to put a set of arms on it. just emailed straub technologies to see what they recommend and can offer me.
 

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The stock head gaskets will not hold up long with boost. If you replaced the valves, cam, springs, rockers, head gaskets and keep the boost low it should live. The valve train is the weak link.
 
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