3.890 5.3 tt
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Joined: Nov 2003
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From: Norn Iron
Is there any real need to push the engine capacity to the very limit ?
IMO just build it with sensible CR, good heads/cam/valvetrain to handle constant high rpm's and let the boost take care of the power. Do not be afraid of boost !
The smaller cube engine will also be happier spinning at the higher rpm's too
Thread Starter
Staging Lane
Joined: May 2014
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The jet pump (drive) is most efficent at 6000-6500, it runs between 4-6500 most of the time at 6500, the boat is hard on the engine and hi 20-25lbs boost is hard on everything outside of the
Say if it was factory ported heads flow 250 @ .500 lift 700 hp 20lbs of boost
Wouldn't the mast heads flow 350@ .500 at 700hp bring the boost back to say 15?
Say if it was factory ported heads flow 250 @ .500 lift 700 hp 20lbs of boost
Wouldn't the mast heads flow 350@ .500 at 700hp bring the boost back to say 15?
9 Second Club
Joined: Nov 2003
Posts: 13,616
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From: Norn Iron
The jet pump (drive) is most efficent at 6000-6500, it runs between 4-6500 most of the time at 6500, the boat is hard on the engine and hi 20-25lbs boost is hard on everything outside of the
Say if it was factory ported heads flow 250 @ .500 lift 700 hp 20lbs of boost
Wouldn't the mast heads flow 350@ .500 at 700hp bring the boost back to say 15?
Say if it was factory ported heads flow 250 @ .500 lift 700 hp 20lbs of boost
Wouldn't the mast heads flow 350@ .500 at 700hp bring the boost back to say 15?
Plus it just isnt as simple as a port claiming to flow more air, actually makes more power
I'm not saying the boost may not decrease, but how much...can't see an easy way to answer other than trying it
Unless some Dynosim type software is really that good
Launching!
Joined: Jun 2010
Posts: 255
Likes: 1
From: Alberta, Canada
The jet pump (drive) is most efficent at 6000-6500, it runs between 4-6500 most of the time at 6500, the boat is hard on the engine and hi 20-25lbs boost is hard on everything outside of the
Say if it was factory ported heads flow 250 @ .500 lift 700 hp 20lbs of boost
Wouldn't the mast heads flow 350@ .500 at 700hp bring the boost back to say 15?
Say if it was factory ported heads flow 250 @ .500 lift 700 hp 20lbs of boost
Wouldn't the mast heads flow 350@ .500 at 700hp bring the boost back to say 15?
Thread Starter
Staging Lane
Joined: May 2014
Posts: 61
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Your cylinder volume is only so big. I would think there would think there would be a point where the volume of the cylinder would decide boost. I am not an expert, but if it were me, I would set up the the heads/intake so it's geared toward that rpm range in N/A form. Compressor/turbine will play a huge part in the required boost. The lower the back pressure and the more efficient the compressor is in that range, the more it will mimic the N/A torque curve (only on a much higher scale). The engine will ingest about the same volume of air whether it is N/A or boosted for any given rpm range. But when you are boosted, that volume is compressed, allowing you to bring more fuel to compensate, giving you more power. That's my view on this whole thing. Someone please correct me if this thinking is wrong.
An na motor needs heads to accelerate air in to fill the cylinder, heads too small restrict air, and heads to big do not accelerate the air
On a Fi engine big heads allow you to fill the cylinder to create more cylinder pressure with less restrictions, but I could also be wrong, this is how I have come to interpret it.
Launching!
Joined: Jun 2010
Posts: 255
Likes: 1
From: Alberta, Canada
I can't correct you as I'm in the same boat, the way I view it is that torque is based on cylinder pressure, boost only being the restriction build up.
An na motor needs heads to accelerate air in to fill the cylinder, heads too small restrict air, and heads to big do not accelerate the air
On a Fi engine big heads allow you to fill the cylinder to create more cylinder pressure with less restrictions, but I could also be wrong, this is how I have come to interpret it.
An na motor needs heads to accelerate air in to fill the cylinder, heads too small restrict air, and heads to big do not accelerate the air
On a Fi engine big heads allow you to fill the cylinder to create more cylinder pressure with less restrictions, but I could also be wrong, this is how I have come to interpret it.
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Joined: Nov 2003
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From: Norn Iron
I can't correct you as I'm in the same boat, the way I view it is that torque is based on cylinder pressure, boost only being the restriction build up.
An na motor needs heads to accelerate air in to fill the cylinder, heads too small restrict air, and heads to big do not accelerate the air
On a Fi engine big heads allow you to fill the cylinder to create more cylinder pressure with less restrictions, but I could also be wrong, this is how I have come to interpret it.
An na motor needs heads to accelerate air in to fill the cylinder, heads too small restrict air, and heads to big do not accelerate the air
On a Fi engine big heads allow you to fill the cylinder to create more cylinder pressure with less restrictions, but I could also be wrong, this is how I have come to interpret it.
Or low velocity port...and high velocity port...
Not so clear which is better here. Bigger may not always be better
Also if you're going to have a small bore, huge ports and valves which ultimately get shrouded in a small chamber/bore may not be the way to go at all.
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Staging Lane
Joined: May 2014
Posts: 61
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Thanks for all the input, more help the better, the mast heads are 11 degree and made for min bore of 3.890, I could go to a 3.910 to help for shrouding,
Before I come across the heads, bore /stroke combo, I was looking with my engine builder about the 3.780 bore with cathedral afr 210 heads, however he thought that they could not breath enough to reach our goals,
It's a hard one because it's unusual build, other guys run the Lexus v8. Which hits a wall at 800hp, the vh41 nissan make good power and some running 3.4 Toyota supra motors exceeding 800, under 20psi.
I think the 260 lsx would be cool and could work. Just how?
Before I come across the heads, bore /stroke combo, I was looking with my engine builder about the 3.780 bore with cathedral afr 210 heads, however he thought that they could not breath enough to reach our goals,
It's a hard one because it's unusual build, other guys run the Lexus v8. Which hits a wall at 800hp, the vh41 nissan make good power and some running 3.4 Toyota supra motors exceeding 800, under 20psi.
I think the 260 lsx would be cool and could work. Just how?
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Thanks for all the input, more help the better, the mast heads are 11 degree and made for min bore of 3.890, I could go to a 3.910 to help for shrouding,
Before I come across the heads, bore /stroke combo, I was looking with my engine builder about the 3.780 bore with cathedral afr 210 heads, however he thought that they could not breath enough to reach our goals,
It's a hard one because it's unusual build, other guys run the Lexus v8. Which hits a wall at 800hp, the vh41 nissan make good power and some running 3.4 Toyota supra motors exceeding 800, under 20psi.
I think the 260 lsx would be cool and could work. Just how?
Before I come across the heads, bore /stroke combo, I was looking with my engine builder about the 3.780 bore with cathedral afr 210 heads, however he thought that they could not breath enough to reach our goals,
It's a hard one because it's unusual build, other guys run the Lexus v8. Which hits a wall at 800hp, the vh41 nissan make good power and some running 3.4 Toyota supra motors exceeding 800, under 20psi.
I think the 260 lsx would be cool and could work. Just how?
Thread Starter
Staging Lane
Joined: May 2014
Posts: 61
Likes: 0
Thread Starter
Staging Lane
Joined: May 2014
Posts: 61
Likes: 0
Depends how the jet drive loads the engine. I wont pretend to know when the turbos would come online. IMO, What your asking for doesnt exist. A small engine isnt going to spool a 1:1 back pressure twin turbo setup at low rpm. If the majority of your rpm is at 6k+, thats where u need to target the power. Small shot of nitrous could also be used to get the boost going, then shut off over say 8lbs or so. Otherwise u need to pick a power band.
Thread Starter
Staging Lane
Joined: May 2014
Posts: 61
Likes: 0
Depends how the jet drive loads the engine. I wont pretend to know when the turbos would come online. IMO, What your asking for doesnt exist. A small engine isnt going to spool a 1:1 back pressure twin turbo setup at low rpm. If the majority of your rpm is at 6k+, thats where u need to target the power. Small shot of nitrous could also be used to get the boost going, then shut off over say 8lbs or so. Otherwise u need to pick a power band.
I am yet too learn about turbos all the same
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From: Norn Iron
Of course smaller turbos will spool faster, but they may require you need more boost to achieve any power goals.
You also have to remember you're much reduced engine capacity compared to what other guys here are doing for racing, which will of course affect spool.
There is no issue finding turbos that will produce good boost at 3k if the engine is loaded though.
Again, dont be afraid of boost to make whatever power you need.
If that means smaller turbos, wide power range, lots of boost...then so be it. Just build the engine to accommodate it.
You also have to remember you're much reduced engine capacity compared to what other guys here are doing for racing, which will of course affect spool.
There is no issue finding turbos that will produce good boost at 3k if the engine is loaded though.
Again, dont be afraid of boost to make whatever power you need.
If that means smaller turbos, wide power range, lots of boost...then so be it. Just build the engine to accommodate it.
You said you spend most of your time in the upper rpm. The s200 turbo hotside/wheel is pretty small. That will limit overall flow and build up back pressure requiring a smaller cam. Putting a nice flowing head in place and restricting the exh makes no sense to me. Better off with with 300 series, good head, healthy cam. If you want quicker spool drop the compressor wheel from a 66 down to a 62ish range.
Last edited by Forcefed86; Oct 20, 2014 at 04:01 PM.
9 Second Club
Joined: Nov 2003
Posts: 13,616
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From: Norn Iron
I dont see a S200 being a problem. Dont forget he's also reducing engine capacity for this, I think he said around 280ci ?
That's not a big motor for twins
It will not be spooling any S300 by 3k
That's not a big motor for twins
It will not be spooling any S300 by 3k