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RHS 427 blower build

1808 Views 34 Replies 7 Participants Last post by  Tony480
Starting a new build. Not for a car though. So looking for a little help. This is going in an airboat.
Here’s what I got so far
RHS 9.240 deck 4.125 bore
Callies magnum 4” crank
Callies Ultra Enforcer Rods
Pistons TBD.
FED m311 Boost monster heads
Ported LSA blower
Trying to decide on compression.
plan on running e85
Looking for info from some of the experts as to what I can get away with as far as compression? Any other tips and ideas I’m open to suggestions
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There are some actual experts around here that can likely give you the real info.
It's going to come down to power goal/how fast you're going to spin the blower versus CR versus fuel %.

My build (with a 2650) is only 9.2cr and with my pulleys I can't run pump 93.
Power goals…Im trying to make all of it!! lol
Gonna turn it about 6500 wot. Not sure what pullies yet. No cam picked yet. Shooting for 900 crankshaft horsepower. Plan on running e85
Power goals…Im trying to make all of it!! lol
Gonna turn it about 6500 wot. Not sure what pullies yet. No cam picked yet. Shooting for 900 crankshaft horsepower. Plan on running e85
For an airboat, you'll be running at high RPM for long periods of time.

Heat will be the biggest issue I'd think - I'd go conservative on blower pullies as you'll need either a good air/water intercooler, or if you're going air/air I'd think even more conservative.

I'd keep stock pullies on the blower and monitor IAT2 temps. E85 will allow you to run higher timing in spite of the higher Temps, I'd still think running average compression would be a good safety margin - something like 9.5 or 9.8:1.

Rubber Duck told me that larger cubes help torque, but not peak HP. Probably a good thing for an airboat?

I'd say peak HP isn't really the goal here, correct? Clarify your cooling system for the blower and that will help.
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For an airboat, you'll be running at high RPM for long periods of time.

Heat will be the biggest issue I'd think - I'd go conservative on blower pullies as you'll need either a good air/water intercooler, or if you're going air/air I'd think even more conservative.

I'd keep stock pullies on the blower and monitor IAT2 temps. E85 will allow you to run higher timing in spite of the higher Temps, I'd still think running average compression would be a good safety margin - something like 9.5 or 9.8:1.

Rubber Duck told me that larger cubes help torque, but not peak HP. Probably a good thing for an airboat?

I'd say peak HP isn't really the goal here, correct? Clarify your cooling system for the blower and that will help.
It will have an air to water intercooler. But it will also have an 82” prop constantly pulling air across it. It depends on what you consider high rpms. It will cruise around 3k rpm. Maybe less depending on conditions and load. Torque is all well and good but will only get you so far.
Probably 10.5:1 CR with a 1900 and 427. Maybe even more.


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It will have an air to water intercooler. But it will also have an 82” prop constantly pulling air across it. It depends on what you consider high rpms. It will cruise around 3k rpm. Maybe less depending on conditions and load. Torque is all well and good but will only get you so far.

Ah! Okay - 3k RPM is nothing, and that's a good call about the airflow. I'd still be conservative- so I don't have to swim if something pops, but in light of those details I'd agree with Karch that a more aggressive CR would work well.
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I haven’t ordered pistons because we’ve been trying to narrow down a CR. No cam picked obviously. The plan is m311 boost monsters unless there’s something better. I have a new blower that I’m going to send off to be ported,by who is still up in the air. Trying to get as much info from you guys who have more experience with it then me. I appreciate all the help
I might be way off on this, but the blower is pretty small for a 427… Overspin it creating more heat.

So, is it possible to use the water you will be floating on to keep it cool? Always a fresh, cooler supply…. Would keep the IAT temps more consistent, and pretty low I would think.
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I might be way off on this, but the blower is pretty small for a 427… Overspin it creating more heat.

So, is it possible to use the water you will be floating on to keep it cool? Always a fresh, cooler supply…. Would keep the IAT temps more consistent, and pretty low I would think.
No. As a lot of the time we aren’t even in water. These boats go as fast on land as they do in water.
Ah, makes sense. I have never seen one in person, but they seem bad ass. What does the frame work look like? I would assume the bottoms must be fairly heavy duty, in order to hit land and keep flying…

So, when do we get some pics?
Here is the new one we are building. It will be going to paint in another week

Here is the current one. It has a NA 11.5-1 418
Automotive tire Automotive design Motor vehicle Vehicle Automotive exterior


Yes! Pitchas!
Also, what gearbox?
Prop rpm/thou?
It will have a 2.68 Oxdrive gear box. And an 8 blade 82” prop.

Here’s a few more pics of it in progress
Bicycle tire Automotive tire Wheel Door Bicycle part

Aircraft Airplane Bicycle hub Hub gear Automotive tire

Tire Automotive tire Motor vehicle Wheel Vehicle


But he wants 900 hp and also wants to spin it to 6500 RPM.

Increasing the size of the engine will automatically generate more torque assuming the static compression ratio remains the same.

In order to generate more horsepower, one will need to increase the flow through the cylinder heads. Possibly more camshaft duration also,… Depends!

With what has been written above, I would certainly not attempt to tune this engine for MBT…

Cheers
What is your suggestion. I was just putting a number out there. I’ve always been an NA guy and this is my first jump into a blower motor. That’s why I’m looking for suggestions and help from guys like you. I appreciate any advice and tips you can give

But he wants 900 hp and also wants to spin it to 6500 RPM.

Increasing the size of the engine will automatically generate more torque assuming the static compression ratio remains the same.

In order to generate more horsepower, one will need to increase the flow through the cylinder heads. Possibly more camshaft duration also,… Depends!

With what has been written above, I would certainly not attempt to tune this engine for MBT…

Cheers
MBT? Sorry for my ignorance

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Ah! Okay - 3k RPM is nothing, and that's a good call about the airflow. I'd still be conservative- so I don't have to swim if something pops, but in light of those details I'd agree with Karch that a more aggressive CR would work well.
But he wants 900 hp and also wants to spin it to 6500 RPM.

Increasing the size of the engine will automatically generate more torque assuming the static compression ratio remains the same.

In order to generate more horsepower, one will need to increase the flow through the cylinder heads. Possibly more camshaft duration also,… Depends!

With what has been written above, I would certainly not attempt to tune this engine for MBT…

Cheers
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Here is the new one we are building. It will be going to paint in another week

Here is the current one. It has a NA 11.5-1 418 View attachment 166378


It will have a 2.68 Oxdrive gear box. And an 8 blade 82” prop.

Here’s a few more pics of it in progress View attachment 166379




What is your suggestion. I was just putting a number out there. I’ve always been an NA guy and this is my first jump into a blower motor. That’s why I’m looking for suggestions and help from guys like you. I appreciate any advice and tips you can give


MBT? Sorry for my ignorance
MBT stands for Maximum Brake Torque.

At MBT the cylinder pressures are at their highest, as VE% is at it's highest.

After Peak Torque Engine RPM, the VE% begins to decline.

You can see this on an engine dyno.
As VE% declines, so does your torque.

This simply means that volumetric efficiency, given as a percent (VE%) is not filling the cylinders as efficiently as it was at the lower engine rpm.

-------------------------------------------------

Regarding your engine build. . . .

Today, I am not into boats, so I don't have answers for you.

Years back I built a 427 CID Chevrolet Engine for customer, who put it in a boat.

He asked me to go to the lake with him to help tune it.

All I remember is charging around the lake at WOT.
So I did not build any boat motors after that. . lol

I know that different type boats, require very different camshafts.
But I don't have your answers.

I would not spend anymore money on such things as pistons, cylinder heads, etc. until you find a person, a professional who understands what your needs are.

But larger internal volume engines do produce more torque, more efficiently, than attempting to stuff more air into a smaller engine.

Stuffing small engines with large amounts of air is not as efficient as starting out with a larger engine.

Now, if one has a large engine, one should also note having a high static / geometric compression ratio, also lends to efficiency. Anything over about 10.25:1 Cr is what one should be looking for.

Think about it this way. . .

If the compression ratio is 8.5:1, then your looking at about an 85% efficiency.
If the compression ratio is 10.25:1, then your looking at about a 100% efficiency.

The above is not entirely accurate, but gets across the
message regarding compression versus efficiency.

Actually, an engine with 15.2:1 static compression ratio has an %ASE efficiency of 67%. But lowering the static compression ratio below 15.2:1, also lowers the %ASE number.

Typically we match the static compression ratio number to the VE% the customers engine requires. This is determined by the customers HP requirements.

So my approach to building such an engine would be. . . .

Large Internal Volume (CID).
Appropriate Cr. . .Depending on the fuel.
Low Boost

Best flowing heads one can afford.
This allows one to use the shortest duration camshaft.

And you already have an engine with a 4" Stroke you
will have to deal with regarding the camshaft.

Remember. . .HP is simply Torque X Engine RPM.

I think that 900 HP for your applications, particularly the
way some posting here are suggesting you approach it,
most likely will lead to issues regarding breakage.

High torque is what I would be looking for.

---------------------------------------

Finally. . .
Spinning your engine to 6500 rpm, will only generate a piston speed that would present an engine demand of about 760 HP. In order to generate more HP, one will need to 'force' more air into the engine.

To do that with a 1.9L / 115.6 CID Roots Blower, means one needs to spin the Hell out of the blower. And all Roots Blowers are highly in-efficient.

I don't think you would desire to be charging
around a lake all day with that. . JMHO

Sorry my post reads so negative, that's why I did not respond earlier.

But I hate to see people do the wrong things. . .

Cheers
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But he wants 900 hp and also wants to spin it to 6500 RPM.

Increasing the size of the engine will automatically generate more torque assuming the static compression ratio remains the same.

In order to generate more horsepower, one will need to increase the flow through the cylinder heads. Possibly more camshaft duration also,… Depends!

With what has been written above, I would certainly not attempt to tune this engine for MBT…

Cheers
Would it be that much more beneficial for me to go to a 2650. I could put a kong2650 on it if needed. But do to height restrictions i can’t put a maggy or harrop on it
Would it be that much more beneficial for me to go to a 2650. I could put a kong2650 on it if needed. But do to height restrictions i can’t put a maggy or harrop on it
I would!

In race trim the 376 needs ~2300 CC's.
And most have had very good luck with the Kong 2650 on the 427 engines.

For your engine, I just would not want any epoxy used in the blower.

Adjust your HP goals downward, locate a compressor map for the 2650, and from that you can calculate the pulley ratio required to meet your HP demands.

For an efficient engine. . .
(900 Hp * 1.5 / 0.87)= 1551 cfm.
(800 Hp * 1.5 / 0.87)= 1380 cfm.
(750 Hp * 1.5 / 0.87)= 1293 cfm.

And if we take the reciprocal of 1.5, or => 1 / 1.5,
we find that we get the 67% ASE (Air Standard Efficiency).

Also, at 6,500 engine rpm, with a crank having a 4" stroke, your 'mean' piston speed will be 4,333 fpm. Peak piston speeds can be as high as +6,800 fpm. Headed down the drag strip for a short 10.00 seconds or so, not a bad deal.

You might consider reducing your engine speed down a bit. . .

And don't tune the engine for MBT.
Soften the tune at or around MBT.

Don't choose your camshaft until you know the
flow numbers for the cylinder heads.

If you desire to do any calculations regarding flow or velocity profiling, you need to get the MCSA, or the Minimum Circular Square Area of the head. With these heads it is usually the bowl area just under the valve seat.

This also is very helpful in choosing the correct camshaft. . . .

@MrSurly wanted 1000 rwHP.

That meant his heads and camshaft package needed to flow
375 cfm @ or around convergence lift. His MCSA was 3.23 Sq.".

=> (375 / 1.5)= 250 Hp / Cylinder, equals 1000 HP.

His velocity then would be. . .
=> (375 * 2.4 / 3.23)= 279 fps.

Even on a 10° head, that is a high velocity number to achieve.
It takes a very good head to flow those numbers.

So you might desire to speak to him about those MAST Heads.

I don't get too impressed very often regarding cylinder heads, but I was impressed when he laid down about 1016 rwHP, on the first pull. . . .

But I would bore the engine to 4.155" for those
heads, as they use a 2.250" Valve.

Your engine then would be a 434 CID.
Leaning on that engine just a bit, it should make +880 HP.
***When I say 'just a bit' I am being conservative here at 880 HP.

You will most likely need to spin the engine to 6800 for that.
Then simply put a limiter on the engine, maybe 6200 on the lakes.

For endurance I would also bush the lifter bores and
have them machined for a 'Keyed Lifter'.

What you need to know on the camshaft is. . .
How much overlap can you safely run?

If your not going to hook up with someone on this forum for your cam, I have someone that has much experience with these boat engines, and grinds very good cams with the correct finish. Many cam companies Don't!

Good Luck..(y)
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I would!

In race trim the 376 needs ~2300 CC's.
And most have had very good luck with the Kong 2650 on the 427 engines.

For your engine, I just would not want any epoxy used in the blower.

Adjust your HP goals downward, locate a compressor map for the 2650, and from that you can calculate the pulley ratio required to meet your HP demands.

For an efficient engine. . .
(900 Hp * 1.5 / 0.87)= 1551 cfm.
(800 Hp * 1.5 / 0.87)= 1380 cfm.
(750 Hp * 1.5 / 0.87)= 1293 cfm.

And if we take the reciprocal of 1.5, or => 1 / 1.5,
we find that we get the 67% ASE (Air Standard Efficiency).

Also, at 6,500 engine rpm, with a crank having a 4" stroke, your 'mean' piston speed will be 4,333 fpm. Peak piston speeds can be as high as +6,800 fpm. Headed down the drag strip for a short 10.00 seconds or so, not a bad deal.

You might consider reducing your engine speed down a bit. . .

And don't tune the engine for MBT.
Soften the tune at or around MBT.

Don't choose your camshaft until you know the
flow numbers for the cylinder heads.

If you desire to do any calculations regarding flow or velocity profiling, you need to get the MCSA, or the Minimum Circular Square Area of the head. With these heads it is usually the bowl area just under the valve seat.

This also is very helpful in choosing the correct camshaft. . . .

@MrSurly wanted 1000 rwHP.

That meant his heads and camshaft package needed to flow
375 cfm @ or around convergence lift. His MCSA was 3.23 Sq.".

=> (375 / 1.5)= 250 Hp / Cylinder, equals 1000 HP.

His velocity then would be. . .
=> (375 * 2.4 / 3.23)= 279 fps.

Even on a 10° head, that is a high velocity number to achieve.
It takes a very good head to flow those numbers.

So you might desire to speak to him about those MAST Heads.

I don't get too impressed very often regarding cylinder heads, but I was impressed when he laid down about 1016 rwHP, on the first pull. . . .

But I would bore the engine to 4.155" for those
heads, as they use a 2.250" Valve.

Your engine then would be a 434 CID.
Leaning on that engine just a bit, it should make +880 HP.
***When I say 'just a bit' I am being conservative here at 880 HP.

You will most likely need to spin the engine to 6800 for that.
Then simply put a limiter on the engine, maybe 6200 on the lakes.

For endurance I would also bush the lifter bores and
have them machined for a 'Keyed Lifter'.

What you need to know on the camshaft is. . .
How much overlap can you safely run?

If your not going to hook up with someone on this forum for your cam, I have someone that has much experience with these boat engines, and grinds very good cams with the correct finish. Many cam companies Don't!

Good Luck..(y)
I greatly appreciate your advice. I tried to private message you but I can’t figure out how. I don’t have to turn it 6500. I currently spin my 418 6200. 900 horse was just a number. I just want to make as much as i can and be efficient and dependable if that’s an option. lol
I greatly appreciate your advice. I tried to private message you but I can’t figure out how. I don’t have to turn it 6500. I currently spin my 418 6200. 900 horse was just a number. I just want to make as much as i can and be efficient and dependable if that’s an option. lol
I had to turn my PM off years back, as it was literally becoming a second job.

I just think it best to hold it wherever a safe / soft tune puts it.
But you could always set it up to run two tunes.

The main issue is tuning around Peak Torque RPM.

If an NA Engine should show peak torque at 5500 rpm.

Put 1-BAR of boost on the engine, and it will make peak
torque at something like 3750 rpm.

Some of these engines make around 250 PSI of BMEP.
And that is a 'Huge #'!

Now, take that to the lake and put the throttle down,
no ET / MPH Clocks or shutdown area to deal with,
and at some point the engine is going to expire.

On E-85 and your engine, I am thinking you should
hold it at 775 hp to 800 hp, in the performance mode
if you can run two tunes.

But opinions are opinions, and you might choose another number..lol

Cheers
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