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One thing with the mast ls3 castings over stock is you can use a lot more lift before running into PTV issues
It is actually not the lift that causes the piston-to-valve clearance issues. It is the intake valve open point and the exhaust valve close point. The valve timing is what causes the issues.
Either the AFR LS3 or MAST Medium Bore LS3 out of the box
Probably the TFS LS3 also, will Easily Exceed 750 RWHP
with 10-12 Lbs and a medium sized cam with 427"+.
I would also use the Mid Length FAST 102.
I don't see the reason to use small Bore heads in a street
car with your Bore size and needing so much lift to reach
350+ CFM VS the other heads mentioned.
What kind of boost? Turbo engines have different considerations than supercharged. Even a centrifugal blower will have different volumetric efficiency curves than a positive displacement blowers. So, it is best to be specific about what type of forced induction as well as the RPM range. The intake manifold matters too.
It is actually not the lift that causes the piston-to-valve clearance issues. It is the intake valve open point and the exhaust valve close point. The valve timing is what causes the issues.
Yes I know. Everyone just says lift instead of more aggressive valve events
And lift is part of the equation just not all of it :p
I guess if I read you correctly, one cannot use shorter runners to help narrow runners flow better, nor can one use broader runners to make up for too much length.
In all actuality, I'd think longer, narrow runners go quite well for low and midrange rpm volumetric efficiency, and shorter, broader runners for high rpm volumetric efficiency.
Then add the cam to the mix. The cam should be chosen to match the runner design and the runner design to match the intended purpose of the engine.
Is that approximately correct? If maybe oversimplified.
Yes, for sure. That is what I was saying, but I have to qualify that it is not absolute. (The danger of generalizations)
Here is an example:
Back in the day, I used to build old school engines like the Buick 455s and the Mopar 440s. Both of these engines are examples of large displacement wedge (inline valve) engines where the factory cylinder heads were small for the displacement. The Buick 455 was the worst of the two. No matter how much camshaft you put in one of these engines, it was all done before 6000 RPM. Back then, Offenhauser made a short tunnel ram where the runners were only about 2 inches long. One would think that a runner that short would kill the torque, but the velocity was so high through the heads, that this intake was about the fastest thing you could put on a big block Buick. This is an extreme example. With that being said, when the aftermarket started making cylinder heads with a much larger cross sectional area, it changed the power and RPM potential of these engines dramatically. So, in this case a shorter runner did provide a slight improvement in power even though the head was much too small. But what really made these engine come alive was a bigger head.
Yes, for sure. That is what I was saying, but I have to qualify that it is not absolute. (The danger of generalizations)
Here is an example:
Back in the day, I used to build old school engines like the Buick 455s and the Mopar 440s. Both of these engines are examples of large displacement wedge (inline valve) engines where the factory cylinder heads were small for the displacement. The Buick 455 was the worst of the two. No matter how much camshaft you put in one of these engines, it was all done before 6000 RPM. Back then, Offenhauser made a short tunnel ram where the runners were only about 2 inches long. One would think that a runner that short would kill the torque, but the velocity was so high through the heads, that this intake was about the fastest thing you could put on a big block Buick. This is an extreme example. With that being said, when the aftermarket started making cylinder heads with a much larger cross sectional area, it changed the power and RPM potential of these engines dramatically. So, in this case a shorter runner did provide a slight improvement in power even though the head was much too small. But what really made these engine come alive was a bigger head.
SpeedTigger
At what RPM range would you suggest the short Race Runners for
Hammers Engine for example? Would he extend his existing
Set up 300 or 500 RPM to Peak without changing the cam?
How much torque would he lose, and with 4.56s would it matter?
Also with a 4" stroke and 10.5% more piston speed would you
Suggest mid length runners in a 416" peaking over 6500 VS
the standard length runners?
SpeedTigger
At what RPM range would you suggest the short Race Runners for
Hammers Engine for example? Would he extend his existing
Set up 300 or 500 RPM to Peak without changing the cam?
How much torque would he lose, and with 4.56s would it matter?
Also with a 4" stroke and 10.5% more piston speed would you
Suggest mid length runners in a 416" peaking over 6500 VS
the standard length runners?
PS sent you a PM about a week ago
Just like you alluded to, I offer that it is all about the overall combo and how you use the vehicle. In a car with 4.56 gears, you are only below torque peak for a very short period of time if at all when racing. After that, it is all about the top 1200 or so RPM. Obviously the game is to set the car up to keep the engine at the highest average horsepower during maximum acceleration.
Yes, for sure. That is what I was saying, but I have to qualify that it is not absolute. (The danger of generalizations)
Here is an example:
Back in the day, I used to build old school engines like the Buick 455s and the Mopar 440s. Both of these engines are examples of large displacement wedge (inline valve) engines where the factory cylinder heads were small for the displacement. The Buick 455 was the worst of the two. No matter how much camshaft you put in one of these engines, it was all done before 6000 RPM. Back then, Offenhauser made a short tunnel ram where the runners were only about 2 inches long. One would think that a runner that short would kill the torque, but the velocity was so high through the heads, that this intake was about the fastest thing you could put on a big block Buick. This is an extreme example. With that being said, when the aftermarket started making cylinder heads with a much larger cross sectional area, it changed the power and RPM potential of these engines dramatically. So, in this case a shorter runner did provide a slight improvement in power even though the head was much too small. But what really made these engine come alive was a bigger head.
I think that what sometimes people fail to see is the length of the runner is from the valve to the plenum. If you're breathing through a straw, and cut the straw in half, it's easier to breathe. Sometimes the intake runner on the head is a straw...
I've seen what you described on the Buick big block with the LS7. MSD short runner LS7 intake made more torque than the long runner fast in the same engine back to back.
Obviously the game is to set the car up to keep the engine at the highest average horsepower during maximum acceleration.
EXACTLY^^^^^
I'll use my engine for example.... peak power at 6800 ish rpm. If I shift at 6800, I drop to 4550, which lands me at 413 tq and 357 hp. But I also drop from 4373 tq at the tires to 3021 due to gear multiplication. Average HP = about 430.
Same curve, no cheating. I shift at 7400, I drop to 4950 rpm. I'm now going a few mph faster at shift, got there faster vs shifting at 6800, and STILL drop from 3957 tq at the tires to 3150 at the tires, but I only lost HALF the torque vs shifting at peak. Average HP = about 475. Honestly I should shift around 7700, but SBE. I'm nervous going past 7500.
I don't worry too much about tq anymore. Because what I've seen consistently is that at any given MPH, my car accelerates fastest in whatever gear the engine is making the most HP. Gearing provides you all the tq multiplication you need.
Anyway that was to illustrate why maxing out your average HP works - but don't forget all that power past peak.
Yes, for sure. That is what I was saying, but I have to qualify that it is not absolute. (The danger of generalizations)
Here is an example:
Back in the day, I used to build old school engines like the Buick 455s and the Mopar 440s. Both of these engines are examples of large displacement wedge (inline valve) engines where the factory cylinder heads were small for the displacement. The Buick 455 was the worst of the two. No matter how much camshaft you put in one of these engines, it was all done before 6000 RPM. Back then, Offenhauser made a short tunnel ram where the runners were only about 2 inches long. One would think that a runner that short would kill the torque, but the velocity was so high through the heads, that this intake was about the fastest thing you could put on a big block Buick. This is an extreme example. With that being said, when the aftermarket started making cylinder heads with a much larger cross sectional area, it changed the power and RPM potential of these engines dramatically. So, in this case a shorter runner did provide a slight improvement in power even though the head was much too small. But what really made these engine come alive was a bigger head.
I think that what sometimes people fail to see is the length of the runner is from the valve to the plenum. If you're breathing through a straw, and cut the straw in half, it's easier to breathe. Sometimes the intake runner on the head is a straw...
Yep. That is a great analogy that anyone can demonstrate to themselves.
Originally Posted by Darth_V8r
EXACTLY^^^^^
I'll use my engine for example.... peak power at 6800 ish rpm. If I shift at 6800, I drop to 4550, which lands me at 413 tq and 357 hp. But I also drop from 4373 tq at the tires to 3021 due to gear multiplication. Average HP = about 430.
Same curve, no cheating. I shift at 7400, I drop to 4950 rpm. I'm now going a few mph faster at shift, got there faster vs shifting at 6800, and STILL drop from 3957 tq at the tires to 3150 at the tires, but I only lost HALF the torque vs shifting at peak. Average HP = about 475. Honestly I should shift around 7700, but SBE. I'm nervous going past 7500.
I don't worry too much about tq anymore. Because what I've seen consistently is that at any given MPH, my car accelerates fastest in whatever gear the engine is making the most HP. Gearing provides you all the tq multiplication you need.
Anyway that was to illustrate why maxing out your average HP works - but don't forget all that power past peak.
This is especially true in manual transmission cars compared to an automatic with a loose stall. The manual car will drop a lot more on the shifts and needs good power after peak and a broader power curve.
Originally Posted by big hammer
Pontiacs were bad for that too
All those big wedge engines were pretty bad. Most were designed to haul #5000 luxury barges around at 2000 RPM. Back in the day, I ported a lot of cast iron cylinder heads to within .100" or less of the water jackets and pushrod holes trying to get some air through them. It would take a lot of money to get me to ever port a cast iron head again.
Yep. That is a great analogy that anyone can demonstrate to themselves.
This is especially true in manual transmission cars compared to an automatic with a loose stall. The manual car will drop a lot more on the shifts and needs good power after peak and a broader power curve.
All those big wedge engines were pretty bad. Most were designed to haul #5000 luxury barges around at 2000 RPM. Back in the day, I ported a lot of cast iron cylinder heads to within .100" or less of the water jackets and pushrod holes trying to get some air through them. It would take a lot of money to get me to ever port a cast iron head again.
I think I'd rather **** glass than port iron parts
Let's warm this back up with some interesting data:
Here is a comparison you might find interesting. It is a dyno comparison between rectangle port heads and cathedral port heads. It is two different engines, but done on the same dyno at Westech. This test is using two nearly identical engines with the same camshaft (231/247 113+4 .617"/.624") and same model intake manifolds.
Here are the comparison engines:
Cathedral Port Engine
370" Iron Block 4.030 x 3.622
11:1
AFR 230cc cathedral port heads
Rectangle Port Engine
376" Aluminum Block 4.065 x 3.622
11:1
Chevrolet Performance 276cc CNC LS3 Heads
First, lets have a look at this dyno comparison using the Holley Hi-Ram:
As you can see, with this intake and camshaft, the Chevrolet Performance LS3 heads outperform the AFR 230 CC heads pretty decisively.
Now lets look at the same two engine wearing a FAST 102 intake:
Interesting isn't it. We have so many threads making claims about the advantages of each head.
Now, many would argue that the AFR 230 is one of the best cathedral ports while not many would argue that the Chevrolet Performance CNC LS3 heads are the best of the rectangle ports. How do these dyno results compare to what you thought would happen?
07-23-2017, 06:07 AM
