Not 95, not 100, not 105 or 110, but the 120- 190 range

How is this done? I've heard some wispers of supersonic airspeeds inside the intake manifold.

You look at some supercars achieving 1.15-1.25 VE and they have some I.M.'s that you'd think would be counter productive!

For example, the S7 & Enzo intake has LONG runners and primaries;
http://www.fordmuscle.com/archives/2...een/engine.jpg
http://www.catsspeed.co.jp/test/MODE...ari-engine.jpg
Coincidence? Doubtful. So what’s the deal with these things? How do they achieve such high VE's? How do F1's tinker with 2.0?

Thanks in advance!

 

Some of those long runners are relatively short compared to something on a LSx motor.

The idea is the natural internal supercharging effect that happens. Bascially the engine, if matched properly, can achieve a natural supercharger. It starts as the pressure wave bounces off the intake vavle. It runs back to the entrance of the intake runner. Then, the pressure wave turns and heads back toward the intake valve. This happens several times while the intake valve is closed. If timed right, this pressure wave will reach the intake valve as it is closing "forcing" extra air into the cylinder.

I heard somewhere that NASCAR engines can create somewhere in the neighborhood of 6psi of natrual boost.

 

yes, I understand the pulse/wave thing and how it works in conjuction with exhaust scavaging and exhuast waves/pulses.

However, I thought that "alone" was only good enough for abpit 108-ish. I was hearing something about restrictors to increase the velocity of air to near mach1 speeeds in order to do this... or maybe i'm wrong. I dont think you can JUST do the above and achieve 1.35-2.0.

Also, is it for a very short period of time/rpm?

 

[QUOTE=mastrdrver]Some of those long runners are relatively short compared to something on a LSx motor.

QUOTE]

I agree those runners are not very LONG. Longer than some , but not LOOOOONG. Apparently long enough to get the job done as far as ram tuning , but not to long.

There looks like good plenum volume also, plus we can't see what all is going on inside.

 

>>>I heard somewhere that NASCAR engines can create somewhere in the neighborhood of 6psi of natrual boost.<<<

6 psi would be approx = 853.3 fps = .765 Mach = 140.83 Ve%

thats a little too high for a NASCAR engine that has Fuel limits inorder to finish a Race + even the SB2.2 heads/intake as good as it is, still has different length Intake Manifold runner lengths..

you would have to have excellent scavenging assist from Overlap Period and Exhaust system that would "waste" too much Air/Fuel mixture out of exhaust ports

pumping losses would be too high as well at .765 Mach to make HP and fuel mileage at same time

maybe more like 4 psi max = 696.7 fps = 127.22 Ve% = .6243 Mach
(127.22 % Ve actually trapped inside the Cylinder)

still 3 to 4 psi "Free supercharge effect" from wave tunning and mixture velocity is still pretty good numbers !

usually its extremely hard to make HP/Torque after 700 fps = .6272 Mach

 

That's probably a reasonable number, BUT that is not maintained throughout the inlet period, it's just near intake valve closing and crams some more air in. Of course this assumes the inlet port length and valve timing are optimized for this effect. It will occur in a fairly narrow rpm range, but if you are running a "plate" engine in a 200 or so rpm range, that should be ideal.

If you have a chance to view the intake tuning pressure graphics on a good engine simulator you can get a pretty good feel for that effect.

In order to spread the effect over the entire engine operating band you'd probably need continuously variable inlet port length as well as variable valve closing point.

Is it significant that one proposed new rule for Formula 1 engines is to ban variable inlet length?

As far as VE's in the "120-190 range", 120 probably, but 190? Not even in F1, IMO.

Also, IMO, torque per cubic inch at horsepower peak is a fair way to compare different engines and their relative VEs. If you make an assumption that the max hp point is around 92-95% of max rpm point on and endurance engine like F1 or Cup, the 900 hp 19200 max rpm 183 cube F1 engine makes about 1.44 lb-ft/cubic inch at 18000 rpm, and the 825 hp 9300 max rpm (today at Kansas) 358 cube Cup engine makes about 1.38 lb-ft/cubic inch at 8800 rpm. That's within about 4%, which amazes me.

My highly opinionated $.02

 

"intertial supercharging" is what it is called, i think.

 

Oldsstroker i have a question. what about the position of the piston when the valve. from open to close. its said that the waves bounce off of the valve and back through the the runners and back down again creating more pressure for it to go into the cylinder. if it goes in and the piston is at the wrong point, couldnt the pressure escape? also, what about the shape of the runner. would you want these pressure waves to bounce off the back of the valves and hit something flat (idealy) then come back? but i guess the shape would be construed (sp?) since the back of the valves aren't flat.

to me it sounds pretty rediculous to even try to calculate it, lol. taking into consideration the shape of the runners, valve, materials (reflecting the wave), valve timing, and the extention of the piston/rod at high rpms. but then again i have no idea what those f1 folks do, test i guess.

 

I do agree that those intakes are better tuned then any mass production engine coming out of GM. The 6psi was a guess. I knew it fairly low, but I thought it was higher then 3-4psi.

I don't think that the pressure wave cares too much about the shape of the back of the valve as much as it cares that there is something there to stop its momentium. Also, I don't think there is a wrong place for the pistion to be as much as there is a wrong timing for the valve. The superhcharging that is happening is forcing more air then what the displacement of the cylinder is, hence the high VE. It is important not that the pistion be at the right place as is the valve. Remember that one of Newtons laws is that an object that is in motion tends to stay in motion. Even with the pistion coming up in the cylinder, the air is still going in bcuz of this. If the valve is left open too long, the action of the pistion coming up will force the air out of the cylinder. The idea is to catch the extra air going into the cylinder by closing the vavle just after the pressure wave forces extra air into the cylinder.

 

but, the higher the rpms the less thats true.

 

As for the shape of the valves, production valves have a taper to them, Delwest titanium valves that I have for my Z28 are flat as can be on the top.
As for the position of the piston and valve.
On a big cam it start with over lap.
The intake valve opens as much as 15 and some times as much as 20 degrees (20 is more for 14,000rpm motor cycle engines) BTDC.
The exhaust valve closes lets say 8-10 degrees ATDC when the piston is moving down there is still exhaust getting blown out.
At low rpms this is bad. exhaust gets sucked into the intake runner at low rpms while there is vacuum in the intake. To take full advantage of this there must be positive pressure on the intake valve at high rpms when the intake valve starts opening at 15 degrees BTDC There is a slight vacuum in the chamber. because the exhaust valve opened before BDC, letting the exploding gas blowing its self out. but I'm not going to get to far into that.
As the intake valve starts realy opening with the piston at 5-8 degrees (I mean open enough to let some air move) BTDC. There is intake air being sucked in and getting forced into the chamber chasing out the exhaust while the piston is moving up in the cylinder.
As both valves are open there most (about 1/16'') at the same time and the piston is at TDC the exhaust is sucking all of its self out and the intake air is starting to force its self and it is taking over.
Onec the exhaust valve closes all the way the intake air is trapped and the piston is moving down.
The intake valve is open its most well after 90 ATDC. Its open it's most around 30-50 degrees before BDC depending on if its a big turbo cam or big N/A cam.
And closes as late as 40 degrees ABDC (don't think I have seen any that close later than that), that is when most of the air is sucked into the cylinder (ABDC). Yes there is a lot of air still getting sucked into the chamber because the runner air was accelerated during the time when the piston was between around 90 ATDC and full valve open. So now that the piston is moving up and air is getting into the chamber by means of some unseen force.
At this point the engine is super charging its self. The amout of self super chargine is determined by a lot of factors, rpm, runners, valve timing (mainly intake open ABDC), spark timing comes into play a lot when you do FI and more.
The self super charging realy starts with the exhaust opening well before BDC on the power stroke and the exhaust blows its self out creating a slight vacuum sucking the piston up the bore and some times contaminating the chamber with oil if you don't have good oil control.

 

#77;
yes, intake charge can certainly be reversed and "shot up" the intake runner. it is called reversion. It can also take residual exhuast with it, and does, which causes more problems.

A lot of what is being said is because air has momentum. That is why we do not use the "idea" engine (IVO AT TDC). It is also why you can get more air in by opening the intake valve while the piston is still on the exhuast stroke. even through the piston is going up, the momentum of air allows it to keep going in- partially aided by exhuast scavaging.

You REALLY want to make sure that intake charge is going in, and not residual exhuast going out- that would be a bad thing. Not only would you have residual inert gas in the cylinder (hot, taking up space etc) but now you have hot inert gasses in your intake manifold, not a good thing.

At higher rpm, this is less of an issue because air usually has a higher velocity.

someone please correct me if i am offbase.

 

Can the vacuum created from the pistion create enough negative pressure that the pressure wave in the intake track would actually change direction before it reaches the opening?

 

The exhasut gas ending up where it shouldn't be hapens all the time when the engine is a lower speeds.
That is why you run a higher idel, less vaccume and get more air momentum with a big cam.
That is also why high compression lets you idel lower, it makes the pistons movements better felt up inside the runner (it make the intake and exhasut velocitys faster at lower engine speeds), and it pushes more exhasut out making room for more clean air.
They realy breath better with higher compression.
What masterdrver is asking is can you have so much vacuum force that it starts to work against you if that is what you are asking?
Well when the air goes super sonic that might hapen for a small fraction of a second.
What you should shoot for is not to just go super sonic but to accelerate the air to supersonic speed as soon as you can and keep it going that fast for as long as you can.
Air has mass (or density), it can be compressed and it has natural resonance frequencies. all subject to change.

 

I get the tq/CI, but not why at peak hp?how much tq do those F1 engines make?