Differences in Supercharged verses normally aspirated heads

[AA Performance]

Tell me how you are suppose to get two times the amount of air from a cylinder if you have the same size exhaust port & valve. At 1 atmosphere of boost , you have filled twice the amount of air into the cylinder. Supercharged & turbocharged exhaust design are totally different & work on different principles.Sorry, but don't agree with you max.

[SWR]

Tell me how you are suppose to get two times the amount of air from a cylinder if you have the same size exhaust port & valve. At 1 atmosphere of boost , you have filled twice the amount of air into the cylinder. Supercharged & turbocharged exhaust design are totally different & work on different principles.Sorry, but don't agree with you max.

Easy. You have close to twice the pressure differential. Unless you're hampered by big backpressure in the exhaust,but then it's not the head doing it.

7000+ hp T/F's have one 1.94" exhaust valve... Why are they not running intake valve sizes on the exhaust and vice versa when the have so much boost coming in and "need to relive that pressure"?

[AA Performance]

OH! So they do run big exhaust valves, unless you think that a 1.94" is small for a 500 cube?

[Ron E]

OH! So they do run big exhaust valves, unless you think that a 1.94" is small for a 500 cube?

1.94" is the OE valve size for a hemi. They could easily give up some intake size and fit a 2.100" or so exhaust valve in the head, as well as a larger exhaust port to support it. It's been tried. What has shown to work is bigger intake valves.
Any conceivable valve diameter arrangement has been tried. That happens with stable rules. Gaining from their R&D is cost effective.

[MadBill]

One of the problems with TF engines is getting the exhaust valve to open at all, against the residual cylinder pressure of as much as 1,000 psi. I've been told the valve opens not when the cam dictates, but when the pressure drops enough that the 1/2" or more push rod can finally straighten out. A larger valve would make the problem worse.

To this discussion however, I believe a similar displacement PS engine uses a much smaller valve, perhaps only 1.625"...

[Ron E]

One of the problems with TF engines is getting the exhaust valve to open at all, against the residual cylinder pressure of as much as 1,000 psi. I've been told the valve opens not when the cam dictates, but when the pressure drops enough that the 1/2" or more push rod can finally straighten out. A larger valve would make the problem worse.

To this discussion however, I believe a similar displacement PS engine uses a much smaller valve, perhaps only 1.625"...

Bill, thats true, however if you look at the MB 2V Ilmor engine, the valve diameters are pretty much in line with a NA engine. They found, even with the squeeze, a good flowing intake gave them the better net power. Of course, thats a turbo, and Ah's don't know nuthin' 'bouts no turbos!

With a belt driven blower, the exhaust's ability to dump the trash should be better....Right?

[MadBill]

Hi Ron. Yes, turbos have a lot of back pressure relative to mechanically driven blowers, so the little I know of them suggests that with the best matched parts they are more like an NA engine being operated at 30,000 ft. below sea level and so would likely need NA-style flow and valve size percentages. The ill-matched ones I believe need negative overlap, etc...

[SWR]

Hi Ron. Yes, turbos have a lot of back pressure relative to mechanically driven blowers, so the little I know of them suggests that with the best matched parts they are more like an NA engine being operated at 30,000 ft. below sea level and so would likely need NA-style flow and valve size percentages. The ill-matched ones I believe need negative overlap, etc...

...which is why we tune turbo setups to always have lower backpressure than boost.. We're filling the intake port at 30.000 ft below the sea level and dumps it at 12.000 ft...if all is right. Makes for a really long port,that..

[maxracesoftware]

Tell me how you are suppose to get two times the amount of air from a cylinder if you have the same size exhaust port & valve. At 1 atmosphere of boost , you have filled twice the amount of air into the cylinder. Supercharged & turbocharged exhaust design are totally different & work on different principles.Sorry, but don't agree with you max.

No one is running an Exhaust Valve thats larger than an Intake Valve
in any Blower or Turbo application.

What you do find out is its still basically the
Intake -to- Exhaust Valve diameter size ratios,
with a little greater bias/or increase of exh valve diameter.

Simple quick math explanation->

generally understood that .257 Flow_Factor is a pretty good measure
of HP expected per Cylinder for certain Flow gain
in N.A. engines

15 psi Boost Pressure has a potential pressure differential of =
approx 412.0 inches of water

( 412 / 28 ) ^ .5 = 3.837

3.837 * 20 CFM = 76.75 CFM increase @ 15 psi Boost

76.75 CFM times .257 * 8 Cylinders = 157.8 Potential HP gains
.....so subtracting various pumping + heat losses, etc.
gaining around at least double Intake Flow gains
which should easily be approx 82+ HP potential

the Intake Ports are very critical with Boost applications


TopFuel is ultimate test of SuperCharger

8000 HP still only needs to exit thru
1.94 to 2.000 exh valve

on 8000 HP, the Exh valve is still sized smaller than the Intake valve
( not the opposite )
the Exh to Int valve ratios sizes are relatively close to the same as N.A.

8000 HP only needs a relatively very small exh pipe diameter change
than a 500 cid 1400+ NA Engine

Your making 8000 HP..... you are not gaining 8000 HP
with a SuperCharger with mods on the Exhaust side,
instead your overwhelming gains of 8000 HP is from
the Intake Port side.

[maxracesoftware]

Quote from Kallita in National Dragster ->


Top Fuel Dragster - Doug Kalitta - { High Wing DownForce model }
April 2003 Houston, Texas 10 Feet Elevation { NHRA specs }
30.04 Sea-Level Corr.Barometer, 66 deg.F, 45 % Rh, 91 F Track surface

60 Ft= .847
330 Ft= 2.150
660 Ft= 3.058 - 279.04 MPH
1000 Ft= 3.822
1320 Ft= 4.486 - 333.91 MPH

2250 Lbs. 496 CID 4.187 Bore x 4.500 Stroke

Peak HP= 7933 @ 6715 RPM Peak TQ=6205 { 8550 RPM limit }

6.8:1 Compression Ratio , 2.400 Intake 1.940 Exhaust valves
39.3 % overdrive on Blower
62 deg BTDC at Starting Line & 58 BTDC at Finish Line


1.940 / 2.400 = .80833 E/I Valve Ratio

2.020 SBC Chevy Intake Valve = 1.632 exh Valve at that same
Top Fuel Supercharger application

the Power is on the Intake side !

[Abbottracingheads]

My findings over the years show that the extensive exhaust port work and sizing is way over exagerrated. As Larry says the intake side is still the most important. The blower will push exhaust out. If you have too much overlap all of your power and fuel will be blown out of the exhaust port.

[PackardV8]

It is always about intake efficiency. A supercharger/turbocharger is an air pump staged in front of another air pump. Compression of air in the intake is not the desired goal, but movement/volume is. Boost is the measure of how much supercharger work was used, but did not push fuel/air into the cylinder to make power. Back in the glory days of turbos, F1 and Champ engines made astronomical HP/CuIn with relatively low boost. The DOHC 4V porting breathed so well, the cylinder was filled without wasting work and heating air. There are tractor pullers running 100# of boost on OHV 2V intake-restricted engines and not making anywhere near the same HP/CuIn the F1/Champ cars made at one-third that boost.

fuel will be blown out of the exhaust port.

Conversely, the Offy was competitive as long as huge volumes of methanol could be pumped through to keep everything cool. When Indy went to fuel economy rules and boost level rules. the Offy was no longer competitive.

thnx, jack vines

[MadBill]

Here's a (probably not original, given my penchant for reinventing the wheel) thought about highly supercharged engine cam timing: Since the charge density may be two or three times that of an NA engine, so will be its inertia, thus it should be possible to leave IVC much later without reversion detracting from the trapped V.E.

Along the same lines, although charge density does not affect the speed of sound in the mixture, temperature does and a high boost engine, even with a good intercooler, will almost inevitably have much higher mixture temps. Thus a higher fps port velocity will correspond to a given optimum Mach number and so minimum port areas might need a re-think ...

[judgement_impared]

So do all of the standard rules apply for the boosted applications as far as the intake ports go? IE: good velocity, low turbulence, more higher lift flow with no real concern for killing low lift flow, etc...
I understand the intake port's importance Vs. exhaust and that a boosted application will somewhat "Band-aid" a "Too-BIG" head for what would be a typical NA application, but where's the limits?

Is there a general rule of thumb or formula for it?

[Ron E]

So do all of the standard rules apply for the boosted applications as far as the intake ports go? IE: good velocity, low turbulence, more higher lift flow with no real concern for killing low lift flow, etc...
I understand the intake port's importance Vs. exhaust and that a boosted application will somewhat "Band-aid" a "Too-BIG" head for what would be a typical NA application, but where's the limits?

Is there a general rule of thumb or formula for it?

Good question on what's to big on boosted motors. At least in alky and T/F type motors. They ain't scared of a big intake port. I've seen some with the port area well above the valve area. I don't know if that's normal or junk.