Next Project: Ideal throttle body size?

[greenberet]

Does anyone have any mathematical formulas ... ?

Here you go: the following formulas should give you an idea how large the throttle body in your naturally aspirated NSX should be if you want to maintain the same maximum airspeed past the throttle plate as is seen in a stock NA1. The formulas don’t take into account that the friction in the engine may increase exponentially, not linearly, with increasing horsepower so the diameter may need to be a touch larger than is calculated to take that into account.

Paste the following into one cell in Excel to calculate the diameter of the throttle body in mm based on crank hp:
=(6.2*2+((6.2*2)^2+270*10.236574228392*4*PI())^0.5)/PI()
note: get rid of the space betweeen 0.5 and ) towards the end of the formula. I don't konw why that space is getting inserted into the post

To calculate based on rear wheel hp, paste the following into a cell in Excel:
=(6.2*2+((6.2*2)^2+235*11.7611703900674*4*PI())^0.5)/PI()
note: get rid of the space between 0. and 5 towards the end of the formula

In the formulas, 6.2 is the thickness of the stock throttle spindle in mm when the throttle is completely open (actually it's 6.1 mm plus two mounting screws sticking into the airflow, so let's call it 6.2 mm thick on average). If the throttle body you’re looking at installing has a different spindle thickness, change both 6.2’s in the formulas to whatever you want. 270 is the crank horsepower of the engine in the first formula and 235 is the rwhp in the second. Change those figures to whatever naturally aspirated horsepower you’re shooting for to see what throttle plate diameter in mm should get you an airspeed close to a stock NA1’s. In a stock NSX, the throttle plate has a diameter of 63.4 mm.

When shooting for a horsepower target, please note that almost no dynos are accurate. To determine how many horsepower your car really has, it would be good to take a stock NA1 along as a benchmark, assume it puts out 270 crank hp or 235 wheel hp regardless what the dyno says, and then calculate the percentage difference between your car and the bone stock car.

 

[Mr2NSX]

L_RAO, since you have the PROSPEED bbtb, could you give us some of its measurement in mm. for example SOS bbtb is:
ID INLET= 70.8 mm
ID OUTLET = 65.9 mm
THROTTLE PLATE = 66.4 mm (which is only 2mm larger than stock)
PLATE & SPINDLE = 6.1 mm

thank u
pete

 

[A.S. Motorsport]

Here you go: the following formulas should give you an idea how large the throttle body in your naturally aspirated NSX should be if you want to maintain the same maximum airspeed past the throttle plate as is seen in a stock NA1. The formulas don’t take into account that the friction in the engine may increase exponentially, not linearly, with increasing horsepower so the diameter may need to be a touch larger than is calculated to take that into account.

Paste the following into one cell in Excel to calculate the diameter of the throttle body in mm based on crank hp:
=(6.2*2+((6.2*2)^2+270*10.236574228392*4*PI())^0.5)/PI()
note: get rid of the space betweeen 0.5 and ) towards the end of the formula. I don't konw why that space is getting inserted into the post

To calculate based on rear wheel hp, paste the following into a cell in Excel:
=(6.2*2+((6.2*2)^2+235*11.7611703900674*4*PI())^0.5)/PI()
note: get rid of the space between 0. and 5 towards the end of the formula

In the formulas, 6.2 is the thickness of the stock throttle spindle in mm when the throttle is completely open (actually it's 6.1 mm plus two mounting screws sticking into the airflow, so let's call it 6.2 mm thick on average). If the throttle body you’re looking at installing has a different spindle thickness, change both 6.2’s in the formulas to whatever you want. 270 is the crank horsepower of the engine in the first formula and 235 is the rwhp in the second. Change those figures to whatever naturally aspirated horsepower you’re shooting for to see what throttle plate diameter in mm should get you an airspeed close to a stock NA1’s. In a stock NSX, the throttle plate has a diameter of 63.4 mm.

When shooting for a horsepower target, please note that almost no dynos are accurate. To determine how many horsepower your car really has, it would be good to take a stock NA1 along as a benchmark, assume it puts out 270 crank hp or 235 wheel hp regardless what the dyno says, and then calculate the percentage difference between your car and the bone stock car.

That excel formula doesn't work here? (I'm using open office but it works the same)

Anyway i agree with you very much so on the fact that Dyno's are not ultra accurate certainly not axle setups.

I mathematically calculate it as well before hand.
What I'm interested in is to see if a increase in plenum volume coupled with or with out larger TB would improve high rpm engine breathing.
Let's say in V-Tec, with a full exhaust system.

This does pose issues, since lowering the plenum pan isn't possible you'd need increase it with a space on the throttle body, that's how i solved it on a Legend.

Swaping in a different TB is a option if you can make a large enough intake neck, i don't see the use of a 80mm TB though.

 

[greenberet]

Maybe the formula doesn't work for you because of the decimal points. I used periods as decimal points (as is usual in many English-speaking countries) instead of commas (rest of world). Also, make sure you remove the space towards the end of the formula.

Also, I should update the formulas, given that the OEM throttle plate has a diameter of 64.4 mm, not 63.4 mm. So, paste the following formulas into a cell in Excel:

Throttle body diameter based on CRANK HP
=(6.2*2+((6.2*2)^2+270*10.5853663961039*4*PI())^0.5)/PI()
note: get rid of the space between 0. and 5 towards the end of the formula. I don’t know why vBulletin keeps inserting that. Maybe it only accepts a certain "word length".

Throttle body diameter based on REAR WHEEL HP
=(6.2*2+((6.2*2)^2+235*12.1619103274385*4*PI())^0.5)/PI()
note: get rid of the space between 0. and 5 towards the end of the formula

Again, in the formulas, 6.2 is the thickness of the stock throttle spindle in mm when the throttle is completely open (actually it's 6.1 mm plus two mounting screws sticking into the airflow, so let's call it 6.2 mm thick on average). If the throttle body you’re looking at installing has a different spindle thickness, change both 6.2’s in the formulas to whatever you want. 270 is the crank horsepower of the engine in the first formula and 235 is the rwhp in the second. Change those figures to whatever naturally aspirated horsepower you’re shooting for to see what throttle plate diameter in mm should get you an airspeed close to a stock NA1’s.

 

[L_RAO]

Here is a teaser update on my 74 mm throttle body...

Enjoy!

 

[A.S. Motorsport]

Planning on something like that for the race car as well.
Just out of curiosity what donor car did you use?
As 74mm is generally not a tb universal size

 

[L_RAO]

It's a Blox B-series 74 mm TB.

I actually will have a batch of flange/adapters laying around when the project is done, since the machine shop needed a minimum order. Let me know if you want to buy one.

I am having a bracket for the cable fab'd as well, and I will be making a new throttle cable if necessary.

 

[A.S. Motorsport]

It's a Blox B-series 74 mm TB.

I actually will have a batch of flange/adapters laying around when the project is done, since the machine shop needed a minimum order. Let me know if you want to buy one.

I am having a bracket for the cable fab'd as well, and I will be making a new throttle cable if necessary.

Minimum order? that sucks!
You should have mailed me I'd have made one out of plastic for you. (better insulation)

Anyway I will be machining one to be mounted to a CTSC.
looking to go 75-80mm to feed the SC.

Here is one on a C32A/C35A

 

[L_RAO]

The largest that will fit on the OEM snout is 72-73 mm. With 74 mm+, you need to cut off the snout and weld a new flange (like I did).

For 80 mm to feed the SC, I would look at the Q45 throttle body (83 mm) or a Mustang 5.0L Accufab 90 mm.

 

[A.S. Motorsport]

The largest that will fit on the OEM snout is 72-73 mm. With 74 mm+, you need to cut off the snout and weld a new flange (like I did).

For 80 mm to feed the SC, I would look at the Q45 throttle body (83 mm) or a Mustang 5.0L Accufab 90 mm.

Yes that was what I was thinking, 90mm is a bit over doing it but Q45 is a good one.

On the SC there isn't the problem of the restrictive neck.
I'd love to run GM LT tb's just because they are twin (pointless though)
Would require a custom intake snout and vacuum lines + IAC mounts.

I'll probably do a Q45 setup or have a custom TB if I where to make the mod public if it works well on the race car.

 

[jaffaz32]

Minimum order? that sucks!
You should have mailed me I'd have made one out of plastic for you. (better insulation)

Anyway I will be machining one to be mounted to a CTSC.
looking to go 75-80mm to feed the SC.

Here is one on a C32A/C35A

ooo... prices?

Will it work with factory throttle body mount holes?

I have a 72mm Throttle body at home which uses the factory mount holes.

 

[RYU]

Minimum order? that sucks!
You should have mailed me I'd have made one out of plastic for you. (better insulation)

Anyway I will be machining one to be mounted to a CTSC.
looking to go 75-80mm to feed the SC.

Here is one on a C32A/C35A

That looks pretty and all but the bottleneck is the intake manifold inlet itself. Even if you make a 200mm TB it still has to go thru a small 72'ish mm neck. How did you solve this problem?

 

[A.S. Motorsport]

That looks pretty and all but the bottleneck is the intake manifold inlet itself. Even if you make a 200mm TB it still has to go thru a small 72'ish mm neck. How did you solve this problem?

Correct, this is a shot of a prototype I made.
Production versions are black for the stealth look.

Anyway that is a spacer to enlarge plenum volume at high rpm, (a effect 928 owners here will know).

A conversion spacer for the NSX could be made. to convert the OE bolt pattern (which is rather random in shape) to the new TB.

The conversion will only work if your neck supports the increase.
for the CTSC I'm planning to make a flange adaptor to mount a larger TB,
CTSC intakes are straight and if needed can be bored out easily.

Cost? those are about $65-75 I'd need to check current exchange rate.


Back on topic..
Enlarging the OE TB should be enough for most NA people here, 70mm should feed 300-320hp nicely.

 

[jaffaz32]

Correct, this is a shot of a prototype I made.
Production versions are black for the stealth look.

Anyway that is a spacer to enlarge plenum volume at high rpm, (a effect 928 owners here will know).

A conversion spacer for the NSX could be made. to convert the OE bolt pattern (which is rather random in shape) to the new TB.

The conversion will only work if your neck supports the increase.
for the CTSC I'm planning to make a flange adaptor to mount a larger TB,
CTSC intakes are straight and if needed can be bored out easily.

Cost? those are about $65-75 I'd need to check current exchange rate.


Back on topic..
Enlarging the OE TB should be enough for most NA people here, 70mm should feed 300-320hp nicely.

Cool and the oem throttle body bolts straight up to it? not worrying about the actual bore size just the bolt alignment.

I will need to confirm exit size of Throttle body, would it be machined to my needed size? i'm pretty sure it's a 72mm.

 

[jaffaz32]

Here are some pics, currently in development

 

[Honcho]

That looks pretty and all but the bottleneck is the intake manifold inlet itself. Even if you make a 200mm TB it still has to go thru a small 72'ish mm neck. How did you solve this problem?

Totally agree. The only way I know of to increase the intake volume is extrude honing the inlet and runners. Comptech used to do that.

 

[L_RAO]

Totally agree. The only way I know of to increase the intake volume is extrude honing the inlet and runners. Comptech used to do that.

Or you can actually port the runners and inlet. I also had the center divider removed. All in all, my IM is about 3 lbs. lighter than before!

 

[A.S. Motorsport]

jaffaz32,

Are you running a velocity stack straight to the TB?
That's a bit what i was thinking of going from 3/2.5 inch to a bell mouth > tb

DF Stack intake does that as well GruppeM's kevlar ram does the same

 

[A.S. Motorsport]

Or you can actually port the runners and inlet. I also had the center divider removed. All in all, my IM is about 3 lbs. lighter than before!

Well separating banks is a part of resonance tuning that might hurt torque going to far,

Look at all highly developed V engines they have separated banks.
Nearly all V12's run two banks, C30A,C32,C35 all have runners separated until the VISS

C32A/C35A split intake in the TB neck.
Take a look at a 300ZX or J-Series engine they also work with twin plenum's

What would be a very cool setup is a relocating alternator and running a custom lower plenum pan with twin intakes left and right.

 

[L_RAO]

I agree with your comments but overall I feel that the factory design has too many compromises, period, and is a lost cause.

• The entire manifold only has about 2.4L of volume; it now has a little bit more.
• The TB is too small.
• The runners are too short.
• The turns from the upper chamber into the runners are too sharp.
• The VVIS system was designed for drivability, not all-out power. Plus the VVIS screws are one more thing to worry about.
• The casting imperfections in the runners are pitiful for an OEM offering, they are now gone.

In a perfect world someone (FXMD?) will bring a dual plenum, long-runnered, dual throttle bodied with integrated bellmouths intake manifold to market. But there simply isn't any money in it. My setup is what I believe to be the best solution for the current problems.

Well separating banks is a part of resonance tuning that might hurt torque going to far,

Look at all highly developed V engines they have separated banks.
Nearly all V12's run two banks, C30A,C32,C35 all have runners separated until the VISS

C32A/C35A split intake in the TB neck.
Take a look at a 300ZX or J-Series engine they also work with twin plenum's

What would be a very cool setup is a relocating alternator and running a custom lower plenum pan with twin intakes left and right.

 

[L_RAO]

Sorry, but I do not have the Prospeed BBTB.

L_RAO, since you have the PROSPEED bbtb, could you give us some of its measurement in mm. for example SOS bbtb is:
ID INLET= 70.8 mm
ID OUTLET = 65.9 mm
THROTTLE PLATE = 66.4 mm (which is only 2mm larger than stock)
PLATE & SPINDLE = 6.1 mm

thank u
pete

 

[A.S. Motorsport]

I agree with your comments but overall I feel that the factory design has too many compromises, period, and is a lost cause.

• The entire manifold only has about 2.4L of volume; it now has a little bit more.
• The TB is too small.
• The runners are too short.
• The turns from the upper chamber into the runners are too sharp.
• The VVIS system was designed for drivability, not all-out power. Plus the VVIS screws are one more thing to worry about.
• The casting imperfections in the runners are pitiful for an OEM offering, they are now gone.

In a perfect world someone (FXMD?) will bring a dual plenum, long-runnered, dual throttle bodied with integrated bellmouths intake manifold to market. But there simply isn't any money in it. My setup is what I believe to be the best solution for the current problems.

Very true, certainly on the short runners.
Personally I prefer longer runner for better low-end & midrange response.

Casting imperfections, next time i'll take a better look.
I do recall seeing those in the runners them self.

Although a CTSC cast manifold has them as well which is to be expected for a low volume after market piece.
Then again I'm a perfectionist.

A other idea would be to go Lamborghini / Ferrari style in the intake manifold we do have the space to go vertical.
I'll mail you some drawings.

 

[A.S. Motorsport]

A cutaway of a NSX intake manifold including fuel rails & upper EGR

 

[greenberet]

The only way I know of to increase the intake volume is extrude honing the inlet and runners. Comptech used to do that.

Back in the mid-1990’s, Comptech offered an intake manifold porting and polishing service. Did they stop doing that by hand at some point and start sending the manifolds to Extrude Hone instead?

Enlarging the OE TB should be enough for most NA people here, 70mm should feed 300-320hp nicely.

A 70mm throttle body has an effective cross section about 19% larger than stock. Since the stock throttle body doesn’t measurably choke stock or lightly modified NA1 five-speeds and just starts to choke NA2s, a 70mm throttle body shouldn’t measurably choke NSXs until they are putting out somewhere north of 330 or maybe 340hp. Do you know anyone who bores the OEM NSX intake manifolds out to 70mm?

A cutaway of a NSX intake manifold including fuel rails & upper EGR

That picture nicely shows what an angle the intake manifold exit is at compared to the airflow – which makes it tricky to install a thick spacer in there without disrupting the airflow.

 

[greenberet]

The entire manifold only has about 2.4L of volume

Cool - I can't remember ever seeing the volume of the intake manifold mentioned before. Is that the entire volume of the intake plenum (top and bottom halves so basically the volume of air in the entire intake manifold assembly minus the volume in the runners)? If you measured the volume - how did you do it?