Lasershop

iTrader: (2)

Like the title says.... Most every build is not exactly the same. Performance goals will vary greatly. Like to ask a valid question. I ask lots of questions. Some are pretty basic, some are out there. Only answers I don't respond well to are the ones that imply that I'm wasting my time. Me and ridicule are very old friends, I have had plenty.

Im revisiting and re-analyzing some parts I made in the past in this case my custom throttle body. I have tried to look this up on my own but there are no better pro setup and tuning geeks out there than on LS1Tech.

I have a LS1, 1997 first year. Stock bore and stroke. Far from stock all forged components. Has a comp XER281HR-12. .595/.598" lift. Has LQ9 ported and polished heads. Big Manley valves. Custom made rev kit. Very nice headers with merge collectors into twin TO4S turbo's. Custom sheet metal tunnel ram with a 1.76 ratio plenum. 96# injectors. That takes care of the breathing.

Would like to spin 7k RPM and with my rev kit I hope to do 8.

One more data bit is planning on about 8 to 10# of boost and its just a street car with occasional straight line pedal to the metal.

Question is, what would the throttle body CFM requirement be? Am I asking the right question?

My current setup is an inline, 4 port TB with 50mm a piece butterfly's. Taking into account the blades and shafts it comes out to an area of 105mm.

Another more just curious question is, does anyone know what the Horsepower rating would be for that particular unit?

HexenLord

More than 1000 HP has been made on the stock truck throttle body. 1300+ whp has been made on the stock ls6 intake and its 78mm opening.

You're greatly over thinking this

Lasershop

iTrader: (2)

I have absolutely no doubt about that. Anything worth doing is worth overdoing.....

HexenLord

The CFM rating will dictate the N/A HP. Boost will multiply it.

Lasershop

iTrader: (2)

Still like to know. Most products advertise "will support X horsepower". There must be some formula. I would like to know what it is and what the variables are. Must also be an equation for the required CFM of any combination. I guess I really dont need to know how to figure it out but I still would like to know what that number is. I mean..... Who wouldn't????

Forcefed86

iTrader: (4)

Not true, you'll see no benefits with an overly large throttlebody on an FI engine. This is why you see some of the fastest FI motors in the country run 90mm or smaller. Boost pressure has nothing to do with TB sizing. Size the TB to the motors flow capabilities in NA form. The OEM 78mm TB isn't going to be a bottle neck on your setup IMHO. And spending the money on a quality monster aftermarket TB is a complete waste of money and usually results in poor throttle response.

Here is a good example:
2800hp
10:1 482ci @ 7200rpm
40+lbs of boost
Twin 91mm turbos
90mm throttlebody

Also note this engine uses smallish charge piping and 2.5" collectors on the exh. manifolds. Bigger is NOT always better.



I could take a guess at answering your question. (not saying I'm right) Just remember the same rules may not apply when choosing a TB for an NA engine. Especially if there are other restrictions inline. Airfilters, intake piping etc...

None of the numbers are exact, but I believe they would be close.

First the TB would have to be flow tested.

This TB testing was done at 28"...

http://www.accufabracing.com/index.p...d=40&Itemid=88

Chevy LS-1, 1998-1999 and up (with mechanical linkage)
Stock – 798cfm
75mm – 920cfm
90mm – 1369cfm

Quick and dirty way to find CFM requirement is to multiply your crank HP by 1.5.

So even if you make 500 crank HP, you only need a TB that flows 750 CFM. So the stock LS1 TB would flow more than enough no matter what boost you run.

HexenLord

Like I said, CFM dictates N/A HP. Roughly 158 CFM for every 100 HP. A stock sized throttle body flows enough for 500 HP N/A as shown before. This is at 1 atmosphere. A general rule is that the HP rating scales with atmospheres (although its not a perfect conversion). So at 14.7 PSI this same throttle body will support 1000 HP. At 29.4 PSI it will support 1500 HP.

Your 105mm TB should support 1100 HP N/A (there are an awful lot of people with a fast 102 on a 500HP car), and almost 1700 HP at just 8 PSI.

stevieturbo

And greatly over-throttling it.

Using excessively large throttle blades can make low speed driving horrible, as you end up with no throttle resolution.

You might only end up with a 0-30% actually functional throttle for example. Because at 30% opening the actual area might already sufficient for all the power the engine would make.

Which of course would be mental.

slowlsx

iTrader: (28)

Get a custom twin 90mm throttle body built cause anything worth doing is worth over doing. Youll break records with the amount of extra hp youll gwt

Lasershop

iTrader: (2)

See, now we are getting somewhere. Good or bad, real numbers.

stevieturbo

Put it like this. Go too big and you'll just end up with **** drivability.

Stay stock size of say 78mm and you'll have enough TB to easily support over 1000hp...and then some and with great driveability.

Win win really.

What size boost plumbing are you using leading to the intake/TB ?