What size throttle body?

[Mathi]

Hi guys,

What size would you guys recommend for my LS engine?
I'm looking for a single throttle intake.
The engine makes 550 hp on the wheels and 690hp on the crankshaft.
Is 102 mm good? I want to have a smooth driver and nothing too serious.

The other details of my engine:
Nelson Racing 474 Injected LSX Hot Rod Series

Engine Block:​Gm Lsx engine block 9.7 deck height
Bore/Stroke:​474c.i. 4.165”/4.350”
Crank Shaft:​Callies 4.250 magnum 4340 Forged Steel Crank Shaft
Connecting Rods:​ 4340 forged connecting rods
Bearings:​Clevite 77 H Main and Rod Bearings
Cam Bearings:​Durabond HP Cam Bearings
Rear Seal:​Fel-Pro Viton Rear Seal
Balanced:​SFI Internal Balancing dynamic within 1 gram
Block Work for
Crank:​Block Fully Clearenced for Stroker Crank
Pistons:​Manley 10 to 1 Forged Pistons
Piston Rings:​Manley Pro Rings
Wrist Pins:​ Je Steel Wrist Pins
Camshaft:​Custom Nre Hyd Roller Cam

Lifters:​Gm racing hydraulic roller Lifters
Pushrods:​Smith Bros pushrods
Timing Chain:​Gm timing set with damper
Timing Chain
Cover:​Gm front cover
Timing Chain
Cover Gasket:​Gm Timing Chain Cover Gasket
Cylinder Heads:​Lsx cyl heads with 6 bolt pattern
Main/Head Bolts:​ARP Head Bolts gm Main Bolts
Head Gaskets:​Felpro
Valves: Stainless Steel Valves 2.160” Intake, inconel 1.6” Exhaust ” One Piece
Valve Locks:​ Machined Steel Valve Locks
Seals:​​Viton Valve Seals
Valve Springs:​190 seat 380 open Double Valve Springs
​
Retainers:​1.250
​

Fel-Pro Intake Gaskets Button head Stainless Steel ​Intake Bolts
Fuel Management: Electromotive tec gt fully lap top programmable along with aeromotive fuel pump and filters
Igniton System: Electromotive 60 tooth crank trigger ignition with ignition coils
Autolite 3924 spark plugs
• Autocrafters oil pan
• Fel-Pro Oil Pan Gasket
• Gm High Volume Oil
• Oil Filter Adapter w/ Oil Filter
20W50 Racing Oil
. Valve Covers w/ Stainless Steel Valve Cover Bolts
• Professionally Blueprinted

[badazz81z28]

How big can you get? I personally would look at the Fast 102/102.

[nokones]

If it will flow around 1250+ cfm, you should be good.

[Mathi]

No idea if the 102 mm throttle will flow 1250+cfm...

[nokones]

The throttlebody maker should be able to tell you what it will flow. The reason why I say 1250+ will work is because I am using a TPIS mono blade 1250 CFM Throttlebody on my Lingenfelter SBC 427 with the TPIS miniram and even Lingenfelter was impressed by the performance of the injection system. My motor puts out 646 at the crank. The was more than Lingenfelter estimated that the motor would do.

[another69]

It makes sense to go bigger with forced induction, but when do you step up the size NA? If you go bigger does low rpm driving suffer? I think stock is around 90mm. I have the same dilemma, I need to buy a new TB but don't know what size to get

[Mathi]

Well, that's the most difficult, bigger is not always better at low rpm. So I want best of both worlds. I don't have a stock engine so I'm guessing that I need to go with the 102 mm...

[71RS/SS396]

From my dyno testing on big cubic inch LS engines with LS7 port design heads the Fast 102 intake tb combination runs out of breath at about 6,200 rpm. You're really limited on intake options with LS7 ports. Even with 4 bbl tb's you need to use the 4500 tb and not the 4150 to get enough air to the engine. I ultimately went to a twin 90 mm tb intake which resulted in a 50 hp gain over the 102 and the engine made power all the way up to max rpm.

[Mathi]

Ok, that's interesting. I have LSX LS3 heads 9.700 deck block. Do you think I will have enough air with a 102mm for my setup?

[71RS/SS396]

Ok, that's interesting. I have LSX LS3 heads 9.700 deck block. Do you think I will have enough air with a 102mm for my setup?

What intake do you plan on using? The Fast 102 intake will run out of breath at about 6,200-6,300 rpm on a big inch engine. The LS3 heads are about the same as the LS7 head until about 6,500-6,800 on a 427, the LS7 head really shines above 6,000.

[andrewb70]

From my dyno testing on big cubic inch LS engines with LS7 port design heads the Fast 102 intake tb combination runs out of breath at about 6,200 rpm. You're really limited on intake options with LS7 ports. Even with 4 bbl tb's you need to use the 4500 tb and not the 4150 to get enough air to the engine. I ultimately went to a twin 90 mm tb intake which resulted in a 50 hp gain over the 102 and the engine made power all the way up to max rpm.

Ironically, he is selling a dual TB intake, which is on the engine now.

Andrew