IR TB bore size

[Caprimaniac]

Hi.

I might be blind, but.... I didn't find any threads on IR TB / 8- stack bore size facts/ thoughts in this forum???

Someone please point me in the right direction, or start discussing here.'

I might switch from Webers to Jenvey IDF TB's and wonder wether 45, 48 or 50 mm boresize would be "best" for a streetable 3-8000 rpm powerband 347.

Thanks
rune/S

[Gaz64]

Rune,

My understanding is for IR applications whether carb or injection, the throttle butterfly should equal the inlet valve diameter.

[Caprimaniac]

Hi. Fond this Individual Throttle Body Dimensions - Team Integra Forums - Team Integra

Seems like 45 or 48 will be the way to go, leaning toward the last of the two.

RS

[bobcowan]

With a carb, bore size is pretty important. To big of a bore can causing bogging and loss of low end power.

With EFI, that's not much of an issue. EFI is much less sensative to charge velocity. I would go for the biggest bore you can get, as that will leave you room to grow.

Port and valve size is critical. If they are any bigger than the TB bores, you'll lose all your low end power.

[Caprimaniac]

That will mean that 50mm (largest available) will be better that the 48mm (because of the 2.02 valve size).

[bobcowan]

50mm = 1.97".

My bores are 52mm (2.05"), and my intake valves are 2.02". Intake charge velocity is very good, creating a broad flat torque curve. Last year I tried heads with bigger ports and valves; I lost all my low end torque, and did not gain any upper rpm power.

[Caprimaniac]

Interesting, Bob... What volume did your inlet ports have, and what volume on that other pair of heads where you lost the low end?

Was it like 205 to 225? And the larger valves, they were 2.08?

RS

[bobcowan]

The heads I have now are Dart Pro-1, 195cc, with 2.02" intakes. The others were Brodix 225, with 2.10" intakes.

I might gain a little power if I go to something like a 2.05" intake, and maybe 210-215cc intake runners. Maybe. That's a lot of money to spend on maybe.

[Dumpling]

Throttle Body Sizing Calculator | REVTRONIX

[Caprimaniac]

That revtronix page seem to be retarded. Hacked & nonworking...

Interesting, Bob. As i haven't been to the dyno and have used this pair of 205CC heads only, I have nothing to compare with. Seems like going to 225 isn't very smart, unless a much bigger cam is installed....

I'll choose the 50mm bores, if I ever get that far. A new gearbox & a set of good adjustable dampers will be the first to go.

[bobcowan]

Well, that's what we were doing. Went to a bigger cam, and bigger heads. The cam was OK, but the heads were way too much.

Here's the dyno sheet for comparison. The blue line is the stock Dart Pro-1 heads, right out of the box. The red line is with the bigger cam, and the big Brodix heads.