St Itb’s Too Small For Big Port Head?

[Rolliac]

Hi.

 

I have a 4age 16v big port head I was considering putting Silver Top ITB’s on. Although after measuring the area of the inlet port v’s the throttle area it seems that the 42mm throttle area is smaller than the big port inlet port area.

 

I’m just wandering if this would choke the head of its flow capabilities.

 

Now I’m no mathematician so my calculations could be wrong. But this is to the best of my knowledge.

 

Port area:

Area of Big Port inlet ports = 14.93cm squared

Area of Small Port inlet ports = 10.68cm squared

 

Throttle area:

Area of Silver Top throttle = 13.85cm squared

Area of Black Top throttle = 15.90cm squared

 

I measured the diameter of the ports with veneer calipers about 1cm inside them.

 

I’m thinking ST throttles would suit Small Port heads and BT throttles (45mm) would suit Big Port heads.

[kiahn]

what will the engine be used for? does it need top end or mid range power??

if you go black top ITB you wil have a better top end due to free flow but the low end will disappear (like like you take the TVIS off a stock bigport)

the ST ITB will speed up the air flow much like the TVIS system

if you put in some decent size cams and extractors then id say go for black top ITB

if your keeping the engine mainly stock the Silver top ITB's will be great

several years of highschool physics :wink:

 

correct me if I'm wrong

[Rolliac]

Thanks Kiahn

 

Wanted to use my Big Port head and go all out.

Already got some silver top throttles. As you say might be too small.

 

The biggest issue I thought was that the port area on the Big Port was actually bigger than the area of the 42mm throttle. So like might be choking flow.

 

Anyway might just use ‘em on my Small Port head. Wishing I had waited for some BT’s now.

[kiahn]

the wont be a problem on your bigport, but if you upgrade the engine to a degree

where you would usually weld up the TVIS open then then would be too small, so unless your going to rev its tits off all the time then the BT ones might be overkill

[kiahn]

hey mate just wanted to let you know i found this

http://www.rollaclub.com/board/?showtopic=...=90#entry348367

 

page 7 has a ST ITB setup on it

[trav_555]

Thats my page :wink:

 

Yep I was going to run silvertop ITB's on my bigport.

 

They would be big enough I mean seriously think about it, you have this tiny little throttle on the front of your stock bigport manifold. I'm sure using 4 of those silvertop throttles will do you just fine for what your after. silvertop throttles are a bit over double the size id say (if you add the area together of all throttles versus single stock throttle), I can remember exactly.

 

I'm no longer putting silvertop ITBS on my bigport engine though, I'm going smallport.

 

I have a feeling it is going to be way more worth it, you can make ports bigger, but you can't make them smaller easily, bigport ports are too big.

 

What manifold are you using, I'm making a bigport manifold at the moment, its almost finished. It isnt as pretty as those 350+ dollar ones from T3 but it gets the job done, If your interested ill send you a few pics in a couple of weeks when its done.

 

Blacktop would only do you better if you were building your 4age to a formula atlantic spec in ym opinion, what are you doing for the rest of the build?

 

Need more information

 

Travis

Edited July 3, 2009 by trav_555

[philbey]

Your 1tb's wont choke the flow, remember they're made to flow enough air to feed a motor with an extra valve per cylinder than yours.

 

What you'll probably find is that you'll lose some lower end torque because your inlet port size will cause a drop in the intake velocity.

[trav_555]

Too right Philby.

 

And with biggish cams you can pretty much kiss your low end torque goodbye anyway :wink:

 

Travis

[Rolliac]

Your 1tb's wont choke the flow, remember they're made to flow enough air to feed a motor with an extra valve per cylinder than yours.

 

What you'll probably find is that you'll lose some lower end torque because your inlet port size will cause a drop in the intake velocity.

 

 

Hmmm didn’t think of that Philbey. Thanks.

 

16v heads have 2 X 3cm inlet valves. Total area of 14cm squared.

20v heads have 3 X 2.6cm inlet valves. Total area of 16cm squared.

 

20v must make power higher in the rev range than 16v?

 

Yes I think to 42mm ST throttles will do nicely. Think I’ll go Small Port though. Not seeing any benefit of the Big Port when the throttle area is smaller than the port area.

 

You see I need to decide which head coz they both need a recon.

[Rolliac]

P.S Thanks for the help guys. Just to let ya know my intentions for the engine.

 

Max power and speed!

 

You see, my good friend George has a 13b mild port with 48 weber in his Capella. He thinks “If it aint a rota it aint a motor”.

 

Another mate has an EG Civic type R. He say’s “I change gears at 9 grand”, “V-tec this and V-tec that”.

 

I just feel the 4age is the mighty engine everyone forgot about and want to give them a run for their money. Can’t go turbo coz this is an NA battle.

 

Wanna do some drifting too. I’ll make a project thread soon.

Edited July 3, 2009 by Rolliac

[irokin]

20v must make power higher in the rev range than 16v?

 

You've never heard a 20v at full noise have you? I think my ears are still recovering.

[kiahn]

use the head with the best water channels and that needs least work, my head was gonna cost 550 to get a 0.010" warp out of it, acid dip, clean water channels, rebuild and tune with cams. i only got offered $550 for the job coz i knew the guy. normal price would have been 1600