Single throttle body setups

[mrblyoung]

I agree with you though, that I wouldn't expect it to do very well NA on other than a stock engine.

I learned this first hand... I ran mine for a year NA while building the turbo header and gathering parts.. It's a 2276 and pulled about as hard as my friends 1776 with dual webers.

Here is a pic pre-turbo...

2276 only pulling as hard as a 1776? Was the engine built to be a turbo motor and you ran it N/A before going turbo? Low compression? You would think something that big would pull pretty hard regardless....

I think the moral of the story here is... that generally people with single throttle bodies are looking to go forced induction. Not to say it cant work NA, but it will take a LOT more development work than bolting on a set of ITB's for NA performance.

Totally agree with you on this one. I was just looking to see if anyone had done it with good results. And if they did, trying to find examples of what worked vs what didn't work. Always pays to do your homework before attempting something.

[risk]

Do you have any details on this motor hat you would care to share?

Sure what do you want to know?

I think the moral of the story here is... that generally people with single throttle bodies are looking to go forced induction. Not to say it cant work NA, but it will take a LOT more development work than bolting on a set of ITB's for NA performance.

Yep mine ran out of breath around 5000 rpm and the power just "flattened" out.. When I put the turbo on all that went away.

I know that most of you guys that are running single throttle bodies are running turbo's. Not that you cant turbo with ITB's, but a single TB simplifies the system.

What about a single centermount two barrel weber style throttle body and the EFI end castings.. thats something I considered early on.

[risk]

Was the engine built to be a turbo motor and you ran it N/A before going turbo? Low compression? You would think something that big would pull pretty hard regardless....

yes it was built for turbo and I ran it NA for a while.. It was originally 7.8:1 but I have since pulled the copper head shims so its closer to 9:1 now

[Devastator]

What about a single centermount two barrel weber style throttle body and the EFI end castings.. thats something I considered early on.

That would be cool.

[helowrench]

Risk, I will write out a PM with my questions so we don't clutter up this thread.

Thanks
Rob

[aircooledtechguy]

Here's mine. N/A 2056cc T-4. Porsche 2.0L runners, modified Porsche 914 plenum (clocked so the runners match-up) w/ a Porsche 2.0L TB (50mm I think). Runs like a screamin' Banshi.

[Steve Arndt]

I did a quick test a while ago on my high compression N/A engine. I normally run 45mm ITBs. I tested one of my dual throat ITBs on a standard IDF style center section intake with CB end castings. I ported out the CB end castings a small amount to almost match my heads but I didn't hog them all the way to a close math so that I could still sell them as unported later.

My engine with ITBs normally idles warmed up at 1000 rpms and 49 to 54 Kpa at idle oscillating. It has a super hard hit when it gets on the cam. I can hit positive manifold pressure at torque peak.

I moved my injectors from the ITBs to the CB end castings. With the weber centermount intake and one of my duals for the throttle along with CB end castings I measured the following. Keep in mind the standard weber center has 1/2 combined, and 3/4 combined. So one throat to 1/2 from the dual ITB, and one throat to 3/4. I connected both throats to my map sensor. The idle was ~60 Kpa, and higher, 1200 RPM idle speed. It wouldn't idle smooth below 1200 RPMs. When revving up it would pull a lot more vacuum from the mini plenum effect. With the ITBs it will redline the engine at ~5% throttle opening. With the center mount I could open the throttle a mile (30%) and it would pull more and more vacuum like it was choking for air.

Driving on a short test drive with only a few mapping changes I actually sort of liked how the single performed. It was less twitching taking off from a stop. It was lazy feeling though. No top end hard pull, and no mid range hit. It felt strangled. It also didn't have the cool "weber" intake bark that dual duals have. It was restrictive empirically too, never hitting + atmospheric barometric pressure or "boosting" like the ITBs do.

I run sequential injection. I found with the CB end castings I retarded the injection events 30 degrees later compared to my ITB setup to get the same idle AFRs and minimal pulse width. My ITBs are up on tall manifolds and the injector is 10" from the valve. With CB end castings that dimension is closer to 5 inches or less. That reminds me, the CB end castings needed 2.7 ms at idle and my ITBs need 2.5 ms. Big difference. I think it is due to reversion from the siamese intake design.

I quickly went back to ITBs after the test. I am still interested in building a single center intake, but it will be individual runner design.

[Redline Weber]

Hi Steve, well written.

YOU may be one of the only here that could create a proper Helmholtz Resonator intake manifold.

They deliver great boost pressure but only in a short range.

Call if your are interested.

Lance

[juki48]

there are plenty of people running single throttle bodies on large NA engines, but it's just too darn easy to add the turbo once you have everything else. I didn't like the price of the efi end castings so I made my own setup.