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CC limit of OEM throttle body
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BKiller
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PostPosted: Sun Mar 02, 2014 7:55 am    Post subject: CC limit of OEM throttle body Reply with quote

I'm looking at using the OEM throttle body intake system with a megasquirt fuel and spark management.
I'm currently running an 1800cc engine with big valved heads.
Will the stock system flow enough air to support this engine?
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Mike Fisher
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PostPosted: Sun Mar 02, 2014 1:05 pm    Post subject: Reply with quote

Russ Wolfe said 1800cc was the upper limit, so go for it! Woreign has a 1776 with stock FI w/Mercedes injectors. Seems wise to me reuse all that German engineering & cool air supply.
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Ma77
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PostPosted: Mon Mar 03, 2014 6:10 am    Post subject: Reply with quote

I was running the stock 1600 engine turbo'd and am now running a turbo 2.1L on the stock FI intake system controlled with megasquirt. Can be done and does work but I am guessing its quite restrictive. It does make for a very tidy install and it looks like its only the throttle butterfly that is too small. I have seen this replaced with a larger one which is on my list of things to do.
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Bobnotch
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PostPosted: Mon Mar 03, 2014 9:18 am    Post subject: Reply with quote

In the "D-jet PhD" sticky (at the top of the forum page), I believe it was found that a 1776 was real close to the upper limit, and 1800 was at it. Anything above that point, and you run out of air to supply the engine. You can do a couple of things, like adding a small boxed section to the end plate, to increase the size of the IAD, but the runner tubes will become the next restriction. Take a look at that thread, as it might help you out.
Note; there are several people here using the stock FI on larger engines, but a few also went with MS.
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PostPosted: Tue Mar 04, 2014 4:27 am    Post subject: Reply with quote

From running 1835 on megasquirt I have found that after 4500 you begin to drop manifold pressure from atmospheric.

Image may have been reduced in size. Click image to view fullscreen.


sorry no scale on this just the one reference point

note tp = 100
as rpm rises map begins to fall and the rpm stops increasing indicating power of engine = power of resistance ( test was in 4th at full load)
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PostPosted: Tue Mar 04, 2014 4:59 pm    Post subject: Reply with quote

Add boost - air flow solved
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PostPosted: Wed Mar 05, 2014 4:26 pm    Post subject: Reply with quote

Willo357 wrote:
From running 1835 on megasquirt I have found that after 4500 you begin to drop manifold pressure from atmospheric.

Image may have been reduced in size. Click image to view fullscreen.


sorry no scale on this just the one reference point

note tp = 100
as rpm rises map begins to fall and the rpm stops increasing indicating power of engine = power of resistance ( test was in 4th at full load)


Scaling would sure be helpful but thanks for posting that. True empirical data for sure. You can see that the MAP begins to drop from atmospheric well below the RPMs finish their climb indicating that it is restricting flow.

The size of the TB is only one part of the equation. The runner sizing and total volume of the plenum/runners also plays a major part in how well a plenum based system will work. It is common in OEM plenum based cars to have plenum/runner volume that is around the same volume as the motor.

When things are only off by a few hundred CCs, a lot of this stuff can only be truly seen on a dyno print-out and may not be felt by the seat of the pants. Just know that things are different and it's very likely that the stock plenum/runners may act as a governor at the higher RPMs. Hopefully you have a cam that is complimentary to that.
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PostPosted: Wed Mar 05, 2014 6:12 pm    Post subject: Reply with quote

I always felt the stock EFI type 3s died in the ass at high rpm. Where the bottom end was way better than carbs.

The runner length would play its roll in this, but that graph shows its more than that.
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PostPosted: Thu Mar 06, 2014 3:23 am    Post subject: Reply with quote

Nate M. wrote:
Willo357 wrote:
From running 1835 on megasquirt I have found that after 4500 you begin to drop manifold pressure from atmospheric.

Image may have been reduced in size. Click image to view fullscreen.


sorry no scale on this just the one reference point

note tp = 100
as rpm rises map begins to fall and the rpm stops increasing indicating power of engine = power of resistance ( test was in 4th at full load)


Scaling would sure be helpful but thanks for posting that. True empirical data for sure. You can see that the MAP begins to drop from atmospheric well below the RPMs finish their climb indicating that it is restricting flow.

The size of the TB is only one part of the equation. The runner sizing and total volume of the plenum/runners also plays a major part in how well a plenum based system will work. It is common in OEM plenum based cars to have plenum/runner volume that is around the same volume as the motor.

When things are only off by a few hundred CCs, a lot of this stuff can only be truly seen on a dyno print-out and may not be felt by the seat of the pants. Just know that things are different and it's very likely that the stock plenum/runners may act as a governor at the higher RPMs. Hopefully you have a cam that is complimentary to that.



yeh sorry about the pic it is an old one from another debate that happened to vaguely show some evidence of the stock intake system and an 1835 engine. I actually did alot of testing with the stock intake runner and the number 4500 resonates in my head as the point in which significant restriction occurs. since I was using a stock camshaft I felt that the stock intake is well suited with a stock cam.

From my experimentation the stock intake and stock camshaft works better with 1776 and 1835 than with a 1585, the larger capacities have a much more proportional torque to TP relationship resulting in a really nice driving car.
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