Tuned the 3-rotor. I was wrong :) vid inside.
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From: Kitchener Ontario Canada
If he's seeing vacum at higher rpm's then that definatly means the TB is restrictive.
The engine is sucking in so much air the TB cant flow enough causing vacum in the intake manifold.
The engine is sucking in so much air the TB cant flow enough causing vacum in the intake manifold.
I know how this works, it doesn't mean the the TB is the limiting factor. It just means there is something to gain from a less restrictive one.
How else do you expalain half again more power with half again more displacment.
How else do you expalain half again more power with half again more displacment.
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From: Cleveland, Ohio, USA
See my earlier explanation about intake pulses and "smoothness" of intake flow.
But if it's pulling vacuum even at WOT then the throttle body is definitely a restriction. I highly doubt that the ducting (which is much larger than the TB) or the air filter (ditto) are the restriction. What else is left? Pulling so much air that the world's air density goes down?
Note that Cup cars had no problem making well over 700hp on 390cfm carbs. Were they pulling vacuum at full power? Yep! Did the engines care? Well, a bit... but they compensated with weird ignition timing and compression ratios more suitable for Diesel engines. I understand that the compression ratios have been limited now, I haven't much attention in the past 15 years.
But if it's pulling vacuum even at WOT then the throttle body is definitely a restriction. I highly doubt that the ducting (which is much larger than the TB) or the air filter (ditto) are the restriction. What else is left? Pulling so much air that the world's air density goes down?
Note that Cup cars had no problem making well over 700hp on 390cfm carbs. Were they pulling vacuum at full power? Yep! Did the engines care? Well, a bit...
but they compensated with weird ignition timing and compression ratios more suitable for Diesel engines. I understand that the compression ratios have been limited now, I haven't much attention in the past 15 years.
I finally put some good miles on the FD, and did some dyno tuning. I have to admit I was wrong. I was estimating that the stock intake manifold would only yeild 275rwhp with a good street port, and good header, and 9.7 rotors. But after some fine tuning, put out 313rwhp and 221 Rwhtq. I am very surprised. This is on a dyna-pack keep in mind, so dyno-jet numbers would be in the 340rwhp.
That still is one hell of an increase with the stock mani. Was the LIM that short on the older 245rwhp dyno run from a few years back? I know removing the few inches from the runner length will move the torque peak higher in the power band. I see yours keeps rising. I also know having a larger entry into the TB helps with the top end as well. Most NA 20b dyno's I've seen had the stock elbow that has a 2.5" entry and is more restrictive. You engineered this set-up very nicely.
I remember that...
They tried to limit power by cutting the carb size down by 50% or so and it only brought power down by like 30hp or something.
Thats what I am saying really, I don't think getting a new TB on there is going to be good for that much power.
They tried to limit power by cutting the carb size down by 50% or so and it only brought power down by like 30hp or something.
Thats what I am saying really, I don't think getting a new TB on there is going to be good for that much power.
See my earlier explanation about intake pulses and "smoothness" of intake flow.
But if it's pulling vacuum even at WOT then the throttle body is definitely a restriction. I highly doubt that the ducting (which is much larger than the TB) or the air filter (ditto) are the restriction. What else is left? Pulling so much air that the world's air density goes down?
Note that Cup cars had no problem making well over 700hp on 390cfm carbs. Were they pulling vacuum at full power? Yep! Did the engines care? Well, a bit... but they compensated with weird ignition timing and compression ratios more suitable for Diesel engines. I understand that the compression ratios have been limited now, I haven't much attention in the past 15 years.
But if it's pulling vacuum even at WOT then the throttle body is definitely a restriction. I highly doubt that the ducting (which is much larger than the TB) or the air filter (ditto) are the restriction. What else is left? Pulling so much air that the world's air density goes down?
Note that Cup cars had no problem making well over 700hp on 390cfm carbs. Were they pulling vacuum at full power? Yep! Did the engines care? Well, a bit...
but they compensated with weird ignition timing and compression ratios more suitable for Diesel engines. I understand that the compression ratios have been limited now, I haven't much attention in the past 15 years.
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Well, my car is still making less power than it did 2.5 years ago with a custom intake. If you want some physical proof that the stock TB is restrictive, I sold my old 3x 55mm throttle body setup to a forum member on here-- Rotary20B. He was running a extended port n/a 3-rotor with nice headers. Seriously unbolted the stock 20B intake, and bolted my throttle body setup on and made 50rwhp gain (check his signature). This is on a dyno-dynamics which reads the lowest out of any dyno. Dyno-jet would show a 60-65rwhp gain. I feel its safe to say that the stock TB of the 20b is restrictive, and IS a limiting factor. 50% more displacement, 0% larger throttle body.
Last edited by GtoRx7; Mar 20, 2008 at 01:09 AM.
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That still is one hell of an increase with the stock mani. Was the LIM that short on the older 245rwhp dyno run from a few years back? I know removing the few inches from the runner length will move the torque peak higher in the power band. I see yours keeps rising. I also know having a larger entry into the TB helps with the top end as well. Most NA 20b dyno's I've seen had the stock elbow that has a 2.5" entry and is more restrictive. You engineered this set-up very nicely.
Thanks T-von for the compliments.
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From: https://www2.mazda.com/en/100th/
we used to see 1-2psi of POSITIVE pressure on the race car (stock port s5, stock intake, paul yaw inspired exhaust)
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Was this a 6 port? The aux ports will creat some positive pressure due to it's later port closing location. The rotor will be on it's beginning stages of the compression stroke before the aux port fully closes creating some slight back pressure. Now if this was done on a 4 port, that would be really impressive.
The biggest problem with the throttlebody is the 3 plate design. One plate feeds all 3 rotor's primary ports while the other 2 plates with twice the area feed all the secondaries. The primary plate is the primary restriction. If you were to use the stock TB on a single plenum rather than the divided dual design that it comes with, you'd notice top end power pick up. It would affect low end and low load driving a bit though. I played around alot with different manifolds and throttlebodies on 13B's several years ago and I saw some neat things from it.
I never have ran the stock intake before. Last time I went straight to custom, and avoided it. Of all the dyno's with stock intakes I searched, the highest was 250rwhp on a street port with headers. This season I was just using the stocker for the break-in, and then wanted a baseline dyno so later I could show the gains of a ITB setup. But you are wise and correct. Our 20b conversion kit kills two birds with one stone. It makes the hood clearance possible with stock subframe, and also adds hp by shifting torque roughly 500rpms. Good for turbo and n/a Thanks T-von for the compliments.
Thanks T-von for the compliments.I'm actually going with longer runners to see how much I improve on the low end. Should be pretty interesting! I'm trying to see whats the most bottom end I can get out of the stock ports below 4.5k. I'll worry about peak numbers later. I should be up and running next month. Fingers crossed! I can't wait to see what those pp's numbers will be. Summertime maybe?
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I was very close to adapting a GM 75mm throttlebody (free to me, bad IAC and the only way to get an IAC was to get a new TB assembly, so I dumpster-dived it) to my -SE manifold but the other work in blending it together was more than I really wanted to do, since I wanted a "baseline" before I did any manifold tweaking.
I still may do it on an S4 manifold, though. Those seem to be much easier to find than GSL-SE manifolds.
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it was 16 sec ramp time. It was on the long side, but I like to see how air temps, and afr's stay under a longer load time. I am sure it wasnt the best for peak power though. This friday I will be going to a friends shop so I can get dyno-jet numbers. I'll keep you guys posted.
it was 16 sec ramp time. It was on the long side, but I like to see how air temps, and afr's stay under a longer load time. I am sure it wasnt the best for peak power though. This friday I will be going to a friends shop so I can get dyno-jet numbers. I'll keep you guys posted.
