TPI Intakes: Throttle Bodies and Plenum Entrances

NewbVetteGuy

NewbVetteGuy

Well-Known Member
Grumpy et al,

I'm curious why TPI intakes seem to all have dual throttle bodies, even in the aftermarket, vs a single, larger throttle body. Is there some sort of benefit to having dual throttle bodies with a TPI-style intake -like a higher velocity of air effect from a plenum divider or something? If you had a single throttle body that flowed the same amount of air do you expect to see any different results?


My next question is somewhat related; I purchased a FIRST Fuel Injection intake and the outlet of the single throttle body has a strange bump right in the center of the bottom of the throttle body which then become the EGR "bump" in the bottom of the plenum, very similar to a stock TPI plenum at that point.

I'm trying to determine if this bump has any potential positive impact and reason to be there. The newest FIRST castings have a fully solid EGR passage and do not have any EGR passageway cast in, nor drilled in. My thought is to completely eliminate the air-restricting bump and make the entry into the plenum smooth, but I'm wondering if it serves some sort of purpose....

Image of the plenum entrance here: https://scontent-sea1-1.xx.fbcdn.ne...=5632bb707ec4b092b60632ef02c838ea&oe=5B214865

Crappy photo showing the bump at the back of the throttle body: https://www.facebook.com/photo.php?fbid=10156324305191929&l=2355fb17ff


I asked Ken @ FIRST about it and all he would say was that the company that designed the FIRST knew what they were doing and he doesn't advocate making change that could screw up the air flow. (I half removed the bump already until I killed my sandpaper flapper wheel and I'm trying to figure out whether to stop where I am with a half height bump or just kill it, which I'd really think would improve air flow, but maybe hurt distribution to the first set of runners for some reason...???)


Adam
 
For what it's worth, I went with a Holley HP EFI to control the whole thing: my application will be MAP only; MAF is off-the-table as an option.

Adam
 
If you drive a Modern LS Car or truck its feels strong of course.
But if you note they do not start pulling real hard to 2800-3000 rpms.
Its not the cam doing it.
Its the Airflow Velocity nature of LS Catherdral and retangular port heads.
All the Trans Am Guys that have LS Swapped have noted the same recent on another forum I am on.

So a Single Large Mono Throttle blade opening fast like 101 mm does not really matter.
Because airflow velocity optimum is not there till 3000 rpm anyhow.

My theory.
 
Maniacmechanic1 said:
If you drive a Modern LS Car or truck its feels strong of course.
But if you note they do not start pulling real hard to 2800-3000 rpms.
Its not the cam doing it.
Its the Airflow Velocity nature of LS Catherdral and retangular port heads.
All the Trans Am Guys that have LS Swapped have noted the same recent on another forum I am on.

So a Single Large Mono Throttle blade opening fast like 101 mm does not really matter.
Because airflow velocity optimum is not there till 3000 rpm anyhow.

My theory.
Click to expand...

Airflow velocity is primarily dependant upon the cross-sectional area of the heads' intake ports (and RPM/piston speed, obviously); LS heads obviously have huge ports by volume compared to 23 Deg SBC heads designed for the same RPM range and cubes, but they have more velocity for the intake volume because the CSAs are slighly smaller as a result of the decreased valve angles and the longer yet narrower intake ports that result from the reduced valve angles.

I think if you compared a 23 DEG SBC and an LS of the same displacement with the same intake port volume you'd actually see slightly more average port velocity and torque with the LS head than the SBC.


Interesting discussion that this is, I don't think it approaches the subject of WHY an engineer would go with a dual throttle body vs a single throttle body. What's the pros and cons of each options?



And for my "REAL" bottom-line question: Does the "EGR" "BUMP" in my FIRST intake potentially do anything other than restrict air flow? (The TPIs and even the FIRST TPI-style intake have fairly notoriously variable air flow cylinder-to-cylinder; could this bump be there to possibly increase the air flow into the 1st 2 runners (the front, passenger side pair of runners and the rear two runners where the plenum narrows have the worst out-of-box airflow). -I'm concerned with making the airflow to the 1st 2 runners even worse by getting rid of the bump.
 
The 1st Gen LS had 15 degree valve inclination angles.
Next Gen has 11 degrees I recall hearing.
Pontiac V8 1967-81 had 14 degree heads..
Olds V8 1964 330 & 1965 all up had 6 degree valve inclination heads.

Lot more going on than ever reported in basic Peak flow tests.
Velocity numbers seldom shared in feet per second.
 
Tpi is supposed to be decent for airflow distribution.
Its all the Mailbox style Tuned port intakes that are problems to optimize or equal Balance Airflow per cylinder.
Why guys ran 375-400 cfm ports with them in the past in the Corvette C4 World.
Airflow bounces off the rear of main plenum I was told.
Engine takes in what it can at that given moment.
 
Maibox as in the Callaway prototype intake used on a few Twin Turbo 1988 C4 Corvettes.
Ultra rare. 3-5 made.
Seem pictures in the past.

Became the C4 LT-1 & LT4 intake .
 
NewbVetteGuy said:
Grumpy et al,

I'm curious why TPI intakes seem to all have dual throttle bodies, even in the aftermarket, vs a single, larger throttle body. Is there some sort of benefit to having dual throttle bodies with a TPI-style intake -like a higher velocity of air effect from a plenum divider or something? If you had a single throttle body that flowed the same amount of air do you expect to see any different results?
PDRM1966a.jpg
51000_bb697eb7ebe4189c2b45881e0a9534ca0a18789b.jpg

firstt.png

firstf.png

intake comes with a new throttle body

My next question is somewhat related; I purchased a FIRST Fuel Injection intake and the outlet of the single throttle body has a strange bump right in the center of the bottom of the throttle body which then become the EGR "bump" in the bottom of the plenum, very similar to a stock TPI plenum at that point.

I'm trying to determine if this bump has any potential positive impact and reason to be there. The newest FIRST castings have a fully solid EGR passage and do not have any EGR passageway cast in, nor drilled in. My thought is to completely eliminate the air-restricting bump and make the entry into the plenum smooth, but I'm wondering if it serves some sort of purpose....

Image of the plenum entrance here: https://scontent-sea1-1.xx.fbcdn.ne...=5632bb707ec4b092b60632ef02c838ea&oe=5B214865

Crappy photo showing the bump at the back of the throttle body: https://www.facebook.com/photo.php?fbid=10156324305191929&l=2355fb17ff


I asked Ken @ FIRST about it and all he would say was that the company that designed the FIRST knew what they were doing and he doesn't advocate making change that could screw up the air flow. (I half removed the bump already until I killed my sandpaper flapper wheel and I'm trying to figure out whether to stop where I am with a half height bump or just kill it, which I'd really think would improve air flow, but maybe hurt distribution to the first set of runners for some reason...???)


Adam
Click to expand...

I think you are not looking at the whole picture. You seem to be focused on how that bump is going to restrict flow (a blockage in an open pipe), but don't forget that there is a large throttle blade in front of it that will affect the flow. Picture the throttle blade 1/2 open. Now does that bump make any sense?
It's probably there to help with part throttle distribution.
 
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