When is a throttle body too big?

[johnl]

I'm in the midst of an A/W intercooler install for the Ramerati and about to weld up a new elbow for the IM and that gets me into questions of whether to go to 58 from 52 on the TB. I

The IC outlet is 3" and the ID of the cast long leg elbow is 2.75" (ATP-ALM-020), so the 52mm TB is about 3/4" smaller than the ID of the IM neck.

Do TBs in any way depend on the Bernoulli effect? I mean, why not go big?
Is there a "golden ratio" of TB ID to intake ID?

[minigts]

I like the elbow, like your idea. I assume this is going to look pretty good when you're done with it. You plan to weld a plate on the end of the pipe to mount the TB? That is what I would like to do with the stock two piece, extend the full volume from the TB to the plenum instead of bottle necking it as it is. I have a spare I plan to do it on, when I have time.

[Keito]

I remember Gus testing t bodies
He said anything bigger than stock made little
Performance gain and returned horrible MPG's

[GLHNSLHT2]

I remember Gus testing t bodies
He said anything bigger than stock made little
Performance gain and returned horrible MPG's

That's because Gus only tested TB's on a 1 piece intake that had a little porting done. Of course those would be his results as the 1 piece necks down smaller than a stock 46mmTB right after the TB itself. Bolting a bigger TB onto a 1 piece that you have not modified by adding a 3.3 neck is pointless.



Now John before I give my opinion on what TB to run "you've got some splaining to do" on that exhaust manifold please

[4 l-bodies]

John,
That looks like a good choice, it should work great! Wish the radius was a little larger though. I know, tough to find in cast though. When I made my large plenum manifold for HP 8V application, I too chose 2.75' over 3". It transitioned in and out of 58/60mm TB better. Flow will slow down in short turn radius if it gets too large. I know guy that has welded dividers into intake filter ductwork to keep velocity up. That was Cadillac CTS-V (LS) world but same thing applies. The guy spent a lot of time on flowbench before coming to his conclusions.
Before welding the elbow to manifold talk to Pat M.. He did lots of testing on placement of elbows on his Masi intake manifold. You can easily starve cylinder #4 by welding elbow in wrong place. I would definitely go 58mm 2 bolt or Jeep 60mm 4 bolt TB for that application.
Todd

[johnl]

Thanks guys.

All credit for the exhaust manifold goes to MockGLH; he made an adapter plate to bolt a 2.4 manifold onto the Masi head. Jay, not to knock Mock, he did it to my cheapskate budget. Nowhere near as nice as yours.

The interesting thing, Todd, about the Masi manifold is that originally, as you know, it comes up from below, it points at the bell housing. It is not really a sweep turn, it is pretty tight, but the round entry at the TB quickly transforms into the parallelogram shape of the IM's long run, with the short and long turns being on the long dimension across the inside of the parallelogram; that means that the air on the inside and the outside turns see a pinched dimension. In looking at the stock turn, it appears, to me at least, that the pinch on the inside of the short turn will push more tight turn air farther toward the center while the long turn air, because it too is pinched on the outside corner of the parallelogram, is going to have a higher speed than it other wise would (and more of it also will be closer to the center) so that more of it has a better chance to speed match the air suffering the short turn. Hope I'm making sense here; the design/shape of it is not style, it is function.


Yes, I spoke to Pat about his work with the Masi IM it at our SoCal SDAC meet a couple months ago and I should get back to him about it; thanks for the reminder; I'm kind of in the "excited about it" stage where I just want to get it done. The IM compared to stock, is getting extended on both legs of the L, more so on the IM side because I have to place the IC far enough out to see the timing window. Hopefully that extra distance helps with getting air to #4; that is, the air is not asked to make so much of a 180* degree turn but more the normal 90* turn.

Also, the 2.75" ID of the elbow was selected to sort of match the area of the ID to the area of the IM. The inside of the paralellogram measures 2.25" tall by 2.25" wide with the wide dimension of the X being 3" and the short part being 2 5/8" so I bought that 2.75" ID elbow thinking that its area is smaller than the area of the paralellogram (5.06" vs 5.8") and that my fabber/welder might be able to heat/squeeze it/fake it into a transition to the paralellogram shape . . .

[5DIGITS]

John,
Determine what your peak air flow will be.
Research throttle bodies that support the estimated flow at 80% throttle blade opening, or near 70-75 degrees throttle angle.
This provides a good linear 'response-curve' for throttle while providing over-head for varying operating conditions (altitude, temperature, etc..)

Over sizing the throttle body produces a 'dead-pedal' feel above the engines flow limit.
In other words, go too large and 60-90 degrees of throttle will produce minimal change in output, while driving light throttle driving will be test your patience with "buck-bobble".

Thanks

[johnl]

The thanks are mine, Ken. No monster motor here; it is still a truck; just upgrades in the capacity of the turbo and in the efficiency of the IC. Stock head and IM, except for the re-angling of the neck, and, that requires a different neck since the parallelogram becomes a mismatch when the neck is swung up 45*

Where would I look to find the flow capacities of throttle bodies?

Thank you.

[BadAssPerformance]

John,
Determine what your peak air flow will be.
Research throttle bodies that support the estimated flow at 80% throttle blade opening, or near 70-75 degrees throttle angle.
This provides a good linear 'response-curve' for throttle while providing over-head for varying operating conditions (altitude, temperature, etc..)

Over sizing the throttle body produces a 'dead-pedal' feel above the engines flow limit.
In other words, go too large and 60-90 degrees of throttle will produce minimal change in output, while driving light throttle driving will be test your patience with "buck-bobble".

Thanks

Always wisdom from this guy

True story on the 'dead pedal' feel with the 75mm on the 2.4L at lower rpm pre-spool

[GLHNSLHT2]

Thanks guys.

All credit for the exhaust manifold goes to MockGLH; he made an adapter plate to bolt a 2.4 manifold onto the Masi head. Jay, not to knock Mock, he did it to my cheapskate budget. Nowhere near as nice as yours.

That's a good idea John. I like the newer turbo placement as you can see it. Oh don't think mine isn't cheap. I'm just lucky to work as a Machinist so the only thing I've paid for is the SS T3 flange.

[johnl]

OK, next question, BOV location?

I'm liking on top of the IC (the cold side) for a short straight recirculating run - maybe 4 or 5" max - straight back into the intake. See the fourth pic, the inlet hose, ahead of compressor inlet, is right next to the top of the cold side of the IC. Also, there's plenty of room under the Rampage's power bulge hood right there, and, the IC plenum casting is plenty thick for welding a flange there. That thickness, however is also true on the hot side of the IC but the recirculating run would be longer, maybe 10 or 12" at the outside.

I know that in the typical FMIC, with feet of pipe, there's substantially more heat and pressure on the hot side than on the cold side, and that is said to make the BOV operation quicker. Further, the hot side location puts the BOV closer to what it protects/keeps spooled - the compressor wheel/shaft.

The counter argument, of course, is that the cold side is closer to the source of the problem, the sudden surge caused by that TB snapping shut.

With the very short fat pipes that this A/W IC set up is all about, and with the size of the core, I expect that there will be minimal pressure differential between the two sides.

Then, the last idea is that a BOV on the hot side blows off hot air before that heat load is dumped into the IC (bypassing that increment of heat soak) but if the BOV is on the cold side, then it is dumping cold air and suffering otherwise unnecessary heat soak in doing so. The fact that the cooled air will be recirculated is no help because it will still be hotter than the ambient air that the air cleaner is collecting and that the BOV will dump into.

[BadAssPerformance]

Good question on BOV location. I've typically put them by the TB as you said the source of the problem, but there are definitely good reasons to put it on the hot side too. Hmmm... Maybe we need to drown some olives in Bombay Sapphire to figure this one out LOL

[cordes]

5digits places his close to the turbo to keep shaft speed up betweens shifts if I'm not mistaken. That's what I've always done too, but for me it was more about packaging. My question is, why recirculate it?

[GLHNSLHT2]

OK, next question, BOV location?

I'm liking on top of the IC (the cold side) for a short straight recirculating run - maybe 4 or 5" max - straight back into the intake. See the fourth pic, the inlet hose, ahead of compressor inlet, is right next to the top of the cold side of the IC. Also, there's plenty of room under the Rampage's power bulge hood right there, and, the IC plenum casting is plenty thick for welding a flange there. That thickness, however is also true on the hot side of the IC but the recirculating run would be longer, maybe 10 or 12" at the outside.

I know that in the typical FMIC, with feet of pipe, there's substantially more heat and pressure on the hot side than on the cold side, and that is said to make the BOV operation quicker. Further, the hot side location puts the BOV closer to what it protects/keeps spooled - the compressor wheel/shaft.

The counter argument, of course, is that the cold side is closer to the source of the problem, the sudden surge caused by that TB snapping shut.

With the very short fat pipes that this A/W IC set up is all about, and with the size of the core, I expect that there will be minimal pressure differential between the two sides.

Then, the last idea is that a BOV on the hot side blows off hot air before that heat load is dumped into the IC (bypassing that increment of heat soak) but if the BOV is on the cold side, then it is dumping cold air and suffering otherwise unnecessary heat soak in doing so. The fact that the cooled air will be recirculated is no help because it will still be hotter than the ambient air that the air cleaner is collecting and that the BOV will dump into.

Easy peasy solution. Weld a BOV on each end tank. Arugument null and void.

Here's a talon BOV we put on basically the same IC as you have John.



We took one of these flanges and just milled the pipe side off and welded it directly to the i/c.

[c2xejk]

Always wisdom from this guy

True story on the 'dead pedal' feel with the 75mm on the 2.4L at lower rpm pre-spool

The fix to that is a TB with a progressive linkage. On a prior 3L, I ran twin 58mm TBs. That throttle was VERY touchy. On the other hand some twin 80mm TBs from an Infiniti with a very nice progressive linkage were much more control able. So twin 58's were "too big", but twin 80's were fine...

[BadAssPerformance]

Twin 80mm!? holy smokes!

True, the rocker/cam profile makes a difference. Like putting the 47mm TB cam on a 52mm TB feels like it gives you close to WOT at just over 1/2...

[johnl]

Cordes, yeah, 5 digits' conserving shaft speed and the idea of eliminating avoidable IC heat soak both seem to settle it for BOV on the hot side. You could argue that the shock wave is closer on the cold side but then the hot side has more pressure to help pop the valve open quickly when the vacuum signal arrives from the IM. Mopar practice that I've seen (Mitsu T2) is to place the BOV on the hot side but Nissan and Subaru, I understand, are on the cold side. I like the idea of recirculation because it is quieter, and cleaner, and likely a good way to go since it is OEM practice, although it is probably better to dump that hot air to atmosphere instead of throwing back into the compressor.

JT, yeah, some Bombay Sapphire marinated olives would help us decide this dumb - does it matter? -question. Interesting ideas - twin TBs and the different TB cable cams; I hadn't noticed their differences, just bolted em up.

Jay, yeah, exactly what I had in mind, although, I'm thinking I might be able to find a spot on the lower driver's side on the side of the end tank for that same Talon type flange; the BOV would then sit below the master cylinder and I can point straight up at the compressor inlet pipe.

[Ondonti]

Always wisdom from this guy

True story on the 'dead pedal' feel with the 75mm on the 2.4L at lower rpm pre-spool

I don't think avoiding "dead pedal" in that situation by fitting a smaller TB makes any sense. If you don't like it, create a progressive setup. If you create a non progressive TB that doesn't have dead pedal feel on your same setup at those same pre boost rpms, bet'cha the next paycheck it hurts the bottom line when RPMS go up and you no longer feel "dead pedal" on the large TB setup.
If you make dead pedal go away at low rpms what you have just guaranteed is that you created a bottleneck at low rpms so it will be worse up top. Not saying its going to make a large power difference since it has been pointed out that everything needs to match for a part to get a fair chance to shine.

[5DIGITS]

I don't think avoiding "dead pedal" in that situation by fitting a smaller TB makes any sense. If you don't like it, create a progressive setup. If you create a non progressive TB that doesn't have dead pedal feel on your same setup at those same pre boost rpms, bet'cha the next paycheck it hurts the bottom line when RPMS go up and you no longer feel "dead pedal" on the large TB setup.
If you make dead pedal go away at low rpms what you have just guaranteed is that you created a bottleneck at low rpms so it will be worse up top. Not saying its going to make a large power difference since it has been pointed out that everything needs to match for a part to get a fair chance to shine.

It's expected that there will be different views and approaches to many aspects of building a powertrain and this is no exception.
Where different throttle cam profiles will certainly impact the 'drive-feel', its typically used is to dampen light and low-mid throttle sensitivity.
Although, it's use to re-curve the entire throttle range up to last 1/4" of pedal travel should have most asking why.
This should be a clear indication that the unit is too large for the application and the 'bigger is better' approach has successfully mismatched itself with up/down-stream hardware.
Therefore, most understand that a pure race set-up has but one focused target - WOT, but those that desire a refined street car may benefit from hardware smaller than the local culvert ditch pipe.