75MM TB on a STOCK H.O.?

Topic: 75MM TB on a STOCK H.O.? (Read 5354 times) previous topic - next topic

75MM TB on a STOCK H.O.?

Reply #30 – May 26, 2007, 10:33:38 PM

Alrighty, I guess I'll jump in this now.

Well after reading the whole thread I started thinking about how EFI works as opposed to a carb. I think the main thing to remember is that the same rules don’t apply because a carb meters fuel based on the venturi effect. Too much carb kills torque because the lower air velocity is inefficient in mixing the gasoline with the air. Plus the intake, even in dual plane form, has relatively short runners and the fuel has to be kept in suspension through the intake so air velocity through the carb is critical.

A fuel injected manifold separates air intake and fuel metering functions so the same rules don’t apply to a certain extent. Air velocity is and always will be the major factor in torque production. However, in an EFI application plenum volume, intake runner volume and length are the 3 primary factors that dictate torque production. The EFI intake works on the prinl of ram effect. When the intake valve opens while the piston is traveling down to the bottom of the bore the column of air in the intake runner along with air in the plenum is pulled through the head and into the cylinder. If the air in the intake runners is lazy (I.e. runner volume too big) you can’t pack as much into the cylinder at low engine speed thereby killing torque.

The way I see it is that the TB is the doorway leading to the plenum chamber. It’s the plenum chamber that feeds the intake runners. If your intake runners are properly sized it shouldn’t matter how much air is being allowed into the plenum by the TB. Why… because intake runner volume is what will ultimately dictate how much air and at what velocity it can be rammed into the cylinder.

Now with all that being said if you were to choose a throttle body based on the CFM requirements of an engine at say 6000 RPM a 5.0 would only need roughly 530 CFM based on the Accufab chart. If a 65mm TB is rated at 664 CFM wouldn’t that make it way too big for a 5.0? But in reality we know that a 65mm TB is worth more power than a 50mm TB without sacrificing torque down low.

IMO, the long runner Ford EFI intake design is the reason that proper TB sizing isn’t all that critical. Super ford mag did a dyno series a few years ago where they added one mod at a time and I’m sure they played around with TB sizes. I’ll have to see if I can dig that up.

75MM TB on a STOCK H.O.?

Reply #31 – May 27, 2007, 01:33:12 AM

I was waiting for someone to comment on the over-rating of the PP throttle body...also, it's not as if a TB alone gave the power...that MAF/filter/CAI from Anderson is KNOWN for being excellent at making more power on just about any N/A combo along with his tuning skills. The TB alone was only worth a few horsepower if you break it down.

Next, scientifically speaking, air IS considered a fluid due to the way it flows.

Loss of low end torque comes from a lack in either exhaust gas velocity or intake velocity(weather it's heads or intake), increasing the T/B size will NOT have a negative effect on low end....BECAUSE you are NOT changing the size or length of the intake runners or the intake ports in the heads....yes, you may have to optimize fuel pressure/timing and often times even upgrade the MAF meter.

Velocity depends on a few things...the cross-sectional area of the port or runner, the length of the port or runner, the shape of the port or runner, and valve sizing...NONE of those characteristics change when installing a larger throttle body...it's almost like saying a CAI will reduce low end torque.

Dominator, forced induction and N/A combo's are like apples to oranges when it comes to throttle body and intake manifold selection...a 70MM t/b will flow more CFM on a power adder combo than a N/A combo every time...WHY? Because on an N/A combination, you only have 14.7lbs of atmospheric pressure(@ sea level) acting upon the t/b and intake...in a forced induction set up, you not only have that same 14.7lbs, but you also figure that you're forcing extra air in via s/c or turbo...with 10lbs of boost, it's like having 24.7lbs total pressure...I'm not saying a 10lb s/c kit will give you a 24-25lb boost reading because gauges aren't calibrated that way.

10lbs through a 90mm t/b and a box style intake will blow away a combination with the same boost but stock t/b and intake WHILE UNDER BOOST....HOWEVER, you would subsequently need to change pulleys to get the same pressure acting on the combination with the larger t/b and intake. INTAKE VELOCITY IS COMPLETELY IRRELEVANT ON A FORCED INDUCTION SET-UP, WHILE UNDER BOOST . This is because you have something creating a much more powerful velocity for you.

Guys who cry about losses after large t/b's are usually the ones who add ONLY the t/b and egr spacer and do nothing about MAF meters, fuel pressure, and timing.

1WLD BRD- you make a very valid point in the fact that a box intake will kill low end torque on a stock motor, but we are NOT comparing intakes here...another apples to oranges situation.

Dogcharmer- Nice response!
I AM NOT TRYING TO BURN ANYONE DOWN IN THIS POST, I AM TRYING TO CLEAR THINGS UP SO PLEASE DON'T GET PISSED AT ME IF YOU DON'T LIKE WHAT WAS SAID.

-Don

75MM TB on a STOCK H.O.?

Reply #32 – May 27, 2007, 10:35:32 AM

Quote from: Sick88Tbird;150022

1WLD BRD- you make a very valid point in the fact that a box intake will kill low end torque on a stock motor, but we are NOT comparing intakes here...another apples to oranges situation.

Dogcharmer- Nice response!
I AM NOT TRYING TO BURN ANYONE DOWN IN THIS POST, I AM TRYING TO CLEAR THINGS UP SO PLEASE DON'T GET PISSED AT ME IF YOU DON'T LIKE WHAT WAS SAID.

-Don

I understend that, but he was saying intake velocity HAS NO affect on an EFI motor. I stated that to prove a point. If intake velocity has no affect, we would all be running a box style intake.

And yeah good points both you guys. but look at the dyno charts they show in magazines, in alot of them, they do lose some lower end after a big tb swap. I dunno,

I still say a 75mm TB on a stock HO is like a 4" exhaust on the same car. Doesn't make any sense.

75MM TB on a STOCK H.O.?

Reply #33 – May 27, 2007, 11:12:27 AM

Guess I'll post my perspective as someone who has upgraded to a 65mm, then a 75mm and now an 85mm TB.

1) The size of the TB has little to no relationship to low-end torque on a long-runner tuned-port EFI vehicle.

2) If you do see a bog with a larger TB, it is due to the fact that the EFI computer uses rate of change of TB to add fuel during tip-ins. Imagine how much more air an 85mm TB can let in at 10 degrees tip-in versus a 60mm TB. Believe me, I have had the most issues tuning around this "lean out at tip-in" problem (S/C notwithstanding).

3) At the 330 RWHP level, Kenne Bell only got 4 HP switching from a 65mm TB to a 75mm TB ( http://www.kennebell.net/techinfo/ford-techinfo/blowzilla-flowzilla.pdf ). This is in-line with what you might expect on the typical 250-300 RWHP street engine where you would expect almost NO gain switching from a 65mm TB to a 75mm TB.

75MM TB on a STOCK H.O.?

Reply #34 – May 27, 2007, 11:43:53 AM

Quote from: Cougar5.0;150062

2) If you do see a bog with a larger TB, it is due to the fact that the EFI computer uses rate of change of TB to add fuel during tip-ins. Imagine how much more air an 85mm TB can let in at 10 degrees tip-in versus a 60mm TB. Believe me, I have had the most issues tuning around this "lean out at tip-in" problem (S/C notwithstanding).

Interesting point... I would think that going a little lean on tip in would actually help on a naturally aspirated combo.

BTW, aren't you using a TwEECer. If so how's that going? I'm thinking about going that route when I get N2O and bigger injectors.

75MM TB on a STOCK H.O.?

Reply #35 – May 27, 2007, 12:05:39 PM

Quote from: Dogcharmer;150076

Interesting point... I would think that going a little lean on tip in would actually help on a naturally aspirated combo.

BTW, aren't you using a TwEECer. If so how's that going? I'm thinking about going that route when I get N2O and bigger injectors.

The TwEECer has somewhat of a learning curve, but once you are "hooked into" the lingo and realize the power at your fingertips, you will be very happy :o). There is also additional tuning software that this fellow http://webpages.charter.net/eecbuttstuffyzer/ wrote that helps buttstuffyze datalogs and makes recommendations for changes (EEC buttstuffyzer). He also just recently released a new program called Bin Editor that will let you burn tunes through the TwEECer and datalog on a different tab!! It basically replaces CalEdit and Calcon - the two programs that come with the TwEECer for programming and datalogging respectively. The cool thing is that it lets you change ECU paramaters that aren't even visible in the TwEECer software. There are more advantages, but you would just think I am talking jibberish at this point.

TwEECer + wideband O2 + EEC buttstuffyzer + getting help at http://eectuning.org/forums/ = a good tune :D

75MM TB on a STOCK H.O.?

Reply #36 – May 27, 2007, 12:20:48 PM

Quote

I understend that, but he was saying intake velocity HAS NO affect on an EFI motor.

I dont know if you are referring to something i said or not but I was trying to get an explanation of HOW the TB affects the velocity so i could understand how it would cause a loss of low end.

This last page has been very informative so thank you to all of you.

I would like to expand my knowledge of performance engines. Anybody know of a good book on engine performance?

75MM TB on a STOCK H.O.?

Reply #37 – May 27, 2007, 12:37:44 PM

There are a couple of books specific to the Fox Mustang (applies equally to Cougars & Birds) and the 5L engine that I found very useful when I was just starting out:

"How to Build & Modify Ford Fuel-Injected 5.0-Liter V-8 Engines" by Tom Wilson

&

"Mustang Performance Handbook" by William R. Mathis

Both of these books cover the popular mods from a complete engine rebuild to just bolt-on items. The latter book also covers drivetrain mods including transmission & rear-end. The info is slightly dated, but still very useful - especially for a beginner.

BTW, if anyone wants to experiment to see the effects of switching to a 75mm TB, I have an Accufab 75mm TB and EGR spacer that I don't need any more - I'd sell it to anyone who's interested...

75MM TB on a STOCK H.O.?

Reply #38 – May 27, 2007, 01:02:52 PM

Quote

I have an Accufab 75mm TB and EGR spacer that I don't need any more - I'd sell it to anyone who's interested...

How much? I dont know if i would put it on stock but i would certainly use it when i put the TFS kit on.

75MM TB on a STOCK H.O.?

Reply #39 – May 27, 2007, 03:10:21 PM

No I was refering to softtouch's comment.

I have both those books too. As he said, good information though somewhat dated. My wife stole them on me though, as she bought, and is building a T-top '84-85 Capri. (cant remember the year)

Yeah how much for the TB and spacer?

75MM TB on a STOCK H.O.?

Reply #40 – May 27, 2007, 03:51:22 PM

If velocity didn't matter then why would Ford have designed an 18" ish runner?

75MM TB on a STOCK H.O.?

Reply #41 – May 27, 2007, 10:06:08 PM

I found this to interesting info about intake runners.
http://auto.howstuffworks.com/question517.htm

75MM TB on a STOCK H.O.?

Reply #42 – May 28, 2007, 04:54:32 PM

Quote from: 88sportcoupe;150102

How much? I dont know if i would put it on stock but i would certainly use it when i put the TFS kit on.

PM'ed you...