75mm tb vs. 85mm

mywhite89

Registered User
Magnum powers is all set on us using the 85mm throttlebody. Though, I see that a lot of people use the 75mm throttlebody. Whats the deal? Is the 75 sufficient enough for our cars?

I am starting with the mpII blower for now and sometime working my way up to an AR in the future. My inlet diameter measures 85mm.
 
A 75mm TB will flow 800-900 CFM. A 85mm unit flows 1150-1250 CFM. To date, there are only 3 SCs with a V6 and supercharger that I know of which exceed 900 CFM.

Paul
 
alright then

So, If I had every bolt-on done, Fully built bottom end, along with a 2.0 AR blower, methanol injection, but no nitrous, I would probably need just a 75mm in your best judgement?

thanks, chris
 
mine exceeds 900 CFM with the 1.7L AR and I am using the 85mm I like it better and it doesn't hurt the power at all so go with something you will not have to upgrade later I am going to the 2.0 AR as soon as their ready
 
boosted

Thanks for the info. The fact is, I just know i'll upgrade at some point, and I don't want to have to upgrade already upgraded parts. The main thing is I want to get the car dialed in with an m90, and have the option at some point to make at least a halfway cheap upgrade to an AR without all the dumb little things that end up costing me another $1,500--oh wait this is a supercoupe, add $1,000 to that number!!!! hahaha
 
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boostedbird said:
mine exceeds 900 CFM with the 1.7L AR and I am using the 85mm I like it better and it doesn't hurt the power at all so go with something you will not have to upgrade later I am going to the 2.0 AR as soon as their ready
That's interesting Chris, I didn't know any of the autorotors broke 450RWHP yet. You must be running your 60lbers at over 80% duty cycle? Which fuel pump(s) are you running?

Paul
 
mywhite89 said:
So, If I had every bolt-on done, Fully built bottom end, along with a 2.0 AR blower, methanol injection, but no nitrous, I would probably need just a 75mm in your best judgement?

thanks, chris
On a car that is moving about 1100 CFM, the change from a 75TB to 85TB netted 9RWHP peak. Is $175 for 9HP worth it to you if you reach that point? Personally, I would put a few extra bucks in and put the car on a bottle instead at that point.

Paul
 
Paul, what SC's have broken 450rwhp? Also, are those flow numbers measured? The reason I ask is that my estimates for the flow capacity of those TB's is/was lower than that.
 
With the TB being located before the supercharger inlet, I think bigger is better. While it's true that I only picked up 9 rwhp switching from a 75mm to 85mm TB when I had an MPII, I'm not sure the same would be true with the AR.

David

PS: With TB after the blower or turbo (like my 93), a 75mm will be plenty for 1100 HP.
 
XR7 Dave said:
Paul, what SC's have broken 450rwhp?
I personally haven't witnessed any break 450 RWHP, how many do you know of??
Also, are those flow numbers measured?
The throttle body flow rates I quoted, yes, they are measured. The Accufab 75mm will flow over 900 CFM with some of their 75mm pieces flowing over 1000 CFM. I was being conservative with my estimates. I was actually at Accufab last month checking out John;s racecar and the Ford GTs they are building. The GTs see around 11 HP when stepping up to a 75mm unit vs the stock TB on a highly modified engine.

David Neibert said:
With the TB being located before the supercharger inlet, I think bigger is better. While it's true that I only picked up 9 rwhp switching from a 75mm to 85mm TB when I had an MPII, I'm not sure the same would be true with the AR.
I have a feeling the gains are more a function of allowing the inlet plenum to work better than they are of the throttle body itself being the restriction. From the testing I have seen, the inlet is the bottle neck due to its transitions and the larger TB helps increase density on the outer radius of the inlet. That brings to mind a curious question. Will part throttle inlet flow improve if the throttle body was turned 90* causing the throttle blade to act as a diffuser.

Paul
 
BT Motorsports said:
I personally haven't witnessed any break 450 RWHP, how many do you know of??
I wasn't asking if you'd seen them, I just wanted to know what 3 SC's were exceeding 900cfm that you were referring to and which I assumed were exceeding 450rwhp. Maybe I missunderstood. I know David's car wasn't anywhere near 900cfm with his Eaton and is only getting close with his AR.

The throttle body flow rates I quoted, yes, they are measured. The Accufab 75mm will flow over 900 CFM with some of their 75mm pieces flowing over 1000 CFM. I was being conservative with my estimates. I was actually at Accufab last month checking out John;s racecar and the Ford GTs they are building. The GTs see around 11 HP when stepping up to a 75mm unit vs the stock TB on a highly modified engine.
Accufab also claims a 5 HP increase on a stock GT engine with their dual blade 75MM TB, not a single like ours. In that case the TB should be able to flow somewhere around 1800cfm?

I know this sounds like arguing so which I'm not trying to do, but these are numbers I've seen for the Mustang single blade TB's.

6. THROTTLE BODY AIR FLOW DATA (In CFM):

1.Ford Stock 5.0L 60MM, 526 CFM
2.Accufab 65MM, 616 CFM
3.BBK 70MM, 726 CFM
4.Accufab 75MM, 845 CFM
5.Accufab 90MM, 1225 CFM
Which also correlates with data I've seen based on other tests or standard data. For what it's worth Charles told me that a 76MM C&L flows just as much air as his 85MM TB.

This isn't to say that a 75MM is not enough for most anyone in our group and is in fact what I last ran on my car.
 
XR7 Dave said:
I wasn't asking if you'd seen them, I just wanted to know what 3 SC's were exceeding 900cfm that you were referring to and which I assumed were exceeding 450rwhp. Maybe I missunderstood. I know David's car wasn't anywhere near 900cfm with his Eaton and is only getting close with his AR.
Since I haven't seen them personally, I cannot verify their claims so I would prefer not to identify them. It is my presumption that the owners would or will make that information public if they so choose. I reviewed two data logs that indicated MAF readings over 900CFM and the third person stated they pegged their 80mm C&L MAF with a green tube.
I'd still like to hear what Chris has to say about his though.
Accufab also claims a 5 HP increase on a stock GT engine with their dual blade 75MM TB, not a single like ours. In that case the TB should be able to flow somewhere around 1800cfm?
That sounds about right, their Lightning unit flows around 1700 CFM and is similiar in size. I don't think each butterfly is 75mm though, I think it may be the entrance way since they have a bellmouth entrance. I suppose I could ask Fred if I get time to stop by there next week.

I know this sounds like arguing so which I'm not trying to do, but these are numbers I've seen for the Mustang single blade TB's.

Which also correlates with data I've seen based on other tests or standard data. For what it's worth Charles told me that a 76MM C&L flows just as much air as his 85MM TB.

This isn't to say that a 75MM is not enough for most anyone in our group and is in fact what I last ran on my car.
Not to worry, I haven't taken it as being argumentive, I see it as an opportunity to get the facts straight for everyone.
My #s came direct from the horses mouth, Fred and I had a discussion about this when I was at Accufab. I believe he had just flowed the 65mm unit a few days prior. He also posted exact #s on V6power.net in this thread: http://www.v6power.net/vb/showthread.php?t=26309&highlight=throttle+body+flow
Post # 62 quotes their 65mm V6 mustang specific unit at 640CFM, the 75mm unit for the stang GT @924CFM and their R version of it at 1040CFM.

Exactly what flow rate did Charles quote his 85mm TB at?

Anyhow, I have nothing against the 85mm unit on our cars, I just don't see it as a needed item for over 99% of the SC population and feel the additional cost over the 75mm piece should be invested elsewhere.

Paul
 
Fair enough I guess.

My comments about the MP TB and 76 C&L come from a conversation with Charles. Sorry I don't recal if any specific numbers were mentioned.

I know Kevin is pegging his 85MM C&L MAF but I've come to realize that doesn't necessarily mean everything. I've actually seen people with 42's peg 76's with V8 42lb calibrations as well which shouldn't have happened. One constant that I've learned though my work with SC's is that there are no constants or at least that I've been unable to back them up.

I still think it is reasonable to error on the low side of the TB ratings for tuning purposes. What a part does on the flow bench and what it does in real life can be two totally different things. You eluded to that regarding the transition of air into the plenum and the characteristics of the air once it enters the plenum. Try taking some Stieg heads off a 2 yr old street motor and see what you get. :eek: Or just bolt them onto an SC intake manifold and see what that does.

For maximum performance I would suggest running parts that physically match each other. For example, I feel that a properly formed filter on an 85MM MAF, 3.5" OD intake tube, 85MM TB and MP inlet will flow better than a 75MM MAF, 3.5" intake and 75MM TB and MP inlet. I think most likely you would find that even a continuously sized 3.5" intake tract will flow less as a system than any one of the above components flowed alone.

I do also think that people tend to get way ahead of themselves with this stuff. You won't lose much if you have to upgrade at some point. A 75MM TB will always fetch a decent price at re-sale time if you ever really need to upgrade and the price difference is negligible when you start looking at what it's going to cost to exceed the potential of a 75MM. :)
 
XR7 Dave said:
I know Kevin is pegging his 85MM C&L MAF but I've come to realize that doesn't necessarily mean everything. I've actually seen people with 42's peg 76's with V8 42lb calibrations as well which shouldn't have happened. One constant that I've learned though my work with SC's is that there are no constants or at least that I've been unable to back them up.
Slightly off topic then, is it your opinion that the above mentioned MAF readings were incorrect and the flow rates are actually not as high as the meter is reporting?
Perhaps we would need to monitor injector duty cycle to determine the validity of the MAF reports?

Paul
 
BT Motorsports said:
Slightly off topic then, is it your opinion that the above mentioned MAF readings were incorrect and the flow rates are actually not as high as the meter is reporting?
Perhaps we would need to monitor injector duty cycle to determine the validity of the MAF reports?

Paul

I think the MAF readings are incorrect. I've seen it numerous times and often there is a boost leak involved as well though not always (or at least not that we could find). Monitoring injector duty cycle along with AFR would tell the whole story.
 
Holy crap I leave for a few days after talking about my car and the world comes to an end geez. Sorry bout that I wasn't tryin to disappear I was acually off playin with the family on the lake aboard my buddies turbo charged wave runner, that thing is AWESOME if you haven't tryed it you should!!!!

Anyway back to the subject at hand I can only go off the data that was being taken by the guy here he said that the MAF was showing 965CFM and that was with the 80mm with a blue tube. I am running a 255 LPH in tank with the T-rex inline I had another setup but this one seems to work the best without going lean at the top end (even if it is the loudest) thats with a 48PSI static FPR setting. I have no clue what the injectors were running and I only knew bout the MAF cause he said I might want to upgrade to the 85mm tuner instead to flow more air. But I will probably end up getting a stand alone anyway for the 2.0L AR and eliminating the need for the MAF all together. The readings were taken while making full boost runs in car 1st gear (With MASSIVE wheelspin) 22PSI at 6300RPMs, 2nd gear (still spinning) 23.5PSI at 6400RPMs, 3rd gear good traction after letting up for a sec 24PSI of boost at 6425RPMs, and 21 PSI in 4th at 5400 RPMs then let off, none taken in 5th gear, I was already going WAYYYY too fast but I was at bonniville speedway at the salt flats. AFR readings were good in 1st, 2nd, 3rd and only slightly started to lean at the top of 4th from a good 11.6 to a 12.1. So I am thinking a 72 pound injector will be going in along with the 2.0 and the stand alone so I can control the injector being that it is a different impedence than the 60s that i am already running. This is with the tune that Dave D did when I was in oklahoma before I changed everything. Tune still seems to be spot on, I can only run 18 degrees total timing on the crappy 91 octane we get here and when I want to install the octane plug it brings my timing to 22 degrees but I have to add 3 gallons of 100 octane race gas but it really hauls like that. I have reinstalled my wet shot set up for 35 HP shot right now but haven't had the BALLS to try it yet. I was having a HUGE boost leak but couldn't find it cause unless it was hard boosting it wasn't apparent. come to find out it ended up being that my top plate that goes to the AR I had striped 2 holes and had taken 2 screws off even though it seemed sealed it wasn't, helicoiled them all and reinstalled with the right stuff RTV and hasn't missed a beat! :D I plan on changing to a different camshaft along with a few other things this winter to finish up the beast and have it well over 500 RWHP (without the nitrous) with the stand alone, 6 speed, 2.0L AR, and a much lighter and brighter body this coming summer. The color it will be changed to is called spectra flare, a bright almost chrome silver with 4 different pearls in the clear coats.
 
Chris,

How fast was 5400rpm in 4th? I don't know what gears or tires you have so I can't calculate it. Did they clock you?
 
I was going bout 120+MPH at the time if my speedo is right I think it is but not sure. But it felt like I was going VERY fricken fast no I didnt get clocked cause we were doing a play session me and a few other cars were trying to do some data logging. I will see if he has any other data that i can send you.
 
BT Motorsports said:
A 75mm TB will flow 800-900 CFM. A 85mm unit flows 1150-1250 CFM. To date, there are only 3 SCs with a V6 and supercharger that I know of which exceed 900 CFM.

Paul

Paul, Are the 3 cars you talking about have the M112 on them?

Ken
 
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