10% Lower + 2.5 Upper on a '13

[Jam421]

What do you guys think ? Currently I'm at 16.5-17psi boost @ 680rw with 4.10's under tall MT's ( actually 3.90 gears). Other mods such as 2.4 upper, VMP 67, headers, BPS plenum are below. I'm thinking drop 1lb with the upper swap and add a 10% down below.
Want to stay on 93 octane. Looking to stay just shy of 19psi boost. Think I'll need a BAP?

 

[02GTKB]

I was told when I asked the same question is it is too much for the stock s/c and 93 octane..but maybe I am wrong

 

[03kbredfire]

This is the combo that I run. I see at times 20 psi. As long as your tune is matched for combo I would suspect there would not be a problem. I was trying to achieve the same as a 15% lower. This is as close as I could obtain. I also have 67mm VMP TB as well as other items. Never dyno'd. Only logged info and sent to tuner for rev's. Gas in this area sucks. Therefor tune is basically a 91 oct. tune. Other mods to help your decision are headers, off road H, BPS elbow, 127mm JLT, 373 gears, NGK TR7IX, 170* stat. Very similar setup.

 

[ArchdukePoland]

What does your tuner recommend?

 

[Jam421]

Good question. I just spoke with him briefly on phone. He said the 10% lower with my 2.4 upper is too much for 93 octane. Moving to the 2.5 upper would be the way he'd recommend.

 

[paluka21]

Just make sure you leave margin for error and not ride on the edge of pump gas, unless you're willing to replace the motor. Too many variables to consider when saying a 93 octane tune will be "reliable" under any condition, unless you're spiking the gas with higher octane (like Sunoco 104) all the time, or running E85. I've played around with boosted motors for a long time and know that bad things do happen when you're pushing the envelope.
Just my 2¢

 

[fearthesnake]

Just make sure you leave margin for error and not ride on the edge of pump gas, unless you're willing to replace the motor. Too many variables to consider when saying a 93 octane tune will be "reliable" under any condition, unless you're spiking the gas with higher octane (like Sunoco 104) all the time, or running E85. I've played around with boosted motors for a long time and know that bad things do happen when you're pushing the envelope.
Just my 2¢

Agree, Id do one or the other in his case, not both. On borrowed time with upgraded upper/lower pullies imo.

 

[Catmonkey]

Not all 10%s are that either. IW's 10% is more like 12%. ATI's is a true 10% increase in diameter. 7.1" x 1.1 = 7.81" Diameters are published on both websites. ATI's stock diameter balancer is more like 6% too.

 

[Jam421]

Sometimes I regret starting with the 2.4 upper. I should have gone 10% lower from the jump and I'd likely be an added 1 psi and be safer at mid 17's. Regretfully I don't have the stock upper. Maybe I could consider the VMP hub with a 2.5 or even 2.6 upper + 10% ? Fuel Pump Booster no doubt also a consideration.

A friend of mine just mounted a 13-14 stock upper pulley trinity on an 5.4L '07. He thought he had a 10% IW below but pulled 650rwhp on a Mustang Dyno at 19.8psi max boost. That's 5-6psi over stock ! Maybe his lower was 15% ..don't know. Oh...#52 Injectors. On a Dynojet that could be 690-700rw.
NO BAP. Stock 2007 fuel pumps. I'm dying because I'm was almost pleading for him to get bigger than 52 injectors + definitely BAP ! Dyno pulls were on stock clutch which let go. He's breaking in a new clutch so hasn't jumped on it. He is hard on the car and will go drag racing. I can't EVER imagine that combo on my once owned 2008 coupe. I feel bad because I don't want to be a PIA.
I hoped he'd at least reconsider the BAP. NOPE.

So I hear you fellas. Engine Safety First. It's not worth the risk.
And....I appreciate all the advice. Thx....Jam

 

[fearthesnake]

Sometimes I regret starting with the 2.4 upper. I should have gone 10% lower from the jump and I'd likely be an added 1 psi and be safer at mid 17's. Regretfully I don't have the stock upper. Maybe I could consider the VMP hub with a 2.5 or even 2.6 upper + 10% ? Fuel Pump Booster no doubt also a consideration.

You bring up a good question and point. I currently still have stock upper, just a Intake, Lethal X-Pipe, Custom Tune and 3.73 gears. Have a upper pulley available from a buddy of mine if I want.

However, what is the benefit if I just go with 10% Lower? Any efficiencies gained there, more Torque? Would this be a better mod than swapping to a 2.4 Upper?

I wouldn't mind paying the add'l costs if this particular mod is better over the long haul (Engine wise) than the upper pulley swap.
Paluka21, Norton, Catmonkey? Any of you gurus know?

 

[03kbredfire]

Well I am not one of the preferred mentioned to answer but they have very similar ratios between crank and SC, so very close to same result. Some have claimed slightly higher torque with the lower but the main benefit may be the amount of belt contact available with the stock upper and larger lower. May have greater HP just due to that.

 

[Beercules]

A better harmonic balancer is better for your engine.
When you change power levels, the amplitude of the impulses change and the original balancer no longer works as well. Get in touch with superdampr (ATI) or fluid damper to ask why they put so much thought into their n/a designs.

 

[Catmonkey]

A larger lower and something like VMP's interchangable hub give you a whole lot of options. Car's got too much power, put a bigger upper. Want to run race gas, put a smaller lower. The stock lower and a 2.4 on a TVS should still be in pump gas territory (with all but the G2R on a 5.4), so you limit yourself if you ever want to run higher octane race gas to see what happens.

 

[Jam421]

My upper 2.4 pulley makes 2.5-2.7psi boost. Way up on redline it might hit 3. The 10% crank pulley advertises makes 3-4psi boost likely more consistent delivery . I'm not sure if guys actually get 4psi. Both make HP but the lower is supposed to bring Tq closer to the HP. My Tq with upper was about 30 less than HP.. The guy's car I mentioned above with the lower 10% had about a 35 spread between the two. SOoo...go figure !
With the upper I had belt slip on the stab. Metco tensioner definitely helped as instead of just wrapping the top of the small pulley it held the belt under/around the side as well increasing surface contact dramatically. I also treat my SC belt occasionally with a belt spray. The lower pulley actually decreases belt slip simply because it's larger diameter.....way more belt to pulley contact.
If I could buy a new or undamaged condition stock 2.67 upper pulley for my Trinity I'd likely take the 2.4 upper off and have the crank installed.
I should put a WTB ad on the forums.->).

 

[fearthesnake]

Thanks for the feedback everyone, appreciated.

 

[Jam421]

paluka21 said: " Just make sure you leave margin for error and not ride on the edge of pump gas, unless you're willing to replace the motor."
beercules said : "A better harmonic balancer is better for your engine. "

How does this sound to my fellow 13-14 GT500 owners ?
My shop says " the edge" is 2.5 upper + 10%.
Perhaos the VMP hub with 2.6 upper + 10% ATI lower crank as a combo?
I can hold a 2.5 VMP pulley in my trunk but I'm thinking the 2.6 being just slightly smaller than stock may be enough boost.

 

[Catmonkey]

The ATI 10% with a 2.5" will be a 5.6% increase in blower speed over the stock lower and a 2.4". The 10% with a 2.6" is a 1.5% increase in blower speed. Generally a .1" decrease in pulley size is a 1-1.5 psi increase and ~4% increase in blower speed. I'd err on the side of being under the "edge". In fact, my current setup is the 10% and the 2.6".

 

[Jam421]

Catmonkey....I was kind of leaning in your direction yesterday simply because to me being on the edge can be interpreted as close to breakage. What psi are you running with the 10% & 2.6 upper ?
Do you have headers, axle backs , large TB or O-Sized plenum ?
Did you install the BAP ?
Thnx.........jam

 

[Catmonkey]

I'm just putting that combo together now. Haven't put a boost gauge in the car yet either, but I've got one on the shelf. I'm running a built 5.8 in a '12 with cams and running a ported VMP G2 and their new twin 72mm and long tubes without cats. I also have ID1000s and a BAP, so I'm not sure how well it would compare. My cams are not that aggressive, so I doubt it loses much boost from them. I did run the car with all this without the blower port and running 67mm TB before I started tearing it down to upgrade the chain drives and other components. I ordered another cam with a bit more duration so that's liable to change up the composition further.

I had an ATI stock balancer and a 2.4" upper, so I'm sure I was in the range of 18 psi, at a minimum. I had no traction in first or second and third gets sort of scary with 315s, so I figured reducing the boost wouldn't hurt anything. I just changed the shell on the balancer to the 10%. My thinking was with the adjustable hub, I'd have greater range of adjustability. I got a bigger belt and put a stock sized pulley on my Thump tensioner. I figure I'll probably end up with a 2650, so I'm sure I'll need an ever larger upper pulley. My old VMP Gen I came with 3 pullies and I have pullies up to 3".

The way I see it, the planets have to be in perfect alignment to run a 2.4" on a TVS with pump gas. Sure you can reduce your timing to boost it to 20 psi, but spinning the blower faster than you need still produces heat. Hot IAT2 just go to pull more timing. Granted we have knock sensors, but you never know how old the gas is at the gas station, and if it takes you a while to go through a tank of gas, just how much octane you have, or your car sits up in winter, there's not a lot of drawbacks running less than 18psi. I've already blown a head gasket with just a VMP Gen I and a 2.4" pulley, so I know these motors have their limitations. If you have traction issues to boot, it's just more win. If you track the car, an upper pulley swap is a snap with the adjustable hub. I think for a street setup, I'm going to continue increasing the upper pulley until it no longer feels like I'm running on wet pavement. With our annual rainfall, I'm just not comfortable running drag radials on the street. I also like pushing it in the corners.

Anyway that's my logic in this process. I'm sure I haven't installed my last pulley either.

 

[biminiLX]

I was happy with my IW 15% lower/stock upper and 93 pump with some Torco when racing. Even without Torco the Lund 93 tune was safe on datalogs.
The lower pulley gives you a better SFI balancer and better belt wrap.
I think you'll be happy with the 10%/2.5 .
Jam you seemed to enjoy the drag style like I do, so upgrading to a rear ice tank and HE with fans might be a good idea. Consistent low IATS allows higher boost on pump.
I actually just finished replacing my front bumper with a tubular design, allowing me to add fans to the stock HE and finishing the rear ice tank lines.
Cars ready to rock, going up in 2-3 weekends for some fine tuning and just enjoying the car until fall racing.
-J