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Old 04-14-2019, 05:54 AM   #1
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TimeTrial car, need additional 5-10hp

I need to find 5-10ho in my NASA TT5 car, itís a 2.5L w/ headers, no cats, full exhaust, and a underdrive pulley. Is tuning an option? Poking around on the Internet it doesnít look like this is a popular route. Iíd rather not buy a 2.7l engine but might have to. Any ideas? If tuning is an option what do you all recommend?

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Stu
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Old 04-15-2019, 11:50 AM   #2
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What is allowed by the rules? Drop weight. It's free. Dropping 85 pounds will be about 10 HP.
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Old 04-15-2019, 12:15 PM   #3
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how about a early 996 plenum w cable throttle body)

or this ...

https://www.ebay.com/itm/OBX-Individual-Throttle-Body-Fits-Watercooled-Porsche-911-Boxster-ITB/182223111819?epid=1986020481&hash=item2a6d58068b:g:mEkAAOSwbsBXmlXx
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Old 04-15-2019, 01:41 PM   #4
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What is allowed by the rules? Drop weight. It's free. Dropping 85 pounds will be about 10 HP.
this is a really interesting one, or at least was for me. I've always thought cars with equal power to weight would have the same acceleration and as a bonus the lower weight car would have less weight to turn and brake. Fixed power to weight time trial has shown me this is very wrong. The problem is that aerodynamic, and rotational drag (and other drag) represent a bigger percentage power loss to the lighter, lower power car. I was at Summit point last week and happened to find myself right next to an S2000 which has the same power to weight but 30 more horsepower. I exited turn 10 at a higher speed only to have him walk right by on the straight. You exit turn 10 at 100mph and my car just doesn't have the power to pull out of the turn like his does at that speed.

Motorcycles are an extreme example of this. They have tremendous power to weight but above 100mph they are dogs compared to cars.
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Old 04-15-2019, 02:23 PM   #5
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Motorcycles are an extreme example of this. They have tremendous power to weight but above 100mph they are dogs compared to cars.
You'll have to sell me on this, Haha. That's not consistent with my own experience.

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Old 04-15-2019, 02:39 PM   #6
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Any bike over 600 cc is not a dog compared to cars! I had a 1000 cc bike that would go from 100 to 140 mph quicker than the Boxster can go from 0 to 40 mph.

But I understand, the power-to-weight thing doesn't really tell the whole story in the real world. The higher the speeds, the less the ratio holds up. I used to race a Datsun 1200 in class based on power-to-weight. That meant my 1600 lb, 72 HP car was up against an Alfa Milano, a turd that weighed over 1,000 lbs more but had over 100 more horsepower. I was much quicker in the turns, but he could rocket by on the straights, where I would then be stuck behind him in the turns the rest of the race.
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Old 04-15-2019, 08:21 PM   #7
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how about a early 996 plenum w cable throttle body...
This is a good way to pick up 5-10hp.
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Old 04-15-2019, 11:06 PM   #8
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I do have a 996 TB on pretty much stock 2.5 with UDP and PSE, like quick throttle response and do not feel loss of low end torque that some typically suggest. Maybe because 2.5 intake pass is larger for most part with only the throttle butterfly that chokes down as the bottle-neck? My intake is all original from snorkel down to holmheltz chamber and it sounds very nice and audible at quick throttle opening.

Anyway I'm wondering if someone did dyno before/ after to ducument the change?

Also the link showing individual throttle body like carb stack, what is that like? Again any documented dyno results?
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Old 04-16-2019, 07:12 AM   #9
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987 airboxes show improvements on S motors. I don't recall feedback from anyone who has tried it with a 2.5.
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Old 04-16-2019, 07:51 AM   #10
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Back when I did TTB and GTS3 with NASA (924S with 3L) I was the lowest HP, but lightest car. Great in many respects but got killed on long straights (where it is easy to pass), by higher HP cars with the same power to weight.

996 TB is a good idea, but finding a good used mechanical unit is not easy and new ones are over $1,000. Have you considered having your TB bored? Not sure if you will get the 10 HP that you need, but you will get some extra HP for those long straights at VIR.

You straight that you have full exhaust, do you mean stock?

You can tune the car and expect to get a few more HP as well. I would stay away from a preset tune and get one done with the car on a dyno for best results.
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Old 04-18-2019, 10:48 AM   #11
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If I were looking for a few more hp here is what I would try. Take this with a grain of salt as I have not done any of these or have proof that they would make more power on a m96 2.5 engine.

Intake: 987 air box and larger smoother intake tube as a minimum or (again a little different but could be easily tested) make a straight and short intake that passes into the trunk to a larger cone filter. Vent the trunk for ample fresh air.
Get a 996 cable throttle body or have the stock one bored out, I believe a 987 intake ďtĒ will fit or do what ben006 did and 3D print one that has a larger and smoother radius.

Engine: Could you live with out power steering? Spinning that pump at 5k would be worth a couple of hp.
Do some at home port and polish on the heads if your comfortable with that much work. (David Vizard has a good book on the subject)

Exhaust: looks like you have most everything covered. The only gripe I have is with the header selection for the 2.5 engines. It seems to me that most headers are oversized for the smaller engine and a custom header with smaller but longer primaries could be worth some midrange to upper end horsepower.

Tune: all of these would benefit more with a custom tune but that seems to be difficult with the 2.5 engine and finding someone to do it.

Again opinions will differ and Iím not saying that all of these will make more power just ideas I had on how to do it. Thank you have a good day
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Old 04-19-2019, 05:30 AM   #12
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Originally Posted by truegearhead View Post
this is a really interesting one, or at least was for me. I've always thought cars with equal power to weight would have the same acceleration and as a bonus the lower weight car would have less weight to turn and brake. Fixed power to weight time trial has shown me this is very wrong. The problem is that aerodynamic, and rotational drag (and other drag) represent a bigger percentage power loss to the lighter, lower power car. I was at Summit point last week and happened to find myself right next to an S2000 which has the same power to weight but 30 more horsepower. I exited turn 10 at a higher speed only to have him walk right by on the straight. You exit turn 10 at 100mph and my car just doesn't have the power to pull out of the turn like his does at that speed.

Motorcycles are an extreme example of this. They have tremendous power to weight but above 100mph they are dogs compared to cars.
The S2000 has a couple things you don't. It cranks to about 8200 RPM, and a 6 speed transmission. I agree that your best option is reduce weight. The rule would ban you from the type of mods that are being suggested here or at the very least cause you to be flipped into a higher class. The Power steering mod with electric PS pump is a good power saver. Then If you haven't done it yet remove the AC compressor, plumbing, and coils at the radiators. A second thing the AC delete does, it allows you to turn on the AC which automatically cycles on the radiator coolers but with the compressor out there is no power loss.
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Old 04-20-2019, 03:32 AM   #13
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The S2000 has a couple things you don't. It cranks to about 8200 RPM, and a 6 speed transmission. I agree that your best option is reduce weight. The rule would ban you from the type of mods that are being suggested here or at the very least cause you to be flipped into a higher class. The Power steering mod with electric PS pump is a good power saver. Then If you haven't done it yet remove the AC compressor, plumbing, and coils at the radiators. A second thing the AC delete does, it allows you to turn on the AC which automatically cycles on the radiator coolers but with the compressor out there is no power loss.
Thanks for all the suggestions guys, I didnít think of the powering steering pump. As far as the tune, who can do this? I canít find any information anywhere on it bring available.
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Old 04-22-2019, 08:04 AM   #14
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Iím looking into the throttle body suggestion and the Pedro Power pack seems like a good deal. Iím sure it doesnít bet 30hp as advertised but itís not crazy expensive. Is anyone running it? I wish he had a dyno to prove the results. Kind of suspect that he doesnít.
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