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Throttle body bored to 50mm

Finally got my TB back that is bored out to 50mm. I also tapped and installed the vacuum advance hose to the distributor. (per Brad Anders advice)
Results,hmmm alittle bit more power at high rpms judging by the seat of my pants. I will take it to a dyno shop for real results soon.
Anyone else done this and their results?
Geoff
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Old 11-17-2002, 09:54 AM
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Very nice. Did you use a '73 TB as a template for the adv location and diameter?

My guess is that you won't see too much on the dyno when compared to your original TB. Flow restriction doesn't seem to be the big breathing limiter on the T4, the exhaust seems to be the big problem from what I've heard.

Does the dyno you use permit part-load measurements? If so, I'd be interested in seeing what the torque difference is between having the advance active and inactive at about 1/4 throttle and 2500 rpm.
Old 11-17-2002, 10:02 AM
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http://members.rennlist.com/chuxter/#ThrottleBody

Scroll up a bit from there as well, and you'll see a pic of a throttle body that CD modified. No specifics, but he says it does "increase performance"...

--DD
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Old 11-17-2002, 10:11 AM
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Yes Dave, I have seen the TB Chuxter did but again it is by the seat of the pants dyno.
Brad, the dyno does do partload tests if I remember right. They owe me (and my son) some favors as this is the shop where his Turbo 1stGen RX7 was stolen from. They were tuning it over a week period. I plan on adjusting a MPS using their A/F meter and then checking it using the Wavetek to your MPS settings.
Right now with the vacuum adv hooked up, it does seem to have more hp/torque at lower rpm's (2000-4000). The retard set up is plugged also.

Geoff
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Old 11-17-2002, 11:26 AM
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To get full benefit of the larger TB you will have to *fiddle* with the injection. I did back to back dyno pulls with and without and only noticed a 1hp difference and a slightly leaner condition (more air)

I wouldnt do it again. I think Porsche did a really good job with the TB sizing given the VE of the 2.0 engine.

B
Old 11-17-2002, 04:59 PM
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RX-7??

Your sons Turbo RX-7 was stolen!!??! That bites..... What a sleeper that car was going to be.
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Old 11-17-2002, 06:10 PM
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Hi Eric, yeah it was at a shop having the aftermaket FI (Wolf) tuned. The FI was apart so the thieves had to use a dolly to steal it. My son really wanted to autox it.
Brad, I figured that boring the TB wasn't going to be a high hp mod. I had been told it was worth atleast 5hp, but so are some stickers. How much hp is the ALL914 sticker I have on my worth?
Geoff
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Old 11-18-2002, 08:58 AM
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Quote:
Originally posted by Brad Roberts
To get full benefit of the larger TB you will have to *fiddle* with the injection. I did back to back dyno pulls with and without and only noticed a 1hp difference and a slightly leaner condition (more air)

I wouldnt do it again. I think Porsche did a really good job with the TB sizing given the VE of the 2.0 engine.

B
Increasing the TB bore doesn't change the shape of the VE curve significantly, just moves it up the scale. The only fiddling that would need to be done would be either to slightly elevate fuel pressure or adjust the main mixture screw in the MPS (Geoff knows how to do this).

I have no idea of why in the case you describe it wanted a leaner mixture. But then, I have no idea of why when I was on a local Porsche drive this weekend, that my car wouldn't idle at altitude (going from 1000 to about 4,500 feet) without my RICHENING the mixture. D-Jet will be the death of me.
Old 11-18-2002, 09:34 AM
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My car does "seem" to like it more at higher rpms, 4500-6000. It also "seems" stronger at the 2000-4000 range, that might be due to the hooking up of the vacuum advance.
My engine is also a 2056 with 42x38 valves and ported intakes and exhausts ports. This might be why it "seems" to be able to take advantage of more air.
On previous dyno tests, max hp was at 5200 not the stock 4500 posted by Dave D.
I did adjust the partload & WOT screws on the MPS just a tad richer.
I still have it timed at 32 degrees at 3500rpms. Under heavy load, like WOT going up a steep Seattle hill it is just starting to "ping".
Geoff
(can you tell I am bored with nothing to do since it is raining here in Seattle)
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Old 11-18-2002, 12:25 PM
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Peak power is 4800 RPM, 4900 RPM, or 5000 RPM depending on the engine.

Peak torque is at 3500, with 95% of that available from 2500 RPM up through 4500 RPM.

That's when in stock form, according to the factory manuals.

--DD
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Old 11-18-2002, 01:57 PM
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So, a rev limiter is to allow for maximum power/torque at peak?
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Old 11-18-2002, 02:23 PM
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Ahhh, no... Usually the rev-limiter is there to keep someone from overrevving the motor and scattering the pieces all over the road.

Engines can only be built to take so many RPMs before they blow. They can also be built to make power at some specific RPM range. It is quite possible to build an engine that will blow up before it gets to its peak power.

--DD
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Old 11-18-2002, 02:32 PM
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The Chuxter was kind enough to also bore out a 73 TB out for me, to 50mm, and did an exemplary job I might add. keep in mind that 50mm is 23.8% larger area than the stock 45mm.

I installed it on my stock 2.0L and used an MPS that I have confirmed is adjusted to run a little rich (compared to the stock settings for an MPS) at all load settings. The rich MPS is newly rebuilt I would add and not otherwise adjusted. I experienced power loss and immediately removed the TB until I could check the A/F mixture properly. I did not bump the fuel pressure...I wanted to get access to the proper equipment to get it right and not take chances.
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Old 11-18-2002, 02:41 PM
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