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Jeff Alton's Avatar
 
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PMO"s, ITB's or carrera intake?

Looking for some thoughts and opinions. I am building a 3.4 based on a 3.2 carrera motor. Motor has 10.5:1, twin plugs, 1 5/8 headers with heat, ARP rod bolts...... The only thing left is cam choice and induction. I already have a complete XDI crankfired ignition.

1. I like the look and feel of carbs, plus I can tune them with tools.

2. I can get Jenvey ITB's at a reasonable cost and would probably use a megasquirt with them. Just not wild about tunning with my laptop, mostly because I have never done that and I am more than a little uneasy about it.

3. Use the carrera manifold and motronic chip for fuel only. Steve Wong says he can make it work no problem. Not too sexy and limits my cam choice somewhat, but it sure is easy to do.

What do you think? Need good midrange and would like power into the 7k range.

Thanks
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Old 12-04-2005, 03:56 PM
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Hi Jeff:

One important parameter has been left out of this question,....

Throttle response!

No matter what one does, or how well programmed the software is, nothing comes close to a one-throttle-per-cylinder intake system.

A well setup pair of PMO's works very well and in some cases is better than many of the low-resolution engine management options. You get what you pay for, but your needs and budget will determine what is best for you.
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Old 12-04-2005, 04:31 PM
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Did I mention I am throttle response Junkie? How are the carbs while the motor is warming up?

Cheers
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Old 12-04-2005, 04:56 PM
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LOL,..I've been using Webers on my own engine since 1979 and I have no problem.

My car has a hand throttle (left over from the CIS) that makes cold start and warmup a simple proposition, but one could add that feature to any 911 if you wanted to.

Properly jetting and setup, carbs work really well. IMHO, people usually blame the parts & components when the vast majority of problems are due to poor setup and configuration.

As the saying goes, "the devil is in the details" and thats the difference between a good running intake system and a bad one.
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Steve Weiner
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Old 12-04-2005, 05:35 PM
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Hmmm, hand throttle, now that is the ticket!

Cheers
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Old 12-04-2005, 05:49 PM
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I'm going through a learning curve with carbs, since it's been well over 20 years since I've had them last. The advantages that I've seen so far with only about a month of driving with them is:

1) Immediate throttle response.
2) Engine runs cooler.
3) The gas mileage is only marginally less, but the performance is exponentially higher.
4) The application of carbs knocked about twenty pounds off my car's overall weight.
5) The sound, the sound, the sound.

Plus, there's all the known benefits of higher compression and more radical cams that can be used if carbs are also used.

EFI is just strange to me. I don't like laptop tuning. If I wanted that, I'd buy a new car. Plus, on a mechanical level, I don't trust it. I mean, $5K or more for a system? TBitz's system seems about right for the money, but here again, used carbs which come up every so often on classifieds cost about the same.

Cold starting is the only detriment, which is easily rectified by simple practice. As my mechanic told me: two pumps of the gas pedal and then press it down to start. Works every time.

You'll need a hand throttle for cold weather starts. But after about a block's worth of driving, you can push it down, and the carbs do the rest.
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Last edited by dd74; 12-04-2005 at 06:07 PM..
Old 12-04-2005, 06:03 PM
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Okay, so I need to get a factory hand throttle set up or is there another option?

Cheers
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Old 12-04-2005, 06:33 PM
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JEff, how about a set of PMO 46's and a set of the "DC44" cams on a 108 lobe seperation. Similar to the DC40-108 ( Mod-S cam on 108 ) except the DC44 cam has more valve lift, and area under the lift curve.
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Old 12-04-2005, 09:06 PM
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Sounds like I should give you a call tomorrow...

Cheers
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Old 12-04-2005, 09:47 PM
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Quote:
Originally posted by catca
Okay, so I need to get a factory hand throttle set up or is there another option?

Cheers
The hand throttle is all you need - it looks to be a rather simple modification. More or less, it's a cable that lowers the accelerator. I've heard it called "a poor man's cruise control."

After that, a well set-up motor with Webers, strong cam and high compression p&cs is no less streetable than a stock 3.0 or 3.2, IMO.
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Old 12-04-2005, 10:11 PM
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I have my Jenvey's all setup and ready to install.....now, just need a car to install them on I really think that ITB's and a reliable ECU is the way to go. For me, living at over 6000', it was a no brainer. I certainly did not want to deal with carbs at that altitude and colder winter weather. I will be using a wide-band O2 sensor and a PLX Devices controller, which will interface with MegaSquirt to assist with tuning and getting the AFR correct. Personally, I like having the control over how the EFI is setup and being able to control varying needs, such as track vs. street driving. MFI would have been cool too, but that was gonna take too much $$ and would have required head work (from what I have been told) to accept the MFI injectors. I also get immediate performance benefits with EFI and can expect more when rebuild time comes.

Good luck with your project and keep us posted.

-B
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Old 12-04-2005, 10:54 PM
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I just finished up a 3.0 with 10.5:1 CR ,GE-60 style cams from camgrinder and 46 mm PMO's. It gave 250 hp at 7500 from the rear axle.

The throttle response is unreal and the sound is great. But it is as drive-able around town as my old box stock '82 SC. The hand throttle works great to help get the engine fired and running.
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Old 12-05-2005, 02:36 PM
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Thanks Tom, I am gonna have to search out all the parts for the hand throttle. If I can get 250 whp out of the 3.4 I will be pretty happy!

Cheers
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Old 12-05-2005, 02:51 PM
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What flywheel would you use with this? Is there any weight difference between SC and carrera flywheels? How about a lightweight aluminum one?

Cheers
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Old 12-05-2005, 05:09 PM
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Quote:
Originally posted by catca
What flywheel would you use with this? Is there any weight difference between SC and carrera flywheels? How about a lightweight aluminum one?

Cheers
Sachs. Don't they make a lwt. flywheel?
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Old 12-05-2005, 05:12 PM
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They make an aluminum pressure plate....

Cheers
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Old 12-05-2005, 05:22 PM
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