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Old 06-26-2005, 01:32 PM
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Comp XE274

Anyone running an XE274 in a 383? I thought I had this problem resolved, but it's popped back up.

I got it to idle at about 850-900 rpms, with 13 degrees initial, and it has about 11-12 in of vacuum. If I bump the timing up to about 18-19 degrees, it has about 14 in. But, at the higher advance, it tends to diesel when turned off. Is 12 in about right?

I had to swap out the light springs in the distributor because the mechanical was coming in waaay to soon and I couldn't get it idle hardly at all below 1200 rpm. Right now, I've got one medium and one heavy spring.

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Old 06-26-2005, 01:35 PM
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I would try and go with 14 to 16 initial.

If you are dieseling, there is some other problem.

Are you sure your balancer and timing light are correct?

Are you running a CD box?
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Old 06-26-2005, 01:51 PM
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I checked the balancer against #1 TDC with a dial indicator before putting the heads on.

The dieseling may be attributable to the high idle. For some reason, it was up to almost 1300-1400 (dash tach) and the timing was about 19 degrees when I first checked it today. I don't understand the creep up.

I'm currently running an old points distributor because my Pertronix went belly up last year. I'm trying to keep a "327 look" so I don't want to drop an HEI in.

Do you feel 12 in of vacuum is acceptable?
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Old 06-26-2005, 02:21 PM
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Quote:
Originally Posted by MI2600
I checked the balancer against #1 TDC with a dial indicator before putting the heads on.

The dieseling may be attributable to the high idle. For some reason, it was up to almost 1300-1400 (dash tach) and the timing was about 19 degrees when I first checked it today. I don't understand the creep up.

I'm currently running an old points distributor because my Pertronix went belly up last year. I'm trying to keep a "327 look" so I don't want to drop an HEI in.

Do you feel 12 in of vacuum is acceptable?
Hi Larrie.
According to this:
http://www.compcams.com/Community/Ar...?ID=1108284073
12.4 in/hg is exactly what to expect from this cam.

The MSD billet distributor also shown in this article may be the "look" that you are looking for as well?

Don
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Old 06-26-2005, 02:39 PM
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Thanks, Don.

I was a little concerned about the low vacuum because I don't remember what the power valve is in the Holley. I "reapplied my expertise" and got it to idle at about 850, with 13 or so in of vacuum, and about 16 degrees advance.

I was disappointed at the XE274 which replaced an L79 327 type cam. According to Comp, I should have experienced about a bzillion hp gain...not!
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Old 06-26-2005, 03:30 PM
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Timing; get your hands on a digital retard timing light and set time with vacuum advance disconnected and idle at 1000 rpm. You want total time of 38 degrees.

Vacuum advance; use carb vacuum not port vacuum. With light distributor springs the port vacuum can cause the springs not to recoil.

Advance springs; 2 light springs usually come in at 1000-1100 rpm. So when you pull up to a stop light the mechanical advance will stay engaged. Use one light and one medium spring.

Carb; Now set carb with automatic tranny in drive for highest vacuum. Then set idle to 800 rpm.

The dieseling should be taken care of at this point.
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Old 06-26-2005, 10:23 PM
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I had the Holley specifically built to be a #2818 clone. It's actually a 780 3310, with a exhaust manifold heat choke and a side vacuum fitting for the oil filler PCV tube. It doesn't have ANY vacuum ports below the plates, i.e. nothing on the base plate. I suppose I could draw manifold vacuum off the rear of the intake for the advance canister.
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Old 06-26-2005, 10:23 PM
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Quote:
Originally Posted by MI2600
Thanks, Don.

I was a little concerned about the low vacuum because I don't remember what the power valve is in the Holley.
You're right IMHO. If your power valve is dumping in fuel at idle (due to a lower manifold vaccuum than your present power valve is rated for) it will be running real rich and building carbon deposits which act like glow plugs.

There are 2-stage power valves available for holley carbs that may fix this up for you.

http://www.holley.com/HiOctn/ProdLin...CA/PwrVlv.html

TWO-STAGE POWER VALVES - Model 4160
Part # 1st Stage Opening 2nd Stage Opening
125-206 12.5" Hg 5.5" Hg
125-207 10.5" Hg 5.0" Hg
125-208 10.5" Hg 5.5" Hg
125-213 11.5" Hg 5.0" Hg

I would think that you'd want to experiment with any of the last 3 listed, as the first one would be open at idle if you only have 12" Hg.

I wish that camshaft manufacturers would include the expected in/hg specification in their descriptions, along with an explanation of the results.

What the heck do people use that only have 9.5" Hg? I guess where the "drivability" term comes from.
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Old 06-26-2005, 10:28 PM
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I think you may be right Don. I felt I might be pushing the issue if it's got the standard 6.5 in it.
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Old 06-27-2005, 05:53 AM
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The powervalve does absolutely nothing at idle, whether it's open or closed it has absolutely no effect on idle quality. The only way the power valve would have an effect on idle is if it is ruptured on the gasket is not sealing- these conditions would allow fuel to be drawn down the vacume port that is drilled vertically through the base plate under the cast in power valve well in the main body.

You're fine with the 6.5 powervalve, in fact if the carb is jetted lean you may even want to get a valve that opens sooner. The best way to tune for a power valve selection is to block the PV circuit with a plug, then test run up to a cruize speed-(get on the throttle lightly getting up to speed) Once you're at cruize speed note what amount of vacume you have. Jet the car down till there is a slight girgle- this would be lean, then jet it up till there is no girgle. There will be some hesitation when you open the throttle at cruize because the powervalve circuit is missing when the plug is in. Jet up till you get it where you can slowly open the throttle without any major hesitations. At this point the jetting is close. Now choose a powervalve that is 2-5 below what your cruize speed vacume reading was, many will work but finding the one with the right opening timing will give your throttle much more response when you mash it.

Getting your idle circuit right before anything else would be a good idea. Bob

Last edited by baddbob; 06-27-2005 at 06:06 AM.
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Old 06-27-2005, 06:11 AM
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That XE274 sure would like some headers I bet. I switched from headers to the rams horns on a 350 not long ago and have a small XE4X4 cam and lost quite a bit of power. What kind of cranking compression is she pumping?- this would be an indication if the cam is too long or short.
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Old 06-27-2005, 08:12 AM
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Bob, in keeping with my 327 guise, I put the 2 1/2" ram's horns on it which made a big difference over the 2" ones. The rest of the system is also 2 1/2".

The last time I ran a compression test I think it was in the 170-180 range. The engine only has about 1300 miles on it...and it's about 5 years old!
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Old 06-27-2005, 09:49 AM
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power valve

Did you check to see if the power valve has a hole in the diaphragm?
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Old 06-27-2005, 12:52 PM
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I haven't checked the power valve yet. Last year, when the Pertronix went out it caused some horrific backfires, but it ran ok after I swapped that distributor out and put it away for the winter.
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Old 06-27-2005, 09:09 PM
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Quote:
Originally Posted by MI2600
Bob, in keeping with my 327 guise, I put the 2 1/2" ram's horns on it which made a big difference over the 2" ones. The rest of the system is also 2 1/2".

The last time I ran a compression test I think it was in the 170-180 range. The engine only has about 1300 miles on it...and it's about 5 years old!
170-180 is perfect for pump gas IMO, sounds like your static compression ratio matches the cam good.
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