Comp XE268 power band - Team Camaro Tech
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post #1 of 7 (permalink) Old Dec 19th, 08, 11:43 AM Thread Starter
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Rusty
 
Join Date: May 2007
Location: Georgia
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Comp XE268 power band

I had my car dyno tuned last night after I got tired of fooling around on the carb. I noticed that the engine dropped off after 5500 rpm. The cam is "Rated" from 1800-5800. Anyone in here with a XE268 cam in a small block had their engine dynoed? If so what rpm did your power band drop off at?

1991 Camaro RS, 355 cid, 10.5:1 CR, Scat crank, Speed Pro flat tops, Brodix IK180's. Comp XE268, 1.6 rockers, Perf RPM Air Gap, 650DP Quick Fuel, Hedman long tubes, BTO Level 2 700R4, 3.73 w/ posi.
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post #2 of 7 (permalink) Old Dec 19th, 08, 12:02 PM
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Re: Comp XE268 power band

I never had mine dyno'd, but I know it pulls hard to 5800 and will go to 6K easily. What valve springs are you using, and what is your total timing set at? An efficient head like yours will normally lose power and fall off on the top end with too much timing. You might even try backing the timing off 2*-4* and see if it helps

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post #3 of 7 (permalink) Old Dec 19th, 08, 01:10 PM Thread Starter
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Rusty
 
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Re: Comp XE268 power band

My timing is set at 35*. We tried bumping up the timing to 38* and down to 32* and it liked 35* the best. I'm running a Comp 980 valve spring with 85lb at the seat. I was thinking it might have a little valve float. Driving the car it feels like it pulls to 6K easily but on the dyno it shows it dropping off. Could be that the engine revs so fast that I just don't feel it dropping off.

1991 Camaro RS, 355 cid, 10.5:1 CR, Scat crank, Speed Pro flat tops, Brodix IK180's. Comp XE268, 1.6 rockers, Perf RPM Air Gap, 650DP Quick Fuel, Hedman long tubes, BTO Level 2 700R4, 3.73 w/ posi.
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post #4 of 7 (permalink) Old Dec 19th, 08, 04:02 PM
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Re: Comp XE268 power band

The 980's are too weak for the aggressive profile of the XE268, plus you probably have 2.02/1.60 valves that are most likely heavier than the 1.94's I am running in my vortec heads. The 981-16 is the recommended spring and should drop right in place of your existing 980's. You might even be able to shim your existing springs enough (watch for coil bind) to get the pressure up where it needs to (at least on the seat). I think, off the top of my head, that not only do the 981's have a higher seat pressure, but also a higher rate. I think the 980's are a stock replacement spring.

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post #5 of 7 (permalink) Old Dec 19th, 08, 05:54 PM
 
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Re: Comp XE268 power band

At least Z-28/-142 springs or the later, '70, LT1 springs.

pdq67



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post #6 of 7 (permalink) Old Dec 19th, 08, 09:55 PM
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Carl
 
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Re: Comp XE268 power band

My old engine...

http://www.classictrucks.com/tech/cl...tor/index.html

No need to go past 6000RPM.


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post #7 of 7 (permalink) Old Dec 19th, 08, 11:25 PM
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Mike
 
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Re: Comp XE268 power band

Depending on the weather my car with the 274 runs best dropping the hammer around 6100rpms. I think your out of cam! if you suspect valve float throw a vacumm gauge on it and drop it to the wood, it should flutter on the gauge towards or near you redline, if its floating. Also a good time to see if you have any intake retrictions.

68 RS, 16mpg, 3200lbs, 355ci, 9.6:1, Ported Kemper Perfomance, production 441s, 76cc, 2.02 1.60. Hyd flat tappet XE274,RPM Performer,750 Holley, 1 5/8 tubes, 2.5 Dynomax full exhaust. 3500, 400TH, 3.73s, caltracs, NA [email protected] 1.62 60ft DA 1400ft.
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