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 Post subject: poor performance bbc
 Post Posted: Sun Aug 08, 2010 12:45 pm 
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1st runs this weekend on the 498 in my 70 chevelle.the is 3200 lbs with me.glide, 6000 stall. 488 rear, all the same as the 468. car is only running 133to 134 mph on the throttle stop for 10.90. the weather has something to do with it ;mid 90's with 70 % humidity at topeka. maybe 3 mph more at most than the 12 to one 468 that was in the car for the same conditions. i expected 136-7 and 140 in perfect weather. 13 to 1 498 ,279 286 749 on 110 4 deg advanced same brodix 320 cc heads that were on the 468 freshened up . flow 370 and 305 @ 700 dr j ported 454r intake. 2 circuit 1050 annular. 2.125 headers with 3.125 to 4 in merge collector and about 15 in collector length from the smallest diameter to the end. headers might be too small for this engine and too much collector length. tried timing adjustments and ended up at 38 degs. its a little rich still but should be close. should have ran it on a dyno but needed to get it in. any ideas?gnicholson
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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 1:31 pm 
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What are your short times compared to the 468??
Did you do anything with the converter??

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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 1:54 pm 
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the convertor was a little tight with the 468 so i left it alone. stalls about 6000. i think a little looser would pick it up but dont want to over rev it. on the stop 60 ft times were 1.86 to 8 ,maybe a hair quicker. i need to get the slips for the rest of them but a few hundreths faster on all the increments as far as i can tell


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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 6:47 pm 
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i cant get the slips with the incremental times untill tomorrow. what would you guys say it should run? it doesnt set much lower than stock so the frontal area is some of it im sure


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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 7:01 pm 
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I may be off base on this but that 60' time seems bad...Im thinking it should be in the high 1.50s :-k ....Is the suspension all stock???

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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 7:10 pm 
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that time is with the throttle stop coming on at .010 out. normal 60 ft time is in the mid 130's


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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 7:11 pm 
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Did you reset the T/S for the same rpm on the stop? or was it left alone? How does the converter stall compared to the other engine?

3mph indicates about 40hp increase and maybe more since you are T-Stopping.

Is the cam the same? If so, with a bigger engine it should need shifted earlier than the 468 unless the intake mods helped the top end more.

Sounds like you need to start tuning it with jetting, timing, shift points etc. Maybe not time before the divisional at Topeka, but that's what I'd work on.

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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 7:15 pm 
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thanks. the convertor stalls maybe 100 rpm more. the cam in the 468 was 272 278 708 on 112 so the one in this engine is bigger at 279 286. the stop still goes to 4000 rpm against the convertor. i checked that in mid 90 deg weather.


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 Post subject: Re: poor performance bbc
 Post Posted: Sun Aug 08, 2010 7:16 pm 
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Sorry I missed the whole throttle stop!!! ](*,) ](*,)

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 Post subject: Re: poor performance bbc
 Post Posted: Mon Aug 09, 2010 8:53 pm 
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do you think the heads are holding it back enough to warrant some replacements that will move 400 cfm


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 Post subject: Re: poor performance bbc
 Post Posted: Mon Aug 09, 2010 9:04 pm 
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Hummm, Yeah I'd say those heads might be a problem or sorts. My 18* SBC Dart heads flow that much on the intake side. 254 on the exhaust. That engine is making close to 800hp on a good day.

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 Post subject: Re: poor performance bbc
 Post Posted: Sat Oct 23, 2010 7:07 am 
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Ken0069 wrote:
Hummm, Yeah I'd say those heads might be a problem or sorts. My 18* SBC Dart heads flow that much on the intake side. 254 on the exhaust. That engine is making close to 800hp on a good day.


X2 and I am with Ken on this one, I also think the heads are holding it back as I have the Dart 325's and I have changed from an 1150 to a 1250 thinking it would pick up some but nope!!! ](*,) my heads are what they are and for another $1200. I can gain 2 more tenths, but I am going to spray my engine next year so I will see what kind of gains I can make with it.

My heads flow a tad over 370 on the intake side and I can feel the engine and it is just maxed out for air. =P~ I run a 505 inch engine and buzz to 7900 at the stripe and that is just about all it has at that point and my cam is less than .800 lift. My 2 cents. :-$

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 Post subject: Re: poor performance bbc
 Post Posted: Sat Oct 23, 2010 7:18 pm 
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You may have 370 cfm flow but your not making power from it. the flow quality would be junk, turbulent city, uneven flow cones all that stuff. 370 cfm is enough to make 870hp average on any day or weather on a 412 provided the flow is nice and even around the valve, nice cone, no turbulence etc. But your 498 engine is pulling on the port too hard probably. its not making the HP per cube, its making stuff all really. Suggest getting much better heads.


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