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Exhaust experment
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vwracerdave
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PostPosted: Thu Jul 23, 2015 10:06 pm    Post subject: Exhaust experment Reply with quote

I have a 78X90.5 = 2007cc, CB 40X35.5 044 Magnum heads with home porting, W-120 W/1.25 rockers, 8.6 CR, 44 IDF's with 34mm venturies, and 1 5/8" exhaust. I bracket raced this engine last week in my 1345 Lb. dunebuggy and ran 14.10's shifting at 6400 RPM. I am going to switch to a 1 1/2" header with no other changes and race the Buggy this weekend.

Any guesses if it will run slower or faster? what do you think?
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GTV
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PostPosted: Thu Jul 23, 2015 10:09 pm    Post subject: Reply with quote

I think slightly slower ET but driveability will be slightly improved.
It would be interesting to test 36mm venturies as well.
It runs out of breath by 6400??
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jpaull
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PostPosted: Thu Jul 23, 2015 10:13 pm    Post subject: Reply with quote

My guess is that there will be a different variable that will dictate a change in your ET. Air density with slight change of weather, or traction for that particular run, etc.

Jeff
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mark tucker
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PostPosted: Thu Jul 23, 2015 10:38 pm    Post subject: Reply with quote

quicker but with possiably lower mph. but home porting can be many things, from mild to wild so...let us know how it does. I would think the low cr would like the smaller tubes.
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FreeBug
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PostPosted: Fri Jul 24, 2015 2:08 am    Post subject: Reply with quote

It should shift the torque curve max down a few RPM, probably flatten it out with a little less at the top, but as to how that would translate into your ETs and trap times, I have no clue.

Please share the results of this experiment, enquiring minds want to know.
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Mikedrevguy
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PostPosted: Fri Jul 24, 2015 7:01 am    Post subject: Reply with quote

Where are your 60' times?
With my 2007 DRD L-5 heads CNC ported- DRD 298 cam w/1.25s (equivalent to the fk8) 44's with 36 vents. In full bodied 74 super(2100lbs)
1.5 header w/stinger I've run 1.9sec 60' with 14.59 ET @ 93mph shifting at 6000
Last weekend swapped to the 1 5/8 still managed 93 mph, but had a tough time hooking up and 60' suffered. (Street radials)

Are you looking to lower your shift point?
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vwracerdave
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PostPosted: Fri Jul 24, 2015 5:56 pm    Post subject: Reply with quote

GTV wrote:
It would be interesting to test 36mm venturies as well.


Already tested. It runs faster with the 34mm venturies.
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Mikedrevguy
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PostPosted: Fri Jul 24, 2015 7:00 pm    Post subject: Reply with quote

What's your jetting at, Dave?
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MURZI
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PostPosted: Fri Jul 24, 2015 8:17 pm    Post subject: Reply with quote

Have you ever shoved a wideband on that engine?
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fivelugshortaxle
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PostPosted: Fri Jul 24, 2015 10:33 pm    Post subject: Reply with quote

Just watched your videos, Dave. That Ghia sounds bad ass
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mark tucker
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PostPosted: Sat Jul 25, 2015 10:25 pm    Post subject: Reply with quote

well????????and did it change the jetting requirements?
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vwracerdave
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PostPosted: Sun Jul 26, 2015 8:37 am    Post subject: Reply with quote

Made it to 3rd round and got my ass kicked on the tree.

Engine with 1 1/2" header ran .20-.25 slower ET and 1-1.5 less MPH. That was pretty much what I expected to happen. 60' were the same. All I did was change exhaust no other tuning. Weather was close to the same both weeks. Maybe I might get another 1/10th out of it if I rejetted and tuned, but this is my spare engine and coming out and replaced with the 2165.

Image may have been reduced in size. Click image to view fullscreen.

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mark tucker
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PostPosted: Sun Jul 26, 2015 9:21 am    Post subject: Reply with quote

might need to be shifted sooner. but it was a good test if all else was the same. how about weather? 2 or 3 cheezzee burgers before running Shocked Wink I expected the lower mph,but not realy the lower et. although it is quite different than driving on the street/road corse. were they both the same header just diferent size?
on another note....3rd round is better than 2nd round loss wiytch is better than a 1st round loss witch is always better then loading up a crashed/broken car. a good day at the races is driving back on to the trailer. a great day is with a trophy.awesome day has a check/cash in your hand Wink good work mr dave.
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maui
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PostPosted: Mon Aug 24, 2015 1:27 pm    Post subject: Reply with quote

I say jus put 36 vents and jets only and it will be better times and for regular driving you just adjust your driving habits. Not a big deal.
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