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Author Topic:   Dbl Hump/406 vs. Dart/350 - Opinions?
WesternAuto17
Dirt Forum Champ
Total posts: 569
posted March 18, 2005 08:14 AM  
OK, guys here's the deal. I have a limited budget and a choice to make. I can buy a claimer 350 shortblock for $1000 and put Dart Iron Eagle heads on it for $750. Or I can get a valve job done on existing stock dbl humps for $200 and put them on a $1500 383 shortblock.

Both shortblocks are from Jr Motorsports. The 350 is a claimer type with all stock parts with 9.7 compression and the 383 is a a little more "racey" with Hyper pistons, 10.3 or 11.5 comp, race prepped rods and a Scat crank.

Both sets of heads will be 64cc, 2.02/1.60 valves. The dart's intake runners will be whatever is best for the 350 and I don't know about the runners on the dbl humps (they are not ported or polished).

Carburation will be from a 750 dbl pumper and single plane Victor Jr. The rpms I'm looking at are from 6200-7200. Finally the car is 3000lb street stock running on 1/4 mile tracks with a 6:20 gear. If I choose the smaller motor, I will probably change to a 6:50 gear.

Better flowing heads on a smaller motor or big displacement with heads that are not so good? What will make more power, any thoughts?

Thanks.....

[This message has been edited by WesternAuto17 (edited March 18, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted March 18, 2005 08:42 AM  
I woudl prob go with the 11.5:1 383 because of the extra compression and torque, which you'll prob need in that heavy of a car. Plus it gives you a better shortblock to upgrade later on. Then if you cant afford to put the dart heads on it right away, put a good 3 angle valve job on the double humps for now and in the future put a better set of heads on it. Just keep in mind that the heads are most likely the most restrictive part of that engine so the most gain will be seen from improving them later on.

Raz_900
Dirt Forum Champ
Total posts: 635
posted March 18, 2005 11:35 PM  
I would also go with the 383 and try to keep rpms at 6300 max. It'll probably start laying down around 6000 if the heads are bone stock. With a good 4 or 5 angle valve job (a 70 or 75 degree cutter really helps the bowls out) it'll pull a couple 100rpm higher.

7200 with either one is asking for it. The claimer will pull stock cast pistons apart around 5800-6000. 'Normal' hypers would take about 500rpm more. (T5 heat treat is normal, KB Signature Series are T6 and significantly stronger)

Use a 240ish@.050" cam and run it where it'll work best. With the higher CR and shorter cam, it'll pull harder at low rpms. The Dart heads are too much for a stock shortblock. To get all the extra power from them you'd have to spin it higher than the bottomend could take.

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