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Old 09-23-2010, 08:26 PM
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Dart versus Camel humps

I have a 406 with 5.7 rods and forged Protrue pistons, scat crank and rods. I have a 285B Solid Comp cam 532/543 in a S10 blazer with a 373 12 bolt and a 3500 stall. I run this truck with a set of camel hump 291's 64 cc ported and polished, 1.5 rockers, 2.02/1.60 valves, RPM intake and 850 DP holley. Turning the motor 5k I ran 7.70's.
I installed a set of 215 darts 72 cc w/2.05/1.60 valves, Dart dual plane intake and ran 8.0. I went from 72 f & 76 B jets to 84 F and 92 b and turned it 6500 and still only run a 7.60. Should I use these heads again next year and try 1.6 rockers? Is that to much stall for that compression ratio? Any ideas appreciated.

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Old 09-23-2010, 10:42 PM
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You don't have nearly enough gear and converter for the large runners. What's
the camshaft duration @ 0.050"
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Old 09-23-2010, 10:59 PM
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You lowered the compression ratio almost a full point, thats where the power went. Bigger runners and reduced compression cost you a bunch of low and mid range torque, that is where the ET went.

The bigger heads may not flow any better than your old Camels, especially if the Iron Eagles aren't ported too. Bigger valve and bigger port slowed down mixture velocity, a good indicator of this is having to get crazy rich with the jetting.

Converter may be okay but likely too low, but you need a lot more gear for the bigger head. 4.30-4.56
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Old 09-24-2010, 12:00 PM
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The only cam I see close to what you said is THIS:

Grind Number CS 285B-6
Mechanical flat tappet
Basic Operating RPM Range 3,000-6,500
Duration at .050" 250 int./260 exh.
Advertised Duration 285 int./295 exh.
Intake Valve Lift 0.532"
Exhaust Valve Lift 0.555"
Lobe Separation 106

You need to spin it up like you found when the ET dropped the run that you shifted @ 6500. But that alone will not make all the difference- I would go back to the RPM intake, sort out the timing and see if you can't get the jetting back in the ball park and try it again.

You will need some more CR, not lift- so spend the money on milling the heads instead of the 1.6 rockers. The TC will be enough to start with, but for the beast ET you'll likely need more stall speed. Same thing for the rear gears. 4.11's at least, possibly more if you run tall slicks.

EDIT- I see now that the Dart intake is a dual plane. It still might be big, but might end up working OK- but I still would be tempted to try the RPM. Ultimately, it might ET best w/an open plenum.

Last edited by cobalt327; 09-24-2010 at 12:07 PM.
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Old 09-24-2010, 12:24 PM
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What is the blazer used for, 1/8 mile drag race only?

What are your ET/MPH goals?
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Old 09-24-2010, 01:04 PM
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Cobolt got the specs on the cam. I have run this with a 456 gear and it run in the 790 80 range so hence the 373 to make it more driveable. The cam is a 10 1 compression camshaft so I would think I am ok on compression. Dart told me I still need more jetting. I think I should run in the low 7's at least in the 1/8. I have run several other s10'trucks with 355's and run a hell of a lot better then this 406.
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Old 09-24-2010, 01:09 PM
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I run a standard bore 400 with 5.56 rods, these camel hump heads and a crane 456/480 cam shaft turning it 5k and ran in the 750 760 range with a 373 and a 3k stall. The more I spend the slower I get.
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Old 09-24-2010, 01:23 PM
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Quote:
Originally Posted by Mohocomo
Cobolt got the specs on the cam. I have run this with a 456 gear and it run in the 790 80 range so hence the 373 to make it more driveable. The cam is a 10 1 compression camshaft so I would think I am ok on compression. Dart told me I still need more jetting. I think I should run in the low 7's at least in the 1/8. I have run several other s10'trucks with 355's and run a hell of a lot better then this 406.
You say the 373 gear makes it more drivable, so the truck is street driven?

Once the combination is sorted out and tuned, mid 6 second 1/8 mile ET
is with in reach, this will reduce drivability. It all depends on what you want.
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Old 09-24-2010, 01:26 PM
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When I say driveable I mean I may run to town in it or run to lowe's once or twice a month. I would be happy with 7 flat.
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Old 09-24-2010, 01:39 PM
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Here's what I would do, similar to what cobalt is saying.

Use the dart heads, mill them to get the compression back up. The limit here
will be the fuel up use. The engine will respond to the increase in
compression with your cam.

If not all ready done get a performance valve job done. This is not necessary
for the performance you are looking for but the benefits are worth the
money spent. Porting not needed to meet your goals.

I would go back to the 4.56 gear and switch to a 4500 stall. The limiting
factor here will be traction, target 60 foot times in the 1.4s.

If you make these changes the engine would then like a single plane intake
like a victor jr. The correct size headers are a must with an extended open
collector or free flowing exhaust. A good ignition is also needed.
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Old 09-24-2010, 01:45 PM
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Quote:
Originally Posted by Mohocomo
..I went from 72 f & 76 B jets to 84 F and 92 b .
You went in the right direction with the jet but went too far. I'm assuming
you run a power valve in the front, try 80 front 86 rear with a power valve
and tune from there for best mph at the stripe.

Last edited by automotive breath; 09-24-2010 at 01:57 PM.
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Old 09-24-2010, 01:53 PM
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Quote:
Originally Posted by Mohocomo
I have run several other s10'trucks with 355's and run a hell of a lot better
then this 406.
I run 350s in my camaros (high 6s in the 1/8th) but do a lot of work for others
that run 400s. The bigger engine will out perform the smaller one, you just
need to work on the combination and tuning.

I'm basing my recommendations on this car, flat top 406 with a solid flat
tappet cam larger than the one you run. I ported the dart 215 heads with
64 cc chambers and victor jr intake. He runs a 5000+ stall and if I remember
correctly a 456 gear.

His 60 foot times are in the 1.3s; low 6 1/8th mile times and low 10s at well over
130 mph in the 1/4.


Last edited by automotive breath; 09-24-2010 at 02:15 PM.
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Old 09-24-2010, 02:44 PM
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You can gain about 1/2 point in compression by going from a .038 head gasket to a .018.. You didnt say what you used so I dont know.. Biggest mistake I see people make on older cars that had steel shim head gaskets is replacing them with a standard Fel-pro when they do a rebuild, which cost them about 1/2 point in comp and then they wonder why its slower.

I ran 7 flat with a 355 that had a stock rotating assembly with 11-1 slugs, a cam that had a dur of .250 @ .050, Dart Iron Eagle heads (out of the box), Victor Jr intake an a Holley 800dp. In a 73 Camaro with 4.56 gears and only a 3000 stall..
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Old 09-24-2010, 03:00 PM
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I tried the RPM intake before I bought the dart and it would not seal, ports are to big.
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Old 09-24-2010, 03:56 PM
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Quote:
Originally Posted by Mohocomo
I tried the RPM intake before I bought the dart and it would not seal, ports are to big.
Normally the RPM intake will fit the dart heads just fine, may be a casting
shift that caused the problem.

Are you running a spacer on top the single plane? A 2" open spacer will
increase plenum size resulting in a nice HP gain.
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