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Discussion Starter #1
my uncles car was having this problem last year at the end of the year and since were about a month away from racing again i wanted to see if i could tackle the problem.

The car would stop pulling at about 6000 rpm and would even start to miss and almost even a shutter.best pass we could get out of the car was like a 11.00.

my first question is could it be the cam?(motor specs below): the cam is a comp cams solid roller 250-256 @ .050 with 106 lca and .630/.630 lift....the powerband on cam card stops at 6200..so does that mean it will actually start to run bad after 6200?

i know the first thing everyone is going to say is check the valvesprings for coil bind or floating the valves..which it definitely could be the problem but the heads were setup at a machine shop with the cam specs so......who knows....

could the smaller duration of the cam be causing this problem? if not then what else?

motor: 406 sbc
12.5.1
sportsmen 2 heads/fully ported with 2.08/1.6 valves 58 cc chambers-runners around 212 cc now
cam^^^^ above
victor jr intake
850 hp carb.
car weighs about 3600 pounds with driver

best pass was 1.56 60 ft. 7.04 1/8 mile @ 100 mph and 11.00 @ 123mph

thanks guys
 

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it aint the cam. that thing should pull til at least 7000. sounds like ignition. stock hei modules will break down above 6000
 

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Discussion Starter #3
it aint the cam. that thing should pull til at least 7000. sounds like ignition. stock hei modules will break down above 6000
ignition is mallory hyfire digital with a msd pro billet distributor and blaster coil.

timing around 38 degrees..is it possible the spark plug could be too cold? i believe he was running ngk -8 or -9

i have also heard people talk about this same problem with too much fuel pressure..they recommend 7 and has been running 8...

but yeah my main question was the cam because we were thinking about putting a bigger cam in it...regardless do you think a bigger cam would be faster..i have an extra with a little more duration and lift is why i ask..
 

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What is the fuel system like? Flow it at the carb and see if you can get a gallon in under 25 seconds. Remember fuel pressure isn't volume.
 

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Discussion Starter #7
Valve springs, Fuel pressure @ wot @ 6000k, ignition.
since i did not set up the springs or have any special tools what is the basic way to measure the coil sprigs to check if their installed height is correct..and what all ways can you look for signs of valve float..i have heard some people say it will show up on the valve stem?

i will do a flow pump test and get back with ya..

and as far as the ignition goes i will check and ensure proper wiring and what not...the whole system was new last year...

can too cold of a plug be causing this?
 

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EFI/N2O JUNKIE
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He needs to run a -7 in there. Take a set of rocker arms off and look at the top of the valve. If you see a nice star-shaped wear pattern on the top then you've been floating them. Should see a thin line where the roller had been sweeping-across the stem. If you aren't using roller rockers then forget what I jsut said. If you try to take the springs off and have the smack the hell out of the retainer to break the locks free, you've been floating them! Get a Moroso (or similar) valve spring tester and see where you're at.
 

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Bracket racer
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Sounds like the valve springs might be down on pressure.....
 

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Discussion Starter #13
He needs to run a -7 in there. Take a set of rocker arms off and look at the top of the valve. If you see a nice star-shaped wear pattern on the top then you've been floating them. Should see a thin line where the roller had been sweeping-across the stem. If you aren't using roller rockers then forget what I jsut said. If you try to take the springs off and have the smack the hell out of the retainer to break the locks free, you've been floating them! Get a Moroso (or similar) valve spring tester and see where you're at.
yeah they are harland sharp roller rockers..ill try to get over to his house to look at all these things...the springs are brand new only like 15 passes..i cant remember exactly what plug he run but it was definitely the -8 or -9 and it seemed pretty lean jetting wise but the plugs were always a little dark ( that was however after he idled it to the pits...someday i will convince them to shut it off at the end of the track and get a proper reading lol)
 

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Butch
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IMO that cam and those heads are not gonna pull to 7000rpm, no way

That cam will be done by 5800rpm in a 400 IMO.

When a Sportsman II is properly ported for a ~7600rpm 350 they will pour about 225cc, so I could see the heads working to 6500rpm on a 400.

I dont see that with these, I see 6000rpm sure. If you run a tighter lobe center with the Sportsman II and more duration it can crutch the head for a drag car

Just my opinion,,,,,

If it did rev fine before it started acting up check fuel volume, fuel pressure and valve springs
 

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Discussion Starter #15
IMO that cam and those heads are not gonna pull to 7000rpm, no way

That cam will be done by 5800rpm in a 400 IMO.

When a Sportsman II is properly ported for a ~7600rpm 350 they will pour about 225cc, so I could see the heads working to 6500rpm on a 400.

I dont see that with these, I see 6000rpm sure. If you run a tighter lobe center with the Sportsman II and more duration it can crutch the head for a drag car

Just my opinion,,,,,

If it did rev fine before it started acting up check fuel volume, fuel pressure and valve springs
this is a new motor and in about 20-30 passes it is how it has always ran..i honestly dont know the runners of the heads but they have been extensively ported..put it this way..the throats are 90% of a 2.08 intake valve...i dont wanna go to 7 anyways but would like to be able to go 6500-6800....but yeah i think the cam is too small..car runs pretty darn hard low ..the 60 ft does not show it because the rear end needs set up and it spins every pass.

i have this cam laying around..do you think its too big or just right?

erson cam 268/276 @ .050 294/302 .675/.645 lift 106 lca

powerband is 4500-7500
 

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Butch
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That Erson is a good bracket cam and you will need a 5500 plus stall for a glide

Also with a glide, if the converter is 5500rpm dont shift higher than 1300rpm over the stall and let it run out in high gear unless you have a huge motor with huge power
 

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Discussion Starter #17
That Erson is a good bracket cam and you will need a 5500 plus stall for a glide

Also with a glide, if the converter is 5500rpm dont shift higher than 1300rpm over the stall and let it run out in high gear unless you have a huge motor with huge power

tranny is a turbo 400 and stall is a 5000...do you think this cam would work with this combo?
 
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