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Old 07-02-2012, 05:50 PM
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400 sbc horsepower stumped

I have just finished building a 406 sbc stock crank scat 5.7 7/16 cap screw rods speed pro flat top forged pistons 5 cc valve releifs RHS Pro Action aluminum heads 200 cc runners 72 cc chambers howards hydraulic roller cam,241 int-245ex duration @50 . 545 int 565 ex lift 110 lsa matching lifters crane roller rockers 1.5 ratio, rpm intake holley hp ultra 750 dp cfm carb msd streetfire hei.1 3/4 headman headers .
I had it dynoed on a dynatech roller dyno it showed 427 ft lbs of torque at4200 rpm and only 319 hp at 6000 rpm fuel ratio was perfect throughout the run timing was 34 degrees tried with and without vaccum cannister less torque withe the vaccum canister hooked up fuel pressure was steady at 6 psi i cant figure out why these rear wheel numbers were so low am I doing something wrong does she need more air,such as a team g intake maybe or more fuel or cfm any advice.After 1500 miles took her to the track ran a 12.98@ 105.72 mph in a 1980 Z28 with a 3:42 rear and a M21 4 speed and firestone radials was not to impressed but for a daily cruiser not bad i guess. It just seems there should be more power coming out of of her any advice would be helpfull I was thinking about porting the heads an go with a 2.08 intake valve and perhaps a beehive spring set up. Im stumped any help please would really be appreciated.

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Old 07-02-2012, 06:20 PM
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Something is definatly clipping the top end off.
You are missing about 10 MPH and .6 to .75 sec et.

and 80-100 RWHP.

valvesprings, valve float, bad clutch ignition fault, fuel flow.
restrictive exhaust.

Your car will need more gear
What was the 60ft and the 1/8 et and 1/8th mph?

It is very hard near impossible to get a good |ET at Cayuga with street radials.
I got some DOT slicks that will fix that for you and nail you to the seat.

You may have been spinning the tires on the dyno too. I have seen that before.
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Old 07-02-2012, 10:54 PM
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i'M STUMPED

Thanks for the reply F-BIRD
[I] have comp cams 987-16 springs on the head which is what howards cam recommended for my cam in a double spring ,as well RHS ill try another dyno shop ang see if theinstalls the 987 in their 1244 200 cc head for hydraulic roller applications up to .600 lift,my fuel pump is 120 gph carter with 3/8 fuel lines from the tank to the carb,my exhaust is 1 3/4 headman hedders a 2/1/2 dual flowmaster exhaust with h-pipe and high flow walker catalytic converters,.I shifted @6000 rpm and 6200 rpm even tried 6500rpm went smooth all the up the rpm band,I never thought about the tire slippage but that makes a lot of sense. Thanks again man for the information.Oh yeah I have a LUK 11 Inch clutch in no slipage,my 60 ft is horrible 2.13 but if I launch higher than 2600 rpm i either spin crazy or wheel hop.
On the street though which is 99% of the time the car drives great and is alot of fun but its missing that surge of power around .I'll get back to you with the 1/8 ET and MPH. ps are you selling the street slicks,if not whats your opinion on BF GOODRIDGE STREETSLICKS OR M/T ET STREET SLICKS

Last edited by sapsz28; 07-02-2012 at 11:10 PM. Reason: forgot something
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Old 07-03-2012, 12:41 AM
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You have a PM

You may still have a high rpm fuel delivery issue or a ignition issue.

Not a fan of flowmaster mufflers (restrictive (power loss) and loud)
every car I have tested with flowmasters has picked up ET and MPH (Power)when uncorked.
The Cats are a unknown.
Did you test with open headers

The springs are fine.
What ever it is its really killing the power I would expect from that combo
8-10MPH

Your 60ft should be 1.70 1.80 on the sticky tires and 3.42's
that would get the et to a 12.60 without even finding the power loss

4.10's would get your to a 12.5 12.4 again still with the 330hp you are making now (105MPH)

This car should be running very low 12's @112
(4.10's)

I do got the traction cure for you

can you post the dyno printouts? I would expect 385 to 410 hp from that car.
The track MPH agrees with your dyno test. its not the dyno

Last edited by F-BIRD'88; 07-03-2012 at 01:03 AM.
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Old 07-03-2012, 01:01 AM
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The 1/8th mile time slip info tells me what happened in the last half the drag runs.
compared to the first half. can be revealing.
do you know the true car weight w/ driver ??

what is the carb jetting in the 750?

Last edited by F-BIRD'88; 07-03-2012 at 01:07 AM.
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Old 07-03-2012, 09:07 AM
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Take a look at M&H Drag Radials. I switched to them this year after having horrible traction problems with my MT Sportsmans on my little gasser. First test run with the new M&H DR's I pulled the front wheels off the ground!
I drive this car a lot in all sorts of weather and the tires even hook up good in the rain. Not sure yet how the soft compound will hold up mileage wise, but they sure put the pwoer to the ground.
Drag Radials
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Old 07-03-2012, 02:49 PM
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Dual plain manifolds do not breath well above 5800 rpm. Replace it with a single plain manifold. It will double the amount of CFM per cylinder.
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Old 07-03-2012, 03:33 PM
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horsepower stumped

I was thinking to switch to a weiand team g and 2.08 intake valve over my 2.02's i have now as well as porting my RHS pro action 200 cc heads.what are your thoughts
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Old 07-03-2012, 04:54 PM
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Are you running a rev kit with your hydro roller lifters?? lifters could possibly lofting off the cam lobe with out the rev kit at higher rpms.. Also add a 1" spacer to your rpm manifold, that will raise the power band of the manifold. that will help over 5000 rpm
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Old 07-03-2012, 05:21 PM
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A few thoughts:

Quote:
Originally Posted by sapsz28 View Post
I was thinking to switch to a weiand team g and 2.08 intake valve over my 2.02's i have now as well as porting my RHS pro action 200 cc heads.what are your thoughts
Try as much open spacer under the carb as you have room for. If it picks up you know what to do. Port matching the intake/head (not gasket matching) may show some improvement depending on the mismatch.

Forget about 2.08 valve, at least for now. If you do anything, clean the pockets up and get a decent valve job on it (or at least verify what you have is decent) and maybe backcut the valves if not done already.

Was the valve spring installed height verified?

Was the cam degreed in? If the cam is out of phase or there's some other problem w/the cam/timing set, there can be huge losses.

Were there any unexplained dips or abnormalities in the read out that would lead you to believe the valve train wasn't under control? The pushrods should be =/> 0.080" wall. The geometry spot on?

Having the vacuum advance hooked up should not matter at WOT unless there is a restriction in the induction system causing vacuum to be present. Have you verified that the throttles are wide open when matting the gas pedal from inside the car? What ignition system are you using w/the Streetfire, or is that it?

If you really have a M21 close ratio Muncie (haven't we covered this before?), you need a lot more rear gear. It will be lugging in first and there will be a razor thin line between lugging it off the line and torching the tires unless you have mondo traction.

Last edited by cobalt327; 07-03-2012 at 05:42 PM.
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Old 07-03-2012, 07:28 PM
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Dump the 2.5" for 3", dump the flowmasters, dump the cats, dump the h pipe.

There's your missing 75hp.

Next would be the carb and intake if you're just going after track times, they'll work fine for street use though.
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Old 07-03-2012, 10:36 PM
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Quote:
Originally Posted by lg1969 View Post
Dual plain manifolds do not breath well above 5800 rpm. Replace it with a single plain manifold. It will double the amount of CFM per cylinder.
This is not true. My vortec 406 w dual plane reve easily way past 6000rpm
it traps at 6700rpm (115MPH)

The motor should be running within 2MPH+/- of mine. and be making very similar horsepower. It is not.
This motor has a problem. something is clipping off the top end. And its not the intake manifold.

I build low buck junk 350's with ported 305 heads that run faster than this car is going.
You need to find the cork in the combo. Something is definatily holding this motor back.
The flowmaster mufflers are very suspect. The cats may be just making it all the worse.

Last edited by F-BIRD'88; 07-03-2012 at 10:41 PM.
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Old 07-04-2012, 04:57 AM
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Agreed on the cats, the FM muffs aren't hurting it THAT bad unless they're defective. The H pipe is not hurting it, either.
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Old 07-04-2012, 05:35 AM
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I doubt it's flowmasters. I'm running a 388 with ETec 200 heads, 10.6 SCR and a 234* x 238* @.050" roller cam with a 680 cfm QFT carb and Air Gap manifold that put down 380 hp and 396 lb/ft on a chassis dyno. All in by 5800 rpm. This motor is a bit milder and a few cubes smaller than the OP. I'm guessing cats and/or carb calibration.
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Old 07-04-2012, 06:54 AM
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Quote:
Originally Posted by Greg T View Post
I doubt it's flowmasters. I'm running a 388 with ETec 200 heads, 10.6 SCR and a 234* x 238* @.050" roller cam with a 680 cfm QFT carb and Air Gap manifold that put down 380 hp and 396 lb/ft on a chassis dyno. All in by 5800 rpm. This motor is a bit milder and a few cubes smaller than the OP. I'm guessing cats and/or carb calibration.
That's an early hp peak, and so close to your tq peak is telling me you're probably getting choked off by the exhaust too.
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