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540 not showing power

General engine tech -- Drag Racing to Circle Track

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sjre
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540 not showing power

Post by sjre » Sat Jun 27, 2020 7:16 pm

Local builder refreshed 540 only change was cam. Dyno showed 740 at 6200 , 620 tq 4700. the problem is car went 9.70 at 135 last year 9.90 at 136 best this year .
This year very inconsistent all over the map.Swings as much as 5 tenths.Mph is up a little but crazy. This motor after refresh made more power. combo is 540 11.0-1 comp dart 345 no porting victor single plane comp 272-280@50 737/710 lift 5500 converter th400 4.10 gears 3200 lb car.Old cam 260-270 112 both solid rollers.
Trans and converter fresh as of last sept. Questions are
why peak at only 6200 with 345 heads and why so inconsistent ? Could the cam change affect it that much? Builder said he uses this cam on his street 540s.Could the converter have gone bad? Engine also likes less ign timing than before.60 ft still the same around 1.37
Thanks for any ideas

bob460
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Re: 540 not showing power

Post by bob460 » Sat Jun 27, 2020 8:06 pm

Did he change the valve springs aswell?

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af2
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Re: 540 not showing power

Post by af2 » Sat Jun 27, 2020 8:38 pm

Tires and converter need to be looked at.
GURU is only a name.
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steve cowan
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Re: 540 not showing power

Post by steve cowan » Sun Jun 28, 2020 2:06 am

Seems like alot of duration for the compression and rpm,
At that weight and that power level the car should run over 140 mph.
The induction system might have the volume but being as cast there would likely be some CSA issues that might require attention
Eg- throat size,valve job, air speeds through the port etc.
If possible it would be great to have more specifics as in carb size,launch rpm,shift rpm,finish line rpm etc
steve c

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Re: 540 not showing power

Post by mag2555 » Sun Jun 28, 2020 5:52 am

With that size motor and the weight of that car it should be bunch faster!

I don't think your making enough average cylinder pressure as was posted with a Cam of those duration numbers, also 740 hp should only take some 330 cfm to make and those 345 cc heads should be flowing a bunch more then that!

sjre
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Re: 540 not showing power

Post by sjre » Sun Jun 28, 2020 8:02 am

New valve springs ,new tires and converter was new as of last fall . Carb is a 1050 dominator.
Do you think the cam would make it inconsistent ?

thanks

Old School
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Re: 540 not showing power

Post by Old School » Sun Jun 28, 2020 9:44 am

Get the converter out and have it checked. Doesn't matter if it was new last fall.

The cam will not make the engine inconsistent.

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Re: 540 not showing power

Post by NormS » Sun Jun 28, 2020 9:50 am

I agree with Steve. I think your new cam has too much duration for the compr ratio you have, and that the 1050 Dominator, assuming it hasn't been modified, is probably too small, cfm wise. That dominator is not a very efficient carb, considering cfm versus venturi size and throttle bore size.
Increasing the venturi size by a 1/16", and changing the entry shape of the venturi , can raise the cfm to 1300, without having to enlarge the throttle bore size. As with cylinder head ports,shape is the name of the game. Getting the venturi shape right can dramatically increase cfm, without having to make the venturi size real big, and with an improvement in the accuracy of fuel metering over a wider cfm range. Norm/Comp. Fuel Systems
Competition Fuel Systems Vassar, MI. www.compfuelsystems.com 520-241-2787

sjre
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Re: 540 not showing power

Post by sjre » Sun Jun 28, 2020 10:43 am

carb/ manifold was same as last year and was consistent . Need to know if too large camshaft could cause this or if strictly another problem ? The converter was ok last time out last year, started problems 1st time out this year after freshen/cam change over winter.
thanks

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Re: 540 not showing power

Post by skinny z » Sun Jun 28, 2020 10:54 am

sjre wrote:
Sat Jun 27, 2020 7:16 pm
New cam. 272-280@50 737/710. Old cam 260-270 112
Can you provide full specs for both cams?

Can you post the dyno graph?

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Re: 540 not showing power

Post by dannobee » Sun Jun 28, 2020 11:16 am

740hp @6200 = 626 lb ft tq at 6200 but you said the dyno peaked at 620 lb ft tq? Are you sure those numbers are accurate?

But back to basics and lets assume that it made more power on the dyno than the last combo. What changed when installed in the car? Is the fuel system up to task? And more basic, is the throttle opening all the way? Junk in the fuel cell/tank? Extra floor mats tucked up under the gas pedal?

Since the 60 ft is the same, it's probably not a converter problem. I've pulled apart many. There's usually some glaring indication that something's wrong.

Cam change wouldn't make it inconsistent. And look how big the cams are in Super Stockers, sometimes with less than 9:1 compression.

sjre
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Re: 540 not showing power

Post by sjre » Sun Jun 28, 2020 12:19 pm

thought it might have been fuel , did the flow test just shy of 1 gal in 30 seconds , not sure if it proves anything. Kind of agree not cam but with everything being the same its confusing.

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Re: 540 not showing power

Post by frnkeore » Sun Jun 28, 2020 1:30 pm

I have a couple of questions.

1. What was the HP difference between last and this years engine?

2. When you have your off runs, can you feel a difference and if so, what do you feel and where on the rpm scale, do you feel it?

Since the 60 ft is the same, it shouldn't be a traction or low rpm problem. I would think that it's a mid range problem and maybe a better tuned carb would help. Since your trap speed hasn't really gone up, I wouldn't think your developing much more HP either, at least on the track.

With the same 60 ft, and more HP, the trap speed should go up. Two more questions, is it harder to maintain traction off the line? That would show a HP increase if, it does and how does the air get to the carb?

Overall, I'm unconvinced that you actually have more HP, at least when the engine is setting in the car.
Last edited by frnkeore on Sun Jun 28, 2020 2:08 pm, edited 1 time in total.

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Re: 540 not showing power

Post by mt-engines » Sun Jun 28, 2020 1:41 pm

Could be cam timing. What's the icl

sjre
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Re: 540 not showing power

Post by sjre » Sun Jun 28, 2020 1:55 pm

1st engine was a shafiroff shortblock with dart 345s 112 ls in at 107 never dynoed this one 110 in at 106.Trap speed is 1-2mph better.I dont drive car its a friends giving best possible answers.

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