poor dyno score on 540,s
12-15-2004, 07:19 PM
#23
Gold Member
Re: poor dyno score on 540,s
Drew ,
The cam you are using , I assume is a crane piece . This cam has way too much overlap in it and requires a set of headers to make any power . This cam should also max out at 5800 RPM for HP, and 4600-4800 RPM for torque peak .
I ran the same cam in my 540 and ran it with GILs - The thing was a dog -
I put a set of CMI tubes on it and woke it right up .
Still , it is alot of cam and really is a poor choice unless you have 12:1 compression .
The cam you are using , I assume is a crane piece . This cam has way too much overlap in it and requires a set of headers to make any power . This cam should also max out at 5800 RPM for HP, and 4600-4800 RPM for torque peak .
I ran the same cam in my 540 and ran it with GILs - The thing was a dog -
I put a set of CMI tubes on it and woke it right up .
Still , it is alot of cam and really is a poor choice unless you have 12:1 compression .
12-16-2004, 09:47 AM
#24
MarineKinetics
Platinum Member
Re: poor dyno score on 540,s
Turbojack,
Air fuel ratio is computed as follows;
(Mass air flow)/(Mass fuel flow)=A/F Ratio (gasoline)
stoichiometric= 14.7:1
rule of thumb optimum= 12.8:1-13.2:1
I agree the cam is not optimum for this application, however the engine drops off drastically just in the band (4800 rpm+) where is should just be beginning to work. This cam should be making peak torque @ 5000 rpm+ and peak HP @ 6000 rpm+. Instead its making peak TQ @ 4100 rpm and peak power @ 5100 rpm so I believe there are other mechanical factors in play here other than mis-matched components. Your numbers indicated you drop off 64 lbs/ft TQ in 500 rpm from 4800-5300 with your BSFC #'s increasing .068 in the same span. I would go back to the basics (fuel/air/spark) with an emphasis on ignition. Failing that I would look closely at the cylinder head with emphasis on the exhaust side. In particular valve bounce, spring surge, installed height/coil stack, valves and seats, and seat/nose pressure. The cam has to much overlap and low cylinder pressure due to excessive duration and the resulting late IVC angle but that should be apparent earlier in the pull, not @ 5000 rpm.
Bob
Air fuel ratio is computed as follows;
(Mass air flow)/(Mass fuel flow)=A/F Ratio (gasoline)
stoichiometric= 14.7:1
rule of thumb optimum= 12.8:1-13.2:1
I agree the cam is not optimum for this application, however the engine drops off drastically just in the band (4800 rpm+) where is should just be beginning to work. This cam should be making peak torque @ 5000 rpm+ and peak HP @ 6000 rpm+. Instead its making peak TQ @ 4100 rpm and peak power @ 5100 rpm so I believe there are other mechanical factors in play here other than mis-matched components. Your numbers indicated you drop off 64 lbs/ft TQ in 500 rpm from 4800-5300 with your BSFC #'s increasing .068 in the same span. I would go back to the basics (fuel/air/spark) with an emphasis on ignition. Failing that I would look closely at the cylinder head with emphasis on the exhaust side. In particular valve bounce, spring surge, installed height/coil stack, valves and seats, and seat/nose pressure. The cam has to much overlap and low cylinder pressure due to excessive duration and the resulting late IVC angle but that should be apparent earlier in the pull, not @ 5000 rpm.
Bob
12-16-2004, 10:28 AM
#25
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Join Date: Jan 2004
Location: San Diego, California
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Re: poor dyno score on 540,s
For those of you reading Bobs course here on Dyno intelligence, you are getting a great education. Listen to the "masters" who do this as a lifes work and passion. they will teach you the secrets of real engine power and save you a lot of Dyno time, broken motors and engine performance frustration. For those of you who really want to Graduate Head of the Class, hire someone like Bob to help you in your quest for Power! Its your best return on investment. Heck you don't pull your own teeth do ya!
Ray @ Raylar
Ray @ Raylar
12-16-2004, 09:26 PM
#27
Registered
Re: poor dyno score on 540,s
Jim, are you suggesting loosening the valve lash? I had to tighten mine down to about 1 turn on most and 1.5 on several to quite them down. Could this be costing me power? Been that way for 100 plus hours now with no problems. Crane lifters and Crane gold rockers.
