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Horsepower Gain
- Thread starter Stretch
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Well Dave, you seem to have a very good grasp on cam design, or the same engine simulation program I have. /ubbthreads/images/graemlins/grin.gif I ran some numbers and came up with what you have already said. The best results look to be a BJ8 cam with headers up to 4500 RPM. At that point the Isky cam w/headers starts making more power followed closely by the Chevy grind w/headers. The torque curves tell the same story.
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Hi Greg,
I don't have the program. Just 45 years of experience studying & building high performance engines & a good engineering background. Thanks for the very good illustration. Since torque is what you feel when you drive on the street, torque makes the most noticeable difference in acceleration. OTOH, horsepower is what creates top speed which is seldom needed. I converted your numbers to torque to better illustrate the point. I just compared the two cams without headers. See attached.
D
Well Dave, you seem to have a very good grasp on cam design, or the same engine simulation program I have. /ubbthreads/images/graemlins/grin.gif I ran some numbers and came up with what you have already said. The best results look to be a BJ8 cam with headers up to 4500 RPM. At that point the Isky cam w/headers starts making more power followed closely by the Chevy grind w/headers. The torque curves tell the same story.
[/ QUOTE ]
Hi Greg,
I don't have the program. Just 45 years of experience studying & building high performance engines & a good engineering background. Thanks for the very good illustration. Since torque is what you feel when you drive on the street, torque makes the most noticeable difference in acceleration. OTOH, horsepower is what creates top speed which is seldom needed. I converted your numbers to torque to better illustrate the point. I just compared the two cams without headers. See attached.
D
Attachments
Great info that really helps. I would appreciate if the BJ7 cam performance can be added to the graph. It would ease decision making for me. Can performance with the BJ7's stock 1.75 inch carbs be simulated? I assume with increased exhaust flow and performance that carb settings must be richened. Any comments?
GregW
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Hi Stretch,
Here is the BJ7, BJ8 and BJ8 w/headers. I have tweaked the CFM slightly to reflect the peak HP @ 4600 for the BJ7 and 5250 for the BJ8. Looks like about a 7 horsepower increase from BJ7 to BJ8 w/headers to 3000 RPM. From there the gap increases. The BJ7's torque curve starts to drop earlier, it looses ground near the 3000 RPM range whereas the BJ8 w/headers doesn't loose umph until 4000. Please keep in mind that these are ballpark figures. Having flow bench numbers would increase the accuracy of the simulation. But it isn’t the real world. /ubbthreads/images/graemlins/cryin.gif
Here is the BJ7, BJ8 and BJ8 w/headers. I have tweaked the CFM slightly to reflect the peak HP @ 4600 for the BJ7 and 5250 for the BJ8. Looks like about a 7 horsepower increase from BJ7 to BJ8 w/headers to 3000 RPM. From there the gap increases. The BJ7's torque curve starts to drop earlier, it looses ground near the 3000 RPM range whereas the BJ8 w/headers doesn't loose umph until 4000. Please keep in mind that these are ballpark figures. Having flow bench numbers would increase the accuracy of the simulation. But it isn’t the real world. /ubbthreads/images/graemlins/cryin.gif
anthony7777
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john loftus,i have now once again been mercilessly reminded of the performance discrepancys between the bj7 and the bj8, in that said 7's are equiped with 1.75" carbs while the 8's are vested with the more appropriate 2.00" fosil fuel sucking beasts!i believe [correct me if im wrong]the crank as well as the cam,are identical in both?,due to perehaps the availability of disposable income and or the willingness or lack there of to part with strange bits of rectangular slips of paper containing the portraits of a number selected deceased presidants,we all would love to achieve the "best bang for the buck" as far as our beloved HEALEY power plants are concerned,one might believe the exhaust system in it self could provide this,another might be convinced increasing the intake, i.e "webbers" will do just what is needed,others live and die by the familiar adage "no replacement for displacement"i think you will agree in truth the simple answer to achieving the maximum amount of safe or unsafe for that matter horsepower is the correct combination of all three of these aspects.and keoke,yes i once took the cam from a 1954 6 cyl. chevy ice cream truck and slid it into a 62 healey,its running till today! /ubbthreads/images/graemlins/crazyeyes.gif
John Loftus
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Anthony,
As Greg points out the cams are different but the cranks are the same. The P.O. told me he swapped a pair of 2.0" carbs/inlet manifold on the BJ7 but it didn't run better so he reverted back. The car had tube headers but without the cam, perhaps the motor couldn't take advantage of the increase. Could be that the carb just weren't adjusted properly.
Since we are talking performance mods, I did one bolt-on upgrade that made a difference on my motor. Installed a set of Roller Rockers (from Rocker Arm Specialists) and the motor was much smoother at higher rpms. All seat of the pants comparison but with the valves opening more (true 1.5 ratio) the effect was like changing to a hotter cam.
Cheers,
John
As Greg points out the cams are different but the cranks are the same. The P.O. told me he swapped a pair of 2.0" carbs/inlet manifold on the BJ7 but it didn't run better so he reverted back. The car had tube headers but without the cam, perhaps the motor couldn't take advantage of the increase. Could be that the carb just weren't adjusted properly.
Since we are talking performance mods, I did one bolt-on upgrade that made a difference on my motor. Installed a set of Roller Rockers (from Rocker Arm Specialists) and the motor was much smoother at higher rpms. All seat of the pants comparison but with the valves opening more (true 1.5 ratio) the effect was like changing to a hotter cam.
Cheers,
John
John Loftus
Darth Vader
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nice springs ... True Value?
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[ QUOTE ]
nice springs ... True Value?
[/ QUOTE ]
No John, I think those are J.C. Whitney. Now on sale! /ubbthreads/images/graemlins/cheers.gif
nice springs ... True Value?
[/ QUOTE ]
No John, I think those are J.C. Whitney. Now on sale! /ubbthreads/images/graemlins/cheers.gif
B
BUNDYRUM
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John, i fitted HD8's to my BN7 with the original manifold matched (by me with an electric drill and rotary file) to the head and carbs and i almost couldn't believe the difference in performance. It's just what was needed and has been one of the easiest modifications done to it. I just love the photo of those roller rockers, very nice.
Greg. John says his are 1.5:1 ratio, you say yours are 1.55:1. is one of them a typo? Also, how do you get 372 degrees duration with them? Surely duration is a function of valve timing? Regards, BUNDYRUM.
Greg. John says his are 1.5:1 ratio, you say yours are 1.55:1. is one of them a typo? Also, how do you get 372 degrees duration with them? Surely duration is a function of valve timing? Regards, BUNDYRUM.
GregW
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Hi Bundyrum,
Here’s the link to Rocker Arm Specialists . They have 1.5:1, 1.55:1, and 1.6:1 rocker ratios for the Healey. I believe that’s for both 4 and 6 cylinder engines. The 1.6 would have needed modification of my cylinder head to work and I was reluctant to do that. The springs in the photo were used for mock-up. As John pointed out, they were from a hardware store (I think Ace). The 372 was my way of saying they wouldn’t be strong enough to close the valves on a running engine. Yeah, I know the piston would hit it before 360./ubbthreads/images/graemlins/yesnod.gif
Here’s the link to Rocker Arm Specialists . They have 1.5:1, 1.55:1, and 1.6:1 rocker ratios for the Healey. I believe that’s for both 4 and 6 cylinder engines. The 1.6 would have needed modification of my cylinder head to work and I was reluctant to do that. The springs in the photo were used for mock-up. As John pointed out, they were from a hardware store (I think Ace). The 372 was my way of saying they wouldn’t be strong enough to close the valves on a running engine. Yeah, I know the piston would hit it before 360./ubbthreads/images/graemlins/yesnod.gif
anthony7777
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gregw,wow!i wonder if anyone makes glass rocker covers? /ubbthreads/images/graemlins/yesnod.gif
John Loftus
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About rocker ratios:
When I was investigating roller rockers I came across a company producing them (I think is was DMD in Australia) that had some info about the stock ratios. They said the Healey motor (at least the 6 cylinder)was designed as 1.5:1 but when they tested the true ratio it was something around 1.35:1 so fitting a true 1.5:1 rocker arm would increase the valve opening compared to stock (but to a level originally designed for). Just be aware that if you can run into clearance problems if the head has been skimmed, blocks decked, performance cam installed, or run a higher ratio as Greg points out.
Cheers,
John
When I was investigating roller rockers I came across a company producing them (I think is was DMD in Australia) that had some info about the stock ratios. They said the Healey motor (at least the 6 cylinder)was designed as 1.5:1 but when they tested the true ratio it was something around 1.35:1 so fitting a true 1.5:1 rocker arm would increase the valve opening compared to stock (but to a level originally designed for). Just be aware that if you can run into clearance problems if the head has been skimmed, blocks decked, performance cam installed, or run a higher ratio as Greg points out.
Cheers,
John
B
BUNDYRUM
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Hello Greg, thanks for the link, there was mention that they were roller rockers but i see they are roller tipped rockers. I wonder why they make the Healey ones from 6061 and the others from either 2024 or 7075? Maybe the valve events on a Healey are not as brutal as say a "Hemi".
anthony7777. My sentiments also. I have heard that some manufacturers and race teams actually built clear polycarbonate covers so they could watch the flow of oil and film the rockers in motion. The last bit was to see how much the rockers were bending/distorting in operation.
John Loftus. Yes it was DMD. Regards, BUNDYRUM.
anthony7777. My sentiments also. I have heard that some manufacturers and race teams actually built clear polycarbonate covers so they could watch the flow of oil and film the rockers in motion. The last bit was to see how much the rockers were bending/distorting in operation.
John Loftus. Yes it was DMD. Regards, BUNDYRUM.