Anyone run 108 LSA cams in boat before? 700 HP DYNO proven combos welcome...
08-31-2016, 06:49 PM
#12
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There are lots of aspects of narrowing the LSA other than adding overlap if keeping same duration #'s.
Keeping everything else the same you will open exhaust later, close it later, open intake earlier, and close intake earlier.
So, on lower compression motors, some times, closing intake earlier will trap more a/f charge,,,,,and some times keeping exhaust opening later gives more time for leverage against piston/rod/crank.
That said, high compression motors get there work done quicker (combustion pressure decay % is quicker) and thus opening exhaust earlier is beneficial and closing intake later not a big deal psi wise because we have higher compression....and usually higher compression motors are spun higher so this gives a little more time to get some more intake charge.
I have a ton more on this, like cyl head efficiency and such, but will leave this post saying that on a NA motor using a good amt of duration and a pretty tight LSA (read more overlap) you better have a damn good exhaust. ie: a tuned exhaust...not just a big exhaust.
Keeping everything else the same you will open exhaust later, close it later, open intake earlier, and close intake earlier.
So, on lower compression motors, some times, closing intake earlier will trap more a/f charge,,,,,and some times keeping exhaust opening later gives more time for leverage against piston/rod/crank.
That said, high compression motors get there work done quicker (combustion pressure decay % is quicker) and thus opening exhaust earlier is beneficial and closing intake later not a big deal psi wise because we have higher compression....and usually higher compression motors are spun higher so this gives a little more time to get some more intake charge.
I have a ton more on this, like cyl head efficiency and such, but will leave this post saying that on a NA motor using a good amt of duration and a pretty tight LSA (read more overlap) you better have a damn good exhaust. ie: a tuned exhaust...not just a big exhaust.
Last edited by SB; 08-31-2016 at 07:10 PM. Reason: spelling only
08-31-2016, 08:22 PM
#13
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[QUOTE=SB;4477235]There are lots of aspects of narrowing the LSA other than adding overlap if keeping same duration #'s.
Keeping everything else the same you will open exhaust later, close it later, open intake earlier, and close intake earlier.
So, on lower compression motors, some times, closing intake earlier will trap more a/f charge,,,,,and some times keeping exhaust opening later gives more time for leverage against piston/rod/crank.
That said, high compression motors get there work done quicker (combustion pressure decay % is quicker) and thus opening exhaust earlier is beneficial and closing intake later not a big deal psi wise because we have higher compression....and usually higher compression motors are spun higher so this gives a little more time to get some more intake charge.
I have a ton more on this, like cyl head efficiency and such, but will leave this post saying that on a NA motor using a good amt of duration and a pretty tight LSA (read more overlap) you better have a damn good exhaust. ie: a tuned exhaust...not just a big exhaust.[/QUOT
Good info. There is a bunch of it online that is pretty cut and dry if anybody wants more info but that sums it up. I will say however I am surprised OP was specked out a108 considering... In the wonderful world of engine building its not an easy determination of what might work best for your application with the exception of the so called wizards.
With lsa reflecting hp and torque curve I am curious if it tightens up the gap btwn peak torque and hp? Just popped to mind.
Keeping everything else the same you will open exhaust later, close it later, open intake earlier, and close intake earlier.
So, on lower compression motors, some times, closing intake earlier will trap more a/f charge,,,,,and some times keeping exhaust opening later gives more time for leverage against piston/rod/crank.
That said, high compression motors get there work done quicker (combustion pressure decay % is quicker) and thus opening exhaust earlier is beneficial and closing intake later not a big deal psi wise because we have higher compression....and usually higher compression motors are spun higher so this gives a little more time to get some more intake charge.
I have a ton more on this, like cyl head efficiency and such, but will leave this post saying that on a NA motor using a good amt of duration and a pretty tight LSA (read more overlap) you better have a damn good exhaust. ie: a tuned exhaust...not just a big exhaust.[/QUOT
Good info. There is a bunch of it online that is pretty cut and dry if anybody wants more info but that sums it up. I will say however I am surprised OP was specked out a108 considering... In the wonderful world of engine building its not an easy determination of what might work best for your application with the exception of the so called wizards.
With lsa reflecting hp and torque curve I am curious if it tightens up the gap btwn peak torque and hp? Just popped to mind.
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08-31-2016, 08:28 PM
#16
08-31-2016, 08:29 PM
#17
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There are a ton of car applications, but not all, that power after peak is ultra important.
Last edited by SB; 08-31-2016 at 08:32 PM.
08-31-2016, 08:31 PM
#18
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I ran 106 LSA on a Solid Roller .700 Lift with Dry Exhuast Stellings. Sounded absolutely nasty as hell! Turned a lot of heads. And ran well for the combo but it was a maxed out 454 N/A. Honestly cam was way to big but again I didn't build it. Takes a lot to push a 6k lb. 25' boat past 70!
Last edited by KRAUSMOTORSPORTS; 08-31-2016 at 08:46 PM.
08-31-2016, 08:46 PM
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Curious what specs are for your current cam. I'm putting the finishing touches on an mk combo i started like 2 years ago. I have a 502 gen vi with a 540 stroker kit in it and the afr 325's. He set me up with a 113.1 lsa, 238 duration intake with .66394 lift and a 243.3 duration exhaust with .64567. This was supposed to be spec'd for a dry exhaust combo
