How much top end loss with porting?
- Thread starter Laxpro2
- Start date
- Location
- South Africa
Bored to 760 is fine, can't go further. Shouldn't have lost any top-end unless base of cylinder was skimmed to lower port timing
bored&stroked
Urban redneck
- Location
- AZ
I've never heard of lossing top end, only lossing bottem end with porting.
cookn
Kamikaze
- Location
- where you live
If you are losing any sort of power with porting better find a new engine builder
Quinc
Buy a Superjet
- Location
- California
DAG
Yes, my balls tickled from that landing
- Location
- Charlotte, NC
Is the SJ a 2008 or newer? If not better off just wait for a SXR.
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
10 years ago. It was more about getting bottom end power..... Now. It is a whole different ballgame. With Race Porting you were setting the motor up many times to have much greater top speed. Raise compression and raise the port timing. With a loss of some bottom end power. in 2000, Jeff Jacobs ski was a rocketship. Probably the fastest out there. 2001 they came back with a totally different package, the power was set up more down low to mid. Still fast, but a different way to skin the cat.... Freestyle porting was more about getting the motor to breath more and hit much more at the bottom, Bottom to Mid........ Now, There were some builders that can get both but it was all about finding the combo that worked. Tim Tynan had a good post about this a while back, do a search @tntsuperjet Todd LeChance (TLR Performance) had an incredible package that he did for Rick Roy using 62T cases, 61x cylinders and a single carb conversion using a 44 SBN and boring the bottom side to 48mm. It was good enough for Rick to win multiple world championships.
Quinc
Buy a Superjet
- Location
- California
My skis are setup for bottom end and I still have a decently high top speed. Not so much about how fast your ski can go, but how quickly it can get there. Unless your porting is crap you can prop and pipe your ski for your needs.
bored&stroked
Urban redneck
- Location
- AZ
It widens, not raises the port. On a 4 stroke it would be like putting in a cam with the same duration but higher lift. Race porting is bigger cam in duration, with increases overlap and losses low end but gains top end.
- Location
- Charlotte, NC
'freestyle porting will consist of widening the exhaust ports which will increase torque and horsepower throughout the rpm range, raise transfer ports to increase blowdown timing which will help the engine on low end, and cleanup cases and intake ports. raising the exhaust port timing will raise the rpm range with a loss in bottom end. race setups will have a higher port timing, with much higher compression to help gain the low end rpm power loss along with total loss ignitions that have very light flywheels for less rotating drag on the engine for quicker acceleration. the total loss ignitions now have programmable timing curve so the tuner can have lots of timing advance at lower rpms to increase low end acceleration and retard the timing back at higher rpms so the engine wont detonate. pump setup is equally important for both a freestyle ski and a race ski. freestyle skis will typically run a wet pipe because a cooler pipe will increase low end torque and the race skis will typically run a dry pipe for more rpm.
waxhead
wannabe backflipper
- Location
- gold coast
Raise transfer to increase blow down timing ? are you sure on that one
- Location
- Charlotte, NC
maybe decrease port timing? i know that it has to do with when the fresh fuel charge comes in to help move the burnt fuel out. some will step the transfer ports. please correct me if im wrong since you called me out.
waxhead
wannabe backflipper
- Location
- gold coast
Blow down is the degrees in crankshaft rotation between the exhaust port opening and the transfers opening. if you raise the transfers you decrease the blow down as they open sooner.
Raising the exhaust port will increase the blow down and help the transfers flow more due to having less residual pressure in the cylinder.
"Freestyle" porting is a term from when a Superjet doing a barrel roll was it. With the back flip craze, nobody is trying to get good response from a 701 anymore. The new large engines are using "race" porting for the most power. They get response through displacement, exhaust valves, and programmable ignitions.
Half flip95
Formerly pondracer95
- Location
- Lake Havasu City AZ
There's lots of "ported motors" that run like doo doo. schedule a test ride