turbo motor build

[Rex Schimmer]

JN,
Your idea of flushing the engine before firing it is very smart. The best way would be some way to have high velocity oil surge through the system but doing what you are doing is miles ahead of not doing it. When Nissan was in racing they would do something similar by running the motor with the dyno for a period of time and they used a large 3 micron filter to clean the system.

Good thinking.

Rex

[1212FBGS]

65 not enough on the ex side..... 80 min
kr

[Jonny Hotnuts]

Kent, from what I understand 1 pound increase in spring pressure over stock will yield the ability to have 1 pound boost OVER what boost is capable from stock spring pressure.

Stock springs are 43 psi and are good to about 18 psi boost.
This would make 65 psi springs good for 22 psi over stock.
(*The 65 psi APE springs routinely measure 68 psi, weighing after break in.)
This would yield the ability to make 40 psi (if spring pressure per boost rate was 100% true).

While I dont know anyone making 40 psi with 65 psi springs there are people routinely making over 30 pounds boost without issues, and 30psi boost will make 475-550 (some have made over 600 with 30 psi) boost.


The motor should make 360ish WHP with 20psi. (10-12 hp per pound boost)
We only need about 325-350 to go 220.

This is…..if all my BS is correct.

[fredvance]

Theoretically!!

[McRat]

.02c  (overpriced):

Drive pressure helps the springs out.  Assuming you have a Super Wunderbar Charger, and can hit 1:1 drive pressure ratio, the drive pressure and boost pressure make it a wash as far as the valve goes.  The same exhaust force is pushing the intake valve closed as the boost is trying to force it open.  The exhaust valve always get a power assist closing from the gas flow.

I run higher rate springs to allow me to spin faster without float.  I never saw an advantage to running more spring on a turbo engine if I wasn't spinning faster.  But turbos often will move your powerband up the RPM range if you want, without cam changes.  So it's not really the boost, but what the boost can help you do that requires more spring.

Your results may vary.

[Harold Bettes]

Howdy All,

The boost on the intake side of the engine will try and lift the valve(s) off the seats in an amount of force that is equal to the boost x the effective area of the valve. So, if you have an engine with an intake valve area of 2in² and the boost is 15 psi, then the force is 15 psi x 2in² = 30 lbs force is subtracted from the closure force of the intake spring(s).

The opening point of the exhaust valve(s) is against cylinder pressure. The residual pressure in the exhaust on a turbocharged package (such as the pressure between the exhaust valve(s) and the turbine might very well cause some problems with the force on the exhaust valve(s), however that back pressure should be minimal in well matched packages.

That is a major consideration on most roots blown setups and most highly boosted turbocharged setups. The roots blown units are more prone to ding up exhaust rockers as a result (certainly on nitro loads of greater than 25% or 30%).

At least that is the story I would tell over BBQ! 

Regards to All,
HB2

[Jonny Hotnuts]

The opening point of the exhaust valve(s) is against cylinder pressure. The residual pressure in the exhaust on a turbocharged package (such as the pressure between the exhaust valve(s) and the turbine might very well cause some problems with the force on the exhaust valve(s), however that back pressure should be minimal in well matched packages.

This being said....

Would it not also hold true that a larger turbine would limit back pressure achieved vs a smaller unit?

[McRat]

Unlike a supercharger, the exhaust pressure is pretty high at all times with a turbo when boosting.
When I made 50psi boost, I saw 90 psi drive pressure (pressure in exhaust, pre-turbo).  A given compressor wheel likes a "correct" size turbine to match for the displacement and target boost.  Think of the turbine as a motor;  it need X amount of power to make your booast.  Turbos have a range of exhaust housings (cheap) that you can use to fine tune and adjust RPM with.  Bigger housings numerically reduce drive pressure and move the RPM up at the expense of low RPM performance and width of powerband.  Bigger housings make narrow powerbands as a percent of the RPM range.  So a .90 A/R exhaust housing might make 75% of max power for 33% of your RPM range, yet a 1.15 housing will only make 75% max power for 25%.

But it has been almost 30 years since I turbocharged a bike engine.  I play with high boost diesel engines which are different.  Life begins at 45psi.  But when I turbo'd a 650 Kaw (30psi), I ran stock cams and springs, and spun the engine 3,000 over factory redline with no valve train damage. 

Something I should have noted is that if you get piston erosion, the aluminum will become aluminum oxide crystals and coat the exhaust valve.  Feels like sandpaper grit.  It is something that can happen at high boost.  High spring rates will help the engine run a little longer before the valves seize in their guides and bad things happen.

[1212FBGS]

all i know is what works and what doesn't..... when i ran off the shelf springs the valves moved on the seats and after 2 passes i would get blow by on a leakdown mostly the ex side.... fought the problem for a couple of years having to refresh the valve job after each race.... was a pain in the azz.... an old timer told me to bump the seat pressure to hold the valves and seats in place...  Will at Kibblewhite made me some springs.... problem gone.... good luck using your "should be right" theories...
Kent

[1212FBGS]

oh! boost wasnt the problem!
kent

[Jonny Hotnuts]

good luck using your "should be right" theories...
Kent

Kent,

I only theorize about why it works not IF it works.
It is true that I dont have much in the way experience in building Hayabusa engines.....less the one that I just did. The only thing that made this possible is the vast amount of knowledge available from the years of tens of thousands of people tweaking the busa engines from '99 to present.


I dont mean to imply that I am not sure that 65 pound springs are OK. I only know that these are the norm for boosted busa motors and while heavier than 65 are available the #65s are in more high HP busa motors than any other spring rate and are not known to be a source of failure under reasonable boost conditions (not over 30+ psi)

I don’t doubt that you had issues…..all I am saying is that taking into consideration that your motors start with K are you really all that surprised?

JK

~JH

[Dynoroom]

I've watched this thread progress. Johnny, is it possable that your "knowledge" might come from folks who have never been involved in endurance type racing?
Read between the lines. Kent is not busting your balls he's leading you to water.

JMO as Kent & I do not know each other....

[John Noonan]

I run more than 65 pounds of seat pressure on the exhaust side..

Kent and I have met..


J

[McRat]

Different engines need different tweeks.  No doubt on that.

If someone with seat-time on your engine gives advice, that is a pearl.

I won't alter spring rates based on boost simply because I can't see a correlation on a turbo engine.  That's me though.

[Dynoroom]

The way I read it the advice that was given wasn't due to boost or back pressure....