Turbulence Induces for increasing burn rate 4

[automotivebreath]

Without turbulence in the combustion chamber we would burn the mixture at the laminar burning rate which is ten to twenty times slower than the turbulent rate. Numerous designs beyond common squish areas have been developed to shorten burn times. Does anyone have experience with turbulence inducers and knowledge of the potential impact on the combustion process?

 

[mattsooty]

Automotivebreath

17:1 is about the lean misfire for most stoic. engines - so yes I would agree with you there.

MS

 

[SMOKEY44211]

Good article in popular hot rodding this month part of it touches on this very subject. D. Vizard states .025" minimum as assembled clearance obtained without signs of contact 7,000 rpm with stock rods and hypertunetic pistons SB chev 350. Also reports 7hp loss per .010" increase in clearance between piston and head. I'd love to see a with/without comparison with that single groove aimed at the plug.--------Phil

 

[automotivebreath]

Phil,
Eventually I will be dyno testing the scenario you describe. My experiences to date lead me to believe the results will be very different from D. Vizard's report.

Not long ago I would run tight piston to head clearances, that's no longer the case. My preference now is 0.050" to 0.060" assembled clearance with 35% squish to bore ratio with grooves. I'm find this to be more powerful, reduces HC emissions and lessen detonation tendencies.

 

[patprimmer]

0.025" piston to head might be OK with every thing brand new and tight piston to bore, but as things wear, I have seen 0.035" hit with SBC 350 TRW forged pistons, stock rods stock steel crank, 6000 rpm.

While the piston to bore was beyond recommended wear limit, the need for a rebuild was due to the ring lands closing down from impact and nipping the rings.

I was about to build a 408" SBC engine at 0.038" clearance with non twist forged crank, 6" long Carrillo rods and SRP forged pistons. I would like to see automotivebreath's results before proceeding.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

It is for a boat with raw water cooling and a roller cam with about 235 deg at 0.050 lift duration at 112 deg lobe centres and about 0.600" lift and aftermarket iron heads.

I was hoping to run 10.5:1 with premium unleaded pump fuel with a nominal 98 octane rating.

I don't mean to hijack the thread, but I am guessing what CR I can run with. I would like to run maximum possible CR without need to retard to avoid detonation.

Water temperatures in the head will be about 60 deg C.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[automotivebreath]

Pat,
I would like to know more about the fuel you intend to run and the expected cylinder head temperature.

patprimmer said
"I was hoping to run 10.5:1 with premium unleaded pump fuel with a nominal 98 octane rating"

On another note the Vizard’s example utilized hypereutectic pistons. These allow a much tighter piston to bore clearance eliminating piston rock allowing tighter piston to head clearance.

Agreeing with your example, TRW forged pistons require additional clearance, I consider 0.040" piston to head at assembly safe.

 

[automotivebreath]

Pat,
What cylinder head do you intend to run and what piston top design. My current thinking is to go with the largest squish to bore ratio available, I use RHS.

I missed your CH water temperature post; I see now 60 deg. C