At what compression ratio on a TC do you need to install compression releases?

 

Any TC96 or larger should have them. Any build to an engine that does not have them it should be done as part of the build. To not do so is a cheap short cut you will pay for latter. Many say 10 to one

 

compression ratio is only part, cams can send cylinder pressure up.

 

The motor company put them on stock 103s which have a ccp around 190. So anything over that should have them.

 

========================

WELL SHORT ANS IS " WHEN IT WONT START ESP WHEN IT'S HOT OUT"!/LOL!!!

Just kidding!

ok,getting serious here there isnt a black & white ans to your question because it's not only the amount of compression the motor has that affects its ability to start esp when hot,its also the cond & CCA spec of the battery & cond of starter that also affects starting esp when hot when talking higher compression setups.

And to add to thats its just as much about cam profile meaning the amount of duration & valve overlap (more releases/lowers cyl pressure ) which eases starting when running higher compression ratios making choice of cam profile vs compression a critical choice made be an experienced wrench to avoid detonation and hot start issues along with retaining decent driveability not going with too much cam duration trying to avoid hot start issues resulting in reduced driveability when you dont have comp releases.

LSA/lobe separation angle also has some affect on starting with higher compression too, but it's not as much of an issues as cam duration so i wont get into LSA here.

You can have starting problems with a fairly low 9.0-9.5 compression motor when running a stock or very mild cam with low duration having little to no valve overlap resulting in higher cyl pressure and or higher static cranking compression putting more load on stater & battery.

And the other side of that is you can have considerably higher 10.0-10.5 compression with no starting issues at all as long as your running a fairly hot perf lvl cam thats got enough duration (Valve overlap) to " Effectively Reduce/Bleed Off " some of the higher compression.

So when running a high compression TC motor setup on the street its a fine line to be on choosing a performance cam profile that has enough duration (valve overlap) to effectively lower compression enough for reliable hot starts without going with so much duration thats it kills lower end trq/pwr and drivability too.

But if i had a TC motor with higher compression that had heads without comp releases before i spent the bucks to remove heads to have comp releases installed i'd 1st install a NEW high perf high torque 1.6+kw starter ,New larger hvy dty high capacity battery cables along with a New high perf high output 500-600CCA agm battery on the market these days too.

Then if you install those 3 items all at the same time (doing that ensures your getting full benefit of those 3 items working collectively together as a team to increase starting power & capability) will improve if not eliminate starting issues esp when hot with a higher compression setup.

Yes it costs some bucks to do that but if your motor is running well with no leaks ect why temp fate pulling the heads to have the heads drilled & threaded to install comp releases making it very easy for good old " Murphy's Law " to bite you with head gasket or valve cover leak later on (or worse yet!) if you dont have too?

And it's easy to install a new hi output battery,new hi perf hi trq starter along with larger high capacity battery cables too.

Lastly,another thing you can do to help starting of a higher compression TC HD is to reduce the overall heat given off by the motor that heat soaks the starter and battery reducing their starting pwr/efficiency & srv'c life too.

I did this to my 09 TC 96" last yr which reduced oil temp 50+ deg in hot summer temps resulting in a significant/positive improvement in engine perf and overall driveability right off the bat on my bike which was achieved by installing an Ultracool oil cooler with twin elec thermostatically controlled cooling fans along with Wards cooling fans both at the same time for max cooling efficiency (reduced oil temp 50+ deg ) resulting in:

* LITTLE LESS HEAT SOAKING OF MOTOR ,STARTER & BATTERY RESULTING IN EASIER/FASTER HOT STARTS WITH NO MORE HESITATION & OR SLOW TURNING OVER WHEN HITTING THE STARTER LIKE YOU OFTEN GET ON HOT RESTART POST FUELING UP ON A HOT SOGGY DAY.

* WITH OIL RUNNING 50+ DEG COOLER (REDUCES ENGINE TEMP AT THE SAME TOO) ALSO EQUATES TO LESS HEAT SOAKING OF MOTOR , INTAKE & FUEL SYSTEM IN GENERAL .

THATS ALLOWS THE MOTOR TO RETAIN MOST OF ITS PWR , TRQ & CRISP THROTTLE RESPONSE ON A HOT SOGGY SUMMER DAY VS WITHOUT THE 2 COOLING MODS WHERE MOTOR GOT SOGGY FEELING HAVING NOTICEABLY LESS PWR & TRQ WHEN OIL RUNNING 50+ DEG HOTTER WIHOUT THE 2 COOLING MODS.

* BIKE IS A BIT MORE COMFORTABLE TO RIDE IN HOT OUTSIDE TEMPS TOO.

* MOTOR RETAINS SIGNIFICANTLY BETTER/HIGHER OIL PRESSURE ON HOT SOGGY SUMMER DAYS TOO ,BEFORE INSTALLING THE 2 COOLING MODS OIL PRESSURE ON A HOT SOGGY SUMMER DAY USED TO BE 8-10PSI @ IDLE & 32-35PSI @ CRUISE.

POST INSTALLING THE 2 COOLING MODS OIL PRESSURE ON HOT SOGGY SUMMER DAYS IS 18-20PSI @ IDLE & 45-48PSI @ CRUISE WITH STOCK ORIGINAL HD STD VOL & STD PRESSURE OIL PUMP & SPRING USING THE SAME SPECTRO MOTORCYCLE SPECIFIC 20W-50 OIL THATS DESIGNED & FORMULATED FOR LRG AIR COOLED HD V-TWINS.

* MOTOR STOPPED DETONATING ON HD'S REC 91 OCTANE FUEL IN MY 96" TC MOTOR.

* VALVE TRAIN REMAINS QUIET ON HOT DAYS.

* OIL RUNNING 50+ DEG COOLER (MOTOR RUNNING COOLER TOO)
SHOULD THEORETICALLY IMPROVE/EXTEND SRVC LIFE OF FOR EXAMPLE,SEALS (ESP VALVE SEALS) & GASKETS,RUBBING BLOCKS ON CAM & PRIM CHAIN TENSIONERS THAT ARE KNOW TO CRACK/SLIT/BREAK APART AT TIMES WHICH COULD BE ATTRIBUTED TO OVERHEATING OF THE OIL & PLASTIC-TEFLON MATERIAL RUBBING BLOCKS ON CAM & PRIM CHAIN TENSIONERS ARE MADE OF WHILE ALSO EXTENDING THE ENGINES OVERALL SRV'C LIFE TOO.

INSTALLING THE 2 COOLING SYSTEM MODS WERE BY FAR THE BEST BUCKS & TIME I HAVE SPENT THUS FAR ON MY BIKE THAT RESULTED IN MULTIPLE POSITIVE IMPROVEMENTS IN THE BIKES OVERALL PERF & DRIVEABILITY ESP ON HOT SOGGY SUMMER DAYS.

So question becomes does someone running a high compression tc motor upgade to a hi perf hi cca battery ,hi trq starter along with install the 2 cooling mods all of which improve riding comfort ,driveability and engine perf every mile & minute you ride the bike over the time you one it or do you avoid doing all the above to corrects some root cause issues and opt to just go with installing comp releases thus putting up with hot motor that gets soggy perf on hot days with lower oil pressure,noiser valves,more uncomfortable to ride etc,that would be a no brainer for me .

But i am not everyone & am sure a lot of guys would rather have a hotter running bike that looses power feeling soggy on hotter days along with also having significantly with less oil pressure thinning oil motor for noisier valvetrain that also detonates on hot days too because many guys here dont agree with this when i posted it in the past where they had never tried it like i did to see what the true benefit was.

I go by results which i got in spades with mult improvements right off the bat & not BS like the guys that posted here they felt reducing oil temp on hot days in an air cooled TC HD motor was neither needed or beneficial at all which is just not case ,end of story.

Scott

 

==================

" cams can send cylinder pressure up "

OR CAN REDUCE CYL PRESSURE TOO!

But thats as long as there is ample cam duration/valve overlap to effectively reduce cyl pressure (static compression) enough to aid in starting esp for example on a hot sogy summer day 5 mins later post fueling up.

Scott

 

When ever you remove the heads is time for compression releases. I plan on outomatic ones when my heads come off. Starters should last a bit longer.

 

I just finished putting in an HD 103 big bore kit with Wood Performance 222 cams. Ran it 75 miles in the break in. Ran great. No issues.
Took it out another day to do some Power Vison tunes, turning off the bike to flash the ecm. With each successive restart, the bike was harder to start.
Reason: I didn't put in compression releases.
Bike is back up on the lift, entire exhaust system is off along with the rocker boxes and heads again. Heads are with a machinist now getting ACRs installed. The starter and battery would need replaced in a very short time based on how much they labored to turn the engine over.


Your results may vary. Past performance cannot predict future results.

 

My evo is 12.5; 1 and I wish it had them. Sucker is harder then a mother to get started.

 

Basically anything over 185 psi ccp, and a larger bore(ring friction)can aggravate things also.
Another thing that can inhibit the intial "roll-over", or "flop" is valve spring pressure.
Scott