Nova_Dust

Just wondering what makes an engine rev so high while some can only stop at 7000 or even less? Does it have to do with compression ratio?

imported_gatherer

ECU thats all that stops an engine's revs... carbed engines are alot easier to "over rev" the ECU is programmed with the rev limiter and thats set by the engineers to protect the engine from the G forces seen in the engine by the crank shaft and rods and pistons.... g forces that could blow it all apart

punkindrublic

harmonics within the engine can also blow it up... little vibrations can be deadly over time

Nova_Dust

ECU that controls the rev limit but what parts enable the engine to rev? I mean, if I use a different ECU that has a rev limit of 9000 on my D16, obviously, my block can't take it. So what do I have to do inorder to make it achieve that rev limit? Will a stronger internal make it happen?

Like a B18C-R vs a B18C, one can rev higher than the other, other then the ECU are different, the cams are different, what elses give the B18C-R the ability to rev high?

punkindrublic

type r engines both ctr and itr are signifigantly more resiliant to rpms then there non type r counterparts....

you just gotta make sure the rods and crank can handle the rpms... then make sure everything is balanced...

gcivic

Don't go screwing around your rpms unless you have a lot of cash to build your engine properly and to fix it if it breaks and believe it will, just like racecar engines.

imported_gatherer

ok let me clarify ... yes parts can break if the revs go to high ..... what stops the revs from going to high? the ECU... plain and simple .... a cam will go faster and faster it it shatters and so will the pistons and crank and rods.... all the parts that rotate can eventually gain enough speed to suffer from the harmonics and vibrations and g forces to shatter and break....

what stops this and limits how fast the parts turn? the ECU... there that answers his question the ECU limits the speed of the engin eto keep it within safe specs....

ohhh and heed gcivic's warning it's good advice...

the cam the rocker arms the pistons crankshaft and rods and cylinder side walls and combustion chamber have nothing to do with limiting the speed.... yes hey have a rotational limit before they shatter or break or rip apart.... but what really stops them from going to those limits is the ECU....

to change parts in an engine to with stand a higher rev limit just ask for the specs from the manufacturers... they should be able to tell you .... plus if you know the stroke measurement you can easily calculate the force acting on the rods and piston as the crackshaft turns.

if the crackshaft was the red line limiter we'd all be rebuilding engines evreryday.... it would become a chore....

kwikb16a2

Whats going on here?

imported_gatherer

sometimes people type tired.... it's been fixed

bbarbulo

iTrader: (2)

Hahaha LOL

anyways, bottom end geometry is what determines "safe" operating speeds - the rod to stroke ratio. So the crankshaft, rods, bore, stroke... that determines displacement and ultimately determines rpm. So why can't 4 bangers rev 2x as much as a V8... well, they kinda do! 9000 rpm Honda S2000 vs a 4800 Dodge 5.9 V8 R/T so it's close kinda....

The next thing that determines "safe" operating speed is the valvetrain... so if you start to rev your B16A over the prescribed 8200 rpm, the valves now accelerate enough to counter the force of the valvespring and they start to get some "hang time" in the combuston chamber as the piston is coming up, so if the hang time is long enough and far enough, the piston will bitchslap the valve and either bend it or shatter it - either way NOT GOOD. This is why ppl put in stiffer valve springs, Titanium retainers (cuz the lower mass makes the force after acceleration a little less, so the spring has less work to do slowing it down).

DirtyLude

The max safe rpm a bottom end can handle reliably is determined by a combination of engine geometry, rotating/reciprocating mass, and strength.

Not just total stroke alone determines the stress on the bottom end, but the rod/stroke ratio determines how fast the piston ultimately comes to a stop and starts accelerating again. Total stroke will tell you the average piston speed at a given rpm, but the faster the change in speed, the higher the inertial stress.

The weight of the rotating/reciprocating mass. Obviously a heavier piston/rod, is more difficult to throw around in the engine. A lighter bottom end will give less inertial stress.

Then obviously if you have stronger rods, pistons, crank, etc... the engine can take higher stress without breaking.

Nova_Dust

Thanks for the info. I am not going to modify the D16, but I figure this info is something I need to know if I am going to pursue my interests in cars.

I wondered because Spoon CTR has a peak power of 9900 RPM and can red line to 15000, that's what got me thinking...

bbarbulo

iTrader: (2)

So... motorcycles redline at 12, sometimes 13,000. HP is a function of torque and rpm AT a certain rpm, so small displacement engines can put out lots of hp at high rpm.

There used to be a car called the NSU Prince in the... early to mid 70s I guess, and the redline on that bad boy was over 10,000 rpm STOCK!

Nova_Dust

So D16 can rev higher with stronger internals right?

bbarbulo

iTrader: (2)

yeah, but why? for an extra 20 or 30 hp? That money spent on a snail will get you an extra 70 hp EASY. I'd rather shift at 5000 rpm to prevent wheelspin, plus lower rpm shifting is easier on the synchros.

T-Shirt Ninja

And just to add a pointless fact, r/c car motors, typically around 2.5cc can develop up to 1.5hp and rev up to 35000+ rpm. The smaller you go, the mor revs ya need.

Nova_Dust

Relax B, I was just applying the theory to a D16, not actually going to do so. The current D16 is good enough for me.

bbarbulo

iTrader: (2)

was I not relaxed enough? *calm blue ocean, calm blue ocean* j/k Nova... I was just sayin, no sense in going to an all motor D series when everyone knows two cams are better than one

Nova_Dust

ya I see what you are saying.