Raising the CR + power increase

[Johnnyg]

I'm using a CBR600F4i and i'm int he process of rasing the CR from 12 to 13 by skimming hte head, does any one know how much more extra power this will give me?

[Johnnyg]

I'm using a CBR600F4i and i'm int he process of rasing the CR from 12 to 13 by skimming hte head, does any one know how much more extra power this will give me?

[Ben Beacock]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Johnnyg:
I'm using a CBR600F4i and i'm int he process of rasing the CR from 12 to 13 by skimming hte head, does any one know how much more extra power this will give me? </div></BLOCKQUOTE>

-100% when the valves hit the pistons

[DaveC]

here you go (http://fsae.com/eve/forums/a/tpc/f/125607348/m/39110487821)

[Denny Trimble]

Wiseco sells high-compression pistons for the F4 / F4i.

[osubeaver]

Why waste time with that when you can get 5-10 HP with a Type-R sticker?

[Charlie]

Boy this forum used to be so free of BS.. now 3 of 4 answers are un-informative sarcasm. People who have been here a couple months playing the newbie card- now that's funny!

We went from 12.0:1 to ~13.7:1 in 2004. Sim showed 1 ft-lb across the RPM range. Dyno testing showed roughly that amount, maybe a bit more. Can't remember what HP gain that calculates out to be at the top end.

So there is a small consistent gain there. But you gotta worry about clearances to avoid some serious headaches.

[Denny Trimble]

And, make sure your wrist pin clips are in correctly (http://students.washington.edu/dennyt/fsae/thrown_rod_web/).

[DaveC]

Charlie, you are a saint, I'm afraid many do not have your patience (including me, unfortunately). Forums are the same all over the internet, most have posting suggestions on stickies. This not being one of them, some subjects come up once a week. Compared to some forums this is very polite criticism for someone who posts on a subject that is probably mentioned five times in the first three pages.

Anyway to be helpful, measure your valve/piston clearances and decide on a safe value. You can use clay placed in the valve relief to measure this. There is some disagreement on what is safe, so I wont comment because I dont know what is actually safe for a f4i. I have heard thinner head gaskets are available. If so, Wiseco pistons and a thinner gasket may get you there without shaving the cylinder head or deck surfaces.

One question I havent heard answered on this subject is what peoples experiences have been with valve clearances. Maybe posting what valve clearances you have run, and if it worked or not would be constructive. Besides, stories that start with "when the piston hit the valve..." are always entertaining http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[Chris Davin]

Forgive me for maybe sounding pedantic, but wouldn't you want to understand how much you expect to gain before undertaking a project like this? You'll be able to see if it's worth the effort, and the design judges will be much more impressed if you show them a logical development process as opposed to isolated projects without a common goal.

Since no one has said it yet, here's how to estimate: your expected power at a new compression ratio will be your old power multiplied by the ratio of ideal Otto cycle efficiencies. Any decent thermodynamics text will have that formula.

Good luck.

[osubeaver]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Charlie:
Boy this forum used to be so free of BS.. now 3 of 4 answers are un-informative sarcasm. People who have been here a couple months playing the newbie card- now that's funny!

We went from 12.0:1 to ~13.7:1 in 2004. Sim showed 1 ft-lb across the RPM range. Dyno testing showed roughly that amount, maybe a bit more. Can't remember what HP gain that calculates out to be at the top end.

So there is a small consistent gain there. But you gotta worry about clearances to avoid some serious headaches. </div></BLOCKQUOTE>

Charlie,

Look at the original post:

"I'm using a CBR600F4i and i'm int he process of rasing the CR from 12 to 13 by skimming hte head, does any one know how much more extra power this will give me?"

I hate to say it, but the question "how much extra power will this give me" was asking to be ripped into, as this not a cut and dry issue like "what will happen if I heat water to 100 degrees C at 1 atm pressure". It would have helped a whole lot to just say "For those teams who have raised their compression ratio on their F4i, what kind of power increases have you seen? Can I see your data, etc...".

Johnnyg,

I know it kind of sucks that a bunch of people ripped into your post and I'm sorry I jumped on the bandwagon. However, I think you will get a lot better results if you post your question from a more objective engineering standpoint (this is an engineering forum, after all).

[Chris Boyden]

A local mini sprint engine builder uses a neat trick to measure piston to valve clearances. I've also seen it used for solar thermal stirling engine piston clearance adjustment at Sandia Labs.....so it must be good http://fsae.com/groupee_common/emoticons/icon_wink.gif

Take a length of electrical solder with the spark plug out....put a slight bend in the end, but not so much that you can't put it in the hole. Turn the crank by hand until the piston smashes the solder against the closed valve. Remove the solder and mic it. Not to bash clay...but solder should hold it's dimensions better when you go to measure it.

The engine builder recommended 20 mils of piston to valve clearance after milling/new pistons/decking...whatever. He mentioned that any less clearance is asking for contact. He also mentioned to be careful with oil passages with the aftermarket head gaskets. The thinner version didn't match the original oil port and I believe reduced oiling to the head resulting in cam bearing failure. It might have been the other way around...too much oil to the head which reduced oil to the rest of the engine causing failure/reduced life....etc..something to look out for. Just compare head gaskets and think about what is happening. The duty cycles that mini sprints see are more like 90% at 14k to 15k rpm...so they are a little harder on the engines than FSAE teams.

[Marshall Grice]

where's John Bucknell when you need him? I'm sure he would have a whole bunch of cool eqn's and other interesting tricks like chris' solder trick to add.

[VFR750R]

We use a lightweight test spring on our engines at work. With a dial indicator on the valve, push the valve down until it contacts the piston. You end up measuring total clearence from seated valve to piston with piston at TDC. You can then subtract the lift to get a P to V clearence number. Requires you to have lift values, but then you can check it quickly on every valve on an assembled engine. It also is more accurate.

[mangel83]

Hey Charlie when you guys raised the CR to 13.7:1 I assume you used 100 octane gas... did the engine knock using that fuel?

[Charlie]

No knock, would be suprised if you can get these engines to knock unless the timing was well past MBT.

Sorry guys I was feeling a bit testy I guess... if you think posts are stupid all it takes is no answer. I can understand that. I don't understand why you'd take time to post nonsense. But I digress http://fsae.com/groupee_common/emoticons/icon_wink.gif

[osubeaver]

True indeed. Its pretty tough to get these naturally aspirated restricted bike motors to knock. I have yet to see anyone do it. I don't know about turbos, but i'm not even gonna go there.

[Perry Harrington]

Yeah, the rod to stroke ratio keeps the piston at TDC for such a small time that it greatly benefits anti-knock. It also probably benefits the intake stroke because the piston is on the down stroke so quickly. The "butterfly" chambers have a lot to do with knock as well, providing a pent-roof like chamber with almost no squish area to generate hot spots. Although, you trade swirl, which I believe is then made up for by the low TDC dwell.

--Perry

[VFR750R]

It couldn't just be the low volume to surface area ratio, piston only 2.6 inches across, a centrally located sparkplug, and high tumble assoctiated with a 4 valve head? http://fsae.com/groupee_common/emoticons/icon_wink.gif

Not that I doubt that rod length has an effect on combustion, I just doubt it is the most significant factor of knock in a motorcycle engine. There are many engines out there with an even shorter rod to stroke ratio like the QR25DE Nissan with it's 1.6ratio that doesn't have a measurable gain in knock resistance over simialar sized and performance rated engines.

[John Bucknell]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marshall Grice:
where's John Bucknell when you need him? I'm sure he would have a whole bunch of cool eqn's and other interesting tricks like chris' solder trick to add. </div></BLOCKQUOTE>

Sorry all, life has been more crazy than usual....

How much power is going to depend on several things - but one thing to keep in mind is how much mass are you trapping relative to the engine as originally designed (especially once the restrictor is choked)? The pistons, head gasket, main bearings, etc are all designed for a cylinder pressure generated by an unrestricted engine - and the compression ratio is almost certainly optimized around making power. That is to say, the cylinder pressure at MBT will almost certainly not induce knock on pump gas - while making 110 bhp or so. The amount of compression you can safely add (ignoring valve clash) is a function primarily of octane and cylinder pressure, and some simple thermodynamic equations will give you an idea what the differential in cylinder pressure would be.

The downside of adding compression beyond what the engine was designed for is the combustion chamber (the underside of the head and the piston crown) diverges further and further from the ideal (a perfect sphere). This divergence slows burn rate down (ie you'll need 40 deg of advance, where about 20 is optimum in most cases), and adds heat transfer to the piston (ie it gets hotter and therefore needs better cooling). Eventually, cylinder head designers reduce included valve angle to make the piston crown less 'bumpy' (from cuts in the piston crown for valve clearance) and offset the lost valve diameter by opening up the bore - eventually you have F1 bore-stroke ratios around 3:1.

[Superfast Matt McCoy]

I keep reading about thinner head gaskets for the F4i on the message board, but i can't seem to find any. Where do you find these elusive thin head gaskets?

-Matt

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by SoonerMatt:
I keep reading about thinner head gaskets for the F4i on the message board, but i can't seem to find any. Where do you find these elusive thin head gaskets?

-Matt </div></BLOCKQUOTE>

I can't help you out with the Honda motors, as we run a J-series Kawi. The Kawi's come with the 3 layer head gasket....one 0.10mm layer sandwiched between two 0.25mm layers. We simply remove one of the 0.25mm layers to achieve our desired CR. We've been doing this for a while now, and it is fairly common in the Kawi 600 sportbike racing circles....it's proven to be pretty reliable.

Hope that helps!

[BeaverGuy]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jdstuff:

I can't help you out with the Honda motors, as we run a J-series Kawi. The Kawi's come with the 3 layer head gasket....one 0.10mm layer sandwiched between two 0.25mm layers. We simply remove one of the 0.25mm layers to achieve our desired CR. We've been doing this for a while now, and it is fairly common in the Kawi 600 sportbike racing circles....it's proven to be pretty reliable.

Hope that helps! </div></BLOCKQUOTE>


Have you measured the clearance volume with that modification in order to calculate the new CR? Just a quick hand calc has the new CR at 13.6. Which if right is very close to the 6RR motors.

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BeaverGuy:
...new CR at 13.6.... </div></BLOCKQUOTE>

Josh,

Yep, that's right on. We continue using the J-series motors because we have a pretty good (and cheap) supplier from a local cycle shop. Also, we've been running that particular motor for 5 years now and it is absolutely bulletproof! To this day, we've never blown one up &lt;knock on wood&gt;, which is a lot more than can be said for the days when we ran the F3's.

I noticed at competition that you guys also run a Kawi...I'm assuming that it's a 600RR, which is why you brought it up? In your opinion, are there any major advantages to the RR vs. the R for our application? I haven't really looked into it that much...

[BeaverGuy]

We are still running the J series. However, I have looked at the RR quite a bit. The biggest advantage I can see is the higher compression ratio. There are also some differences in the gearing on the latest versions, first is closer to second. The only other possible advantage I really see with the RR is the availability of a programable factory ECU, it isn't stock but is available.

With the exception of '01 when they seized pistons twice, due to excessive boost from the turbo we haven't blown up any motors.

[Anthony V]

Josh, i have read a lot about the new RR motor too. mainly because im big into sportbikes as well. a few other things to note is that the pistons and combustion chambers were significantly changed in 04 vs 03. the valves were sized differently as well (cant remember whether it was intake or exhaust). and then the whole motor got a slight work over again in 05.

Anyways, my thoughts are this with regard to the 6rr motors (and any newer motor for that matter). The way 600cc sportbike development has been going, the performance range of the motors keeps getting pushed into higher and higher rpm ranges because everyone is chasing after huge HP numbers which can be useful on an open race track (where these bikes play and compete). However, given the types of courses we run in FSAE, and especially the fact that we are forced to run a restrictor, reving our motors to the moon doesnt do much good. a definite advantage of the newer motors is weight. however, i dont see it outweighing where the useable power of the engine is. haha, i think Stuff has heard me talk about his before. Anyways, your thoughts???

Now, if you got custom cam grinds on one of those new motors to move the power down in the rpm range where we are not being murdered by the restrictor as bad it could be a different story...but thats a whole 'nother can of worms i dont have time for this year.

[Anthony V]

on a similar note with regard to where certain motors make their power...I'm pretty sure Cornell doesnt run a YZF600R in their torque monsters for nothing. Someone there knew a little something about the lineage of 600cc sportbikes.

Hint: I have seen stock torque and HP curves of a YZF600R vs YZF-R6 overlayed. Guess what? The 600R walks all over the R6 till about 8 or 9 grand if i remember correctly. I'll have to see if I still have that article. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[BeaverGuy]

I completely agree about the design of the newer motors being less and less suitable for FSAE. I was on the Kawi website last night and their peak torque for the '06 is 50 ft-lbs at 12 kRP. I don't think an engine with those natural dynamics would be too suitable to FSAE.

There has been talk around our team about switching engines. I don't see any reason to do it and newer motor wouldn't be at the top of my list because they rev so high and only the 6RR has a higher compression ratio than our current engine. Most of these engines have a bore to stroke ratio of about 1.5 which will tend to make them high reving engines. However, the FZR600 from 99 has a bore to stroke ratio of 1.1 and the YZF600 are at 1.25. If I was to select a different 600 4 cyl it would probably be a YZF or FZR though I would also look at things the Katana and F2/F3 engines because they are meant to be run at lower engine speeds than the newer bikes.