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Thread: Installshield's NA Build

  1. #16
    Gothenburg Superiority Installshield 2's Avatar


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    #2 contd

    So now that stroke changes and the effects are known, there is another equally important aspect of stroke...and particularly, how the length of a connecting rod comes in to all this.

    Any given piston oriented engine has something known as a connecting rod ratio. That ratio is the length of the connecting rods (center of big end to center of little end) in relation to stroke...the FS-DE has 135mm connecting rods, and 92mm of stroke. The rod ratio is Rod Length/Stroke, which gives a ratio of ~1.47. The FP-DE has 129.2mm connecting rods with a stroke of 85mm, giving a ratio of 1.52. Those numbers are not very far apart, but its a very significant difference. Rod ratios range from low 1.4 to only mid 1.7 or so for most production 4 cylinder engines, with anything above 1.65 getting very rare anymore.

    The rod ratio is used to correlate piston acceleration, and for a lot reasons...the math with this gets pretty messy and equally confusing, so i'm just going to skip it for now. Piston acceleration factors in to how quickly a piston reaches the top or bottom of its stroke, how long it 'dwells' there, and how long it takes to leave...These acceleration figures factor into where the engine reaches max ve, similar to MPS (they are closely related)...But while mean piston speed is only used as a general measurement for an engine, piston acceleration is actually the more important piece of data...as its a more precise measurement of the stress these parts are under...high piston acceleration is what will quickly destroy an engine, at least at specific locations...The 'messy' part of acceleration is that it'll be increased at certain thresholds, and decreased at others...so without a bunch of math being thrown around, we can just say longer rods are 'better' for lowering acceleration in areas that we want it lowered...

    The lower the rod ratio, the higher the piston acceleration at reaching and leaving TDC...and the less amount of piston dwell time, in degrees, a piston sits at top dead center...for obvious reasons, a low rod ratio is not ideal for high rpm...and therefor high horsepower...The dwell time is also an important aspect for tuning principles like ignition timing and fuel requirements, as well as cam shaft overlap...

    So to increase the rod ratio for better higher end power and stability...you simply increase the length of the rods.

    Thats the biggest aspect of this build. I'm attacking the rod ratio from both directions in order to increase it (longer rods and less stroke) Using a FP crank in a FS block automatically gives at the very least 7mm extra rod length to work with (just need to source the parts)...but when you factor in running higher compression, location of the wrist pin on the piston skirts, ring location, etc...i'll be able to run even more than that...one thing is certain though, the FP connecting rods will be out the window...They're so short it would take some extremely goofy pistons to make any compression. Even the short FS rods would need some funny pistons too...i'm hoping to run some rods that are 12mm longer than stock, so 147mm total...which yields a ratio of ~1.73...lowering piston acceleration to the point of making 9,000+ rpm not much of an issue...that isn't concrete yet, as i need some measurements of piston to deck level at TDC, which i won't be able to do until i get the new block...

    The only other aspect of the assembly to really touch on would be the compression ratio...and that is straight forward and easy...Compression of an engine just means how tightly it squeezes the intake charge...mechanically its simply how close the piston gets to the top of the block deck (where the head and gasket meat the block) at top dead center...the FS stock is 9:1 (at BDC the empty cylinder space is 9 times the size of TDC)...I'm looking to run around 12:1...Squeezing the charge more, makes it push back harder during ignition...since a lot of the compression stroke is utilizing the inertial mass of the spinning assembly, high compression is an easy way to get a bump in output for basically free...it just puts more emphasis on proper tuning of spark and fuel...as well as gas quality...there is a limit to what streetable compression you can run, and it is directly proportional to how long the pistons dwell...but many production engines run 12:1 or higher stock, with similar rod ratios to what i'll be making...

    That pretty much concludes the principles behind the assembly changes...I'll get going on the head tomorrow most likely...
    Last edited by Installshield 2; 01-28-2013 at 12:37 PM.
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  2. #17
    Gothenburg Superiority Installshield 2's Avatar


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    Quote Originally Posted by hat1018 View Post
    Head spinning a little. I'll read it again later.
    ha no problem man. In the past, especially when the NA side of this car was a little more active...we would get asked the same questions over and over about certain things...the main reason for all that BS is simply so I can link back to it for any newer users that may show up farther along in the build...and it should answer more than they'd want to know...

    And again, anyone only interested in eventually seeing a protege with an engine that revs pretty high...can skip all that and it won't matter...its for those interested in the tech behind it...I could think of a lot of things a lot more fun than reading that, so i won't be offended if everyone skips it haha.
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  3. #18
    Pursuit of HP happiness MakeMeGoFast's Avatar
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    Top notch info as always.

    On a side note I believe it was said that SR20 rods would be a good candidate for longer rods. Not sure of the specs though.

    There was A LOT of good info thrown around the N/A race to 100hp/l thread. It's a bit of a task sifting through the off topic posts though.
    Last edited by MakeMeGoFast; 01-25-2013 at 09:21 AM.

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  4. #19
    Gothenburg Superiority Installshield 2's Avatar


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    ^thanks man,

    yeah i need to go through that again. The Australian's are tremendously helpful with some of the those internal measurements, and i'm looking into SR20 rods too...I was also informed of rods from a particular Mercedes that may be exactly what i need, but not sure on availability yet...I'll keep digging...

    Its a shame we lost Andrew (twilightprotege) through the twiggy thing, he was really pushing his...sucks the way that all went down, and kind of bittersweet that now i'm holding an unused set of those cams almost 6 years later...
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  5. #20
    Uxor Sport23's Avatar
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    Sub!

    Could you do a tech article on static vs. dynamic compression. It will help explain why going from 9:1 to 12:1 compression ratio is not extreme, especially given your cams and cam gears.

    I'll see what I have still have for rod and piston info. I followed a lot of your old posts and was considering swapping an FP crank and sourcing some rods and pistons for my wife's P5. Have you talked to wiseco about getting just the pistons from the FS long rod kit that used to be offered?

    I know what you mean about BNIB twiggy's and focus cam gears being bitter sweet.... one day they'll be installed!
    Last edited by Sport23; 01-24-2013 at 09:16 PM.
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  6. #21
    Gothenburg Superiority Installshield 2's Avatar


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    Yeah, I'll do one for differences with compression measurements...and the cylinder head. As this goes on ill probably go back through and clean them up so it's easier to get only the important info. Consider it unedited for now.

    And as far as wiseco. I've been talking to an engineer there named Mark, who has been helping with the rods and pistons. So far he is saying pistons will be easy, so whatever I come up with he can cut...they just won't be off the shelf, so I'll have to wait a few weeks for them to be made. It's the rods that are goin to be tough...so I'll really get in to looking at that stuff shortly.

    Twiggys are going in tomorrow for a break in period...then pulling the entire engine out and going over everything. Will check valve lifter clearance after break in, and paint the cover plus cut a window for the gears. Will do the vtcs delete and port match, water pump, new timing belt, clutch and flywheel, etc.

    Ill take a lot of pictures during the install, try to have them up tomorrow night or Sunday.
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  7. #22
    Registered Member DOMO's Avatar

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    Nice read I learned a bit from ur posts that's for sure lol. I got a question , since you are gonna go for a higher compression ratio why not use a pistons like the ones in the skyactiv engines since they produce a 14:1 ratio? I'm not sure of the dimensions of the pistons but if they fit Do you think that would be something you could use in your build?

    Also could you explain about how the air fuel ratio and the spark play into the whole hp and trq thing ? Would like to learn more about my car and the inner workings

  8. #23
    Gothenburg Superiority Installshield 2's Avatar


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    ^^ as long as people are interested, i'll discuss anything you guys want...All this stuff is basically what i went to college for (BS in mechanical engineering), so its mostly info i'm familiar with.

    As far as the Skyactiv engines...Most modern engines now use direct injection, which is a newer type of fuel injection that gives better control over the amount of fuel delivered...and more importantly, how its burned...It uses a far higher pressure pump and lines, different injectors entirely, and some radically high resolution fuel management...

    direct injection usually gives the same displacement engine slightly better gas mileage...but also allows the same engine to run some pretty intense compression ratios...The way the fuel is delivered at very high pressure directly into the hot chambers, it instantly aerosolizes (sp?) with the intake charge of air...and gives a very even burn...its also used in conjunction with a computer that can very quickly react to detonation (a common worry of high compression)...

    for those reasons...that high of compression isn't likely to be very friendly on our engines...
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  9. #24
    Registered Member DOMO's Avatar

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    Oic so the 12:1 ratio that you are going for would you call it the sweet spot without doing harm to the engine? Also what kind of design of the piston heads are you gonna go for that would get you to that high compression, as in the sky active engines have like a " volcano" kinda shape to add more compression. So of you use that kind of shape would it a good thing or a more simple flat design would be ideal for your engine?

    I'm new to all this so the more I can learn the better lol

  10. #25
    Gothenburg Superiority Installshield 2's Avatar


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    haven't yet determined piston faces...probably won't utilize anything all that exotic, just for expense purposes...but I'll use close to 'race crowns'...which have the upper compression ring not far from the piston face...that is good for expansion, and makes the expanding flame front immediately build up on the piston...and it also leaves room on the skirts for raising the wrist pins, which helps with balancing...

    the things i just mentioned, especially the race crowns...are not great for handling detonation though, and detonation is just an uneven or poorly timed flame expansion...which i'll go over soon in a 'chemistry of an engine' thing...

    so yeah, you're right...in a way 12:1 is kind of a sweet spot...Increasing the rod ratio also increases piston dwell time...which is great for breathing, but changes requirements on compression (you can't run as much safely, everything else being equal)...as well as ignition timing (you can't advance timing as much with longer dwell times)...So for a 1.73'ish rod ratio, i wouldn't find it fun to babysit the tune for higher compression than that...there would be a lot of factors trying to get the fuel to burn weirdly...it could be done, but not really ideal for driven engine...
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  11. #26
    Registered Member DOMO's Avatar

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    Oic very interesting. So since u said that increasing the bore doesn't really help on these size engines, are you goin to increase the bore on your project block.

    Also since you are increasing the compression does it mean that you have to increase how much fuel goes into the cylinder during the intake stroke ( not sure if that's the right wording or not) ?

  12. #27
    Gothenburg Superiority Installshield 2's Avatar


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    The FS engine itself is actually one of the last production versions of the F series Mazda 4 cylinder designs...There were a few others before the FS, namely the FE...which many regard as one of the very best 4 cylinders Mazda ever made...it just wasn't in very many cars, and was physically very large for such a small displacement...

    the S in FS basically meant 'short'...and it makes sense, as the FS is one of the shortest designs around (from the timing belt to bell housing end)...that makes it pretty light and compact, and easily transversely mounted for FWD...but leaves very little room between cylinders for boring..So yeah, as i said in that tech thing...You simply don't have enough room in there to over bore the cylinders for anything other than a marginal difference in output...I'll probably go with a .050" over-bore, which is still within mazda's service limits for the block...and will make up a handful of cc's to counter the reduction to stroke...I'll basically end up with a roughly 1.9L engine when said and done...

    I don't want to make bore size irrelevant...its a VERY good thing for certain engines, especially when you multiply that increase across a lot of cylinders...but for inline engines, its usually not a realistic place to start looking for more power...

    On the compression side, in terms of fuel requirements...thats tricky, and i'll include that in the chemistry thing i'll do...there is an area of chemistry known as 'stoichiometry', which is related to the ingredients of reactions, the left over byproducts...and more specifically, the balance of reactions...compression does fit in with this, and changes some aspects of the fuel requirements...but not in one easy to understand fashion...high compression can require tons of fuel for cold starts, but then less fuel at rpm ranges that you would think it would need more...its kind of goofy, but we'll get through it...for now, just think of higher compression as needing more attention and more precise control...not necessarily 'more' of anything...
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  13. #28
    Registered Member JaLMP5's Avatar

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    Sub! There's a lot of good info here, thanks for taking the time to share this with everyone on the site.

  14. #29
    Gothenburg Superiority Installshield 2's Avatar


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    Installed the Twiggy's and FocusMSP gears on Saturday...everything dropped in perfectly...

    Its been a while since i've been in a car with bump like this haha. I'll get some sound or video clips up soon. I wanted to get the cams in and get a few hundred miles on them, then check and adjust valve clearance if its needed...and also finish the valve cover, as i didn't cut a window in it yet...or even replace the cover's gasket, which is definitely needed...

    The gears need some attention, adjustment wise, though...It'll start and idle fine...but lifting throttle and letting the revs fall nearly guarantees a stall...these cams have a fixed overlap of 12* at .050" lift...and the stock MP3 computer has a hard time catching the rev decline in time to prevent the stall...when it does catch it, its just bumps at idle perfect...and sounds incredible...but since i don't have much control over idle speed right now, i'll have to dial in that overlap a bit to keep dynamic compression up...its bleeding a lot of pressure off currently...and 4 out of 5 times; i'll lose the idle pulling up to an intersection haha...
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  15. #30
    Registered Member tweety2300's Avatar

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    There is already more usefull information in this one thread than the entire Wikipedia database

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