stroker crank?
 

hey does anyone know a good place to get a stroker crank, to make the 1.8 into a 2.0? is there a crank from another "B" engine that will fit but has a longer throw? the only place i've seen one is on flying miata, and they want like 3.5k for the rods, pistons, and crank. just wondering if there were any other options.

on another note, how come people lower the compression of their engines when building a turbo motor? i would think that you would want high compression to make more power, and be able to use a smaller turbo so it spools up sooner. but it seems that everyone in the industry builds a low compression engine for turboing. Theres probably something really simple that i'm missing here but i can't really figure it out.

Lower compression prevents detonation...
@ 15psi you add 2x as much air and fuel into the chamber... Don't you guess that it should be lower??
As for stroker cranks... Racing mazda has some too... not as nice as the FM's...

Flyin Miata
Replika Maschinen

as for compression, the trade off for dropping compression is generally always favorable because the amount of boost you can add increases power way more than the loss of compression.

that just doesn't make sense to me. greddymx5 i'm talking like say i wanna make 350hp. if i had a high compression engine i wouldn't need to have 15psi to reach my hp goal.

Y8s- isn't adding a turbo effectively increasing compression anyways? if detionation is your limit how can you run more boost by lowering the compression and end up with more hp?

thanks for the links the the other sites. still wondering though if you could swap in like a "B20" crank into the 1.8 miata motor.

No matter how hard you compress 6psi from a turbo, you still only have 6psi worth of oxygen to burn. Drop the compression down a little bit and get to 12 or 15 or 18psi and you have 2-3x the oxygen to burn even if you aren't squeezing it quite as hard. Less compression and more boost is the way to get power.

If you could swap a B-series crank into the Miata, FM wouldn't have gone through the trouble to have their cranks custom-made.

:confused: What?

Higher compression is always better for power and response.
Lower compression is easier to tune and can run on lower octane fuel.
Trade offs.

A well tuned high compression motor will pull away from a well tuned low compression motor. Assuming both are properly fueled.

I was talking straight out of my ass, but I still don't believe that higher compression is always better. Take superchargers for E46 M3s, for instance. AA and Dinan both keep stock compression, but EVOsport drops it down and makes like 100 more hp.

No arguement


I don't know the first thing about blowing a BMW, but there is more going on than EVO lowering compression to make more power. All other things equal, lower compression means LESS power.

want lower compression ... cheapest way possible. Get a thicker head gasket.

Ben- you said that you can use lower octane fuel. Thats why probably most people run a lower compression engine. how low do you think you can go? how much power can someone running 8:1 CR or 9:1 make? wouldn't lower compression me you could run less timing advance also? if that is the case how come people don't make 7:1 or 6:1 compression ratios? logically if you did that (destroked the engine) wouldn't you be able to run like 12psi without too much timing advance on pump gas? talkin theortically here now...

sucks about the crank, could you imagine how fun it would be to have a cheap 2.0 miata engine?

The toyota supra runs a 8:5:1 CR and they make 1000whp on stock block.

No argument that less compression = less power, but EVOsport is able to CRANK the boost when they dump the compression. Can you explain theoretically why it is better to compress less air harder vs. compressing more air more softly?

cheapest way is to get two head gaskets and stack em.

doesn't sound as reliable as one thick gasket... but whatever floats your boat.

For some reason I remember that the flame propogation gets affected with higher compression because you are affecting the quench point for the cylinder. This has many advantages, but can be really bad when you start to add boost into the mix. Don't quote me, but I think that it has something to do with this.

lower compression + boost = safe power

Higher compression + boost = More power but my homie dangerous gets involved

there is a book called Maximum Boost, read it!!

put 12-1 pistons in youre car then run 15lbs from a t78- for the win.

^ Turbonetics T-106 thumper.

Why i'm sure he can go with a GT55-90

Moldex is the company that makes the stroker crank for FM. They will build you a crank based on that crank or even longer stroke if you want it. FM based their specs on the most stroke without modifications to the block. If you go to a longer stroke, you will have to clearance the block.
The rods can also be purchased from Carrillo, they are 4mm longer than stock. The problem you get into, is that the individual cost of the components is higher than the cost of the kit from FM. AND you know that all of the components work together. Additionally, Moldex will take 6-8 weeks to do your crank, while FM probably has it on the shelf.

As for compression, There is NO doubt that higher compression means MORE power! Pour 70 grains of gunpowder on your table, light it and it will burn, ignite it in a pop bottle and it may produce enough power to rupture the bottle, put the same 70 gr in a high power rifle and you will accelerate a 300 gr projectile to over 2900 feet per sec.

The primary concern as you increase compression is the burn characteristics of the fuel you are using. The slower your fuel burns the higher the compression you can run without detonation. Higher octane fuels burn slower so are more often used in high compression / high boost applications.
Many forced induction alcohol motors are high compression engines but the very slow / cold burn characteristics of alcohol allow such a configuration.

that being said, you CAN boost a high compression engine, AS LONG AS YOU CAN CONTROL DETONATION!

...just my two cents...

Wrong. Higher octane gas burns just as fast as lower octane gas. It's just harder to ignite.

no it actually burns slower .. just a little bit, but slower.

thanks for the crank info, i guess it would be worth it if you were going to tear the block apart for forged internals anyways. i think i'll probably build a system with room to grow if i decide to do the 2.0 crank.

sooooo i'm still not sure on the whole high compression thing. the gunpowder example isn't really great because there is no compression in one and it loaded into a bullet in the other.

there has to be a limit to the ammount the gas from the explosion can expand. assuming detonation isn't a problem, wouldn't the most molecules of gas and air being pushed together in and engine be the best? you aren't compressing them as much but technically you are cause you just raised the atomospheric conditions of the combustion chamber. i mean think of a compression test. you are getting like what 180psi on a high compression engine? (assuming its like normally 150 psi) you could add 30psi of boost and be at the same power level right?

If only it worked that way. remember you fill the intake plenum to 30 psig+ not just the CC the CC is alot smaller and the mass of air flowing in there raises it significantly even in NA form esp around peak torque. you are mistaking static compression for dynamic compression bud static just gives you a ball park dynamic is the real working compression and is pretty damn hard to measure for the shadetree mechanic.

wait a second now, your logic is way off on this one. Think about how each cycle of a piston works (Suck, Squish, Bang, Blow). Now imagine two single piston engines, one with 10:1 CR and the other with 20:1 CR. At The same displacement and at atmospheric pressure, the 20:1 will make more power. Why? because while they may have similar ammounts of fuel being consumed, in the 20:1 it is made to do more work and is closer to using the theoritical maximum potential energy. The ammount of boost needed to make the 10:1 equal the other in power output I do not know, but it is probably close to twice the atmospheric pressure. Following this logic, at the same boost pressure, i would bet that between a 9:1 and 10:1 CR the 10:1 would make about 10% more power. Limiting factor as other have said is knock, and that kills engines and only allows us to produce so much power.

Oh ya and Magna is right about the static compression thing, it goes up quite a bit when the engine is spinning faster.

That have alot to do with the engine's ve I would think.

This is as good a place as any to ask my question.

I have a crank with 3 spun bearings and I'm building my new engine now with 3 options.

#1: Rebuild spun crankshaft (weld/regrind)
#2: Rebuild spun crank and regrind it stroked.
#3: Good used, or new crankshaft.

Option 1 is the cheapest since I can get it done for $75. Although I found a used crank for $40+ship+risk. Option 2 is $100 but I have to have rods made and maybe block work so in the long run that gets expencive but hella braging rights. =) More importantly is how strong is a welded/reground crank compaired to the forged steel oem? I know welded cast cranks are weakened and tend to crack under extreems. Steel cranks are much more forgiving.
Anyone have a CLEAN crankshaft forsale? 1.8L btw.

Savington was not talking out of his ass. He was completely right. The reason it is more effective to lower compression and up boost is because an na with 10:1 compression will make more power than an na car with 9:1 compression. This is not because there is more air in the combustion cycle, but because the gasses are combusted at a higher pressure (compression) which results in higher horsepower with 10:1 than 9:1.
A 9:1 turbo engine with the intake air charge compressed to say 15psi, will although having less static compression than the 10:1 na, make much more power than the na engine. This is because the na engine can only take in so much air per stroke even with max volumetric efficiency. The turbo engine can still take in much more air and therefore although the 9:1 turbo motor statically compresses the air/fuel mixture less than the na will still make much more power. To make a long story short, an na motor can't take enough air in per stroke to make as much power as a turbo motor (in general) even if the na is compressing the air/fuel mixture 10:1 while the turbo is only statically compressing the air/fuel mixture 9:1

p.s. we're comparing relatively close displacement motors here between the na vs fi.

i wouldn't trust a welded crank. but on the other hand i wouldn't really trust anything i weld :)


how did you spin your bearings?

there was someone writing on a thread here that said that you could get a remanfactured crank for 150 with a core charge or something like that. i would probably go that route knowing that your crank will last you a bit instead of streching and breaking in half and completely destroying your block.

i though replikamaschinen f@#$ peoples motors up and thats why FM stopped using them.
Do a search on M.net

doesn't Stoid have one too?

If you are wanting a 2.0L why not just bore out the block instead of stroking it?

I didn't :) I'm building a better engine for my turbo '94 :bigtu:

The engine ($150) with the spun bearings was from a '97 with 75k that didn't get an oil change for 2 years because some ignorant teen owned it. :vash: The abuse took it's toll on 3 of the rod bearings. Mains didn't spin. I have a great starter block and alot of parts and pieces to clean and paint to make this a one day swap since the engine was complete as pulled with all accessories. First thing is to get a nice crank, then pistons and rods and get the bottom end done. Then get the head done or go VVT/VICS. Any opinions on VVT/VICS in a turbo application?

"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites." (c) HowStuffWorks

+1 :bigtu:

who knows. FM says they did. RM says they didn't. cover your OWN ass if you use them?

HAHAHA i'm that teenager, not that one exactaly but i haven't changed the oil in my commuter in like 17,000 miles! the worst thing i did was take an automotive class when my teacher said that oil doesn't go bad just the detergents in it.....its been bad news since.

MIATA KILLER!! :vash: He is right but it's those agents that keep things clean. Once there gone the oil 'burns' quickly. If you put off oil changes then may I suggest you switch to synthetic? :bigtu:

Oil change is a hell of a lot cheaper than an engine rebuild!

yeah i'll probably change it this weekend. its just a pain in the ass! when i drove a 1990 land cruiser i could pretty much reach underneath it and pull the plug, AND the oil filter was actually easy to get too!!

Go buy the oil and filter then take it to a western autoor some other small town shop.
Here locally, if I take the materials, they change it for about 7 bucks. For that, it's not worth me jacking the car up to do it! And I work on cars!

I can reach the plug on mine. Maybe my arms are long. I do the filter from above. It's a 15min job. Ofcorse... if the last filter was cranked on to tight and 2 filter wrenches, a flat blade thru the filter, and a pipe wrench doesn't get it loose then it's a 2 hour job since the manifold bracket has to come off to get at it cause the sending unit is in the way due to turbo cooling lines... -sigh- That was a bad day. :sad2:

The filter is a bitch to get to with big hands, took me the better part of an hour to contort my arms under the intake manifold. In other news: I agree that lower compression makes room for more boost, but while out of boost you better be running nitrous to make up for the power you took away because you can't always be in full boost. Take a look at yadayada's turbo setup, he's running 10:1's and making 230hp at 8psi; true he can't boost as high as 9 or 8:1's can but he still has power out of boost and doesn't have to run as much boost to get the same power as 9:1's do. But as someone has already stated, this is my ass speaking.

haha good point, i totally didn't think of pre-boost. when i get on this site i kinda get tunnel vision.

has anyone run the T3/T4 with 50 trim setup? how did that work out for them. i'm debating on if i should just keep the HP lower, (t25 turbo) or go all out (T3/T4) i'd want the more power and could put up with the lag, but is it worth the time and effort to build up the motor for the t3/t4?

AND is it possible to run low boost with the t3/t4 and still enjoy the car (basically trying to save the stockie parts until i buy the new ones) ?

i need to go do something productive.....

haha had to get the 20th post to be "miataturbo" LEGAL!!

What a great thread.

Surely the whole purpose of lowering compression is to reduce the det threshold?

If you Fi a Miata at 20 psi your gonna have to retard the timing by a fair margin unless you have WI or use high octane fuel.

The result of retarding timing is astronomical EGT's, even retarding my stock timing by 6 degrees from a 14btdc base gives me over 900c EGT's at only 9psi.

Now double your boost and retard your timing even more and your starting to get in engine component melting temps.

Lower the compression though, and hey presto all of a sudden you can start clawing timing advance back in turn steadily watching your EGT's drop.

Until you up the boost again of course :)


Also remember that your MBT will change dramatically depending on your compression and boost.

From what i've seen so far, reaching MBT before det starts occurring is the real balancing act, with boost playing the lead role.

I've never worked on a Miata running over 20psi of boost, but i imagine on the stock compression ratio its virtually impossible to reach MBT before knock starts raising its ugly head.

Anyone running 20psi + on stock compression ratios?
Can you get anywhere near MBT without WI?


Cheers
Mark

EUNOS thanks for the info but it puts up a question i asked in another thread. if you are screwing around with the timing that much, can you set up your turbo to only hit 4 psi and then put it on a switch for 15? evryone was saying that you can with an MBC or multiple MBCs blah blah blah but its not the actual ammount of boost, how would timing be affected for the switch? or would you just tun timing to the high boost level and suffer with a subtuned engine at 4psi?

yeah this thread is good cause its like theortical so every can pitch in.

well it depends on what ignition retard :cjerk: systems you have on the car. Some systems will automatically retard timing if knock starts to occur, so if you have a system like this you can switch back and forth all day and the system will read this change and therefore change your timing...... i think

What he said,

I'm probably not the best bloke to ask as i'm running a SC.

But don't the PRofec E-01 and EMB or EMU work together?
If the EMU could control the boost, then you could switch between timing maps on the front panel.

You'd also need 2 injection maps to switch between as well though, the fuelling needs at 7000rpm at 4psi are a damn sight different to the fuelling needs at 7000rpm at 15psi.


Cheers
Mark

Eliminator77 from the miata.net forum recently posted a 493hp dyno using the 50 trim hybrid. Keep in mind he has done a lot to get to that point and is looking for maximum power.
If you are wanting something that spools fast, his setup might not work for you.
You need to determine your hp goals, then match your turbo to that goal. In general, the more power you want, the more lag you will have to put up with.

As for the stock internals, I have heard of several people running 8-10 psi on otherwise stock engines. If I were you, I would upgrade the injectors so that you minimize the chance of a lean down condition due to fuel starvation under boost.

cool yeah thats like 150 more hp than i was thinkin :) i wanted to be between 300 and 350 with forged internals. i was thinkin the gt28rs but from what i read that maxes out at 320 and with my lead foot i wouldn't want to overstress the turbo. so i'm looking for the next best alternative, thats why i was thinkin the T3/T4. i would upgrade the injectors and stuff, basically i want to make a kit thats detuned for the stock engine while i save up money for the forged goodies that way i can run boost while i'm waiting, and by the time i get sick of only 160 hp i'll be able to swap in a different motor and get twice that!

Get a t3/t4 50 trim with a .43 ar hot side. The small hotside will spool relatively quick at the cost of top end power. Later you can upgrade to a .63 or .82 ar hotside housing for minimal cost, you just unbolt your hotside housing from the chra, bolt the new one one and go. That would probably be your most cost effective solution, and only require buying one turbo.

The advantage: You could use all the same connections, and just change springs in your wastegate and bov when you want to add boost, or use a manual boost control valve.

dude 160 hp are you getting a M45 :gay: go with a 3271 and the 300-350 is doable. with less lag. And remember people it isnt the boost it is the air flow that kills us.

airflow or boost i just wanna make sure i'll have a turbo that can support the level of power i want it to.

Boost is POWER! You increase boost, up to a point of diminishing returns, you create more power!

Airflow is efficiency, The more airflow your engine is capable of, the more power it can make on a given AMOUNT of boost.

A stock engine will produce significantly less power on 8 psi, than a built engine with lower reciprocating mass, larger valves, extensive flow work on the head, etc.
He wants a turbo that is CAPABLE of giving him the power levels he wants, AND still have some room to grow. I still stand by my former suggestion. The 50 trim t3/t4 WILL be a bit more sluggish on his stock engine, but as he adds to his engine, INCREASES the airflow capability of his engine, the turbo will spool faster and make more power in the long run.

cool thanks, yeah i'd probably do a mild port and polish myself, and at least get larger valves. upgrading the cams would be like last on my list of stuff to do. what about the turbo on this site? (the one that retails for 489) http://www.westcoast-turbo.com/turboa.html

Crower will cut you a one-off crank starting at $2400 or a full 4 cyl one off stroker kit for $4000 or 6 Cyl kit for $5500.

http://www.crower.com/cat/stroker.shtml

If they are reputable, that is a hard price to beat! I got mine at cost and still paid more than $500 for it.

racing mazda uses stoid

Yes, with a .48 hot side you can have a very enjoyable T3/T4 at low boost. Even with the .63 hot side at low boost you can have a lot of fun. Is it worth it, oh hell ya, the delay in boost is worth every bit of HP. 300 RWHP is very enlightening and considering that this was happening at 17 PSI of boost, there was a lot left in that T3/T4. It felt VERY solid at 10 PSI of boost although it was late to spool (1st gear spool was 5000 RPM, 3rd gear 4500 RPM, 4th and above was around 4200 RPM spool.)

Mark

Guitar,
I found something you might want to read bfore buying from WestCoast!

http://www.turbod16.com/viewtopic.ph...c772e7021d8ef8