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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 04-09-2007, 03:11 PM   #21
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Originally Posted by guitarrc6 View Post
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.
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...
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Old 04-09-2007, 05:44 PM   #22
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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.
Wrong. Higher octane gas burns just as fast as lower octane gas. It's just harder to ignite.
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Old 04-09-2007, 06:04 PM   #23
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no it actually burns slower .. just a little bit, but slower.
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Old 04-09-2007, 10:20 PM   #24
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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?
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Old 04-09-2007, 10:32 PM   #25
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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.
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Old 04-09-2007, 10:46 PM   #26
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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.
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Old 04-09-2007, 11:42 PM   #27
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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.
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Old 04-09-2007, 11:50 PM   #28
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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.
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Old 04-10-2007, 12:36 AM   #29
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Savington was not talking out of his ***. 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.
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Old 04-10-2007, 02:33 AM   #30
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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.
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Old 04-10-2007, 02:51 AM   #31
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i though replikamaschinen [email protected]#$ peoples motors up and thats why FM stopped using them.
Do a search on M.net

doesn't Stoid have one too?
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Old 04-10-2007, 03:23 AM   #32
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If you are wanting a 2.0L why not just bore out the block instead of stroking it?
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Old 04-10-2007, 06:08 AM   #33
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Originally Posted by guitarrc6 View Post
how did you spin your bearings?
I didn't I'm building a better engine for my turbo '94

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. 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?
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Old 04-10-2007, 06:14 AM   #34
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Wrong. Higher octane gas burns just as fast as lower octane gas. It's just harder to ignite.
"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites." (c) HowStuffWorks

+1
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Old 04-10-2007, 11:36 AM   #35
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i though replikamaschinen [email protected]#$ peoples motors up and thats why FM stopped using them.
Do a search on M.net

doesn't Stoid have one too?
who knows. FM says they did. RM says they didn't. cover your OWN *** if you use them?
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Old 04-10-2007, 05:16 PM   #36
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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.
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Old 04-10-2007, 05:36 PM   #37
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Originally Posted by guitarrc6 View Post
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!! 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?
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Old 04-10-2007, 05:52 PM   #38
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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.
Oil change is a hell of a lot cheaper than an engine rebuild!
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Old 04-10-2007, 06:37 PM   #39
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yeah i'll probably change it this weekend. its just a pain in the ***! 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!!
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Old 04-10-2007, 06:41 PM   #40
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yeah i'll probably change it this weekend. its just a pain in the ***! 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!
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