Need help choosing a compression ratio

[BACARDI_DWB]

Alright guys. I am about to order my custom pistons from wiseco within the next month or so. block is at the machinist and i am thinking about overboring to 86mm vice what i was originally go with just a 84mm. I am really concidering the 86mm to beable to get going a little faster. now where i am stuck at is my compression ratio that i want to run. I want to keep it low since i am basically building this engine as a boost dependant engine. so i am thinking 8.0:1 or a 7.5:1. This would require alot more boost out of the turbo to run the same hp as if i would run 8.5:1 or 9.0:1. i know for sure i do not want to run more than 8.5:1. I already have a GT35R set aside for me, SO i already know i am going to need to run high boost levels to get any sort of good power out of that turbo.

Thoughts?

btw power goals are 500+ hp custom intake is being fab'd up right now. head is at ferrara for larger ports/ valve designrods are pauterexhaust manifold is custom equal length. 44mm external wga.63 ar housingcam specs have not been decided quite yet1000cc injectors will be in the works managed by SDS EM4

what do you guys think?7.8:18.0:18.5:1or something inbetween...

[Swedish Mike]

Alright guys. I am about to order my custom pistons from wiseco within the next month or so. block is at the machinist and i am thinking about overboring to 86mm vice what i was originally go with just a 84mm. I am really concidering the 86mm to beable to get going a little faster. now where i am stuck at is my compression ratio that i want to run. I want to keep it low since i am basically building this engine as a boost dependant engine. so i am thinking 8.0:1 or a 7.5:1. This would require alot more boost out of the turbo to run the same hp as if i would run 8.5:1 or 9.0:1. i know for sure i do not want to run more than 8.5:1. I already have a GT35R set aside for me, SO i already know i am going to need to run high boost levels to get any sort of good power out of that turbo.

Thoughts?

btw power goals are 500+ hp custom intake is being fab'd up right now. head is at ferrara for larger ports/ valve designrods are pauterexhaust manifold is custom equal length. 44mm external wga.63 ar housingcam specs have not been decided quite yet1000cc injectors will be in the works managed by SDS EM4

what do you guys think?7.8:18.0:18.5:1or something inbetween...

8:5, you got both fuel options and the SDS to keep detonation away, the engine will feel much better to drive if you go higher comp.I built a 7.7:1 CA a few years ago, veeery laggy compared to a 8:5 one.Couldn´t feel the difference at high revs but boring when you wanted to drive around in town at low speeds.

[BACARDI_DWB]

my main reason for concidering a lower compression is to not have to worry about detonation around town due to the crappy gas in california. i have had a bad tank of gas before in my neon and it ran like crap (almost broke it) just want to be careful thats all. plus i know some high end engine builders build 800hp engines on low compression daily drivers. you can't even tell that they have 800hp till they get on it.

[nocwage]

Has anyone overbored it that much before?I know it's an iron block but is there the space to add another 3mm per cylinder??

[float_6969]

Why not bump the compression up to 9.5-10:1 and run it on E85? 100-105 octane. I'm working on doing that right now so what I can run more optimal timing. Even with premium I'm only running 5° total timing at 14psi with my AFR's down around 11:1, and I still get some knock now and then. I've added Toluene to the tank and gotten the octane up to about 100 and I was able to run about 15° total timing at 14psi and by my butt-o-meter I picked up an extra 10-20HP. I might have been able to run even more timing, but I was getting low on gas.

Of course if E85 isn't readily available in your area, then ignore everything I've just said....

[davidricardo86]

Why not bump the compression up to 9.5-10:1 and run it on E85? 100-105 octane. I'm working on doing that right now so what I can run more optimal timing. Even with premium I'm only running 5° total timing at 14psi with my AFR's down around 11:1, and I still get some knock now and then. I've added Toluene to the tank and gotten the octane up to about 100 and I was able to run about 15° total timing at 14psi and by my butt-o-meter I picked up an extra 10-20HP. I might have been able to run even more timing, but I was getting low on gas.

Of course if E85 isn't readily available in your area, then ignore everything I've just said....

I can get E85 fairly easy. I have 8.5:1 compression. Can i use it?

[dattodude]

What lift cams are you running?. Got oversize valves? It's all a balance when you start dragging the last few ponies from the stable.

[float_6969]

Well it's a little more complicated than what I just stated, but do your research and you should be all set. I could write for 20 min explaining it all, but I don't want to jack this thread anymore than I have.

[BACARDI_DWB]

yeah low compression is where i want to stay. thinking about 8.3-8.5 now as what sweedish mike was warning me about around town driving.

head is at ferrara for valve sizing.

about having a CA with 86mm pistons here you go:

http://www.hot.ee/nscw/driftking6.jpg86.5mm to be precise. but that could be a fudge so i am going to let my machinist tell me

[Swedish Mike]

yeah low compression is where i want to stay. thinking about 8.3-8.5 now as what sweedish mike was warning me about around town driving.

head is at ferrara for valve sizing.

about having a CA with 86mm pistons here you go:

http://www.hot.ee/nscw/driftking6.jpg86.5mm to be precise. but that could be a fudge so i am going to let my machinist tell me

I´ve tuned a few cars in CA using your 93 octane, no problems there. Not the same engines but 8.5:1 and higher.Used the same settings as our 98 octane and got the same results.My next CA will run at least 9.5:1 and E85, really nice to have that angry bottom torque.

IIRC the Evo´s run 9:1 stock, not sure but I think so.

[BACARDI_DWB]

well i know audi's run 10.1:1 stock on low 6psi of boost and make good horsepower but they also have a better fuel atomization. i am trying to research that now.

[new200guy]

well i know audi's run 10.1:1 stock on low 6psi of boost and make good horsepower but they also have a better fuel atomization. i am trying to research that now.

My euro spec 1997 audi a3 1.8t with 150hp runs a 9.5:1 with a max boost of about 12-13psi. i am pretty sure the head design is a lot better for sure. and 20V does seem to help quite a bit.

[Swedish Mike]

My euro spec 1997 audi a3 1.8t with 150hp runs a 9.5:1 with a max boost of about 12-13psi. i am pretty sure the head design is a lot better for sure. and 20V does seem to help quite a bit.

I´m pretty sure he´s talking about the newer FSI engine, direct injected and high comp ratio.

[BACARDI_DWB]

what do you guys think of this idea. trying to come up with a 8 port manifold (8 injectors also)

getting rid of all stock stuff. going to do a custom plate and yes custom water passage too. what do you guys think of this idea of side by side full 8 port design, no 8-4 like stock.

[Swedish Mike]

I would line them up like the old Audi IMSA manifolds, the had 10 pipes in a row (8 in your case).Would make the manifold thinner and easier if you want to use 8 injectors.

But why not, try it? Cool to see new solutions.

[BACARDI_DWB]

i like the longer idea but if i do it this way i can run a smaller plenum. and since this is going into a datsun 510 small er/compact the better. i don't think i am going to run velocity stacks. (haven't quite decided) either way we will see what space i have in the engine bay when i start fabbing it up.

[dash]

sounds like the motor you're dreamin' about, may be just the beast that "teamnissan" has racked up over 20k street miles on.I'd start with the details of that impressive build.

[BACARDI_DWB]

dash, do you have a link for that beast that you speak of?

[dash]

http://www.yellowmunsontuning.com/PT67CA18.htmsetup looks as 'intense' as any.... may be right up your alley.His email is there and it appears he's got this motor all figured outSome results posted in the 1/4 mile sticky

[BACARDI_DWB]

That is AWESOME. good to see. thanks bud

I have decided to go with 7.8:1 compression ratio. after looking at a whole bunch of turbo'd 4 banger designs, primarily the RS200 ford cosworth design. i decided to go with a lower compression ratio.

[BACARDI_DWB]

damn dash the more i read about his setup the more i am like "damn this guy thinks like i do" haha, we are pretty much going with the same setup but he went with a piggyback and i am going full standalone, and he went with standard 83mm pistons from cp. i am going with an overbore and a knife-edged lightened crank, few different things here and there