Chiburbian

iTrader: (1)

I have been looking for the answer here with the search function but I haven't found the answer I am looking for.

I know that 10:1 is compatible with turbocharging - and that the "trick" is in the tune. However, what do we loose with staying with stock compression and the "proper" tune? What is the gotcha, if there is any?

Conversely, what do you gain/loose with going to 8.5:1 or so as many do?

Noob'tionary:
ABDC = After Bottom Dead Center
SCR = Static Compression Ratio
DCR = Dynamic Compression Ratio
MBT = ?

Jfornachon

iTrader: (23)

By going 8.5:1 you loose the right to say that you are boosting 25psi. With 10:1 you still have better lower end power but you can't max out as much. You will still make power up high, but like you said its all in the tune.

Have a great day,
Jared

Techsalvager

what cams will you use and for the intake side what is valve closing ABDC. You can have a high SCR and still have a low DCR.

jtothawhat

iTrader: (7)

10:1 built motor on E85 should handle as much power and boost as you can throw on it with a better over all powerband.

18psi

iTrader: (76)

10:1 + e85 = win. There is no down side.
10:1 + pump gas = possible but spark advance and boost are limited, and if they're not you better have a damn good tune cause you're leaving very little room for error, and even then you're a bit limited.

Savington

iTrader: (31)

I disagree - the 8.5:1 motor will make more low-end torque than the 10:1 motor will. The 8.5:1 motor can run more timing, and more timing = more torque, end of story. The 10:1 motor might beat it on the top end, but that assumes the 10:1 motor can find MBT at the top - if not, the 8.5:1 will be just as good if not better.

E85 obviously changes the game, but by the time you take advantage of the E85 on even a 2560R, you're well past the limits of the stock shortblock.

fxmd-mx5

key is to keep cylinder pressure down but still make the desired power so i would have to say 10:1-1 is way to go, not saying its better , just using my set up as a reference , and i have a 1.6l making 357/271 for last 4 yrs

nitrodann

Jay what comp are you gonna run on the new setup?

Dann

Full_Tilt_Boogie

iTrader: (1)

Age old debate.

You can certainly run 10:1+ CR on pump gas, people do it all the time. Youll just be more knock limited with the timing. Technically the best setup would be one where you can reach MBT without detonation for whatever gas youre running on, while still maintain as much compression as you can.

Since most turbos will be in their sweet spot with quite a bit of boost, often times fairly low compression will be required to get an optimal ignition map on pump gas, but if it were not for that limitation of the fuel, much high compression would be desirable.
You look at drag cars running very high octane, E85, alcohol, etc and youll see them running 30+ psi of boost on top of 12:1+ CR. On the opposite side of the coin you see people running similar amounts of boost 93 octane with very low CR.

A very good example is the D-series Honda world. A huge number of people have teken to using Suzuki Vitara pistons because of their common bore, slightly shorter compression height, and sizable dish, which allows for ~7:1 CR on a stock length rod. People are running 15, 20, 25+ psi of boost on 93 octane and putting down 400+hp on otherwise stock engines, and some as high as 700 with built heads, all from a 1.6L economy engine.
The point being, nobody was making power this easily back when the piston of choice was a 9:1 CR forged piece.


What it really comes down to is what you want to do. If youre interested in maximum power on pump gas, youre going to be looking at a pretty low CR. If you desire more response and fast spool and are not looking for huge power youre going to want more CR.

jtothawhat

iTrader: (7)

10.5:1 most likely, I still have to get my billet mains and machine work sorted out.

Chiburbian

iTrader: (1)

Great guys thanks. I am considering going e85 - but I need to find out where my local stations in advance.

Say I run E85 and have a target HP goal of 290hp. This on an e85 GT2560... First - is this conservative on e85 on a stock motor? Would it be rational to run dual manual boost control electronically switched to allow me to run pump 93 in a pinch?

If I optimized my tune for e85, how much would I have to turn down the boost/hp levels to make this safe? OR, can Megasquirt be made to compensate the tune automatically?

The assumptions here are daily driver, not for track use, GT2560 (BEGI S4 kit?), Megasquirted with proper sized injectors for e85, stock motor @ 10:1.

curly

iTrader: (25)

I dont think you want two MBCs, you want two .msqs

Chiburbian

iTrader: (1)

But that would require me to keep a computer in the car correct? I guess that isn't too big of a deal, but I like the safety margin that turning the boost down would provide. Am I incorrect in this?

The reason for the two boost settings is to limit the potential for damage. Also it would allow me to turn the boost down in the off chance that I need to loan the car out. I haven't seen (either picture, video, or my own eyes) an in car adjustable boost controller that impressed me. What I am concerned about is repeatability of a setting. I would rather have two boost settings - for example 6 and 12psi than have a dial that isn't calibrated to "exact" psi levels.

curly

iTrader: (25)

Lowering boost is a good idea, but I don't think it'll run correctly if at all by JUST switching boost levels. Maps need to change.

MS3 has switchable maps. Aka: no computer required.

Chiburbian

iTrader: (1)

Ahh ok. That would be ideal.

Doppelgänger

iTrader: (12)

The stock 01+ VVT engines are 10:1....and I'm running 14psi w/2560 on pump with no problems....been doing so for years. When I had an engine failure last year, I was pleasantly surprised to find pretty much no signs on detonation when I pulled the head. To this day the failure is still a mystery and wasn't a catastrophic failure...no holed pistons, no pretzeled rods, no bent valves...it wasn't boost/tune/fuel related.

Once I get my hands on a squaretop IM, I'll be on the dyno and going for 290+rwhp on my stock engine...or whatever I can get from the 2560 at 16-17psi.

nitrodann

This is my current compression on e85. Sweet haha, Thats assuming you know what your doing.

Dann

musanovic

iTrader: (2)

can you share your timing map?
Please
just trying to compare mine and yours.
or you can PM me.

Techsalvager

I want the VVT so I can increase compression out of boost hopfully netting power sooner

shuiend

iTrader: (24)

Off topic, but why do you want a square top manifold so much? Why not do one of the honda manifolds?