superchargers and high compression

[jaybone]

How safe would it be to run a supercharger at no more than 10 psi on a fully built B18C1 2.0L with 11:1 compression? Ive heard you should run low compression when using boost.

[AcidLotus]

You should use low compression when using boost, especially at lower altitudes. I know a guy who had a 12.5:1 N/A LS/VTEC that was pinging at idle with 91 octane at 5800 feet ASL. The price for higher octane gas isn't worth it, and adding boost to it is a recipe for destruction. Lower your compression before considering boost, particularly in the range of 10 PSI.

[wenlyone]

actually, the main reason why most people choose to go low compression for boost is only because it is simpler to do so. lower compression motor just givesyou more margin for error (e.g. little error on setting the a/f ratio). if you know a great tuner, or yourself is a great tuner, a higher compression motor will be a better choice. the truth is, at higher compression, the same motor with the same boost will make more horses than that of the lower compression.

the whole point of this is... if you want a powerful and lasting car, you got to tune and tune until it is perfect. by lowering the compression you can be lazier.. but yet, the car won't be making as much power in boost, and even worse, it will run crappier out of boost.

[jaybone]

Thanks for the feedback guys. My question was based on the issue that I am having an B18C1 built right now and we're sleeving and stroking it to a 2.0L and raising comp to 11:1 among numerous other mods. I plan to run N/A for at least a year and then add direct port N2O. I was just curious if a supercharger might be an option to add to this motor down the road if I start craving boost. Thanks again and keep it comin.

[AcidLotus]

Personally I think the Nitrous is better on the higher compression engines, just that you have to turn the knob to use it and refill it.

[wenlyone]

if you are going to run nitro and boost you will be better off with lower compression than 11:1 even with the perfect tune. The reason is simple. At that compression, the cylinders might not be able to complete the compression stroke with constant time due to the amount of molecules in the cylinders. Or even worse, your cylinder walls can not handle the pressure the power stroke is exerting.

just in case you don't understand what i mean by conpression stroke, i'll briefly explain. our engines are 4 stroke engines. 1. intake stroke = exhaust valve closed, intake valve open; pistons going down pulling air in (in your case letting the compressed air + nitro in to the cylinder) till the Bottom Dead Center (BDC). 2. compression stroke = intake valves closed (remember the exhaust valves are closed too); pistons moving back up to the Top Dead Center (TDC), hense compressing all the air/fuel(/with your nitro) mixture; then when pistons hits TDC the ignition fires the spark plug, boom! in the cylinder. 3. the power stroke = the heat and pressure of the explosion = power that pushes the pistons down from TDC back down to BDC there by turning the crank shaft by the connecting rod. when the piston reaches the BDC, exhaust valve opens. Then the final 4. Exhaust stroke, where by piston goes from BDC back to TDC pushing the burned gas out of the exhaust valve. then the cycle starts all over again.

2nd and 3rd stroke is where you will have the problem if the pistons have to much to compress there by causing the rings to fail or too fast of an explosion causing our famous open deck to crack.

[AcidLotus]

are you talking to me or him? because I have nitrous and boost. However, I merely suggested only nitrous for him, since nitrous tends to favor high compression a bit more than boost does without as much in depth tuning.

[jaybone]

It is going to be sleeved. understand your logic though. I know people do put SCs on stock setup at around 6 psi with their stock 10:1. Thanks for the compression 101 appreciate the feedback

[wenlyone]

ex, i was talking to him, you already know everything i wrote. i don't think i know anything you don't know.

[96gsrvtech]

i had a friend with a jdm gsr motor built with 11:5 (i think, if not around that) with a jackson running 12psi and it was safe and it ran good

[jaybone]

Nice. my motor is gonna be bored to 2.0L and sleeved with forged internals(refer to bottom of sig). Comp raised only from 10:1 to 11:1. I only wanna run like 6-8psi cause im bottlefeeding as well. I would think it would be like supercharging a B18C5 ITR but hell, I will be sleeved. Its long term, just thinkin about the future. Anybody else think I can do it? Thanks

[uoboarder]

I think if you ran 5-6psi on 11:1 with your built engine and a good day of tuning with a Hondata system you might be okay. However, I'd trust your engine to withstand 150 shot all day long more than I would boost.

If its not too late to call the machine shop tell them you want 10:1 JE pistons and then 10psi with a turbo or even a SC would be fine! I'd bet that 10psi, 100 direct shot, at 10:1 CR as long as your well tuned would do fine.

[jaybone]

Thanks man. Very nice civic, hella clean! Props on the kills! So you dont think 11:1, maybe only 5-6psi and 150shot would work? Im doin the build for all motor first, then adding nitrous, then Id like to add a supercharger instead of building another car. Thanks for your input man, hit me back. Anyone else? Thanks

[AcidLotus]

I'd say build the car for boost first, and then add nitrous in small increments later. I still think your compression will be way too high, ductile sleeves or not. If you really want to pursue that, I'd recommend a standalone ECU and/or J&S UltraSafeguard, and probably a progressive nitrous controller like the Mastermind.
You'll probably need huge injectors, and you think that will run on pump gas? Just remember that even if you start off with 11:1 compression, adding boost and/or nitrous increases your effective compression. If you're doing 150 shot + 5-6 lbs of boost, you're probably looking at somewhere near 20:1 effective compression or more (guesstimate). You think 91 octane, ductile sleeves and forged internals will handle that? I'd talk to some more people, I don't see it happening. 150 shot is huge, and the heat inside the compression chamber will probably fry a couple rings, and burn some valves really badly... If you're willing to spend the money to make it near bulletproof, go for it, but I can think of other places I'd much rather spend my cash.

[93solsi/gsr]

You will be ok as long as it is tuned properly, Blownsol from the HV forum has a fully built Type R 11.1 w/ 9 psi and his cars runs good and is very fast, it isn't a daily driver but is driven often.