Higher Compression vs. more boost.

[Avram]

I was wondering about say... upping the compression rather than raising boost.

This is why I was thinking about it: higher compression wouldn't necessitate fuel mods (assuming they are currently adequate) only higher-octane to prevent detonation, right? (maybe timing retard?)… high boost will require both. Higher compression wouldn’t require (read require, it still would benefit from) a larger and/or more efficient intercooler. Also, because the injectors wouldn’t need to work more, they should be fine-- the ECU shouldn’t need to be messed with (although I would think some way to control the AF ratios would still be in the best interests).

And the cost of the pistons vs. the price of a new turbo/intercooler/injectors might just be worth it short term goals. Anyone know the compression the DE pistons would yield?or other alternatives?

Someone please contradict me... or give me examples if this has been done, advantages/disadvantages, etc. I know I’m overlooking something, but this idea was tempting and has been floating around in my head. I know people have said that it’s more efficient to run more boost rather than higher compression for bigger numbers, but it also yields poorer fuel economy, so it seems like an okay trade off to me.

Thanks in advance.

[sapix @ RHIT]

First off, any time you increase power, your using more fuel. This means you need more tuning.

Second, running increases compression with boost requires very accurate tuning.

Third, If you increase compression, increase boost, and get the tuning right, you have the best combination. Generally compression is decreased as boost is increased because of tunability and available fuel, but if you look at a drag car setup, they often run 10:1 compression and 20+ psi of boost. This can be done if the tuning is there. It is an excellent solution, but be prepared to have to tune (possibly stand alone?) when you decide to up the boost. You may even need to lower the boost in the mean time, I'm not really sure.

[Avram]

First off, any time you increase power, your using more fuel. This means you need more tuning.

Except when you increase the efficiency of the process, like increasing compression. If what you say is true, the opposite should also be true, and I could run 4.0:1 compression and get 100 mpg.

Quote »Second, running increases compression with boost requires very accurate tuning.[/quote]Probably, though I have no precedents to judge by.

I have people that can help me with the tuning if it ever comes to that, but I'm basically asking what is wrong of the concept based on money and feasibility or usefulness

[sapix @ RHIT]

Forgot to mention the whole thing about the efficiency rating (4 stroke engines are really inefficient), that makes a big difference, wasn't thinking.

I don't see anything wrong with the concept as long as you have people to help you with tuning, but it will require tuning. Everything should work out well, but its not something that is done often, so be prepared to run into unexpected problems. Might want to ask the question in the technical board, its not really engine specific, so someone in there should be able to answer your question accurately (sp).

[Movingviolation240]

IMHO your just asking for trouble, I've held the DE pistons (9.5-1) and they are pretty weak. I could get you a set of 550cc injectors for $200, no matter what you do you'd have to upgrade the turbo..... so that dosn't count.... and you would require a hell of a lot LESS dyno time if you kept it all stock, did a T3/T4 with a nice FMIC and some 550's.

High compression is great on paper, and on a bigger motor like the KA that's the route I'd take. But when you only have 1.8L of displacement you really need to cram the air into the motor to make it worth doing. Your better off upgradeing everything for high boost (since it's still cheeper than going to the 1.8DE pistons) and making 'real' HP rather than trying to do somthing different with some weak pistons that you may or may not have to replace in 2 weeks time.

High compression turbo motors are a lot of fun, but they require a LOT of tunning to be safe and the theory only works well on larger displacement motors IMHO.

later,

Paul

[alfred183]

Rise from the dead, old thread!!!!

Ok, I want to do high compression CA now... I'm doing S14 T28 BB...I autocross and drift, and for both, lag is death. With a high compression engine, the turbo should be spooled more quickly and the engine itself would be quicker off boost. I think I only need to do 9:1 to get the results I need with the T28 I have. You guys know if there's a piston set I could get to do this? Or will I have to get some custom made?Btw, I know there was talk about how this would work better in a KA, but just look at the Honda guys that run turbo setups with high compression. Those things are mad quick!

[CA19DET]

why not get a supercharger if you want no lag and boost?

[chezina]

I think I only need to do 9:1 to get the results I need with the T28 I have. You guys know if there's a piston set I could get to do this? Or will I have to get some custom made?

You could get a thinner headgasket (there are some metal head gaskets that come in 1.0mm instead of the stock 1.2mm) and shave the head a bit to get that kind of compression ratio.

[float_6969]

If your wanting to increase compression, I think chezina's idea is probabally the best and safest. I also autocross with my car and so we'll see how the turbo lag treats me next year.

[NeedCAforS13]

I'm running 9.5:1 DE pistons... we'll see how that works around winter break when I do my swap (again;))

Sean

[float_6969]

You don't count Sean. You're turboing a DE motor...

[NeedCAforS13]

<---- CHEAPA$S!:D

Sean

[float_6969]

Oh, I thought it was dumba$$ hehehe.

[iliketocrash]

why not get a supercharger if you want no lag and boost?

i agree. if you're so concerned about lag, then why not supercharge?

[float_6969]

The lag really isn't too bad. I was really concerned about it too, and I'm very happy with my motor now.

[Vetal]

Would like to raise this thread once again...So, why do we need to lower compression to run higher boost/power, and do we really need it? Or we can just stay stock 8.5:1?

[Notchbackca]

Its not a simple as you are making it out to be, its not just fuel and timingfor instance, the endyn civic13.44 C/R1.5 liter24lbs of boost92 octane480whpI don't know how well the CA chamber's and pistons are designed as far as knock prevention but if you get your pistons made by someone who knows what they are doing than you can run high CR and plenty of boost and not worry about knock

[Vetal]

for instance, the endyn civic13.44 C/R1.5 liter24lbs of boost92 octane480whp

Unreal i would say :rolleyes

[Notchbackca]

its actually notits all about combustion chamber shapeof course just getting pistons would not allow for such a high CRbut with a full endyn build they ley down a bead and reshape your entire combustion chamberwith a set of endyn pistons you could probably run about 10.5-1 with a fair amount of boost and no knock, tho the old one would need a CA head to design pistons for the engine

[float_6969]

It's all about the $$$

[Notchbackca]

you'd be suprised,a set of pistons from him will run you about 450-550after I make some money this summer I am gonna try and get him to design some CA pistons for high 9 to low 10s CR and have him push the wrist pin up so I can use longer rods that way I can drop my piston speeds significantlywe will see how it all works out tho

[quest]

who is endyn, some magician ?We'd all like to put up good numbers running pump gas but, I dunno why anyone would want to run 13.4:1what are the specs on that turbo ?Lotsa hi hp small motors make no useable torque, with narrow peaky powerbands... their ETs usually stink for their lightweight.

[Vetal]

People always try to fool physics laws I think HKS, Tomei and others long time ago would have designed such pistons and heads that would let us run atmo CR's with 15-20 psi

[Notchbackca]

what physics laws might you be refering to?

Chamber shape is everthing, and its often ignoredthe old one is just the best at what he doesBMW is buying his MINI headback in the day he could add 70whp to mustangs just from porting the headshe has recently built a 2 litre to put out 400Whp natural(can't say which one just yet)he desgined an intake manifold that adds 20whp across the entire powerband, with a peak addition of 40hp(it costs a cool 1500 bucks)he has been doing this stuff for over 40 yearsa full engine build from him costs around 20k(porting internals reworking of the combustion chamber)go check it out yourself http://www.theoldone.comthey are switching over to a new server right now so the site is downthe math involved in what he does is mind boggling

most of the crap that HKS tomei and jun sell is based on appearence, and the stuff that is actually performance has very little understanding of fluid dynamics involved(tomei does make some cool pistons but the top of them is the same a stock ones its just the other features that are cool)

A guy that got a nice fat slice of endyn cake has a B20 in his car that lays ~ 400 on 9lbs of boost, he isn't running as high of compression but its the CR is in the 9s

a little bit of actuall engineering goes a long way

[float_6969]

I'd love to learn about that stuff. I like tinkering with formula's and such. Plus the idea of having an idea of what a change in your car will do befor just doing it is kinda cool too.

[Vetal]

I'm just a bit sceptic about such guys who knows more than Nissan engineers all together. I also am sure that no race commands can make 400hp out of 2.0L high compression engine on pump gas (without revving it to some 10000-12000rpm). So, I'm a bit sceptic when I hear that somebody in his garage made revolution in engine building I'll be happy to be wrong Will check thi site when it's up again

[biosehnsucht]

You can't mass produce the best chamber and piston designs, they have to be carefully crafted.

While the 400HP NA 2litre claim is kinda out there, I wouldn't go so far as to say its flat out IMPOSSIBLE..

[Notchbackca]

just wait and see... when he announces it your jaws will drop... and no it doesn't rev that high...