How come Hondas can make good power with the GT35R boosting only 10-15psi? I thought the effiency range of the GT35R was 25+psi. Evos need to boost up to 30psi to get good power out of it but I always see Hondas with 1.8L-2.0L engines making 400+whp on 10-15psi on pump gas!

I am just trying to understand how they are able to spool up the turbo and make great power with such low boost on the GT35R.

Here is an example of a K20A I-VTEC stock motor with a GT35R

460whp 324wtq IPS Cams @ 15psi - 93 pump gas

515whp 359wtq @18psi - 93 pump and c16 mix

 

they are high compression which they make power with little pounds of boost but not reliable compare to low compresssion and turning up the boost.

 

The efficiency maps are based on boost(pressure ratio) and lbs/min, which is dictated by the flow of the head. In the case of a honda the head flows more so for a given pressure ratio you are further to the right on the map. This may provide some insight to your question.

 

The real answer to your question is many fold. First off, the static compression of the k20a(2)(Z1) is 11.0:1. When you add boost to this motor there is another compression ration called effective compression. For example, this engine(which is a beast) runs 11.0:1 static cr. If you are running 10psi your effective CR is 18.48 :1 @ sea level.

Now, if you were running this same engine with a static CR of 8.8:1(stock 4G63 static CR) with 10psi your effective CR would be 14.79 :1@sea level. You can see there is a major difference in effective cr's between these two static CR set-up. In order to make up for the loss of effective compression when static compression has been lowered, you make it up by raising boost pressures. in order for the 8.8:1 static CR engine to have the same effective CR as the 11.0:1 static CR engine, you would have to run 16.2psi which will net you a effective CR of 18.50 :1.

So, 11.0:1 static CR runs 10psi which nets 18.48:1 effective CR and the 8.8:1 static CR engine has to run 16.2psi to net roughly the same effective CR.

Now that we understand the difference between static and effective compression, lets move on.

The reason why we recommend a static CR decrease when running boost is for many reasons. One being, that it lowers the cylinder temps and pressures and which thus lowers EGT's and allows us to run more ignition timing(due to a higher detonation threshold), which also in turns allows us to run more boost which allows us to increase effective compression even more. When you run a engine with a high static CR, there is usually a limit that you will reach where you cant run any more boost because ignition timing is too retarded, which only adds to the EGT problem. This keeps the detonation threshold low and makes it difficult to extract more power. This is componded even more if you are using a turbo that has a small turbine section and backpressure becomes a problem, thus making matters worse. There are many engines out there that run high static CR's and lots of boost that make lots of power, but the reason why they can do this is because they have the correct setup and very large turbo's with very little backpressure. This allows them to run more ignition timing which keeps EGT's low, and makes more power, also allowing them to run more boost safely. They are also usually running race gas of 110octane or more to help raise the detonation threshold.

ok, not that we have that out of the way, let's discuss the head of the i-VTEC K20. First off, it's a well known fact that this head is one of the best flowing heads ever in stock form for ANY reciprocated, internal combustion engine. This is because of many reason. One being the excellent engineering of the intake and exhaust ports and the valve seats. But the biggest reason is the cams that are involved. The "i" in i-VTEC stands for Intelligent. VTC(Variable Timing Control) is what Honda is reffering to when they added the "i" to VTEC(Variable Timing Electronic lift Control). This is a variable intake cam that can phase the cam angle +/- 25 crank degs on the fly to adapt and adjust for any condition met. Factor this with the large VTEC cam lobes on the high speed cam and you have a very good flowing head that's very complex and is a GREAT head for boosted applications.

The 4G63 head does not feature a variable timing system like the VTEC Honda engines, but since 2006 does have a system similar to the VTC on the Honda engines. IT's called MIVEC. This allows the intake cam to phase like the Honda K-series engines. But because the 4G63 does not have VTEC, the cams can only be built for one specific duty. They can feature a certain lift and duration for peak power or low end torque or whatever Mitsubishi decided, but that setup would be effected throughout the entire rev range. You cannot have the best of both worlds with only one cam setup. Thats what makes the VTEC engines do well with boost especially with aftermarket cams that feature massive high speed cam lobes. This allows the VTEC engine to idle like stock and get stock gas mileage, but in VTEC(on the high speed cam) make lots of power.

There it is in the nutshell.

CJ

 

I think this that has been discussed like 2 weeks back!
No point in discussing over and over again!

 

your right, i already covered it all. lol. i didnt post in the other one, but i covered evrything in this one, so dont worry.

CJ

 

Just like that. My buddy's old b16 civic Si with GT30 @ 7psi = 246whp. Our larger engines at almost triple the boost make roughly the same hp, due to that disparity in compression ratios.

 

Compression ratio's aside, the B16-B18 heads are a fairly good flowing head as well. Although, not as good as the k20A(2)(Z1) head, but good. In my opinion, the b16 head probably flows better than the 4G63 head. I don't believe the 4G63 head is very effecient, which does not suprise me on a turbo charged engine. You see, Honda has to make big power naturally aspirated, so they HAVE to have a good flowing head to achieve this, but this also makes them a very effecient forced induction platform. They really knocked the ball out of the park with the K20 head and bottom end.........thats how they improved upon the proven b-series and killed it.

CJ

 

im confused on what your tryin to say here????? are you sayin that a 4g63 w/ a
gt30 is gonna make "246 awhp" on say 21psi ???? please explain!!!!
waaaaaay off!!!!!

 

He's off on that of course, but at 7psi thru a GT30 we're not going to get anywhere near 250whp... I think that was his point...

 

because they have better engines!!!!!!!
the b seris or k seris vtec head design flows much better than the evo and has a much higher ve.
you can have the same compression, same turbo on a evo and a honda and the honda will always make way more power at the same boost level.

with drive train design and compression ratio a side. honda engine will just always make more power because they have better design more efficeany engines (mainly better head desigh due to vtec)

but we have better cars


the evo would be so much better if it has something like vtec or vvtli. someting with duel cam profiling.
mivec is a joke compared to vtec. mivec is just like hondas I in ivtec. mivec does not have a completely different cam profile on both cams.

the 4g63 head design is just inferior to the head design of a b seris and k seris vtec head.

some how if you can fit a b seris or k seris in a awd evo it would be the perfect car in my eyes.

 

im always quik to remind people when the whole debate of variable valve timing is brought up. this is a little off topic but should be adressed cause its the future! arguing over who has better head/ valve train designs is kindda a waste of time right at this point cause there will be big jumps ie: valvetronic, alittle complicated to explain so search (google) bmw's valvetrain design is so far ahead of ALL of these companies its rediculous! so talkin about who has the better current design is alittle erelevant. its all gonna be old hat in a couple of years (think toyota has something) so lets save it for when the good stuff comes out (imo honda will be on top w the japs) honda is and will always have good head designs as long as there n/a.

 

Not always the case. Most of the time when a Honda enthusiast builds their motor, it sees low compression so you can run more boost and have less risk of detonation.

I agree with that fact that it involves how well the head flows. Honda's Vtec heads are very nice from the factory. Infact, I have seen ITR heads outflow p&p'd heads.

 

Damn! Someone knows their S$%t!

 

Question... If honda engines were better motors, wouldn't they be able to handle 22psi stock, or 30# with headstuds?