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Discussion Starter #1
So...............can we finalise the debate on whether high compression is a good thing or not.

How do you run good power with high compression as the theory/fact is you cant run lots of boost due to det.

I have slightly high compression and have a similar setup to kismet, yet I could not get anywhere near 1.9 bar:runaway:

If you cannot possibly run higher boost levels because of high compression then what is the BEST way to lower the compression....thicker gasket?


Someone stated this on the forum before:
with higher compression you get bigger power from each burn in the cylinder. The higher the compression the more difficult it is to control det so a common route seems to be lower the compression ratio to allow a bit more boost to be run.

Naturally this affects off boost performance, the decision is then up to the owner/tuner as to how much of a problem this is.
 

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Cam choice and timing make a huge difference to dynamic compression ratio which is arguably considerably more important than static compression ratio.

I'm not being RB specific here, I don't have a clue about the RB, but it applies to every other engine.

http://www.motorsport-developments.co.uk/stus.html

Some excellent articles in the above link. I have no connection to MSD, but the articles are good and cover cams and compression nicely.

John B Heywood Fundamentals of Internal Combustion is good too if you want a deeper analysis.
 

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im very interested in this thread as i have been thinking about it for the past few days.

some people seem to talk about the removal of squish pads which lowers compression however some say that this is not good practice, im not entirely sure why! views?

kev:thumbsup:

(i hope you dont think im hijacking the thread,:D i just think were kind of searching for the same answer)


some good reading material there thiste thanks for sharing, im thinking about doing motorsport technology next year so will help no end im sure.
 

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Depending on what the car is for. Higher compression is good as it increases throttle response,economy and bhp per psi of boost as stated by Corky Bell. Im sure if you wanted to run higher boost you could always use water/alcohol injection. Also making sure your intercooler is correctly sized so it is working at its optimal efficiency.
 

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Discussion Starter #5
So your intercooler should not be too big?

Does anyone agree that high compression is a good thing even though it limits the boost you can safely run?

Water/alcohol injection allows you to run more boost safely in this scenario then. Anyone confirm this?

I have a similar setup to alot of people running 600bhp on here forged bottom end (n1 block) 87mm pistons, head has been ported flowed hks cams in and out. I guess I just want more boost on my -5's without detonation.

Ive actually had one tuner say high compression wasnt good and one tuner telling me it was better. I'm talking around .75.
 

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So your intercooler should not be too big?

Does anyone agree that high compression is a good thing even though it limits the boost you can safely run?

Water/alcohol injection allows you to run more boost safely in this scenario then. Anyone confirm this?

I have a similar setup to alot of people running 600bhp on here forged bottom end (n1 block) 87mm pistons, head has been ported flowed hks cams in and out. I guess I just want more boost on my -5's without detonation.

Ive actually had one tuner say high compression wasnt good and one tuner telling me it was better. I'm talking around .75.
yes high compression + high boost is always better.. but you need to cool the air comming in.. water air intercooler... or some crazy subzero method would be better...... dunno the water's specific heat resistance but ive heard that if you inject water alone you can really run massive amount of boost ...


the tuner saying high comp is bad .. is not right nor wrong.... he's right in the sense that if when the air is compressed by the piston is too hot and ignite the fuel before the right time then kaboom... but its possible to hyper cool the air comming in... one day someone will try a couple of things.. and prove my statement that high compression at upward of 10 and boost upward of 30 psi is possible if the air is cooled bellow zero ....



will it be complicated??? of course... the only 2 method i know of would have to be either for dyno testing.. LN2... or build a modified air conditioner system that coold a liquid tank that feeds liquid to the water/air intercooler.. its all theorie at one point but its been proven to some extent ..... why would some guy put ice water in his water/air intercooler or even dry ice for a fact if the concept is not working????

please add your point of view guys if you think there's a small possibility that my theorie might even be doable and profitable
 

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How high is "slightly high compression"?
 

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Some 4G63 happily run >10:1 static CR with >2 bar boost with E85.

Some direct injection petrol engine run >10:1 and tolerate fairly high boost levels.
 

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the trick with gasoline direct injection is that the fuel can be added just before the piston reach tdc or comes close to it.. there's lots of info id like to learn about gdi if anyone have any link would be apreciated
 

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Discussion Starter #11
Rob. I'm running approx 1.75, but this still does not seem to give me the capability to run the -5's to their full potential.

Is water injection the answer then?

What makes you have high compression, too thinner gasket?
 

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I'm running approx 1.75. 1.75 what? Higher compression pistons. If you dont have these I wouldnt worry. What is your static compression ratio or what have you done to raise your compression.
 

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Discussion Starter #13
175psi across all cylinders. Pistons are pretty standard 87mm coated wiseco (forged).

The engine build was done this way and thats all the info I can ascertain at the moment.

I'd like to find out more about being able to increase boost safely with this higher compression. Water injection..toulene............or should one try to go with the majority and reduce the compression by putting in a thicker gasket?

I'm only running just under 1.4 bar.........would love to get to 1.8bar.:clap::thumbsup:
 

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I dont see why you couldnt up the boost. Your only 4psi higher than standard. Just make sure it gets tuned properly.
 

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175psi is not your compression ratio, its just a psi reading from a compression test.

Alot of things can effect the psi reading you get such as engine temp, throttle position while doing the test, compression ratio, engine condition, type of engine oil etc.

All you need to do is chose the fuel you want to use and have it mapped to suit that fuel while keeping an ear out for det etc.

Once on the dyno with the correct equipment hooked up a good mapper will easily be able to tune and increase boost to find a safe level for you and it may well be over 1.8 bar depending on the fuel you use.

Rob
 

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Rob. I'm running approx 1.75, but this still does not seem to give me the capability to run the -5's to their full potential.
Thats one of the funniest things I have ever read from someone asking a technical question about a highly technical subject...........who clearly doesnt understand the very first thing anyone replying is talking about !!

You might as well be Jeremy Clarkson saying torques are "that much" holding your hands a foot apart !!! pmsl

This debate will never have a definitive answer as there are always pros and cons for everything in life, especially considering the use you wish to apply them to.........are singles or twins better, 2.6 or RB30, 4wd or RWD, road use, drag use, track use etc etc

The simple asnwer is...

Find a tuner you trust
Agree a spec with them based on what you want power and drive wise
Let them do the tech as thats what you are paying for - their experience

Pay your bill, drive your car, happy in the knowledge that you have a nice motor. Dont sit on internet forums worrying that you havent got this CR or that spark plug etc etc as frankly thats all just bollox !!

J.
 

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Alot of it is as broad as it is long, but I have been reading on this forum trying to find a difinitive answer on whether higher compression is good or bad. What I have learnt over the past few years is IT IS better to ask questions on here, rather than take one tuners/persons opinion.

Its funny that........I asked a question, because I did not know the answer even after searching back several years on this forum. ????

Someones response: Higher compression is good as it increases throttle response,economy and bhp per psi of boost as stated by Corky Bell. Im sure if you wanted to run higher boost you could always use water/alcohol injection. Also making sure your intercooler is correctly sized so it is working at its optimal efficiency.

Now even with my limited techy brain:D , I find that very comprehendable and like learning these things out from more experienced/knowledgeable people in this field.

I can also gain a majority opinion which is rarely wrong.

What I seem to understand less is that if higher compression gives these benefits why do majority then all run the same known standard psi levels?

This thread can also cover the topic of the squish pad removal which was covered a bit more on a long thread years ago. There was a lot of debate on the subject but I agree that could come down to what level of tune you are looking for ......more so in this scenario (squish pads), as I think it was stated that only very high hp cars should remove/part remove them.

J, I put 101% trust in to one tuner on the south coast before and he proved to be a total ****. Other users who have 1000+ horses that used him years ago all got screwed too as they gave money up front and he could never account for it. Its just a pity they never post it up on here......but thats old news. £22k+ with a negative experience is enough to make me ask questions to gain the knowledge I need, before I trust anyone ....thanks.

Oh and I thought thats what a forum is for.:thumbsup:
 

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Mel, your compression ratio will be dependent on many things, for example; the thickness of head gasket used; any material removed from the head in the in cylinder area as part of a gas flow process; what pistons you have (as in crown profile and thus CR); cam profiles, perhaps what capacity you are running and how, etc.

I would guess you will be around 8:1, it might be less (unlikely) or possibly more, but not a lot more, below 8.5 say. You can measure it!

Increased CR delivers 'positive' results across the rev range through higher power (torque). So in that sense its beneficial. However, if you run (relatively) high CR on a turbo engine running high boost (2+) this increases incylinder pressures, propencity for det, and a whole host of other things. Some of this can be 'managed' through high octane fuel (Tol or Xyl is good) which is det avert, and/or water or water+meth injection. This controls the det element, but if you push the cylinder pressures too high you will blow a gasket or lift the head, which you do not want to do!

As has been pointed out, the intended use dictates much. If you want max power (800+) derived through substantial boost then you need to be near 8 on quality fuel and/or WI. If its user friendly road use, then don't chase big boost, stay lower and run the higher CR as this will give you bottom end/mid-range at the cost of max. The compromise is probably run 8.X, pump fuel, add WI and limit to max 1.8Bar, that should deliver more than enough at the wheels for you with decent bottom/mid-range.

DaveG
 

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Discussion Starter #19
Thanks Dave

I knew that all along!!:D



Thats brilliant, I've got more of an understanding now and that gives me something to think about.

:thumbsup:
 

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wow dave a great post there.:thumbsup:

kev
 
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