<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DLB1994 &raquo;</TD></TR><TR><TD CLASS="quote">you dont see many non-vtec's make 337whp with 313wtq at only 12psi it has to be the comp </TD></TR></TABLE>

yeah i forgot to say: nice #'s, nice setup!

 

I run 10:0:1 in my lsvtec and works good for me.

 

what brand pistons are you guys running. JE , wiseco, arias, CP? most of the all motor click runs WISECO jes wanted to hear what forced Induction people are running.

 

High compression forced induction loads the roads, bearings, rod bolts far greater than low compression higher boost. You are placing the internal components under greater stress, so the likelyhood of bearing/rod failure is greater. Without doing extensive number crunching, the stresses should be at least 5-10% greater. I used to run a 11:1 compression b16a engine turbo'd on pump gas. It was nice off boost, and in boost. It produced alot of torque for the engine displacement, and the powerband was very linear. Dropping down to 9:1 compression range later on with a gsr block, the throttle response was down just a bit. I tuned the engine with some more aggressive timing off boost and most of the response came back. I was able to run higher boost levels on pump gas, and therefore made more torque. From making more torque, more power was produced. The static compression of an engine whether its 9:1 or 11:1 gives the powerband its characteristics among other things. I prefer to let the turbocharger make the power, not the engine as with a higher compression set-up. To me driving on pump gas with the highest amount of detonation-free boost is key, which only a lower compression set-up will yield. In the end both are fast, both have different powerbands and both are fun to drive in their own ways.

 

yup, it all boils down to your preferences, and what you want/can afford... I'm running 9:1 C/r. Off boost throttle response is low, but i've added in as much timing as i feel safe off boost.. once boost hits it hits pretty hard.

a lower static C/r engine theoretically will always outperform a higher C/r engine, because you can extract the heat from the dynamic compresion (boost) with an intercooler, you can't remove heat from the combustion chamber (hence why higher C/r will detonate faster, higher cyl temps) but that's the price you pay for faster turbocharger spool.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">High compression forced induction loads the roads, bearings, rod bolts far greater than low compression higher boost. You are placing the internal components under greater stress, so the likelyhood of bearing/rod failure is greater. Without doing extensive number crunching, the stresses should be at least 5-10% greater. I used to run a 11:1 compression b16a engine turbo'd on pump gas. It was nice off boost, and in boost. It produced alot of torque for the engine displacement, and the powerband was very linear. Dropping down to 9:1 compression range later on with a gsr block, the throttle response was down just a bit. I tuned the engine with some more aggressive timing off boost and most of the response came back. I was able to run higher boost levels on pump gas, and therefore made more torque. From making more torque, more power was produced. The static compression of an engine whether its 9:1 or 11:1 gives the powerband its characteristics among other things. I prefer to let the turbocharger make the power, not the engine as with a higher compression set-up. To me driving on pump gas with the highest amount of detonation-free boost is key, which only a lower compression set-up will yield. In the end both are fast, both have different powerbands and both are fun to drive in their own ways. </TD></TR></TABLE>

your trying to compare a b16 to a b18c sorry thats just something you cant do no matter what the comp is

 

wtf are you talking about?????

anyways.
lots of people run (Say 10:1) with an fmu and blow something up then they say high comp is bad. (which is wrong)
boosted pretty much summed it all up nicely.
lower comp just gives you a bigger window for tuning. It doesnt have to be 100% precise. You can be off a little bit and still be ok.

 

High Compression high boost!!!

 

I have 10.5:1 pistons in an LS block, with a b16a head on there, so Im assuming Im close to 11:1.
I chose to have the block sleeved/bored at stock size, because I knew that I was going to run some big numbers, and more material made sense to me.

As for detonation, I have a 5 gallon water cell for my WAIC, and I might as well hook up something for water injection too. 5 gallons is alot, plus I have a full/empty guage on the resevior. This will take care of my detonation.

so Yes, high compression, High boost. Im hoping to see 20psi on race gas, and judging by the numbers that BoostedHybrid posted....
Tom Payn will be tuning eventually for the full-throttle runs.
AEM EMS w/1680cc injectors ;

 

I would probably run 9.5.1 i figure its not too low and i still have some room for error. I love the power R's make but tuning tuning tuning. I guess its just up to personal preference.

 

Actually you can directly compare both engines if you are looking at how the powerband characteristics change from the stock compression to higher or lower compression ratios. I was simply making the point that higher compression yields greater torque curve, and makes the engine more linear feeling in boost. While the lower compression engine is peakier, and gives that exagerated turbo feeling. I have had all b-series engines and varients in my car at one point, with various compression levels. While each engine is distinctly different by its volumetric efficiency, displacement, compression and cylinder head design they all have a characteristic powerband you can compare to another.

 

But you said it yourself. Why would you want an exagerated boost feeling when you can get the same thing with higher CR. To me like everyone has been saying before it all depends on what you want to do with your motor and the numbers you want to have. But to me 10:1 seems like a good middle ground to start with and then you can decide to go up on down from there depending on the rest of your setup..

I like the idea of having the turbo do most of the work for you though.. Great thread.

 

I have been saying that for the longest time now. 10:1 is perfect for street cars.

 

hehe I really need to come by the shop one of these days just to say hello to you guys and see what new things you are working on...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">High compression forced induction loads the roads, bearings, rod bolts far greater than low compression higher boost. You are placing the internal components under greater stress, so the likelyhood of bearing/rod failure is greater. Without doing extensive number crunching, the stresses should be at least 5-10% greater. I used to run a 11:1 compression b16a engine turbo'd on pump gas. It was nice off boost, and in boost. It produced alot of torque for the engine displacement, and the powerband was very linear. Dropping down to 9:1 compression range later on with a gsr block, the throttle response was down just a bit. I tuned the engine with some more aggressive timing off boost and most of the response came back. I was able to run higher boost levels on pump gas, and therefore made more torque. From making more torque, more power was produced. The static compression of an engine whether its 9:1 or 11:1 gives the powerband its characteristics among other things. I prefer to let the turbocharger make the power, not the engine as with a higher compression set-up. To me driving on pump gas with the highest amount of detonation-free boost is key, which only a lower compression set-up will yield. In the end both are fast, both have different powerbands and both are fun to drive in their own ways. </TD></TR></TABLE>
-----------------------------------------------------------------------------------------------
Very well said and some good points here. Thanks for your help. I was wondering what kind of boost you were runnning on the higher compression setup?

 

To be honest I wouldnt say that it would put more stress perse. Not to take anything away from the beautiful response. But the main factor here is HEAT. Higher CR will give you more heat hence greater change for detonation, preignition, or any other type of failure when compared to lower CR. To say it is under any more stress is mute because I can say that more boost causes more wear on components than less boost..

My 2 cents..

 

Does the Surface area of the piston have a lot to do with this as well??

 

But of course. Surface area changes compression.. But you would have to do your research on what are the benefits of differen designs..

 

Anyone know of any pistons that have the best surface areas for different compressoins of pistons? I am trying to figure out all I can. Thanks....

 

Actually there would be more stress with a higher compression set-up. The cylinder pressure would be greater than a lower compression set-up. Retarding the timing is the normal practice to lower cylinder pressure, but you'll find that higher compression engines will also have a higher cylinder pressure even with reducing timing.

As far as heat is concerned, the higher compression will yield a higher energy (heat) per combustion than a lower compression engine. The higher compression makes the engine more efficient thermodynamically with its heat (energy), so you can spool up a larger turbo or gain spool up time on the exsisting turbocharger. There becomes a point where the compression will pre-ignite no matter how cold of spark plug you run, or how much you reduce the timing. I truely believe that 11:1 is pretty much the limits of what can be done on pump gas, without reducing the timing a massive amount. With my 11:1 compression set-up I ran 8lbs daily on 93 octane with heat range 8 plugs gapped .028". The two biggest things are running colder plugs, and reducing the timing around .75 degrees per pound of boost.

 

Actually there would be more stress with a higher compression set-up. The cylinder pressure would be greater than a lower compression set-up. Retarding the timing is the normal practice to lower cylinder pressure, but you'll find that higher compression engines will also have a higher cylinder pressure even with reducing timing.

As far as heat is concerned, the higher compression will yield a higher energy (heat) per combustion than a lower compression engine. The higher compression makes the engine more efficient thermodynamically with its heat (energy), so you can spool up a larger turbo or gain spool up time on the exsisting turbocharger. There becomes a point where the compression will pre-ignite no matter how cold of spark plug you run, or how much you reduce the timing. I truely believe that 11:1 is pretty much the limits of what can be done on pump gas, without reducing the timing a massive amount. With my 11:1 compression set-up I ran 8lbs daily on 93 octane with heat range 8 plugs gapped .028". The two biggest things are running colder plugs, and reducing the timing around .75 degrees per pound of boost.

 

Great points, so do you truly believe that there is higher pressure from 11:1 @ 8psi compared to 9:1 @ 20psi??

Which would produce more wear on components?

 

When comparing boost pressure vs compression you have to be reasonable to the point of each set-up on pump gas. On pump gas your limit with a decent sized t3/t4oe turbocharger 11:1 is around 8lbs, with 9:1 around 15lbs of boost. On the same engine you'll find that on pump gas the 9:1 compression engine is going to make more power. This occurs since the usually t3/t4oe's become very efficient in the 12-18lbs range, so the you'll be directly in the efficiency range with 15psi. Now, power is work per unit time, and work can be thought of as pressure X area. The 9:1 compression engine is going to have the cylinder pressure higher in boost, therefore with the same area (same bore size on piston) you'll have greater power produced. My point is that if you are running close to the same boost pressures, you'll obviously have far greater cylinder pressure by the higher compression set-up. The power levels will not be the same, the higher compression will yield higher power #'s. This is directly related to higher cylinder pressures, with the whole work analogy. I think we are agreeing to some extent on this subject, but I am not just writing this out sort of weird.

Another very interesting note on the cylinder pressure and higher compression set-ups. By the unversal gas law:

Pressure*Volume=*density*R(gas constant)*Temperature

you'll find that the higher compression engine will yield more power due to the higher heat (temperature) it gives off. So by increasing the heat which the engine produces, you are directly increasing the power capability of the engine. Essentially an internal combustion engine is a glorified heat pump, so if you can increase the heat producing capabilities you'll thermodynamically increase the efficiency of the engine. When efficiency goes up, the power goes up.

 

Yeah I wasnt disagreeing with you perse, just playing devils advocate.. And again you summarize that CR is not the only factor to consider when choosing your turbo setup. Things as the turbo's efficiency range, piston surface, etc has a lot to do with whether your going to be making power efficiently.. Pound for pound higher CR will always yeild more power, but the key is finding your medium so that you balance power with efficiency for whatever you are trying to have your car do be it road racing, auto cross, drag, blah blah blah..

Thanks for the insight.

 

What I would really like to see is all other things left constant like engine size, turbo, and gas... What would the dyno charts look like if the only variable was compression/ boost pressure respectively and how would it affect horsepower/torque..