If your turbo goes out you will not have a quick car, you will be towing it.

 

it's true that all motors are different, and also true that a low c.r. is safer for boost... but, could it be possible that honda engines make more power with more compression than ford or porsche?... considering also that porsche engines are a completely different design? Can someone prove that what danimal is saying is relevant to hondas?

 

Dont look at it like that, rather think of it of factory turbo vs aftermarket turbo.
factories need to have a warranty, if they ran high CR's and people put in crap fuel and turn up the boost a little bit, then bye bye engine, and the customer would want the factory to carry the cost. So in that respect it is safer for them to go with cr's that are a bit low. normally they go for 8:1 or 7.8:1 there abouts, this is abit too safe for me, I think from 8.8 to 9.5:1 is the best compromise.

For an all out drag racecar, go 7.5 to 8:1 and boost that **** all the way!!
This is simply cause of traction issues, look at the dyno sheets on posted here, and you will see what the curves look like.

Cheers

 

Im running a 8:1 cr on my d16 iwth a greddy kit. it feels slow under normal driving but once boost creeps up, people dont know what hit them. Running 91 octane, Chevron Supreme.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danimal &raquo;</TD></TR><TR><TD CLASS="quote">
the problem with boost comparisons is that boost #'s are pretty meaningless, because it's a measurement of resistance to flow... it's kind of the opposite of what you really want, which is boost volume.
</TD></TR></TABLE>


DANIMAL I normally don't agree with anything you ever say on this topic, but this statement is the first thing I agree with, but here's the deal. An engine with high compression can pump more air than an engine with low compression. Allowing you to run much less boost, and spool that larger turbo very effectively.

I also know there are ways to keep the power with-out pulling drastic timing from the top. Keeping the charge cooler is one, but most people are still working with FMIC's still. Until that day when everyone catches up you will be everyone's source.

Where did you get this Thermo eff. of Gasolines?

 

Higher compression will spool the turbo faster, but ultimate power will be reduced. I personally think medium compression(9:1) and boost is the best combo for us mortals

High compression will not pump more air than low compression, but it will have higher thermal efficiency than the low compression engine. Thermal efficiency = more torque in layman's term. Gains are logarithmic. More compression yields less and less thermal efficiency until you hit about 17:1. Then there is theoretically no more to be gained from gasoline.

Personally I don't think breaking the theoretical max limits power in anyway. TE is a measure of power per unit of fuel. You may max out TE, but you can boost until it blows up from detonation

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">Higher compression will spool the turbo faster, but ultimate power will be reduced. I personally think medium compression(9:1) and boost is the best combo for us mortals

1High compression will not pump more air than low compression, but it will have higher thermal efficiency than the low compression engine. Thermal efficiency = more torque in layman's term. Gains are logarithmic.2 More compression yields less and less thermal efficiency until you hit about 17:1. Then there is theoretically no more to be gained from gasoline.

3Personally I don't think breaking the theoretical max limits power in anyway. TE is a measure of power per unit of fuel. You may max out TE, but you can boost until it blows up from detonation </TD></TR></TABLE>


1 High compression provides greater pressure changes inside the cylinder when the piston goes on the intake stroke, and the valve opens. This greater pressure change in turn translate's into more air being pulled in. If more air is pulled in there then more air is being pumped. Relying on the turbo to do the work is thinking like there are no pistons. TE only explains the heat to power ratio's. In other words the point of diminishing returns. Unfortunately, there's a lot more involved in the engine than thermodynamics. Fluid control, and flow are the biggest part. Yeah, I took thermo too, but I'm also aware it's not the end all to everything. Try using your physic's classes, too.
2 I know this, but I'm trying to figure out where this guy found this law defining method to figure out that the fuel itself can't handle more than that. If this was true then these turbo cars I see putting out over 400HP with like 20psi on 8:1 compression shouldn't be able to do this because that's over the 17:1 limit where gasoline is supposed to just detonate.(I had this arguement with him before, and I didn't see any proof to this.) I know that it's possible to push it if you stack your numbers in your favor. I won't say anymore on this because I'd rather not be burned on a cross like a witch. People that haven't tried other things tend to be biased.
3 This is confusing I think I know what you are trying to say, but the first sentence contradicts the rest of the statement.


edit: I spell like a mute guy speaks.

 

bahhhh!!.... you guys are confusing! everyone has their own opinion...

 

danimal,

I ahve seen you post this before, yet it totally ignores alot of facts by oversimplifying the tunign process. The ingnition timing that they were runnign in those tests were so far out of whack that it makes me choke laughing. 32 deg of advance on a 10.3 CR engine running 23 psi. LOL. no wonder they couldnt add boost without knock. then they build a 6.8 CR motor and only add 3 deg more timing? something there doesnt add up. hell on 8.5:1 SR's I only run 21-22 deg @ 23 psi on a similar fuel. thye were way to agressive on their timing. furthermore this "article" completely ignores differences in cylinder head and block design. Honda engines have no probelm running at 12.0 + CR's NA on pump gas. i have never seen any ford engiens from that era acomplish such feats. you cant just assume that becasue it wont work on a particular application that it wont work in general. those SVO motors are crap. If you start with old school engiens you are goign to have to use old school tuning methods to make power. if you start with a better platform you can push the limits alot farther.

I'm building a 10.5:1 RWD SR and lookign for 600 whp @ 26 psi on VPNOS fuel. i'll keep you all posted.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nd_styles &raquo;</TD></TR><TR><TD CLASS="quote">
1 High compression provides greater pressure changes inside the cylinder when the piston goes on the intake stroke, and the valve opens. This greater pressure change in turn translate's into more air being pulled in. If more air is pulled in there then more air is being pumped. Relying on the turbo to do the work is thinking like there are no pistons. </TD></TR></TABLE>

Agreed, but you can't forget that you are turning up the boost with the lower compression so just as much air will get in the cylinders. I think the problem with too high of CR motors is they don't get enough pressure thought the power stroke, they just get a high peak cylinder pressure,but once that 12:1 compression motor is half way through its stroke there isn't much pressure in the cylinder as compared to a 8:1 compression motor that has more fuel and more air in each cylinder. A little math for you, lets say your peak cylinder pressure is 1000PSI on a 12:1 motor, half way through its stroke it'll be @ 166PSI, on a 8:1 CR motor that has a peak cylinder pressure of 1000PSI half way through its stroke it'll be @250 PSI. point: i like low CR for FI apps. any counter arguments?

 

Look at it from a different view, say the ultimate safe peak cylinder pressure is 1500psi, which one would make more power, a 9:1 @ 28psi, or a 11:1 @ 18psi?

My money is on th 9:1

 

Most naturally aspirated engines require between 30 and 38 degress of ignition advance to achieve PCP at the correct crank pin position to make maximum power. By compressing the mixture through turbocharging, the rate of flame front progression increases and slightly less ignition advance is required to achieve PCP at the correct moment. In most cases, less than 5 degrees of retard is required however. We see many people throwing in 15 to 25 degrees of retard in a vain attempt to stop detonation at very high boost pressures for the fuel and compression ratios that they are running. It should be stressed that there are no free rides here. If you plan to achieve high specific outputs on low octane pump fuels for extended periods, you WILL have to reduce the CR. Truly high specific outputs are only available when using high octane fuels or by injecting anti-detonants. There are sound scientific reasons why there are no factory 10 to 1 CR turbocharged engines which produce specific outputs of 175 hp/L. In fact, there is NO production, piston, automotive engine which I am aware of which can achieve a specific output of this level on 92 octane pump fuel anywhere. Despite this fact, many people try to do this with expensive results. High compression ratios and high boost simply don't mix on pump fuel. If you try this, you will either be unhappy with the results or blow up the engine. When I say production engine, I mean one that you can buy off the showroom floor, no modifications, with the factory warranty intact. HP to be tested on a proper engine dyno, not on a chassis dyno with phantom flywheel correction factors applied. If Toyota, Honda or Ford could do this with factory reliability, don't you think that they would? As discussed in some of the reference articles above, set reasonable hp goals and modify the internal components as required to obtain these levels reliably. Be aware that many Japanese spec engines are designed to run on 98-102 octane fuel in their home markets. These engines will not be able to run the same boost levels on North American 92 octane fuel. Expect lots of detonation or spark retard if you attempt this.

Quote from http://www.sdsefi.com/meltdown.htm

 

The way the Japanese and the United States rates fuel octane’s are completely different. The US averages the RON and MON methods, while the Japanese utilize just one method (forget which one). The Japanese method drastically inflates the octane value as compared to what we are used to.

What happens when you place the piston lower in the cylinder? The first thing people usually say is that it reduces compression. This is correct. Another way to look at it is to say "you have just increased the volume of air that can fit in the combustion chamber at bottom dead center". With the extra volume you can first get more air and fuel in the cylinder at the same pressure levels. To make up for lost compression (IE: lost thermodynamic efficiency) you raise the boost levels.

Turbo charging does not increase cylinder pressures as much as it does increase the amount of time the burn takes. Thus, you can increase power by pushing LONGER on the piston instead of pushing harder (such as N2O).

Don't confuse burn time with the volatility of the mixture. You need less spark lead typically under boost in a high boost turbocharged engine as the mixture propagates quickly and you don't want to be doing negative work by pushing a piston down that hasn't reached TDC yet.

However, once the burn starts it keeps burning strongly through the point of maximum mechanical advantage of 90 degrees after TDC.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danl &raquo;</TD></TR><TR><TD CLASS="quote">The way the Japanese and the United States rates fuel octane’s are completely different. The US averages the RON and MON methods, while the Japanese utilize just one method (forget which one). The Japanese method drastically inflates the octane value as compared to what we are used to.
</TD></TR></TABLE>

Just to clarify, the japanese use RON, we use (RON + MON)/2. I wouldn't exactly say it drastically changes the octane. The most i've seen RON and MON differ is 7 points, which is on race gas, which would mean only a 3.5 point difference between the US and japanese #'s.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyphear &raquo;</TD></TR><TR><TD CLASS="quote">

Agreed, but you can't forget that you are turning up the boost with the lower compression so just as much air will get in the cylinders. I think the problem with too high of CR motors is they don't get enough pressure thought the power stroke, they just get a high peak cylinder pressure,but once that 12:1 compression motor is half way through its stroke there isn't much pressure in the cylinder as compared to a 8:1 compression motor that has more fuel and more air in each cylinder. A little math for you, lets say your peak cylinder pressure is 1000PSI on a 12:1 motor, half way through its stroke it'll be @ 166PSI, on a 8:1 CR motor that has a peak cylinder pressure of 1000PSI half way through its stroke it'll be @250 PSI. point: i like low CR for FI apps. any counter arguments?</TD></TR></TABLE>

Nice idea for a world with-out rules, but if you really think about it the more you "squish"(IE higher comp.) the more pressure you will have. The amount of air & fuel in the two different SCR is not even noticable. If fact with high SCR you actually need to add more fuel to balance the ratio. This suggests that there is actually more air.
I'd like to know where you got this math. From what I see of it you magically got rid of a lot of pressure in the chamber on the high SCR motor, but you didn't show equation's or anything to support it.
I would also like to comment that on many of these applications the people aren't using properly sized turbo's or even the cams to fit the profile of the pressure changes. This is also where the actual geometry of the engine start to effect the result's.
Personally I'd rather have a 11.5:1 SCR GSR block with a B17a crank. Add in a pair of ITR or similar cams, and boost it with a GT40(R). Tune it run with 10PSI, and a rev limit set at say 8,500. After that work on the chassis, because after all what's the point of power if your chassis can't make use of it?
BTW I've personally seen ITR's running 15PSI with a SC61 so I know it's a valid combo on pump fuel. Just learn how to tune it right, or pay someone that know's how.

 

I love how everybody states "just learn to tune it right" or "have st00pid tune it" and it'll last forever with 20:1 compression. But the proof is in the pudding, you see at least one, and sometimes as many as 2-3 threads the main page of Forced Induction everyday about broken motors.

I personally thing it is dumb to build a motor on the limit of compression with all your hopes riding on the perfect tune. I guess you just haven't been in the game long enough to know how much the "perfect tune" changes day by day.

If 25:1 compresion with boost was such a feasible alternative on pump fuel you bet your bottom dollor manufactures would try to make it work. High compression motors typically get good low load emissions numbers .

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nd_styles &raquo;</TD></TR><TR><TD CLASS="quote">Nice idea for a world with-out rules, but if you really think about it the more you "squish"(IE higher comp.) the more pressure you will have. </TD></TR></TABLE>
No you also run more boost on lower compression motors.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nd_styles &raquo;</TD></TR><TR><TD CLASS="quote">
The amount of air & fuel in the two different SCR is not even noticable. If fact with high SCR you actually need to add more fuel to balance the ratio. This suggests that there is actually more air. </TD></TR></TABLE>
we are in the FI forum. SCR doesn't mean crap about how much a/f get into the cylinders. Look at the DCRs. I'll simplify it for you, if you have a 1.8 liter motor at 5 psi and one at 25 psi, which will have more a/f?
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nd_styles &raquo;</TD></TR><TR><TD CLASS="quote">I'd like to know where you got this math. From what I see of it you magically got rid of a lot of pressure in the chamber on the high SCR motor, but you didn't show equation's or anything to support it. </TD></TR></TABLE>
I'll work it out for you. 12:1 compression. 1000psi/6 = 166. 8:1 compression. 1000psi/4. The 6 and the 4 are from 6 times the volume and 4 times the volume of peak cylinder pressure.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyphear &raquo;</TD></TR><TR><TD CLASS="quote">There are sound scientific reasons why there are no factory 10 to 1 CR turbocharged engines which produce specific outputs of 175 hp/L. In fact, there is NO production, piston, automotive engine which I am aware of which can achieve a specific output of this level on 92 octane pump fuel anywhere. Despite this fact, many people try to do this with expensive results. High compression ratios and high boost simply don't mix on pump fuel. If you try this, you will either be unhappy with the results or blow up the engine.
Quote from http://www.sdsefi.com/meltdown.htm</TD></TR></TABLE>

The S15 SR20 runs 10:1 CR:
http://www.xatracing.com/xatra....html

 

Yes but thats on 102.5hp/L, not 175hp/L.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LudeToAHatch &raquo;</TD></TR><TR><TD CLASS="quote">

The S15 SR20 runs 10:1 CR:
http://www.xatracing.com/xatra....html</TD></TR></TABLE>


LOL. thats bad info. the s15 SR20DET most definitely runs 8.5:1 compression ratio from the factory.


Anyway, alot of you guys are argueing this from the "pumpgas" point of view. I agree that from a pump gas point of view if you are building a 10.5:1 motor to run 20 psi on pump gas you are in BIG trouble. I'm building a 10.5:1 engine for turbo, but i only plan to run 10 psi on 93 octane. i wouldnt go much higher than that and expect it to be reilable. however i also know it'll do 400 whp at 10 psi anyway and i dont like going much above 400whp on a 4cyl on pump gas.

 

Your going to make 400whp on pump gas with 10.5:1 compression and 10 psi boost. OK, ha ha ha ha.

 

yeah, i guess thats really funny considering my last engine with smaller cams, smaller exhaust side on the turbo, less RPM and 8.5:1 CR did 360 at 10 psi.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danl &raquo;</TD></TR><TR><TD CLASS="quote">Your going to make 400whp on pump gas with 10.5:1 compression and 10 psi boost. OK, ha ha ha ha.</TD></TR></TABLE>

theres been a few people on here that have done that...

 

Just curious, who? And how well is it lasting?

I've heard of 400+whp on pump gas without N20 (I wasn't counting N20 BTW) but never heaard of it at 10 psi. If you figure a really great sub 2.0L n/a motor is making ~200whp, that is in excess of 20 hp per PSI boost.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danl &raquo;</TD></TR><TR><TD CLASS="quote"> 1 I personally thing it is dumb to build a motor on the limit of compression with all your hopes riding on the perfect tune. 2 I guess you just haven't been in the game long enough to know how much the "perfect tune" changes day by day.

If 25:1 compresion with boost was such a feasible alternative on pump fuel you bet your bottom dollor manufactures would try to make it work. High compression motors typically get good low load emissions numbers . </TD></TR></TABLE>

1 LOL! I think it's dumb that you have this opinion, yet you've never tried it.

2 How long have you been in it? I've been working with turbo'd cars
since '95. Mind you, I started with carb'd cars too. I really don't rely on
this "perfect" tune. I tune on the street, and soon I won't even need to
do that. Just because you aren't as creative or innovative doesn't mean
that other people can't do things you can't.

I don't remember saying anything about 25:1 compression.