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Fri Apr 04, 2008 9:47 am

sweetlokin66 wrote: Marty Staggs wrote: Jimmy111 wrote: Marty. When you say 7lb of boost, is that gage or total ATM? And you are talking short runs. Yes?
Guage and while driving ON THE STREET or highway.
I have done it.

Hows that twin turbo 3 liter runnin?
Its not - just sitting. Our projects come after customer projects.

Fri Apr 04, 2008 10:35 am

Marty Staggs wrote: Again, I will try to pass on some knowledge -

Two motors - identical except the compression.

#1 motor - 8.5 - 1 runs 7 pounds of boost on PUMP GAS.
#2 motor - 7.5 - 1 and runs 10 pounds of boost on PUMP GAS.

Motor #1 runs better, has more power down low, is nicer to drive and makes more torque.

Of course the numbers are examples and you may be able to go even further before detonation based on cam, heads, fueling and timing control.

Does the dynamic compression end up the same for both examples? Of course the one with a higher static ratio runs better, it has more compression. Like you already said, the ratio affects your detonation threshold (more headroom for boost), so for most people the easiest thing to do is drop it. No one's saying higher compression can't be done...it's just not always practical.

Fri Apr 04, 2008 10:45 am

miniman82 wrote: Does the dynamic compression end up the same for both examples?
Nope

miniman82 wrote: so for most people the easiest thing to do is drop it.

Oh really?

Fri Apr 04, 2008 12:17 pm

Marty Staggs wrote: miniman82 wrote: Does the dynamic compression end up the same for both examples?
Nope

I thought not. The higher static ratio of example #1 is what make it's off boost response better, but I bet it will also ping before example #2 when the boost starts climbing. I guess what I'm getting at here is that once you have boost, you always want more (I do, anyway). For a person like me, the lower C/R is what's needed. If you're the kind of driver that isn't going to push it past 7~10lbs, I don't see a problem with keeping the higher ratio.

Marty Staggs wrote: miniman82 wrote: so for most people the easiest thing to do is drop it.

Oh really?

Why not? Like I said, it's nice to have the headroom to run more if you want. I gladly pump loads of boost through my engines at the expense of a little low end loss.

Here's a compromise VwBuM71: put the kit on how your engine sits. If it doesn't work out, or you notice detonation, drop the C/R some, and see if that helps. Happy boosting!

Fri Apr 04, 2008 12:24 pm

miniman82 wrote:
I thought not. The higher static ratio of example #1 is what make it's off boost response better, but I bet it will also ping before example #2 when the boost starts climbing. I guess what I'm getting at here is that once you have boost, you always want more (I do, anyway). For a person like me, the lower C/R is what's needed. If you're the kind of driver that isn't going to push it past 7~10lbs, I don't see a problem with keeping the higher ratio.

the problem is, folks get hung up on boost numbers... since some of the focus is pump gas and street driving, i'd prefer the better over-all performer, regardless of what the boost guage says... the boost numbers are good for nothing but bragging, the performance is what interests me... if an engine performs better, and makes better/more useable power at a lower boost level than a comperable engine at higher boost, gimme the better performer.... boost numbers don't really impress me, i can boost the shit out of my little turbo engine before i get detonation(on supreme pump gas) and it runs great for what it is, but if it could be better at lower boost, i'm all for it.... my compression is 8.5:1 static with a very mild cam, so it's starting out running okay for a little engine..the boost just makes it better...

Fri Apr 04, 2008 2:48 pm

Quote: the problem is, folks get hung up on boost numbers... since some of the focus is pump gas and street driving, i'd prefer the better over-all performer, regardless of what the boost guage says... the boost numbers are good for nothing but bragging, the performance is what interests me... if an engine performs better, and makes better/more useable power at a lower boost level than a comperable engine at higher boost, gimme the better performer.... boost numbers don't really impress me, i can boost the shit out of my little turbo engine before i get detonation(on supreme pump gas) and it runs great for what it is, but if it could be better at lower boost, i'm all for it.... my compression is 8.5:1 static with a very mild cam, so it's starting out running okay for a little engine..the boost just makes it better...

i agree with you man...i look more for performance then numbers, if it works dont question it lol

Fri Apr 04, 2008 2:49 pm

Quote: Here's a compromise VwBuM71: put the kit on how your engine sits. If it doesn't work out, or you notice detonation, drop the C/R some, and see if that helps. Happy boosting!

thanks man, i will definatly be happy boosting lol. and by the way so y'all know my name is Brian

Fri Apr 04, 2008 3:12 pm

bugninva wrote: miniman82 wrote:
I thought not. The higher static ratio of example #1...

the problem is, folks get hung up on boost numbers...

Not picking a fight, but if your engine pinged on 8lbs and not 7, would you still run 8, and not get 'hung up' on the #'s? I know you wouldn't, I'm just saying... The numbers DO mean something, but the numbers I use here are generalizations. You have to find what works for your engine, and not just run what people say. Every engine is different.

Fri Apr 04, 2008 3:18 pm

Why not water/alky injection for the higher boost applications? Run the CR up for a more drivable car and then add the water/alky injection and life is grand. Lester

Fri Apr 04, 2008 4:31 pm

But with a true street engine, as much as 90% street driving is done under vacuum. To be on an extreme, you could run a 6.5:1 CR and 20 pounds of boost, and only have fun above 3000 RPM.

On the other hand, Jerry Spearn's 1915 was draw-thru, 9:1 CR, and on less than 10 psi (pump gas), made more than 220 hp at the wheels.

The middle ground that MOST agree on is between 7.5:1 and 8.5:1. It's all about finding a balance.

Another thing to keep in mind is the quench. I have 49cc chambers and .090 deck (including .040 copper head gaskets) on my 1776. Not optimum, but I went with what I could do without paying serious cash. For optimum power you want to keep your deck height around 40 to 50 thou, and have bigger (but still tight) chambers to keep your CR in check.

Fri Apr 04, 2008 4:48 pm

So how come nobody has mentioned altitute and its relation to Compression Ratio and its relation to this topic. Everybody is talkin about cr #'s and boost #'s but what about the elevation the motors are run in..........This is playing a factor too.

Fri Apr 04, 2008 4:51 pm

cal63look wrote: So how come nobody has mentioned altitute and its relation to Compression Ratio and its relation to this topic.

Because it seems like many of the people who have enough experience to speak as an authority on these topics live near sea-level... :D

Fri Apr 04, 2008 5:10 pm

Because altitude has little to do with CR on a turbocharged motor. Unless you are at 7000 ft and above. Now on a N/A motor it can make a big differance depending on the VE of the motor.

Tory. you got to tighten up your deck. It is the only thing that keeps your piston cool. Most people understand the relationship with the dwell on their exhaust valve and lack of seat time will burn the valve. Quench is similar. But has to do with keeping your piston surface cool.

Fri Apr 04, 2008 5:28 pm

miniman82 wrote: Not picking a fight, but if your engine pinged on 8lbs and not 7, would you still run 8, and not get 'hung up' on the #'s? I know you wouldn't, I'm just saying... The numbers DO mean something, but the numbers I use here are generalizations. You have to find what works for your engine, and not just run what people say. Every engine is different.

i agree with that Mini... the problem is, folks are real willing to drop the compression to run *higher* boost numbers, even if it doesn't actualy translate to better performance.... it may actually equal out to better hp numbers at top of the RPM range which doesn't do any good unless you are on a track, or really really like abusing the engine everytime you drive it...(which i'm *not* against :wink: )

Fri Apr 04, 2008 5:47 pm

Ive been doing some calculations and there is really no reason why you cant run 9-1 or a little higher on Summer pump gas as long as you can keep your piston and head reasonably cool. But winter gas is more difficult due to the amount of butane and other lighter hydrocarbons they add to it.

To add to that, the pinging that minni refers to is an effect of ignition. not detonation. The pinging that you hear is due to uneven burning. The detonation that causes damage is not something that you can generally hear but you can usually feel it in the response of the motor. When you do hear it it is a knock. can even be mistaken for a rod knock sometimes.

I went over to 68suprise (randy) house and looked at his motor. and he really did have .250" of deck height. :shock: The pistons and cylinder heads had small chunks burned right out of them due to detonation.

Fri Apr 04, 2008 6:01 pm

bugninva wrote: you really really like abusing the engine everytime you drive it...(which i'm *not* against :wink: )

Yes sir, drive it like you stole it! :twisted: It's not a problem for me, I built my engine like most people build race engines-good parts inside and out. I intentionally built it to handle whatever I might throw at it, that way I don't get stranded after 21 PSI runs. :shock:

Fri Apr 04, 2008 8:01 pm

My engine is setup at 8.25:1 and I can run 7 psi on 91 octane. I also run 18 psi on 110 octane. Been doing so for the last 4 years. I have tried lower compression before, but it sacrifices idle quality and the motor takes longer to come on boost. Generally drives like a slug off boost.

Why don't you ask Marty which motor make more power, the 8.5 @ 7 psi, or the 7.5 @ 10 psi.

Fri Apr 04, 2008 11:39 pm

i bet a intercooler and a little bit of dry ice will blow them all away ;)
:twisted:

Mon Apr 07, 2008 9:19 am

comin closer y'all, i just ordered my lc-1 wideband from innovate motorsports yesterday afternoon....as soon as that arrives ill be ready to bolt up the kit, wire up the wideband n start my tuning :D

Mon Apr 07, 2008 11:59 am

VwBuM71 wrote: comin closer y'all, i just ordered my lc-1 wideband from innovate motorsports yesterday afternoon....as soon as that arrives ill be ready to bolt up the kit, wire up the wideband n start my tuning :D

:twisted:

Happy Honduh hunting!