Since the thread is back and alive..

99BlancoSS:

I was intrigued by your Engine Master's quote debating the advantages and disadvantages of compression. Especially your comments on the advantages of gaining the proper VE's by camshaft selection vs additional compression.

If 10:0.1CR can be ran with little risk of engine detonation problems, and 11:0.1CR showed some detonation damage, what do you consider the "sweet-spot" for maximum static CR with little to no risk of engine detonation damage?

With the following caveats:

Since your in the Western U.S. also...where only 91 octane is available.
Your opinion on a proper 91 octane DCR range to remain "detonation safe".

If it is really true that a 1 point increase in SCR only gains you a 2% power increase, it has even me questioning the wisdom of going past a 10:5.1-10:9.1 SCR (DCR 8.25-8.5?).

What about torque loss?

I know this subject has been debated and discussed many times.

Am I missing something here, or is the pursuit of higher compression a risk with limited rewards?

Thanks in advance Blanco. I know from your post count and new business pursuit, you might have some sound advice.

If anybody else has some greater insight feel free to comment.

..WeathermanShawn..

 

bump for the weekend crew

 

That was info from my builder talking in another thread. I answered weatherman in a pm. I'm not an expert, just a student of the man..LOL

 

Blanco wrote a great PM in which he shared his views and that of his superb engine builder discussing various compression, cam selection, along with all their potential gains and pitfalls.

I'll leave it to him to share the PM or his point of views, but the bottom line seems to be that whether it is compression goals, cam selection, etc., always seems to be a "sweet spot' where it all comes together.

I know the original poster asked about optimum compression ratios, but I am beginning to believe you can accomplish that static CR "sweet-spot" at about 10.5 -10.8 on most pump gas across the U.S.

Perhaps maybe even keeping that DCR to no more than 8.5 might give you all the results you need without the unneeded anxiety of possible detonation, perfect tune, and the ever increasing incidence of "bad gas" that many of us seem to be experiencing.

I.E. AFR 205 heads and a more "user-friendly" (milder) can seems to almost always produce some very respectable HP/TQ numbers.

Are we chasing higher CR/DCR numbers that may only produce 1-3% more HP/TQ numbers, and be exposing ourselves to greater problems down the road?

Am I missing something, or is this a point that others may have pondered and may be willing to share some wisdom?

With time I am beginning to understand why for those of us who choose to remain NA, bigger cubes always seems to deliver the power & TQ, and do it with less cam issues and CR/DCR concerns.

Anybody up to tackle this one?

I bet I'm not the only one who wants to know.

Thank You very much. Always appreciative to listen and learn.

..WeathermanShawn..

 

i love south texas 93 octane

 

I hate delaware 93 here is like 91. Most of my import friends that are boosted get gas in maryland.

 

TSP 402
11:1 static
91 octane
TSP's giant cam

Altitude plays a roll for me though...seeing has how being a mile high apparently effectively drops my compression ratio.
I have seen arguements both ways.

 

Hey "Mr. Luos":

Good to hear from you!

Always envious of that 402 of yours.

Curious what kind of "DCR" you are running, and what kind of tune you have dialed in.

Not to detract from the original premise of the thread, but for those of us out West who have higher altitudes and DA's, it's true that "theoretically" we should have an effective lower compression ratio.

In reality, the thinner air and higher DA, coupled by the the fact that 91 octane gas is the highest available (and of questionable quality) makes getting the proper A/F ratio imperative.

I see a number of posts from Arizona and California where others have the same complaint.

Lot of altitude/DA changes. Hard to go SD tune. Have to rely on MAF, and making absolutely sure O2 sensors, MAP sensors, etc., are right on.

For the rest of the U.S., seems like 11:1 static, and DCR's of 8.5-8.8 work out real well.

..WeathermanShawn..

 

It has been a while since I checked the dynamic ratio. It was lower though if I recall.

I will get back to you soon on it, as I have to look it up again. Busy weekend though, so not sure when.
Tune wise, what did you want to know?? Clint has done all my tuning.

 

"Mr.Luos":

Thanks for your reply.

P.M me sometime.

I don't see many Colorado LS1's running NA at all, or for that matter NA and DCR's above 8.0.

Tune-wise? I know Clint was using HP Tuner's. I think I wore him out after spending 12 hours going up and down Colorado's back roads at speeds that the Colorado Highway would not have approved of.

Would get a number of things dialed in, but to do WOT tuning required more dyno time than we could reasonably get.

I'm now using EFI Live as my tuning tool.

Out of deference to the original poster, I'll take this discussion "offline", but my major point is challenging the potential fractional gains in HP/TQ, going from a 10.5:1-10.8-11.1:1 static CR, or a DCR from 8.4-8.8.

Fine line from the "perfect" amount of compression, to the negative consequence's of detonation.

Thread is probably exhausted, so I'll PM you on the other issues.

Thank You.

..WeathermanShawn..

 

12.1:1 with ceramic coated chambers, ports, and piston tops with a 0.035" quench and reverse flow cooling. I can get away with 91 octane for "daily driving" stuff.

 

There's just one thing to remember Detonation is an enemy. The force of detonation is far greater than the force of combustion and it's effects on the piston and rings are felt. It's not just a casual term, it will break a piston up.

Bad batch of gas, hot weather... why take a chance with running on the ragged edge with a street car where you dont control your quality of gas?? What are you gaining?

We wont do it.

 

11.8:1 SCR and 8.8:1 DCR on 93 octane. Upgrade your cooling capacity first to run that sort of compression.

I agree with proper valve events. You match your valve events to your intake manifold, so you optimize the peaks for torque and horsepower. The manifold restricts your heavily on the peaks, so fighting them just kills low-to-mid range power or power after peak.

Another thing about the Engine Master's Challenge, most of the winners have high DCRs - 8.5:1 - but they may not run super high static compression, because they have selected the proper camshaft for the engine/heads/manifold.

Since the FAST is popular, a good IVC for it is around 44-46 degrees at .050" for making good, broad power. An IVC of 44-46 with an XE-R lobe (and I don't care what the specs of the cam are, if it hits an IVC of 44-46, the DCR is going to be universal across the cams, because you'll need a smaller lobe with a higher ICL or a larger lobe on a tighter ICL - thus making them react to compression the same way). Anyway, cams in that range like something around 11.3:1 to 11.5:1 CR. Which is where most engine builders will point you toward as this is a good overall balance of cam valve events and dynamic compression...

As an example, a 224/224 114+0 or a 236/238 112+4 will react to 11.5:1 the same way, giving you 8.7:1 DCR. If you go bigger, or run an ICL (LSA + advance) that is not quite as tight, you'll push the IVC higher and make less torque from the later valve closing and reduction in dynamic compression, thus needing more compression to bring up the bottom end. It's all interrelated.

DCR of 8.3 or so is good for 91 octane, 8.5 for 92 and 8.7 for 93 can be done with good tunes. You can push it higher, but you risk detonation. Also, to run such high compression for your octane, you need to have a very tight quench to "squeeze" the air/fuel mixture more allowing for a more complete burn.

And lastly, 3% at 470+ rwhp is ~15rwhp. People spend a lot more money to get that last 15rwhp (which is everywhere in the RPM range) than the cost of milling the heads to get that power.

 

1 point of compression is worth more than 2%

 

whatever stock ls6 heads+ ls1 shortblock+ .040 head gasket comes out to.

 

im running a 11;8.1 compression on a lsx 408

 

12:1 static compression, 8.7:1 dynamic....... 370ci

 

I live in Corpus Chrsiti so I have a selection of 93 octane available and all of it is of quality except Valero gas.

I have somewere around 11.5-11.6:1 in my TBSS with a 224/230 cam on a 112+4. I can run as much as 25 degrees of timing before I start seeing signs of any KR.

 

I do not believe engine masters guys have benefit ot knock sensors or fuel injection.

 

have 11.68scr