Low compression vs High compression

Rebuilt motor after hurting a piston and used dished pistons to lower compression for the change from nitrous to boost. Originally the motor was 11.4 to 1 static compression and after the rebuild was 9.5 to 1 static compression with custom pistons. Same top end...throttle body, intake, heads, and cam were used. Exact same exhaust was used as well 1 3/4" stainless works headers with off road mid pipes and slp power flow exhaust. Same camera used for both sound clips. Can you hear the difference?

[@groomlake51]

The fact that the higher static numbers make it idle faster for a given IAC position proves how effective high comp numbers are to raise engine output!

[@lsxtuner6126]

Idle speed is the same it only sounds faster.

[@_..-.._..-.._]

The speed of the exhaust pulses are faster despite the same rpm, like something coming towards you vs going away

[@LuganAki]

Such an amazing difference. Awesome video

[@bunkybell1120]

This a great video. definitely sounds crisp in the 2nd one

[@mcocell]

Nice, thanks for posting this!

[@swappedoutZ71]

Nice. I noticed my truck got more deeper and mellow when i upped compression going from 5.7 block to 6.0 block on the same heads and cam but it louder/crisper when i added ported heads and intake. These LS motors can get crazy loud once u have cam heads and a full exhaust

[@bri-manhunter2654]

Same, my 5.7L to 394Ci 6.4L stroker with 11:4:1 compression has a much crisper sound.

[@7000U9ZHIFT]

This is interesting.. thank you for uploading

[@HoweDoYouDo1999]

It definitely sounded a hella different 😂😂😂😂

[@groomlake51]

Yeah like 250-300 rpm🤦‍♂️

[@GregoryShtevensh]

Check out the idle on an Aussie 304...they came with an 8 to 1 ratio and can be turbocharged without any decompression... they have a nice slow idle

[@jessebreyer709]

I’m in Iowa too and you best believe I’m going to be on the lookout to have a run with the car that tag is on

[@lsxtuner6126]

I sold this car many years ago. I have something different now with a TSP short block and procharger on E85 maybe I'll still see you around.

[@ls3jj862]

Good to know...🤙

[@muckman5509]

This was very interesting thanks bro. Never thought that compression would change the note of an engine

[@sbgken]

High compression engines are more high pitch sounding

[@rayman1230]

@@sbgken my favorite kind of engines!

[@GregoryShtevensh]

Look up older cars, you'd find they would often offer both low and high comp engines... high would perform better at high RPMs but low had more effortless power at low rpm... low comp is good for pulling and also needed for boost... high comp is better for high end HP and is ideal for NA

[@_..-.._..-.._]

@@GregoryShtevenshwrong, low-end torque is improved massively with higher comp, the lower comp just seems better at lower rpm’s because the high rpm power was lacking. A 2 stroke engine can feel faster on the top end compared to an identical power 4 stroke because the power comes on suddenly. The timing curve has to be matched to the comp to get the max benefit.

[@_..-.._..-.._]

@@GregoryShtevenshin an identical engine, high comp will always outperform everywhere, assuming timing and fuel are correct for each comp ratio. The low comp models had more restrictions and therefore might’ve felt torquier at lower rpms.

[@DanielOrtegoUSA]

Love the low compression sound. I wonder how it does on the dyno.

[@keegentilley578]

Worse

[@lobmin]

Kind of hard to hear with the echo-y mufflers

[@slowpoke96Z28]

Love to have seen this with gto slp loudmouth lol. Bet the difference would be a lot more noticeable.

[@lsxtuner6126]

It does have the slp loudmouth power flow cat back on it. There are two versions and this is the quieter version found here: www.slponline.com/product/31060--2004-GTO-Loud-Mouth-Exhaust-System-PowerFloX-Crossover-Pipe.html

[@BLACKLACDTS]

Sounds much crisper

[@thomaseverley3847]

Higher compression sounded crisper, but seemed the idle was a tad higher too.

[@lsxtuner6126]

Definitely crisper. I thought it sounded like a faster idle on the higher compression setup as well, but it's actually the same.

[@meanrc9644]

@@lsxtuner6126 The idle is the same, but with higher CR it feels the crispness of the chop, makes you feel like it's slightly quicker chop "note."

[@namechane1758]

maybe the the exhaust energy is getting to your ear quicker 😉

[@independentassesor2630]

How much did you have to mill the heads down and what cam did you use? Sounds tuff. What was the beat you ran?

[@craigstevenson4306]

So I didn't read and take it in but from what I made out the end of the videos was example of low compression Dyslexia is fabulous

[@Texasmule]

Can 9.5 work on 87 gas if I lower my timing?

[@zacc5455]

You could stand to drop the idle now. That cam liked the increase, no doubt there 😆

[@lsxtuner6126]

Idle speed was the same it only sounded different.

[@zacc5455]

@@lsxtuner6126 i figured it was the same. If you dropped it that cam would chop hard. Whats idle set at?

[@lsxtuner6126]

@@zacc5455 I don't have that car anymore. It's been a while, but I want to say 850 as my best guess. Good tune with proper eoit smooths the idle up some as well.

[@mrmete]

High compression sounds more snappy

[@Airman..]

I have lowered my ls3 compression ratio to 10:1 same tune with 178 headers and ls9 cam Idle is rough not as smooth as before Is this normal/expected result? I am a bit worried Ps: idle speed is noticeably lower than before by almost 100rpms and coolant temp fell dramatically

[@lsxtuner6126]

If you lowered the compression by changing heads it adds an additional variable do to possibly having more airflow.

[@brianspangler3771]

The higher compression sounded like it was idling just a little bit faster.

[@lsxtuner6126]

Idle speed was the same.

[@brianspangler3771]

@@lsxtuner6126 Yeah I read through the other comments and saw where you explained. Pretty interesting how different the idle sounds even though its the same.

[@andrewyankee9862]

its a little higher pitched and it sounds less violent

[@Calvin_-fc2np]

Did you manage to see the diff in power from before? Curious how much more power it makes.

[@lsxtuner6126]

Lower compression will not gain power it will lose power with lower compression.

[@_..-.._..-.._]

@@lsxtuner6126?? Is there a missing comment? The question was how much more power the higher comp felt like/dynoed at.

[@CCDProductions]

Sounds more snappy

[@AN-ci6iy]

Guys low compression is good or high fpr engine durability ?

[@bh635]

Hi can you tell me did you notice better fuel economy running with higher compression?

[@lsxtuner6126]

Yes slightly better fuel mileage.

[@JosephNnbs]

Does it rev faster with higher compression?

[@lsxtuner6126]

I wouldn't say there was a noticeable difference in how it revs. There is a noticeable difference in throttle response and low rpm torque.

[@IonIPopa]

What octane gas you used and use now? I accidently took too much from the head and it will make 12.8 hmm

[@lsxtuner6126]

I have a different car now with a boosted LS3 running ethanol and meth/water injection.

[@bh635]

did you notice any difference with your MPGs with the higher compression?

[@lsxtuner6126]

I never keep track of MPG. I would guess the higher compression would help with MPG if that is a concern.

[@racetrackalexander381]

Exhaust performance is directly linked to the speed the cylinder can evacuate exhaust gas. While also maintaining proper backpressure to seal the exhaust valves at speed. When you pop a balloon with a higher pressure, it makes a bigger boom. Higher EGT will have expanded air density and also allow for more oxygen to enter the combustion chamber on the intake stoke. More oxygen = More Power Higher compression = More Power Faster exhaust flow = More power

[@lsxtuner6126]

LOL...

[@sdrawkcabmodnar]

Well yeah, more pressure = more power, it's the whole point of pop-up pistons. If you have a naturally low compression, it's just one of the logical steps to take alongside other tweaks

[@Russeljfinch]

Thanks .i am gonna run a 13.5:1 so would have like to hear that also....I'll search KZbin again

[@Spankymf]

What engine will you be running that compression in

[@Another_Random_Dave]

@@Spankymf whatever it is it probably won’t be for long

[@rakansofyan3934]

@@Another_Random_Dave why not?

[@swappedoutZ71]

@@Another_Random_Dave depends on what hes doing with it, and what cooling system and what fuel hes running. You could run that in a daily driver if u have a big brain and deep pockets.

[@Another_Random_Dave]

@@swappedoutZ71 but you get what I’m saying. That’s a lot of compression lol

[@Willborn11]

Curious if you are running 93 or E85? Do you have any trouble street driving it with detonation?

[@lsxtuner6126]

I was only running 91 octane on that setup without detonation. Correct plugs, afr, and timing advance is key. I usually only recommend E85 on boosted setups unless you want to run over 13 to1 compression NA.

[@Willborn11]

@@lsxtuner6126 very cool, the last thing I was wondering was his big was the cam? Trying to figure out if I need to worry about my dynamic compression ratio or not.

[@TheJMan1K]

What fuel are you running with that compression? Can it still be ram on 93 or is it straight E85?

[@lsxtuner6126]

I used 91 octane back then. I have a different car now with a boosted LS3 running ethanol and water/meth injection.

[@jamesunderdal8976]

Personally I think it sounded better with the 9.5 to 1 but then again I'm not use to EFI either have always ran carburetors and non computerized motors.

[@azooz2015ss]

The sound varies with the cam only, but the compression has nothing to do with that

[@lsxtuner6126]

Both sound clips are with the same cam only difference is the compression. So yes compression ratio absolutely effects the sound.

[@mandoramos4229]

Would high compression do anything bad to the engine?

[@AhmedElWakil911]

The more compression the better efficiency ,but there's a point which u increase the compression the fuel can't burn correctly I mean if the compression ratio of an engine is 10 u can increase to 12 , if u increased more than that the fuel willn't burn correctly

[@mandoramos4229]

@@AhmedElWakil911 thanks, very helpful 👍

[@captainboose8788]

Sounds like it's idling higher

[@lsxtuner6126]

Same idle speed.

[@DannyR2681]

What heads and engine do you have to get 11.4:1 compression? I’m doing the same with lq9 and 862 heads with ls2 gasket should be at 11.4:1 compression as well. Thinking of running a tsp ms3 cam

[@lsxtuner6126]

That setup was a 408 with AFR heads and 242/250 duration cam.

[@heymanmotorsports49]

DGSR I too am building an LQ9 with 862s Howd yours turn out? Any issues dailying?

[@TheJeffe613]

How did the lq9 do with the 862 heads?

[@Uniiiiii]

U cant disagree tho, its hard to beat the sound of a high compression/rpm small block

[@JosephNnbs]

Did you run different fuel?

[@lsxtuner6126]

Both were on 91 octane pump gas

[@zachattack2016]

Open header might be easier to tell

[@lsxtuner6126]

Car was a daily driver so open headers weren't really an option...lol. I've never cared for cutouts either because they all seem to leak at least a little bit.

[@TunedRAMS]

Same cam?

[@lsxtuner6126]

yes

[@darriandk]

Sounds peppier

[@gapingtonbobuah9299]

I can’t hear the difference besides the chop? Low compression sounded better 🤷‍♂️

[@HellaFire-xk8ce]

What was the hp/tq difference?

[@lsxtuner6126]

I didn't dyno the car with lowered compression. My seat of the pants observation was that it lost throttle response and low end torque more than anything else with lowered compression.

[@juanjoselondono8362]

@@lsxtuner6126 Why you went with lower compression?

[@lsxtuner6126]

@@juanjoselondono8362 To run high boost on pump gas.

[@juanjoselondono8362]

​@@lsxtuner6126 ohh sorry, i didn't know that you were running boost, now, how much boost can you handle before start creating pre detonation

[@lsxtuner6126]

@@juanjoselondono8362 I actually have a different GTO now with a procharger running E85. Preignition and detonation are actually two separate phenomenon. Lots of factors to consider and each setup is different when it comes to how much boost it can handle before pre ignition or detonation become a problem. So I'll name a few variables...heat range of the plug being used(plug gets to hot and it can cause pre ignition for example), fuel octane, combustion chamber design, compression ratio both static and dynamic, timing advance, intake air temperature, air fuel ratio, etc. Lots of variables so there isn't one correct answer that "X" amount of boost is the limit before pre ignition or detonation becomes a problem.

[@groomlake51]

If you got it to idle at the same RPM it would be far less noticeable!!!!

[@lsxtuner6126]

Idle speed is the same it only sounds faster.

[@antonitorres5934]

This guy does not tell you, that you can't do increased compression on a stock engine. The engine has to be modified with a cam shaft other than stock. Again increased compression on a stock engine will only cause excessive kocking.

[@trixnhoez2964]

The guy listed he had a cam and yes you can do that .. The ls2 was 11:1 from factory and ran 91.

[@texasstreettunes1310]

All the new cars are running high compression with stock cam specs mustangs 12:1 camaros 11.5:1 even the trucks now run 11:1 and either way it wont knock if you have a tune.

[@zacc5455]

The LS holds know prejudice under the control of a good tuner. My 1500 silverado is at 10:1 with a junkyard lq4 plan to go higher.

[@JoeZelensky]

High compression is much better.

[@Dafastso]

cant hear any difference

[@YY-zw2ec]

9.5 better

[@BakhulSan]

I noticed Soundnlike this Low compression : Deng deng deng Deng deng but there is 1 sec delay High compression : Deng deng deng deng deng but there is no delay