Everyday new people are on here asking about compression and then others weigh in saying it's too much or too little. Sometimes they are told they don't need the extra compression when in fact it wouldn't hurt their combo at all.

There's no secret magic or voodoo to tuning a higher compression combo, It's no more difficult to tune than anything else.

People also are scared of higher calculated DCR ratios, as they may not really understand the full spectrum or purpose of the calculation.

There are many experienced users on here me included, I have ran combos with DCR ranging from 6.5 to 9.3 with no detonation no issues at all. Maybe if we stop calling it DCR and call it a throttle response calculator there would be less confusion about it lol

These engines have an individual coil for each cylinder and the 58x stuff is even more accurate than the 24x stuff we mess around with here however it is still way way way way way better than an old small block where that little bolt that holds the distributor down can wiggle loose and throw your timing off.

10.5 CR used to be a high compression ratio for a street engine when there was just a little bolt holding your distributor in place but that's just not the case anymore.

Obviously engines with varied DCR ratios are going to have different characteristics and this is really what users need to understand. This can affect how low in the RPM range the engine can be loaded or how high it can rev.

There's obviously a lot more to it than I've touched on here I don't claim to know everything about it I just know my own experience and those of others on here.

I see the same questions asked over and over on here however the feedback these users receive is always just dependent on who responds to their post first. People that bought dish pistons because they were scared of compression are going to recommend the same thing to someone asking the same question, Those that understand that 11.5 to 1 is no big deal for the combo will weigh in as well but are often ignored.

Here's what I think.

Generally the more displacement and the more compression you have the later IVC you can run while still maintaining good low-end performance. Maybe just think about compression and IVC and don't worry about the DCR calculation too much.

Here's my generalized approach to compression and IVC

9.5-10.5 Cr ideal ivc could be between 32° and 47°

10.5-11.5 cr ideal IVC could be between 39° and 49°

11.5-12.5 CR ideal IVC could be between 43° and 55°

​​​​​I'm done ranting now hopefully others that understand what I'm trying to do here will weigh in and help me out

 

That seems like a good idea 💡

There's definitely a need to improve understanding on the topic.

 

We have a few great stickies covering all of this actually. DCR is the least understood by far by most, on most automotive forums that I’m on. Static compression is a key element to optimize efficiency on any build, and is important to get right when setting up things. However cylinder pressure is controlled by valve events and DCR is what the engine actually sees. It honestly doesn’t know, nor care what the static compression actually is. Here’s a link to a sticky covering most of the subject matter.
https://ls1tech.com/forums/generatio...editorial.html

 

I've read that thread several times and it's outstanding. Definitely will re-read it.

What IVC works best with a 440 LS with a 4.125 stroke 50? How does one go about figuring out the IVC for a given bore & stroke in general sense?

 

That's a thread titled overlap and valve events, It says nothing about compression or anything like that I've read that thread it's great but nobody that's worried about their compression and doesn't understand that stuff yet is going to search that first and figure everything out

I tried to describe this before the problem that people have when they come on here all the time. Maybe they hear more compression is good and then they calculate What they can build and look at the cam they want to use and then they come on here and freak out about the DCR ratio that they come up with in their calculator. Despite everyone that knows what's going on trying to weigh in they will usually air on the side of much caution and go for a milder or less efficient setup leaving a lot on the table.

Oftentimes these combos people are worried about putting together have less compression than a stock LS2. Hence why I mentioned the whole thing about the 10 and 1/2 to 1 compression small block Chevy.

 

If I was building something like that I would just factor in the cost of two camshafts to get the absolute most out of it.

I spend a lot less money on my valve train than a lot of you guys so I can afford to do this without thinking twice about it.

If you put together a really good motor start with a smaller milder camshaft that is flexible enough to be moved around 8 to 10° or so, install it on whatever ICL You think is a good starting point, then you can move it from there and see how it responds

From here You should have a better idea of what you want or need and you can decide if there's a big cam out there with the right PTV and IVC for you

If you can't find anything in the catalog you like or you want and you think you know what spec will get the most out of it for what you are trying to do go for a custom grind.

 

Agreed. I don’t see many folks here asking about DCR. It comes up on occasion, but it’s rare. Static compression questions are common, and easily figured out quickly. DCR can be figured as well as long as the cam card has enough data on it. The .006 numbers can be guessed at using simple math, but it’s not perfect. I’d say your average poster here has no idea what DCR is, nor cares. It’s more of a concern for the max-effort builds. Great topic here to discuss.

 

I have never been afraid of compression even on a SBC. The OBD2 LT1 and the L31 are both largely unaffected by the distributor as long as the distributor is sparking to the correct cylinder and a P1345 is not set because they get their ignition timing reference off the 4x reluctor.

In 2004 I ran a Q-Jet fed 355 with 52cc 601 305 heads and a small 218/218 cam detonation free at 16° initial and 32° total advance @ 3,600 at WOT and 46° @ 3,600 rpm with the vacuum advance. Idle timing was 32°. It would have the slightest tip-in ping on a really hot day. I used to pull 4° of timing and re-adjust the choke in May and then put it back in about September. In hot weather the Q-Jet needed more tension on the choke speing to keep the electric choke and fast idle from pulling off in ~30 seconds and subsequent stalling. While I know a carb and distributor like the back of my hand and their nostalgia, I love computers just saying.

Compression is torque and part throttle efficiency. I will run as much static compression as I can reasonably get away with and pull a few degrees of WOT, heavy load timing to stay out of detonation. At part-throttle cruising speed the charge density is much less and the timing can be near or at MBT. I spend 98% of my driving at part throttle where the higher compression trumps a full WOT timing curve.

My latest aluminum head 383 is 11:1 and cranks at 225 psi. Several internet experts claimed it would be the PingMaster3000. On 91 octane it runs higher timing values everywhere than the iron vortec head 350 did at 9.6:1.

One other important aspect that gets ignored is quench. I cannot believe how many people falsely believe that a thicker head gasket to lower the static compression will result in less dwtonation when the opposite is true. 0.040-0.045" quench is my target for a street build. A hot rod race kind of engine I shoot for 0.038". I leave a little more clearence for 100+K miles of carbon buildup on a street engine.

 

Excellent post fast355 your setup is ideal for what you are doing with it and that should be everyone's goal when they commit to building an engine and come on here for guidance.

I like as much compression as I can get and a modest amount of duration for a street engine with a wide power band. If done right it's like having your cake and eating it too.

Also the timing thing is another big one.

​​​​The less advance you "need" the more efficient the setup is going to be.

The head gasket thing to drop the compression ratio by way of ruining the quench is deeply terrifying and that's another one we see all the time, where do they get the idea to do that?

I agree there's nothing wrong with the lt1 or any other sbc, my first one was a 71' Chevelle 200 horse 307 power glide with an open 3.08 ten bolt. I sold my 97' Z28 LT1 M6 with 175,xxx on it and it seemed like it only got stronger with age. Good old carbon quench is real folks

 

You're right the 0.006 number can be guessed but it can also vary immensely from lobe to lobe in relation to the number at 0.050. especially the latest spintron designed asymmetrical stuff, I can show you three different LS1 cam cards right now ground in the past year with a considerable difference there.

​​​​​​33 @ 0.050 / 65 @ 0.006 SDPC ls6 PowerMax
41 @ 0.050 / 68 @ 0.006 Comp extreme RPM high lift
45 @ 0.050 / 86 @ 0.006 Comp drift cam

All of these would work for an LS2 depending on the app, however if you raised the static compression over 11.5 with the first cam you will have insane throttle response and great fuel efficiency but the engine will be prone to buck when loaded any more than light throttle under 2k cruising in top gear even with the timing as good as you can get it. In most cases the number @ 0.050 is a lot more telling of what's going to happen when the engine is running so the DCR calculation is really to help you ballpark roughly where you need to be with your Ivc. Early as possible?, somewhere in the middle?, or later man?

 

Thought I would share some tuning methods here and mention some poor practices that some "tuners" have come up with to try to shortcut a proper calibration. People that cannot dial in a combination properly are why there are so many people that knock higher compression combos. They fail because of poor methodology then slam it to anyone that tries to do it.

I had to play with my timing map a little at lower rpm when the converter locked and put the engine down in the 1,200-1,500 rpm range. I had some bucking, a little misfire and some pinging. Pulling a little timing helped, but the best help was to keep the converter unlocked until I was turning ~1,500 rpm. I now have the shift points/lockup set so that the engine will be at atleast 1,400 rpm under load. I have a P01 back in my 97 at the moment so that I can do some Real Time Tuning with HPTuners. I drove over 100 miles, a lot of it running 70-80mph and hand calculated 18.8 mpg at 7,400 lbs total weight.


This slight detonation resulted from cruising at 35 mph in overdrive/lockup and accelerating up an elevated overpass of an onramp to 60 mph. I made it easier to unlock the converter in this situation and pulled a couple degrees of timing, which stopped the knock retard. The knock was not audible at all.



Here is the timing map I am currently running on an 11:1 383 with aluminum heads and a 218/228@ 0.050 on a 108 LSA and 106 ICL with Rhoads V-Max lifters, 225 psi cranking compression. 4L80E with a 2,800 rpm converter and 3.73 gears with 30.47" tall tires. The values on the far left bottom are only used on a WOT stomp from idle and the reduced values at 1,400-1,800 rpm is used while in lockup under heavy load. At heavy to WOT from idle the throttle response is quick off-idle and the engine blasts through the slightly lower timing numbers quickly on the way to the ~2,800 rpm stall speed. Another of my annoyances is people who ZERO out timing tables they have no clue as to what they do. I have found most engines running at stoich require less timing than they do at WOT in Power Enrichment. People blindly ZERO the PE adder table and wonder why their engine pings at part throttle when they have it dyno tuned for maximum output at WOT.




Another annoyance is people that disable the IAT and CTS compensation tables by ZEROing them out of all things. As if sending blow dryer hot air into the intake tract of a fully heat soaked engine in the middle of summer in Texas does not affect burn speed of the mixture. There is ZERO need to touch these tables or the burst knock tables as they are all there to save your engine on a hot day or add driveability in cold weather.





Flat road at 80 mph after getting the tuning close to where it needs to be.


I pulled a ~2-mile long 6-8% grade in overdrive with the converter locked without going into PE. Going into the grade had the cruise control set at 80 mph. Cruise control once opened the throttle blades 75% but for some mechanical reason only opens 65-66% now. This right here is the reason for the PE Spark Adder table. High load at stoichiometric would have the engine pinging its brains out if it were running a dyno tuned spark map that was created with PE enabled. PE Enabled on this 2-mile grade would be drinking fuel and its just not needed until you really get down on the throttle.

 

FWIW, my mom has a 2019 Titan. Even with the torquey VK56VD, running up that same grade it drops from 7th to 6th to 5th gear which is 1:1. It has a 3.36 gear and the tires are a little taller than mine. At 75 mph that 5.6L is turning ~2,600 rpm to climb the grade empty. I was loaded to about 7,400 lbs in the above screenshot.

It amazes me that the 383 just lugs this heavy beast up that hill, loafing along in overdrive.

With the right tuning you can lug down a high compression setup with an early IVC to a fairly low rpm and it will just keep making more grunt almost like a diesel.




Here is the grade being climbed in the Titan one day when I was riding in the passenger seat. The Titan has an Inclimeter built into the factory instrument cluster display. Hill starts out at about 8%, then levels out a bit to 4-5%, then back to 6-7%, 2 miles all together. The Titan is geared so tall in 7th gear it barely makes it 100 ft up the grade before it downshifts.

 

@Fast355 excellent posts, your knowledge is invaluable here. Thanks for continuing to contribute to the thread. You could write a book on the subject easily.

I'll be adding more as well I just don't have time today.

I'll quickly add that my combo is all about performance despite the fact that I have 2.73 gears and 26" tires. My combo of bone stock components in my signature pulls much harder than stock from 1,100 RPM with the converter locked (and practically never unlocks unless on a very very steep grade) in both 3rd and 4th with a 49° IVC event at 0.050".

I didn't do anything new but I needed a wider LSA to get the center lines where I needed them.

Here's what I did.

220/224 115LSA minus -4° for an ICL of 119°

Notice I didn't use a particular word to describe this grind.

I will ask that anyone that posts in this thread not use that word that they're thinking in their head right now. A lot of problems an obstacles people encounter with building and tuning engines has to do with the verbage and in this particular case we need a new way to say this. If we could get around that word a lot of ignorant people out there could be enlightened and they would have much better running cars.


​​​​​Obviously the fuel mileage with my setup is not that great, but it's way More responsive and powerful than a stock 5.7L right off the stock 650 RPM idle with the widest power band possible, the engine doesn't give up until it hits the 7,200 RPM limiter, which for what I'm doing is exactly what I need it to do.
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@ 0.050 my IVC is about 25° at lower rpm if the Rhoads V-max lifters are fully bled off, measuring statically. I assume they bleed down at lower rpm almost entirely since I make 19 in/hg of vacuum at 750 rpm with a 218/228 @ 0.050, 108 LSA and 106 ICL. Rhoads advertises the V-Max as having 20° less @ 0.050 at idle. That is how 11:1 cranks at 225 psi, FWIW. I definately see that reduction statically on an engine stand with a degree wheel. What it does in the actual engine at idle speed, who knows exactly without a Spintron machine using my valvetrain components.

 

I agree with your disdain for certain words used for certain cams.
The one I dislike refers to a very young human to describe a duration smaller than they favor, as if a much larger duration is an adult cam. Pure ignorance.
That term should only apply if the duration is too small for YOUR cam, and yours only.
It might be just right for anyone else.

 

After camming numerous engines from stock to another generic term I loathe (since all engines are "built" by somebody). I have found that usually the cams on the top of the list with the almost laughable looking specs are just enough for good street performance. Which brings the whole 1, 2, 3, 4 thing. Unless we are talking about the name Buick gave one of their muscle car engines aka the Stage 1 455 or Stage 2 455 it is a near pointless meaning similar to the RV or 3/4 name I also have disdain for. .

 

Excellent idea. I get valve events but I must say that I find DCR a bit trickier. The other mystery to me is cam duration split and it's affect on performance. Some say plenty, others say none?

 

So these fast bleed type lifters you speak of sir you seem to have working like they should, I wouldn't think someone inexperienced with setting up a valve train would try this. I wonder if anyone has anything like this going good in an LS app. Growing and shrinking the cam by way of the lifter with RPM would only strengthen the lower end of the power band. How do you go about setting the preload on something like that? Do we have to do any work to the block on the oil passages? What about the oil pump?

The rest of us are stuck trying to decide the best compromise for our application. The flow capabilities of the stock 706 head maxed out to the "choke" point (intake system is not capable of allowing any more air in) on top of a flat 4.065" bore are what I considered most this time around. With that in mind the valve closing events couldn't be compromised I had to make the cut where they opened. High compression is the only reason this works as well as it does.

 

The VMax have to be used with an adjustable valve train. That being said the original design is for use with non-adjustable valvetrains. There was a test, circa 2006ish that were put in a LS1 with an absolutely huge camshaft. Idle manners were far improved, torque output was improved and it just all around ran better.

 

I've often wondered when comparing engine combos what trade off there is exactly between having a lower SCR and earlier IVC or higher SCR and later IVC if both engines DCR and cranking cylinder pressure ends up much the same.

Also nearly all off the shelf cams I've noticed tend to have +4 degrees of advance ground in. If you wanted maximum power from as minimal cam overlap as possible doesn't it seem counterproductive to do this? I would have thought needing to advance cam timing so much indicates maybe the cam duration is excessive in the first place for the intended rpm.