Hey guys, my 2006 Buick Rainier 5.3 started knocking on me, so I'm rebuilding an LS2 block that my buddy had at his shop. Anyways, I'm trying to come up with a compression ratio so I can get a re-tune. However, I've never done this, so I would like to see if somone could verify my math before I send it over to Pat G...

Essentially the only changes are the pistons (and block bore), and the .005" taken off the block to clean it up. I'm using the 799 heads off of the 5.3, and LS9 head gaskets.

The pistons are Wiseco Pro Tru series, P/N PT124H3 (TSP P/N #10-PTS523A3). "Engineers applied a small .090” dome to bump the compression up slightly from stock. Designed for nitrous use, these pistons feature a .280” top land". Per Wiseco, the pistons are 4.030” bore, 3.622” stroke, 6.098” rod length, 1.335” comp ht, +4 dome volume, resulting in a 11.2:1 compression ratio.

I used the Diamond Pistons calculator to come up with somewhere around an 11.2:1 compression ratio. Am I doing this right? My main confusion was the +/- dome volume, the "top ring down" value, and the "piston to deck" value (is it positive or negative?).

http://www.diamondracing.net/tools/

Here are the numbers I plugged into the calculator:
Bore: 4.030
Stroke: 3.622
Rod Length: 6.098
Gasket Bore: 4.100
Comp. Gasket: .051 (also saw .054" listed on some sites)
Block Deck Height: 9.235 (9.240-.005)
Top Ring Down: .280
Chamber Volume: 64.5
Dome/Dish Volume: -4
Piston to Deck: +.007 (I used positive, but should this be a negative value? I'm assuming this is still the same as a stock LS2, .007" above deck..? Also saw .008" on some sites)

So, I'm getting around 11.10 to 11.22, depending on which head gasket thickness (.054"/.051") and piston to deck height (.007"/.008") I use.


P.S. I'm planning on using the 8.1 truck injectors because I'm afraid I'll be maxing the stockers out with the 6.0 block and small (208/214, .550/.550, 112 LSA) cam. Sound good? Other suggestions?

 

The pistons are going to stick out of the hole by about .010" with the block cut .005" so you should be using a -.010" value instead of a +.007".

I wouldn't use a calculator that tries to consider the crevice volume around the top ring land (not that they're doing it right anyways). No one really does that so it's not really comparable when you're looking at what everyone else is getting away with.

I'm seeing closer to 11.7:1 when I use a normal calculator.

 

Thanks for the response, but I'm not at all convinced with your 11.7:1 figure. I think that's too high, and I'm not saying my numbers are correct. (I did try to account for the .005" by taking that off the deck height in the calculator. Seems like that would effectively do the same thing)

According to Wiseco, these pistons will result in an 11.2:1 ratio. I think we can trust that value. The only modification I have done that would differ is the .005" off the block, which would not result in that much more compression. Reference: http://www.wiseco.com/pdfs/wiseco-ch...ls-pistons.pdf

You honestly think that taking .005" off the bock would raise the compression ratio from 11.2:1 to 11.7:1?

I would love to see a calculator that we could put factory LS2 specs in and come up with a 10.9:1 compression ratio...

 

See for yourself...

http://www.wallaceracing.com/cr_test2.php

I got 10.88:1 with stock LS2 specs.

 

Hi Jonas, MY EAP = 11.33 with the .051" HG
To be accurate, you need to state the bore in the .280 Area.
My guess is 4.00"as modeled.

I would fit a FelPro 1041 HG = 11.61 C.R.

THUS Squish would be .034", better for NOS.

I would use a Autolite 3922x "track" Racing Spark Plug with 3923x for "street".

I would Sonic TEST YOUR 6.0 AL block and provide that report.

Lance

 

Hi Lance, thanks for running the numbers for me. 11.33 is about what I had expected. You said you modeled the bore at 4.00", which confuses me a bit. The block was bored 30 over. Is that how you modeled it?

Well, I already bought the LS9 head gasket, and don't plan on ever running NOS. This is not a max effort type thing, just a boring daily, so I'm ok with a lower compression ratio.

I'll check with my builder to see if we can do that. It may already be assembled, so it may be too late :/ at least I'm not going to hit it with nitrous...

 

Hi Jonas, YOUR NOS piston will have a REDUCED diameter above the TOP RING. (the .280)

This is common with any piston with a NOS being a greater reduction in diameter.

The Sonic is easy if the heads are not installed.
GM states NOT to OVERBORE LS-2 blocks.

AT a .050" Squish there will be little Quench benefit.

Lance

 

Thanks again for your response. You're way beyond my knowledge level. I just talked to the guy assembling my motor, and he is going to have it sonic tested for me (heads are still off).

I'll go ahead and get the felpro gasket you recommend, and I'll just set the LS9 gasket on the shelf.

As for the NOS piston (not sure what that stands for) and the area about the top ring being a smaller diameter... I can't confirm that, but I did just send this thread to the guy assembling my motor, so maybe can confirm that... but he did send me a photo of the piston if that will tell you anything:
(This photo is probably useless, considering we are talking about a .030" diametric difference... but I'm sure I can get a measument later if you think it's critical.)

Any other advice would be greatly appreciated. I should probably PayPal you a few bucks for dropping some knowledge on me

 

NOS = Nitrous Oxide System

 

Hi Jonas, thanks for the offer, the first here on LS-1 Tech.
I pay them each month to be here AND try to help members.
I do have a business, Panteraefi.com.
I sell many coils, 200 different coils with knowledge of correct dwell settings given if asked.

I have ALWAYS had a report of a 18HP-22HP increase with better cols.
I have ALWAYS had a report of LOWER fuel consumption.

Your Case : The "tuner" you pick SHOULD know where the Coil Dwell Tabels are to be found.

The settings I could provide if asked.

Lance

 

18-22Hp Gain? With a 100% Stock engine?

What coils were used in this and what did they replace. I use the OEM Mitsubishi Square LS3 coils, what would be a better coil.

I understand a more accurate and hotter spark can gain HP but a 20 HP gain?

 

fair to state that when figuring compression ratio of an aluminum LS block; to just throw out "plus .007" deck height since that figure is checked at room temperature and the expansion growth at operating temp negates that figure. Quite certain the GM compression ratio figures are derived without positive deck................

 

Stock ls2 engine piston protrusion (Piston to Deck Height) is typically .007" to .010" out of the cylinder hole. It is ALWAYS desirable to check this once your shortblock is assembled. Wiseco, the company whose pistons you are using is extremely exacting on production specs. Nevertheless, you really need to know the protrusion on all 8 cylinders as there are variances that occur in machining anything. It's not uncommon to have a variation of .001" to .002" on the protrusion height measured over the whole set of 8 cylinders. Determine your head gasket thickness (for quench) based on the highest protrusion reading you get. Most engine builders seem to prefer a .039" mathematically calculated quench when the engine is at room temperature. Some say that you can run as little as .030" to .035" but I would not run that tight in a street motor that you are going to use as your daily driver. Someone else on here rightly mentioned that having a tight quench is preferable when running nitrous, but you also mentioned you weren't planning on that. As far as your overbore: 4.030 is DEFINITELY pushing the odds of reliability on a stock sleeved ls2. Scoggins Dickey recommends NO more than .020 of overbore on a stock ls2 block. I'm currently rebuilding the ls2 in my goat, and recently had my ls2 block bored .010, and I also had a set of pistons made up by RaceTec - 4.007 diameter with a .003 piston to wall clearance for a bore of 4.010. I also had a 4cc dome machined into them to increase compression ratio to 10.7 (I live in California where the gas is really crap) as I'm running 68.5cc ported ls3 heads and didn't want to risk having to mess with intake fitment to increase compression by milling the heads. So, I got the compression ratio I desired by way of a set of custom made pistons. Im not trying to plug RaceTec, but they turned out very nice and they completely adhered to the measurements I asked for; and also, the pistons turned out to be very affordable. They fit well and look great!. OK, nuff of that - you mentioned you are going to run 11.33/1 CR if I remember right. Thats a little on the high side for 91 to 93 pump gas but doable if you tune well. I'm curious on your head choice (799 castings) but I assume you're using what you have as it makes sense in the scheme of costs. I don't remember seeing what intake you're choosing to use with those heads. Lots of people will tell you that's it's almost mandatory to use ls3 heads on a 6.0 or larger block; but, cathedral port heads can yield really high air velocities and make great power!! Are you going to port them? Anyway, the only thing I see any potential trouble with is that 4.030 bore on the stock block; but, to be fair, I have read about some people who have run that bore in ls2's and have experienced good reliability - FWIW, I would NOT use nitrous with cylinder walls that thin. Good Luck - I will be interested to hear how this all turns out.

 

Hi 07, I have been making/designing ignition coils for thirty five years.
A common report by all of those who fit my coils during a "bench" dyno test, NOT a RWHP report, and the swap is within minutes on a hot engine.
The first report of a LS-1 Tech member was made by a GoKart driver coach with the same remarks AND the requirement of less Spark Advance OVER 5000 RPM. (-1.5*-2*)
The latest LS-1 Tech user IS a GEN-IV coil kit fitment using my 10% more output coils.
The report should be posted soon.

NOW for the OP Jonas : HIS DD request is about compression, sure.
Then he asked for "any" help. (other advice)
This stock EMS will need a "tune".
My help is the requirement to start to find a tuner OR buy HP tuners with my (our LS-1 tech)) help with the object settings.
The fuel is easy, the ignition with dwell settings is not as common.
The Spark Plug Gap, a Day Driver, could be .060" with proper coil dwell and fitted coils.
This will be of great help with HP AND Fuel Consumed.

The Doww post is great, I do know that A DD, the OP's stance, is that of LOWER MAX RPM engine operation which is GOOD for a tight Squish.
The use of a OEM "cracked rod" is also pictured with LESS growth that a Forged Rod.

Lance

 

Thanks again for all the input guys, I really appreciate it.

I will check/verify the protrusion once the block comes back from sonic testing, and I'll bump up this thread with all that info.

As for the head gasket thickness and desired compression ratio... I'll hold off on buying another head gasket for the moment.

Like doww301 mentioned, this is a daily driver, and my number one priority is longevity and reliability.

So... This most likely means that I would want to aim for a lower, more conservative, compression ratio, right? Terms like quench and squish are new to me, so I definitely don't know what is desirable there. Horsepower is not at all a priority. It will have plenty, and I will not be running nitrous, especially considering the engine bore. I am going with the non-ported 799s for this reason, because I got them off my old motor and don't want to spend the money. (I can get my jollies in my LS1 RX7 with the ported 243s and cam, ha). As for the tuner, I'm using Pat G out of Victoria, TX. I have full confidence in him, considering my experience with him so far, and the insane LS cars he tunes. I'll let y'all know.

 

Some very good info here. I can tell you that a fairly standard forged piston top land is usually .055 smaller than the bore when the engine is cold. This clearance goes away under running conditions, hence why most people don't factor it in. The same could be said about aluminum rod vs. steel cold vs. running (pistons have the same running quench distance).

 

Hi TFT, thanks for .055 report.
MOST here at LS-1 TECH believe am I an IDIOT because of my common TRUTH "speak".

I do have friends, the quality 'techs".

NOW FOR the OP, YES you Jonas:

Squish/Quench are the same remarks with DIFFERENT requirements.

The Squish HELPS an engine with HIGHER Static C.R., A FREE HP, engine safety, works better with LOWER fuel consumed. (BSFC)

I would be VERY happy to help Pat with my ignition system knowledge.

Lance