I am building my first LQ4 and have made some miscalculations on CR, hence me being here to ask for advice. It is a Gen 3 LQ4 bored .030 over running 862 heads. I am running a forged crank with a 4.00 stroke, forged 6.125 h beam rods, and Diamond pistons to offset for the longer stroke. Essentially a 408 stroker. I used the heads in hopes of raising compression a bit. Well, I got what I wanted. Plus some. Doing the calculations on it ,on the Summit site, it is showing 12.83:1!! Below is what I plugged in to get my numbers. I am at the end of my budget and cant really throw much more money at this. This is a street car that I want to run on pump gas. I have found some MLS gaskets that have a .080 CT but didn't know if this would be a "safe" route to lower CR or not. Even with those it would only bring it down to around 12.1:1. Below is my setup for this engine. Any advice would be appreciated.

2005 6.0 lq4 bored .030
Elgin Sloppy Stage 2 228/230 duration @ .050 585/585 lift @ .050 and 108 LSA
Eagle Forged Crank with 4.00in stroke.
BTR Forged 6.125in H Beam rods
Diamond Forged Pistons (flat top with valve relief) 1Comp Height is 1.15 and CC is -2.0
862 heads with 61.15 CC Chamber
MLS Head Gasket with .055 CT
Deck Height is 9.24
Deck Clearance at 0.

I may have miscalculated on deck clearance. I have always just built junk motors with extremely low budgets and was finally able to try and put a decent motor together so if you guys see something that don't look right by all means please let me know. Thanks in advance.

 

Where do you actually want the compression to be?
I got 12.21:1 compression with your combo.
If you got some 317 heads (71cc) it would be 10.9:1

 

I think a .080 head gasket, for an NA engine may cause all sorts of problems by making the quench too big and making the motor prone to detonation. I would NOT use an .080 head gasket.

2005 6.0 lq4 bored .030
Eagle Forged Crank with 4.00in stroke.
Diamond Forged Pistons (flat top with valve relief) 1Comp Height is 1.15 and CC is -2.0

Valve relief should be adding +2cc for Summit Calculator

862 heads with 61.15 CC Chamber
MLS Head Gasket with .055 CT

Deck Height is 9.24
Deck Clearance at 0.

Was the block decked to make sure its flat? If so the piston are probably out of the hole.
Both of my strokers had all the pistons out of the hole by a few thousands ~.005 TO ~.008. That will push compression up slightly if they are out of the hole per build sheets

Using Summit's Compression Calculator,
12.2 to 1 if pistons aren't out of the hole.
12.53 to 1 if the pistons are .010 out of the hole (-.010 in Calculator)

Set of 243/799's with stock chamber size (64cc) & .010 out of the hole should end up ~12.15

Set of 317's with stock chamber size (71cc) & .010 out of the hole should end up ~11.2

 

You don't want a large quench with high compression because engine will be much more susceptible to detonation.
GM MLS gaskets are 0.051" compressed height (not sure if your 0.055 was a typo?)

Your dynamic compression ratio is going to be sky high around 9.7 DCR. No chance of pump gas. I'm not sure what is the limit of E85 fuel?

Installing 317 heads with 71cc chamber will get it down around 8.7 DCR which is doable with 93 octane but you better have a good tuner.

 

IIRC the MLS LS9 gaskets are .055" compressed.

 

Hi Blackmaxx. I think i might have a really good solution for you. Swap out the 862 heads for the original 317 6.0l heads. The 317's flow quite a bit better than the 862's and the chamber volume is 71 cc's. They have a larger intake valve and intake runner to help feed the stroker. Use a head gasket something like 0.40" compressed thickness. Read about quench
Your engine will scream on 93 pump gas!

 

I appreciate greatly all the input. I've always just been a shade tree bolt on guy so alot of this is new to me. Looks like I will fall back to the 317's that came on the engine. I called Diamond Pustons and he ran my numbers and came to 11.9:1 CR. He said that their data shows the pistons being -2.00cc but that's because of the valve relief. He said for CR calculations I needed to use +2.00cc. I did have the block surfaced to just ensure flatness so I will need to adjust that. I was wary of going that thick on the head gaskets. That's one reason I asked on here. Again, thanks all.

 

I want to run as high a CR as possible and still be safe on pump gas. This motor will live its life NA so not worried about planning for boost.

 

Appreciate the input. I'm going to gonwith the 317's. Sucks cause I have a very nice set of 862's that I can't use. Lol. Guess I'll do more homework next time.

 

This is what I have already purchased. Started looking into lowering CR and found a bunch of different CT's. I didn't know there were that many options. Thanks.

 

I'm going this route. I really appreciate the input. I'm hoping for somewhere close to 500rwhp. Not sure I'll get there but I believe it will be a blast in my 79 camaro with a t56 either way.

 

What fuel is available where you are? Many guys including myself are running well north of 12:1 on 93 pump. I’m at 12.42 and run 93 pump without additives. But this is static numbers and the truth is that an internal combustion engine doesn’t know or care what the static number is. It’s the dynamic number that the engine (cylinder pressure) actually sees, which is dictated by valve events. Static is set up for combustion efficiency and is not the end all-be all for compression numbers. There are quite a few compression calculators available online that will tell you both your static and dynamic numbers to give you a better idea of what fuel will be required for your application.

 

93 and E85

 

You can safely run up to 12.4 static on pump 93, and still have tunability, with a fuel injected LS. 12.5 and up and you will start to run into tuning issues that will require you having to run a fuel octane additive to get the issues to go away. It’s not a big deal if you don’t mind running the additive at each fill up. The higher the static, the higher the dynamic ratio will be, all things being equal, because chamber volume is one of the many determining factors of dynamic. If you want to go the E85 route, you can reach for the skies with compression. I’ve seen guys run 14:1 static on E85 all day.

 

All BS to the side Weight ...Weight. Weight

Keep it simple, guys wiil have or make more hp but the Et tells of the entire combination.

My thought is this, they can have the dyno war.

I Killed your bigger build and more expensive top and you porter.

 

Joke of the day to all my Ls brothers..

Imagine a 370 killing you fav wit the 427+ as a DD. & both seen as DD just from the opposite side of the lens. Pump gas is a given.

Reroute and have your money...

Lmao. Easy math of bigger builds with more hp & tq not being Able to get a sub 6 sec pass ⅛ mile as a 370 Moostang & hydraulic does so .....easily.

3000 or less sub weight vs 3200+


Your talking hp..Lose weight.
Lmao at the tq curve.. gear it Idiots.


Doesn't take much to out do the avg ..et or dyno

 

Some conversations only are good on the internet..

until one or you lose money... I keep a winners train of thought. I've gotten pass the hype. A hp # is only good for the owner. I'm your op and thinking f you and your internet friends, builder included whether you did so or not...

Big picture besides I got xxxx on a dyno

 

^^^^ Too close to the

 

Wrong thread while having a shot..🤣

 

Smokey B, is that you?