I'm in the same boat. Ive been mulling over this for as long as I've bought this lq9. Same combo, diff vehicle. This whole dcr thing was new to me. I'm old school, so we always based on static number.

But, my combo is at roughly 8.7 with the same .048 gaskets, lq9, 799 heads, and that ghost cam. It does have a late ABDC at 43* @.50. At seat to seat its 67. Which is a pretty good number. I was debating to just use my old BTR stage 2 cam as it was 69. And it would lower the dcr even more.

But, from what I've been reading, ~8.5-9.1 seems to be ok with 91/93. Apparently if the quench is good, and your dynamic compression is less than 200psi, then we should be ok??!?

At least I hope so. @Phobos84 comment about having to run e85 isnt very convincing though

 

Don't let my experience scare you off. I'm fairly new at tuning. Once I learned that my dcr is way lower than I thought I'm betting my tune is off. But I will say my lq9 loves e85.

Everything I read. Says a dcr of 8.5:1 is ok for pump gas.

 

Just throw on some LS3 heads milled .015, Cometic .040 and you'll be at around 11:1 cr. Rectangle Ports performance for price can't be beat, especially when you consider LS3 Intake price as well. Then throw in a TSP Stage 3 231-246 Cam with a 3600 stall and you'll be happy on a budget.

 

My setup is over 9:1 DCR and 225 psi cranking compression and runs great on 91 octane in a ~6,500 lbs vehicle even towing 6,000+ lbs.

 

Yeah, the 799 heads on your lq9 should basically be an iron LS2. The only variable you'd be introducing is the cam

That sounds like a good build but the 862s on my shelf and using my truck intake fit my budget even better hahaha

Good to know! I'm pretty sold on this combo since it looks like it fits my needs and budget. I really prefer working with the heads I already have on hand, there's plenty of other parts to spend some money on.

 

799 heads are NOT iron. They are aluminum cast by a different method than the 243.
But NOT iron

 

Good discussion going here, folks!

There are some things we wanted to point out. ALWAYS calculate dynamic compression at Advertised/.006" for the IVC. Don't take general octane to compression guidelines as go/no go gauges. One combo at 8:1 dynamic could knock and one at 9.2:1+ may not knock at all. It's all in the combo. Things like the weight of the vehicle, fuel, octane, converter, drivetrain, altitude, etc.

 

Never said they were, LQ9 block is

 

Agree with all you have to say. However I will add one of the most important variables is tuning. The old 30* of timing and 13:1 PE AFR that guys would throw in a F-car LS1 back in the day will not come close to working on a high compression engine in a truck that tows a trailer.

 

How does this read to you?? It doesn't say the ENGINE is IRON LS2. The 799 heads ON your LQ9 should be an IRON LS2.
See where I'm coming from??

 

Ok so I have a stupid question about this. Am I correct in assuming that when you calculate the "225 psi" that this is roughly the same number that would show on a standard compression test assuming that everything mechanically was in good order?

 

I got what he was saying. Basically that a LQ9 short block with 799 heads is an iron block LS2.

 

Cool. My apologies to OP. The phrasing threw me off.

 

​​​​​ No problem, I should've clarified I guess.

​​​​

 

@Summitracing I finally have all the parts gathered up to put the LQ9 back together, I did go with the 8715R1 cam and all the other parts we discussed earlier.... 862 heads, flat top lq9 pistions with new rings, bearings, felpro gaskets ect....

Now I'm considering whether I should upgrade the converter while I have it apart. What do you think of the SUM-700335 converter? It says 2800-3200 stall. My car has 3.55 gears and 27" tires.
Will this be good for a street/cruiser setup? Thanks

 

@mmm88ta,

Thank you for your patronage! We understand it takes time to gather parts up and get builds put together.

Onto a converter for the LQ9 with our 8715R1 in your 1970 Pontiac Tempest. Technically, a converter wouldn't be required here. However, getting a stall converter that's matched well to the combo will help get everything out of it. Our SUM-700335 converter would be a good fit for this combo if you planned on staying NA. If a power adder is in the cards we'd recommend upgrading to our SUM-700340 Pro LS series converter. That is furnace-brazed and has an anti-ballooning plate.

When going to a stall converter it's recommended to get an auxiliary transmission cooler. By design, a higher stall converter creates slippage which creates heat. This is potentially damaging to a transmission. This is where an auxiliary cooler comes in. It will help extend the life of your transmission and give you that peace of mind.

 

@Summitracing Thanks for the info. I'm excited to get the car on the road with the new powerplant. Will a converter make a big difference or should I wait until I add a turbo or something in the future. I'd rather buy a $700 converter than a $500 now and $700 later but if it's not a huge difference while I'm still NA I will hold off.

 

Yes. Get a converter! You are thinking about adding a turbo to your high compression engine?

 

@mmm88ta,

A converter will make a big difference. It's not uncommon for folks with stock F-bodies or trucks to put a stall converter in. A stall converter by itself can help off-line performance, 60 ft times, and ET. Even if you're not racing this at the strip a correctly matched stall converter will help get you moving at peak torque. A look into this article will shed light on this. There are some good takeaways on why you want a stall converter and that the car will still move under the stall speed of the converter. There is some in-the-weeds talk about 6,000 rpm converters but that still adds value to why you'd want a stall converter.

With that being said we'd go with our SUM-700340 Pro series converter for this combo. It's going to help get everything out of the current combo. If you change it up in the future and go with a power adder it'll be ready for it.

 

Maybe somewhere down the line, I know I can't leave well enough alone... I've heard different opinions on boosting high compression engines.

Right now the car is just a fun cruiser to beat on on the street and hit cruise nights with the kids. I don't daily it as much as I used to but it still gets driven very often.