Cool story bro, but what point are you trying to make? That they aren't at the limit, they are at the limit and it's fine, or? I run 30 psi with E85 on my setup so technically that's 10 better!

 

Well goddamn I knew it! You aren't taking into account anything else by saying that, like how much more boost you can run and keep the flame front stable, where does timing fall for the particular combo, where the efficiency range is of the power adder, etc. You can't make a blanket statement like that, at all.

 

Blanket statement of course, isn't everything on a forum generalized and a what if scenario. that's why I claimed if everything is planned and designed right. The OP stated 25 pounds of boost, easily doable on E85 even with a higher compression. Efficiency range of the power adder I would figure after I built the motor, don't reverse engineer it. Maybe I have a very good/competent tuner where others don't.....

 

It will be going into a street/strip Fox with a Powerglide. The original plan was SBE but my junkyard 5.3 had some scratches in a cylinder wall so that’s why I am having it bored and going with a forged piston/rod. I am trying to keep it simple, healthy and effective. I have a LJMS Stage 2 turbo cam for it, 243 heads, LS6 intake, Holley HP EFI, 2 Aeromotive 340’s (with a third pump option), -10 and -8 fuel lines. Planned RPM I think would be 6,500-6,800 RPM. Not sure on HP goal but would like the ability to turn it up as the chassis mods come. Thinking maybe an S480 turbo as well. Not sure on exact boost levels but I would like the ability to turn it up to 20+ psi.

 

I'd start off by finding a new builder who is familiar with FI LS engine platform for starters, those old school guys who think 8:1 comp with boost can be self defeating.
I'd go 10:1 or 10.5:1 compression since that's not low or high, my pump gas engine is 9.5:1 and is very forgiving as in has seen 16 lbs on pump only on accident a few times.
You'll still make oodles of power and have a safety margin, plus you could go duel fuel should the need arise.
The PG ans S480 will make for a rippin combo too, your RPM will more likely be in the 7,200-7,500 range, maybe higher.

 

So tell us, how much power is left on the table by running 9.5:1 vs 10.5:1 at 20-25 psi of boost on a "planned and designed right" combo? Being a competent tuner has nothing to do with it since it will make what it makes and as a tuner all you are doing is adding timing until it pings or stops making power for that horsepower number (and checking plugs from time to time). I have done this exact comparison on motors multiple times on various combos with the only difference being a full point change in static compression with everything else being kept constant and I've also seen what happens at the limits so I'm not guessing.

 

For the comments regarding gas vs e85 is like applles and oranges. An true engine builder starts with the fuel used to design/spec the best engine config/combo for the application.

Nic, can you summarize your recommended e85 engine config and why?

 

You'd be better of starting with a power goal. Multiple fuels can give you a given power goal.

 

Correct, I got a head of myself. HP goal may even eliminate lower octane fuel.

 

IMO someone having to ask what compression to run, shouldn't start out with high SCR's.

The high compression band wagon chatter is just that! It's sheep reiterating what the "Big Names" in racing are saying. When asked the question of how much boost or compression to run, the latest "Bro" answer is "All of it!". That's great when you race/tune professionally for 15+ years and have built 50+ LS turbo combos. But for the average guy making average power, it's just plain bad advice.

My advice to all beginners (or anyone asking these general types of questions) is to start out with any GEN4 stock long block. (nothing wrong with a 4.8!) Invest in a good chassis, drive-line, ECU, and Fuel system. They are all reusable and the key to making good power reliably. Size and price turbos according to budget and power goals. Then jump in and get some experience. Worst case you need another $300-500 short block in most cases. Build the turbo setup with pulling the engine out easily in mind. Put "built" forged motors on the shelf for now... they will blow just as easily as an SBE if not tuned correctly and you'll be out of pocket a TON more. Not to mention machine shop time and effort.

Having real world experience with a 8.3:1 through 10:1 small bore LS platforms... I can tell you the differences are minimal once in boost. *IF* you have an auto with a T-brake, both setups spool the S4XX turbos without much effort on a trans brake. Once the turbo is lit, it really doesn't matter! The lower CR motors will have to run a bit more boost, but they can make more power with less "peaky" cylinder pressure, larger tuning window, and aren't as hard on parts. More boost is better! boost is more efficient at making power than bumping SCR. Just be sure to size the turbo(s) correctly for the power goal.

For the guys having issues "spooling" with lower compression engines... The tune, hot-side, colds-side, or converter are wrong. Instead of addressing the real problem, SCR is often blamed. My 4.8 with the Big T6 S480 lights off in about 4 seconds and honestly the converter is still to tight. My 8.3:1 5.3 lit off the S475 in about 7 seconds once dialed in. And that was with a LS9 cam (no low end power) LS1 intake (again poor choice) Overly tight converter (15 stator PTC 9.5) and a 2.5" hotside (way to big!) Yet I was still able to hit 26lbs on the brake if I wanted fairly quickly. Still an 8 sec car. Took about 4-5 more lbs to run similar trap speeds as my 10:1 5.3.

Newbies arguing over 9 through 10:1 is ridiculous! Any CR in that range will quickly spool the common turbos if setup properly. Esp. at the power and boost levels discussed by the OP. My suggestion is to run a factory long block and let CR lie where it lies. Ignore it! Worry more about building a properly sized hot-side and getting the correct parts and tune.

Good luck!

 

Yeah as a couple of guys already said there really isn't just one recommend engine config for E85, lots of other factors involved besides fuel. Static compression is just one variable and surprisingly not that important as far as the final power number goes if octane isn't a factor and you aren't class limited in some way.

 

Most junkyard 5.3's are 9.9:1 CR and people have been boosting them for years with varying levels of success depending on health of engine, build choices, and competency at tuning. There are plenty of vendors / sponsors to lean on who can give you advice because they have been spec'ing and selling turbos, cams, converters, standalone EFI, and more to people running 9's, 8's, and 7's with LS setups.

They often have experience with such cars themselves. Give them a call and start narrowing the focus of your build.

 

6.0 rod and piston ly6 9:3:1 compression s480 E85 makes 11 lb of boost on the brake in 2.8 seconds. 9.80 on wastegate (13lb) in a 3600 lb car on foot brake. A properly set up hotside is more important than compression for spool. And unless you live under a rock any ls with any compression will make power lol

 

(sarcasm alert) You must be one of those Luddites who doesn't understand modern technology or the importance of the tone of a high compression idle.

 

Lol @"tone of a high compression idle".

 

The funny thing about this forum is how upset people get about someone doing things differently then they did.

 

While simultaneously also being bored by the "same ol same ol". I suppose that's the internet. I was shocked I didn't get more H8 with my rear mount build

 

Not everyone has the same goals. I like twin screws, turbos, procharger, and nitrous. Honestly though if I could afford a 600 plus cubic inch 14 to 1 motor and make 800 rwhp NA streetable that’s what I would do.

Plenty of junk yard setups that can beat me at the drag strip, but I didn’t build a drag car. I still believe where budget and octane isn’t an issue more cubic inches and higher compression is always an advantage. I mean they do have bore spacing limits etc in class racing for a reason.

Im currently looking at better options than my gto for a possible 2-3 year long build for a drag car. My gto is already near the roll cage limit and we don’t even have a roll bar in it so it’s time to consider a fox body ls build for track only lol.

 

Yay, NA vs. boost argument! Yes in an ideal world cams have square lobes and intakes/heads/exhaust scavenge so well that you make all the boost without a compressor creating pumping losses or requiring hp to drive.

 

Im not here to make that argument and I don’t care what anyone else does. I only mentioned what I personally like. If I can afford a 600 plus cubic inch motor to put in my fox body drag car that’s what I would do regardless of what anyone else thinks. Heck I’d have a 997 Musi in it if I could afford it.