BURL

Getting ready to pull 58K LS1 to install a forged bottom end of some sort. Original, plan was rebuild LS1 with forged rods, pistons and limit boost to around 10 PSI but been seeing some healthy Mustangs locally and ow am considering 15 PSI boost.

Car specs:
3.46 gears, stock weight, buillt trany (A4), built rear, trans axle brace, all the standard bolt ons, meth injection, safe street tune, 95% street/5% 1/8 mile. Heads (cathederal port/ square port) will depend upon final configuration. Compression will be 9.5 - 10.25 as tuner (who I have not chosen) recommends. ARP bolts top and bottom. Professional machining and build. Small blower cam limited to 6500 RPM.

At about 15 PSI will I be OK with a forged LS!/LS6/LS2 or should I step up to LS3 block. I haven't seen many people on here with block problems. Of course the LS3 block is stronger but is it a necessity?

I have thought I would go no larger than 6.2 liter. I think this would help the life of my drive train as opposed to going 416 or larger. The reduced torque would be gentler on hardware, not to mention easier on the pocket book for gas. Thoughts?

One last thing - if I stick to 6.2 liter wouldn't the smaller port cathedral heads give better response and torque at lower RPM than the substantial larger square ports?

Lot of questions but any guidance would be appreciated.

Turpid porpoise

Boost is just a measure of restriction, 10 psi on a 6766 is not the same amount as 10 psi on a 8892. What you need is a power goal, not a PSI goal.

With that said I feel a forged LS1/6 is will easily hold 7-800whp on the street but I personally would go ls3 for the increased low end grunt.

ysb02

The ls1/6 blocks don't have as long a sleeve as the gen 4 iirc so people keep them 383ci and below. I'd just do a 347 with your current block.

I don't think it worth it to go to the ls3. If you want more block strength and more low end power do a 408ci lq9. Most of the engine builders I've asked recommend iron blocks over 800-900 rwhp.

neverstop

arun went deep into the 8s on an ls6 block i believe and lots of people made plenty of power on ls block. if were me I'd just forge the ls1 with some good rods/pistons, leave crank stock and 346ci and then throw a healthy blower at it

the single most important part of this whole thing is the blower and I don't see any discussion of that. I'd think a D1x would be perfect here

BURL

IF i go LS1/LS2 block you guys see no good reason to put in mild stroker and go 6.2 liter?

I don't want to go 383 because of short liner issue. The 376 would be shorter stroke yet have more guts than a 347. It would also allow a slightly larger cam to achieve the same power at low RPM. I don't want a huge stall and enjoy a nice lumpy idle since I'm a old muscle car dude - I don't want a thumper (will go probably lower 200's on duration with 1 or 2 degrees negative overlap on 114 + 4) . Those thumper days are behind me and I want to be a least semi-stealth. So what's you opinion on 6.2 liter? I'm considering selling my 58 K engine and buying a built short block (Thompson, Mast, etc). If I do that the premium for a forged crank to get the 6.2 liter won't be huge.

hatewhatownsyou

I would suggest you to reconsider your compression ratio and go 10.5:1
One compression point is around 40horse. Low compression has its place in boosted motors but if your not gonna push enough boost to need it then why give up free power.

Ls1 blocks are good to 8-900 safely, if you don't plan on going over that just build the ls1 and be done with it.

neverstop

my last motor was a stroked 402ci ls2 and this motor i have no is a stroked 427ci LSX Block, my next motor will be stock stroke, so many reasons why I think it's superior so if it were me if you go ls2/3 i'd go with stock stroke.

but throw even some lower cost forged rods/pistons in that ls1 and you'll be out the door cheaply and it will easily take 800+whp with a good tune.

ysb02

Why's that? I'd stick to stock displacement on the al blocks but the fe ones seem to handle it much better.

BURL

This is the OP. I'm working on a C5. No reason to go iron - sticking with AL for handling reasons.

BURL

At what approximate boost level with centrifugal charger and meth injection do you think lowering compression is appropriate?

hatewhatownsyou

my motor was 10.8:1 and I was running 12 psi on stock bottom end with no timing- made 650 to the wheel. (We didn't add timing to try to not blow my stock bottom since it made so much power )

I just forged my motor and and kept the compression the same and I'm hoping for a couple more psi in tweaks I made and I added another meth nozzle in front of the blower to help efficiency

I did a lot of searching about this
There's people running 11:1 with e85 and 20psi (idk what this equates to with 93 and meth)
There's various people running 11:1 with meth 93 and 12psi

My car will be dynod Wednesday but I would guess somewhere around the high tens would be the limit, but again this is a guess. Hopefully someone with actual experience will chime in.

I would atleast go to he upper CR range that your engine guy said

neverstop

the longer stroke makes the piston skirt come out of the bottom of the bore and honestly at 800whp+ on the street you don't need more mid range at all as the car will spin even drag radials at 75mph+ on the freeway. Plus the blower/turbo will be more efficient on smaller ci setups and you can rev them higher. I would happily trade 75tq of mid range away for another 700rpm of high end on my setup. It is debatable but I believe that the shorter stroke would be more reliable too at bigger power and probably last longer with less block and crank flex. You don't need a big CI motor to make big power once you move to forced induction as the blower really dictates your power. Lots of guys with smaller displacement motors making big power. Shoot, there are dozens of guys on stock 4.8 and 5.3 motors making 800+hp and going into the 8s and one guy at least in the 7s. I know not apples/apples but look at the torque curve on a 3.8L GTR setup with stock turbos and e85 fbo.

I was stuck between 9.5:1 and 10:1 for my new motor on pump gas/meth and so split the difference and went with 9.75:1 and it's running great on 91 octane with dual meth for a long time now. makes 900whp and 860tq at wheels on an old D1SC procharger and there are a few little things I could change to make it better if I cared to (better headers, etc)

BURL

So you're at 9.75:1 and making 900 +. Do you think you should have gone 10.1:1 or higher as some in here have suggested?

hatewhatownsyou

Never stop- how many psi are you at? 20ish?

neverstop

If I was doing it again I would go higher compression for sure. Maybe 10.5 or so but depends on what fuel you plan to run. My 91 pump gas in my area is terrible so wantes to be conservative but methabol is awesoms.
Car makes 15-16ish psi but psi means not a lot as I could change the cam and make more psi and less whp. Psi just measures resistance or back pressure through the motor. If you get better exhaust youll probably make lower psi but more hp

hatewhatownsyou

Oooo this is with a 427 right


Only thing I don't understand is why would a cam that makes more psi cause you to make less power? I.e. A blower cam?

I understand psi is just a measure of resistance and your engine conbo and how well it breathes will dictate That. I just swapped a XE-R na cam that made 12 psi for a stage 3 blower jam cam to make more psi and power.

neverstop

I'm just making the point that focusing on psi is not correct, you could stuff a potato in the exhaust and block it up completely and make 1 million psi of boost and obviously zero hp. The motor is just an air pump with fuel added and psi just just a measure or restriction in the motor.

I'm not saying any cam will change the psi lower, but if you made a cam that closed the exhaust valve earlier then you'd up the psi and probably make less power since you would ultimately flow less fuel and air through the motor

my setup is 427ci yes, and I should have gone higher on the compression, would have made more power, ran cooler, etc and just been better overall.

Rkreigh

I'm going to try an old turd iron block 4.8 with wiseco pistons and gen 4 rods

I was going to go alum block and forged 4.0 crank, and 3.82 bore alum block, but I think a broader power band, with the smaller displacement will fit my 58 mm ttix turbos better

I also have the champion 3" downpipe, and I'm going to retrofit a c6 3" exhaust and cut the package track to fit it in.

I also have the .82 exh housings that I want to try to help the top end breathing on this system as the turbos should flow enough for 1k at the engine, with 800 plus as rwhp as I believe that's all the suspension and tranny will have any hope.

I'm also dying to try boost by speed and traction control, and I'm hoping the wider power band will help keep the car hooking with a bit less torq at the bottom end but a nice fat mid range and top end pull

Not ideal, but I'm hoping to keep the power planted better.

The car already has an RPM 4l60 Lvl 7 auto swap, and so far it's holding up great. Might be time to freshen it to level 10 and if I save some coin on the short block (already done) I might be able to afford it.

I'm tired of looking at it, and "waiting" for more, time to boost a move.

I was going to put this engine into my old c3, but honestly, it won't handle it and would take too much suspension work to have any hope of hooking the power.

the c5 will plant it and go@!@

hatewhatownsyou

Just to give you some better reference results

I made 737 to the wheel, 10.8:1 on 93 and meth and 16psi
The tuning guy said he only felt comfortable putting 16 degrees in it without race gas

BURL

You seem like a guy I need to talk with in detail. I've decided to go LS2 with mildly ported cathedral port heads. I don't want the larger LS3 bore with cat. heads. I want the cath. heads for higher velocity for low end driveability and torque until the supercharger kicks in. I do not want a high stall - possibly max of 2400 - 2800 RPM. I want to get to about 850 crank HP. I'm assuming about 15 PSI.

I have 72 CC, lightly ported 317 castings (290 CFM @ .600 lift) that can be surfaced to get the compression ratio I want. Locally I can get decent 93 octane but I want to setup and tune for 91 in case on the road I can't find good gas. I'm thinking 10.25 with twin meth jets to kick in when necessary. I'll be using baby blower cam with low twenties duration on a LSA that gives me about -2 degrees overlap. This is an A4 with 3.42 gears.

Suggestions?