LS motors: Big CI vs small CI + FI

Disclaimer: Mods, if you feel this is in the wrong section, I understand if it is moved - since it is a bit cross-platform, I was hoping to get some opinions from the experts.


So I've been giving myself an ulcer thinking about next year's project. I know I'm gonna be shooting for some big power (650+ RWHP) but I'm not exactly on the "How" I wanna get there

I guess it boils down to two categories: Big cubes or small (maybe even stock) cubes with FI.

There are pro's and con's with each obviously. Personally, I have always wanted to do a Procharger setup on maybe a stock-ish (347) cube, built motor. But then I look at it, and I could probably get near the numbers for a bit less money stay with an N/A setup on maybe a 427 or 454.

How about power efficiency? I'm guessing I would be safer on a big cube setup since I would be making a lower HP/CI number. I know both big cubes and FI are both gonna build good torque throughout the curve, but which curve is gonna be better for a mostly-street/some-strip car?

Reliability? I supposed you can make a case for both with proper tuning, fuel system, etc. I'm guessing long term and FI would be a bit more maintenance.

Risk? More could go wrong with FI I would assume, given boost adjustment, detonation, octane issues, etc. I know the LS block can handle good power given the proper tuning... but would this be pushing the limit?

Just thinking a bit out loud here. This topic is directed at my specific LS1 setup, however I supposed it could be compared against all SBC setups. I would appreciate the insight and experiences of people who have hammered out this issue themselves. I didn't make a poll because this is more of brainstorm session than a cut-and-dry decision right now.

Thanks all

I hear you. :D I think for the power level you are looking at you will need a power adder no matter what for a "streetable" car. The larger the motor the less "wild" it will have to be.

Maybe consider a forged SB turbo car with an intermediate cam and compression so that when you are driving it normally it isnt a dog, but doesn't get horrible mileage either.

My thoughts on the subject is to go for a 6.0 or ls2 block for more cubes. Forged crank will drop in and get you 408ci very easily. Run very mild compression and keep the cam simple. Run the best heads you can possibly afford with an eye toward the larger port sizes. Buy a nice big head unit for the supercharger setup so you have a little room to grow and plenty of airflow. That way you have a pretty decent size engine with good manners that will outpull the bigger n/a stuff all over the place.

Don't forget you need a really good rear end and transmission and a hell of a fuel system to keep it reliable and happy. If you dont know a good tuner find one and make very good and sure that they know how to tune forced induction ls1 cars. If you happen to get a hack for a tuner you're going to do nothing but scatter the engine all over the road or dyno.

Go big cubes! You can always add the supercharger to it later. :devil:

FWIW, someday I want to build a 408 for my Z28. :D

Go big cubes! You can always add the supercharger to it later. :devil:

FWIW, someday I want to build a 408 for my Z28. :D

Agreed. Do the 427 now and add the turbos later!:D

I used to ask people that ask this kind of question 1 thing. Are you racing in a class that has a maximum displacement rule? If no, then build the biggest engine that you can.

These days I would also ask how important is fuel economy to you?

Two years ago I saw a 500" LS2 being put together. Now that there are even more tall deck blocks available, I'm wondering why there aren't more of these monster motors out there?

Agreed. Do the 427 now and add the turbos later!:D

Actually it's a bigger decision than that. If he goes NA and shoots for 600hp it's looking at very high flow heads with a long duration cam and high compression ratio.

My 500hp 396ci LT1 is a prime example. The fueling requirements for such in a NA means 39# injectors and a single walbro 255lph pump will suffice. Adding Nitrous for a 100 is pretty easy but beyond that the concerns of the pump keeping up comes into play.

A 600hp NA engine will probably be fine without more than a single pump, but the same design with FI will have less headroom.

To build a 600hp NA engine and "slap on a turbo" later means:
1) turbo, intercooler, plumbing oil lines, headers, ets...
2) fuel pump upgrade... dual probably plus new, BIG injectors.
3) a tranny than can handle 800+hp...
4) new heads... why? because no small cc combustion chamber used in NA is gonna play nice with FI at those levels. If not it gets worse... rebuild the bottom end with new pistons.
5) vaccum pump... not essiental for 600hp, but in a FI application that large you can expect a good amount of blow-up that needs some help.

Slapping on a turbo is NOT cheap, and in a high hp NA it's even worse...

Personally I went with more cubes (396 vs the 383 or 355 options common in LT1s) and decided a nitrous hit will suffice if I need more.

If you're set on FI you're way better off going with the strongest block you can find, cool and vaccume pump it, them boost the sucker with a big ass supercharger (easier to tune and install than a turbo for LT1's, though I imagine the same advantages of rpm-depandace and header availability applies to LS1 engines as well).

Ultimately the NA engine of the same hp will pull harder down low, be lighter, and probably cost less... but the options for more ponies afterwards are limited to Nitrous (and even that will probably require another pump and new pistons depending on how much you want to add).

"Just slapping on a turbo" consits of replacing about have the engine at those levels... it aint' any cheaper.

Superchargers also have the advantage than you can just pull the belt and get better gas milage and less hp (if say you have a kid you wants to borrow the car... although a good tune limited to say 3500rpms and timing retardrd can do just as well I guess).

What is the budget? What fuel does it have to run on? Why 650hp? What parts do you already have? Have you thought through the fact that with that kind of hp, the motor typically ends up only ~40% of the whole project cost? There are many more 650rwhp cars on the internet than on the road and there is a reason for this.

I don't think a hp goal is the way to go about it. I would start with an idea of what I wanted to do with the car and a budget. Get the most for your dollar you can, rather than pick a number.

Rich

Rich, thanks for the new quote in my sig

Rich, thanks for the new quote in my sig

;-)

Get the most for your dollar you can, rather than pick a number.

Rich


Well that is what I was kinda going for. Maybe I phrased it wrong. Money isn't exactly the biggest concern, I just want to make the most efficient, reliable power for the money. I understand that either setup will likely be in the 12k to 16k range when its all said and done.

Currently, its just a heads and cam car. Obviously, with the aim of the setup, the motor would pretty much be thrown out with either direction I go. I understand that I'm going to need a new fuel system, more suspension, etc. The 9 in is about to be ordered and I've already talked with a Trans guy...

I'm not saying that the car HAS to make 650 RWHP for me to deem this project a "success", I'm just kinda using it as a starting point for what I would like to get out of the car. Basically, a radical big cube motor, maybe 427, 454, etc. vs a built 347 with a D1 S/C at 12-15 PSI, blower cam, etc. The target would be 93 octane to retain a respectable amount of "street-ability", but could still make a few adjustments for a nice track setup as well.

I started with the 650 rwhp also as a point of comparison.... which setup, at that power level, would be more efficient? best torque curve? reliable? etc.

Believe me, I'm not one of those "I NEEDZ MOE HORZPOWA" kinda guys. They say every project needs a goal, and I thought I worded this correctly. Now I feel stupid lol :(

Actually it's a bigger decision than that.

I don't know if you noticed the smiley there but I was joking.

I just want to make the most efficient, reliable power for the money... I understand that I'm going to need a new fuel system, more suspension, etc. The 9 in is about to be ordered and I've already talked with a Trans guy...

The target would be 93 octane to retain a respectable amount of "street-ability", but could still make a few adjustments for a nice track setup as well.

... which setup, at that power level, would be more efficient? best torque curve? reliable? etc.

Good to hear you've taken care of some basics already, that'll help a lot. For 650hp in a NA engine you'll need at least 350 cfm from your heads... doable with a LSx design, hopefully your current heads are close already... but I'd wager you'll need closer to 380cfm to really get where you want to be. The more cubes you pull the easier it will be be to cam those heads as well. My 396 pulls a decent curve with a hydralic cam and some pretty aggressive porting. I've never built an LSx engine though so I'm sure someone here can point you in a more detailed direction.

The real issue I guess is streetabliity and the shape of the power curve. Having gone the big cubes direction with a 7000 redline, I'd say it was a good decision, though for 650hp you may not be in such great shape for idle surge... especially in a LSx which don't tend to like as big cams at idle. Once you get it tuned and dialed in you'll be fine, but I'd be careful about trying to break new ground on your first big engine... find some examples of similar builds and see if the owners have any tips on hp goals and specific parts to avoid or endorse. I learnt a lot by building my 396 (or in reality taking direction and supervision from gurus who knew what was up) but like I said, it was a LTx build so the parts and lessons aren't all directly transferable.

650 isn't gonna be easy, but with a high compression engine, and maybe a vaccum pump and the willingness to look at a true shaft rocker design you should be able to get there. With your concerns of idle and low rpm drivabliity I'd seriously consider a custom cam.

FI would make this easier on the engine build (less expensive heads, maybe even the same ones you use now) with some extra work in installation... though once it's built it probably is easier to up a few ponies as needed... plus the idle and drivabliity when off the boost would probably be better than a similar powered NA engine.

If you plan on road racing it or even auto cross I'd have to say big cubes win any contest, but on a strip the FI designs allow for some wicked launches using a transbreak, automatic tranny, and some big set of brass balls. :)

I imagine a auto tranny is a given for this build unless it is a road racer or like me you prefer a stick just for fun factor. Expect a T56 rebuild(s) with this much power... my 396 is chewing up the T56 in only a few months of driving... I expect I'll go with face-plated gears on rebuild. Turbo may be easier in this regard if you plan on sticking with a stick. Heavy torque down low makes it too easy to lug an engine without realizing the damage youre doing.

Nothing about big hp is cheap. :)

It's only a question of money. How much you have or want to spend will dictate what route is best to take. Stock displacement at either 6.0 or 6.2 is plenty big IMO, and will allow re-use of the stock crank which handles big power numbers without fail. With a well tuned twin turbo kit your number is easy to obtain. I think the easiest way to get there right now is building off the LS3 platform, block, crank, and heads. If you are using FI, adding those extra cubic inches for a street car only makes sense if you need to have that "408" or "427" decal on the hood...

I dont really know how to answer your question. Either a 347/348 with a supercharger, turbo or a 427ci+ LS motor will both produce 650rwhp, with reliable power, some street manners, and will be blast to drive.
As far as which one who be more efficient depends on many variables. Same with the TQ curve, etc, etc.

If you want 650rwhp through a a4 your really going to be spending some money, espeically if you go 427+ LS.
I would look into a 455 or larger, I think they stop at 481's but not for sure.
Pick up a set of Ls7 heads and intake work a good amount of work done to them. Get the best heads you can afford/find, because they will dictate the untimate power of the motor. Than find someone to grind you a custom and pick the bottom end.

FI- again get the best heads you can afford/find. Get a fast 90/90 intake, pick your compressor, find a cam guy, and than pick your bottom end.

Either should be able to hit 650rwhp with some reliability, driveabiltity and a little mpgs.

As i said in the begining of my post, you cant really compare the two unless you have some basic parts for a 'Combo" picked out. Than you at least have something to base arguments on.

What ever you do good luck.

An ~750hp NA (~650rwhp) motor is going to be a very highly developed situation. I wouldn't even think of that as a goal unless I had BIG money and lots of time. It is not nearly as easy as the above post suggests. It will be far easier and less expensive (but not cheap) to reach that number with a blower. If I was contemplating a 650 rwhp LS based street vehicle I wouldn't give NA any further thought. IOW - fuggedaboutit.

Just MO.

Rich

I didnt try to make it sound easy. Nor cheap, a well worked set of ls7 heads, and intake, the rest of the valvetrain could easily be 4-6k.
Depending on mild to wild. Than you have to get a good bottom end. another 4-6k(427+ cubes).
Fuel system 1k, trans 2.5k, rear end, 2k, suspension/ chasis 2k, misc. BS 1k. 15-20k total.
If your are paying someone to do everything add another 4-5k. And i probably forgot some stuff too.

trans 2.5k

SixSpeedsInc (formerly T56Rebuilds) will take a T56 and build it for 700rwhp/700rwtq for a lot less than that. CPT will do likewise (although they won't actually stick a horsepower number on it) with a 4L60E.

:shrug:

Like I said, the only practical way (and I use the term loosely) to have street car at those power levels is with forced induction. But everyone is going to have a different opinion. How many of them actually have a car with that kind of power? Then ask how many of them are NA?

Rich

I don't know of any LSx based N/A motors that are putting down over 650rwhp. Even a LSx 454 doesn't put that down, probably closer to 550rwhp. Most forced induction LSx street motors are putting down right around 650 - 700rwhp. Of course there are a few exceptions, but that is what I see mainstream around here in Texas.

What are your performance goals? HP goals don't mean much to me, some people really get into racing dyno's and bragging hp number but the car doesn't run anywhere near it potential. There are plenty of over rated cars out there under-performing and making themselves look bad and the mark look bad.

Built what best suits your interest and your pocket book.

Rapid motorsports has a SR 427 laying down 675rwhp+. Katech(sp) and a few others have 427's+ making 600rwhp+. If you spend a little time reading on LS1tech.com you will see.

PRC broke 400cfm's with ls7 heads. Several other aftermarket head companies are aound 380cfm's @.650.

I am too up to date on trans's, so thats why i was a little high. But i feel that my other numbers are close.

Quote:
Originally Posted by tcr98taws6
624 RWHP with this build as shown in the August 2008 Car Craft Magazine. Oh, it also got 21 MPG at 80MPH average, windows up and A/C running coming home from the 2008 Power Tour last weekend.


From LS1TECH. Dammit it didnt post the article. Think its a 454 by LME, m6.

Starting back in the early 60's with the (in)famous Pontiac GTO v. Ferrari GTO test I learned to read things in car mags with a BIG grain of salt. The Internet is even worse.

Rich

Ya think!!?

I understand all that. I know everyone on here has a 9 second car that no one evers gets to see hear or ride in.

But there is a thread over there titled 600rwhp n/a.
Theres about 5 pages of potential combo's. I know most of them wouldnt touch it on their best day but if you have a 370-390cfm head you should be able to get there. Especially some of the 454,481 solid roller combo's.

I have a 468ci BBC in my race car. The heads flow ~375 CFM. The CR is 13.5:1 and running methanol through a 2000 CFM TB with 2.25" open headers with a SR cam at about .700" lift. It doesn't make 650rwhp, though I suppose it might through a manny tranny. A pump gas 650rwhp NA OHV V-8 of <500ci is a tall order. Probably not impossible, but a lot of R&D is going to go into it. The GMPP 572R is 750hp, so it isn't 650rw and it runs on race gas. The pump gas version makes 620hp - good for a bit >500 at the wheels.

Rich

^^^^^^Thats why I like performance goals versus RWHP goals, a good operator can make the dyno read some pretty bodacious numbers. I agree with Rich, real 600 plus hp NA on pump swill are few and far between.

Back to the original topic, go blown.

Ok, you proved me wrong. I stand corrected, I am starting to understand.

But there are many LS motors that are knocking on the door of 600rwhp, NA, pump gas.

They are all 416,427+ cubes. I starting to see that 600 rw is about the limit for fully worked ls7 heads, a fancy bottom end, and a monster cam. Very few break it, but the majoirty dont. The ones that do are SR cammed, sheetmetal intake, blah blah blah.

Agreeing with others on this thread. Go blown. Cheaper to make the power, driveability will be better, much more reliable, etc.

lol, boy this thread has gotten outta control.... you throw one guess-timated number in parentheses and it becomes the entire thread. ;)

Like I tried to say, I just threw out the 650 number as a base for comparison.

The REAL point of this thread was more to discuss the power efficiency vs. reliability vs. durability of a big cube motor against a small cube motor w/ FI.

I know 650 is a huuuuuge stretch for an all-motor setup, but I was more curious to learn what motor is making "better" power. Which would likely have the better power/torque curve? In a perfect world, which one is more reliable of making that power? etc.

I know 650 is a huuuuuge stretch for an all-motor setup, but I was more curious to learn what motor is making "better" power. Which would likely have the better power/torque curve? In a perfect world, which one is more reliable of making that power? etc.

Whenever you stretch an engine to its power limits by using a ridiculous cam, ridiculous timing, etc, you're going to be looking at a relatively narrower, peakier power band than an engine making the same amount of peak power through less ridiculous means.

This is true regardless of the size of an engine. I can get my LS1 to 500rwhp NA at stock displacement, but I'd have a much smoother powerband and a much more streetable combination if I did it with a blower instead.

A ricer with a 2.0L Honda 4-banger can get up around 300whp NA, but his buddy with a turbo on his 1.6L is going to make the same peak power over a much wider RPM range.

Etc, etc.

The most reliable setup is going to be a naturally-aspirated motor that isn't running anywhere near the peak power potential for an engine of its size. I like ~1rwhp/ci as a rule of thumb (I also like manual transmissions; adjust accordingly if you're going to be losing power through a torque converter). 450rwhp out of a 427 or 454, and you'll never have a second thought about reliability. Sure, you could crank those up past 500 no problem, but the higher you go, the less streetable it's going to be.

Adding forced induction is a great way to add power while retaining streetability, but it's at the risk of reliability. Assuming they're put together equally well and using equal-quality components, no blown motor is ever going to be more reliable than it's lesser-powered NA cousin. The simple fact is that by adding the FI system, you've added more parts that might fail, and you've added more ways the system as a whole can destroy itself.

I'm probably not telling you anything you don't know. :)