bspvette

Hey Gang,
I currently run an LS6 in my C4 AutoX car. My class sets minimum car weight based on engine displacement, so I am thinkning about switching to the 5.3L Aluminum block motor found in some GM truck applications. But this swap will be impractical if getting good power (similar to my LS6) is too difficult.

My current motor is at 490hp stock, except for 1.8 rockers and headers. I was originally planning to swap an ASA cam to get into the low-to-mid 500s with the current motor. But now I'm thinking about going another direction.

Since I know virtually nothing about the 5.3L motor, I'm curious if any of you have an idea whether it is reasonable to get similar power/durability to the LS6. I see that this motor is listed at 310hp from the factory, which is far short of the car based LS options.

Is it just a matter of changing Intake, Heads, & Cam, or are there some potential internal weaknesses because these were intended for lower rpm truck applications?

I appreciate any help/suggestions/advice.

Thanks,
BeerMan

Baconz28

Asa cam is pretty big for a 5.3.... If you on a budget I'll lean towards a ls3 cam or a ls9 cam.

lsxRanger94

The L33 is for all intents and purposes is a 5.3l ls6. 799 casting heads flow the same as ls6, but they don't have sodium filled valves or blue springs. cam is smaller, has flat top pistons(which bumps the compression) and of course all the truck garbage on the long block. So with all your goodies(Cam, Intake, and exhaust) on this engine power will be down due to displacement comparing stock ls6 to stock L33. If I had to guess on power difference, I'd say about 50 hp. Matter of fact all your accessory drive stuff will bolt up without having to drill and tap any holes.

fieroguru

iTrader: (1)

In naturally aspirated form, the replacement for cubic inches is RPM. So to make up for the 9% fewer cubes, you will need to spin the engine 10+% higher and you will still be down on tq at most RPM's.

Most max effort (heads, cam, intake, etc) N/A 5.3L builds I have read about peak in the 505 - 525 fwhp, so that is what I would consider to be the upper limit.

I have about 430 fwhp (382 whp) from my LS4 (aluminum 5.3L with 799 heads and LS2 intake). My engine is stock except for the DoD 224/232 camshaft and the LS2 intake/LS7 exhaust manifolds. I had a non-DoD camshaft spec'd that should take me to just above 400 whp while reducing overlap by 4 degrees, but haven't pulled the trigger to get it and delete DoD.

bspvette

Good info so far. Thanks guys.

My current setup uses a 750 carb with an Edelbrock RPM intake. It runs great, but the extra height is a huge problem. So I was planning to go back to Fuel Injection & get one of the FAST intakes with a big throttle body. But if I go with this 5.3 idea, I'm guessing that the FAST combo would just be too big.

If that assumption is correct, what might be the best intake/TB option for power?

BTW, I failed to mention before that this is a completely stripped down AutoX car at 2200lb, so there is absolutely zero concern about any kind of street use.

Thanks Again,
BeerMan

maddogs15

I have an L33 on a stand waiting to go into a '79 vette when I get to that point so I'm watching this thread. Some great info here as this is a truck engine originally. http://www.truckinweb.com/tech/1208tr_5_3l_bow_tie_builds_mild_to_wild/viewall.html Of note as well is their "wild" 5.3 uses the same flat-top pistons as the L33 that they've put in an LM7. They also run the big 102 FAST as well. Let me know if you'd like to part ways with that intake if you do go efi please as I am looking to keep it carbed in my swap.

lsxRanger94

Since you are going to have to spin it harder to make the same hp or more, I would look into destroking you ls6 to the cube you need for the class. Just for the simple fact the ls6 has a larger bore which helps with unshround the valves. Since this is a race engine, you can't just throw some rod bolts at it and expect it to live @ 7500 rpm all the time. If it was a mostly "street" engine with occasional blasts to 7500 rpm, that's a different story.

check this out. It's a 6.0 destroked though

https://ls1tech.com/forums/dynamomet...p-8000rpm.html

bspvette

The stroke is the same as the LS6, so wouldn't it be logical that it can handle similar rpm? In fact, since the pistons are smaller, wouldn't it handle that rpm a little easier, since it is moving less mass?

We have been shifting the LS6 at 6500rpm just to be conservative, but several people have told me that guys spin these motors to 7200 all the time in race applications, and still get good life out of stock motors.

So it seems that I could spin the 5.3L to 7,200 as well, unless the bottom end is a little weaker. Are the connecting rods, bearing caps, etc. essentially the same as the bigger motor?

Destroking the current LS6 is not an option for me at this point. I won't bore you with the story here, but the bottom line is that if I make a change to different displacement my only option is to start with a different motor. That is a cool story on the destroked 6.0 though.

bspvette

That is a great article. I wonder how those Trick Flow heads compare to the 799 castings that come on the L33. Likewise, I have heard so much good stuff about the ASA cam. I think I will take some time to compare that to the Comp Cam part they used.

I'm a little leery of the 9.9:1 compression ratio. Is it possible to gain some compression by using thinner head gaskets, or do they already have pretty thin ones from the factory?

If I end up going with a different motor & EFI, the old motor is going to be sold as a complete deal, Air Cleaner to Oil Pan. It actually belongs to my partner, and he has a buyer already. But I highly recommend the Edelbrock/MSD 6LS combo. It worked really well on our motor. The only downside is the height. With a standard 2.5" filter, I had to put a 2.5" hood scoop on the car. And the air cleaner lid rubbed the underside of the scoop. It is actually the same height as my old smallblock with a Strip Dominator intake. I bet a 79 Vette might have clearance problems also.

maddogs15

No worries on the intake, I figured it was worth a shot. I am planning to go with the RPM/MSD box combo. I'm not overly concerned with hood clearance as I plan to go with an L88 hood anway.
As far as the 9.9:1 and the trickflow heads, I had been looking into sending my 799 castings out to TEA for a stage 2 CNC and port and polish as I've seen those heads in other articles make big power. Dependent on your cam choice and resulting PTV clearance they can also mill those heads down a bit to bump CR.
As far as the bottom end goes my research so far has shown those truck motor bottom ends to be pretty stout in stock trim. In a hot rod mag article they took a stock bottom end 5.3 (actually 4.8) and slapped twin turbos on it and essentially tried to spin it up and kill it unsuccessfully and made 1200hp at the crank. You can read about it here - http://www.hotrod.com/techarticles/hrdp_1109_stock_gm_ls_engine_big_bang_theory/

bspvette

What kind of cost do you expect to have from TEA on that kind of head work?

bspvette

Never mind, Maddog. I should have looked at their website before posting.

lsxRanger94

If you only plan on turning it to 6500 and are ok with it being down on a little power. Upgrading rod bolts on the lower end is probably all you need to be safe. Since torque will be down too, a rear gear change may be in order to keep lap times the same and help you off the corners.

chiaj144

iTrader: (4)

My L33 sees 6800rpm all the time and I haven't had any problems with it. Been running it like this for 3 years with 9-14lbs of boost. Rod bolts IMHO are a waste of time.

LS1-450

iTrader: (33)

If @ all possible, stay w/ the carb. It accepts more timing @ WOT & is more VE friendly. There are people running as much as 36* max WOT timing on a carb, whereas FI intakes generally max out somewhere between 26*-28* depending on DCR. So, if the goal is a max power 5.3L, the carb intake is the better solution.

Check out the flow/power numbers between the your RPM vs Victor Jr.. The Jr. may be producing better numbers. Although, maybe not in the case of the lower displacement 5.3L. Just a thought as something for you to look into.

bspvette

Yeah, back when we installed the carb, I was surprised to find out that the carb setup worked so well. But my primary reason for going back to the EFI is for hood clearance issues. With the extra height, it's hard to get good visibility on off-camber right turns. If I was drag racing, or running circle track, I wouldn't even dream of ditching the carb.

Unfortunately, I imagine the Victor Jr. would make the problem even worse.

LS1-450

iTrader: (33)

Hmmm...that's odd to me. I've got the Vic Jr. w/ Quickfuel carb & a small air cleaner. Created RAM air w/ a very low 2" in scoop height. The scoop is approx. 14.5"x11"x2." This is in what used to be an NB Miata; (street/road course car). Sounds like the engine in the C4 is mounted pretty high.

bspvette

The LS is mounted in the same location as the original SB. We looked into lowering it, but that would have put the oil pan lower than the front crossmember. And I didn't want to risk blowing a hole in the oil pan if we bottomed out.

I've thought about trying to switch to dry sump setup so we can lower the motor a little, but I think that's probably a little out of my budget right now.

lsxRanger94

If you are shorter than 5'10'' then sitting in a c4 can be pretty low. You could always raise the seat which is super cheap to do and keep your carb setup. 1 inch can do wonders... That's what she said! LOL

LS1-450

iTrader: (33)

Yah, having not seen your car, was thinking that maybe the C4 has a cowl intake hood in order to clear the carb set up. Cowl hoods can be huge & because they extend to the cowl, they do block the sight line. That's kinda why I mentioned the RAM air style scoop as the smallest (uses much less hood space) solution to using the carb. There's also the advantage of a more stable MAP @ WOT throttle.