Steve91T

Hey guys. So I am running a bone stock junkyard LT1 right now. My comp weight is 3400 lbs (fuel and me). NASA TT3 rules has an power to weight ratio of 9.5. Once I put in an LS engine and light flywheel, my comp weight will drop to about 3320 or so. That means I need 340's rwhp. The other thing is I need to spin it to at least 6500 RPM. Maybe even 6800. I'll probably replace the rod bolts to be safe. I would normally shift at a lower RPM but sometimes for short straight aways I need to wind it out to avoid a shift.

I'm considering two options. Picking up an LS1 from hawksthirdgen. He's only an hour and a half away, has dozens and dozens of engines to choose from and is complete....everything I need for the swap for $3k. One stop shopping. Bolt ons and a tune will get me the power I need.

Option two. I start hunting for an aluminum 5.3. Buy all the accessories I need separately and put in a mild cam. With the bolt ons and a tune, it'll give me the power I need.

So what exactly will be the difference in the two engines? My guess is the 5.7 will have more low end torque. The 5.3 will have less low end but the cam will allow it to pull harder at higher rpm?

I'm guessing the price will be about the same for the two. I will admit, I love the sound of a cammed engine. So there's that.

What do you guys think?

big hammer

Could get that hp from a 4.8 and rev to 8000 lol

Steve91T

Ha. If they came in aluminum blocks I'd be interested.

big hammer

I know that's the shitty part

Steve91T

Anyone? I'd like to start shopping soon. Thanks.

redtan

iTrader: (5)

I would take the biggest engine allowed (and that I could afford) and make it reach the desired power levels through tuning and modding.

All else being equal, a 5.7 making 345rwhp will have a much broader and nicer torque curve than a 5.3 making the same 345rwhp like you said. And a broad torque curve is king in a road racing application. Easier to drive due to smooth power delivery and no sudden hits of power plus you can shift less by having power down low in the powerband vs having to always keep it at high revs if it doesn't have good torque everywhere.

If you can, put in an LS3 in there with cathedral ports, low compression and small exhaust. You can de-tune that to only make 345rwhp very reliably (due to low compression, small stock cam etc.) but it will have torque for dayyyyyyyyyys compared to a high strung 5.3 or 4.8.

Steve91T

Yeah I think you're right. I really like gobs of low end torque on the race track because, like you said, being able to leave it in a higher gear and still pull out of the turns means less shifting, which means faster lap times and less wear and tear on the car.


One thing I forgot to mention is the power to weight ratio rule is now an average rwhp over the previous 2500 rpm and also past peak to the limiter. So that means my peak rwhp number will be something higher than 345. Maybe 360's? Just guessing.

So I know a full bolt on LS1 will be in the 340's and if I add a cam, closer to 400. After some research, I'm thinking of putting in a mild cam/springs but using the stock 01-02' manifolds (which flow better than the 98-99'). I'm thinking that'll give me the power I need, allow the engine to be happy at 6500-6800RPM and also fix my ground clearance problem since I won't have the low hanging long tubes to deal with. The money I save on headers would go towards the cam.

The other advantage I see is if I decide to change classes and need more power, all I need to do is add long tubes and retune the car.

I know this is backwards. Most people do LT's then cam, but am I correct in thinking that at my mild power goals the stock manifolds will be just fine?

Really appreciate the help.

BTW, LS3 is out. Possibly an LS2 someday though

usdmholden

Do you think you can rev that high and limit power to only 345 rwhp? The cam which spins that high will likely make more power than that, and it's doubtful that the cam which makes 345 rwhp will rev that high with any useful power curve.

It's almost like you what you would need to do is select your cam compromise and then use a drive by wire setup and tune the ECM to electronically throttle stop the engine to make 340 rwhp over a range of engine speed. I honestly don't even know if that's possible and it would be a lot of trial and error on a dyno.

Steve91T

Well that's why I'm asking here. Remember the 345 number is an average, not peak. Using stock manifolds I'm hoping they are restrictive enough to keep the average numbers below my target.

Drive by wire is an option but I really don't want to go that route.

xdanny510x

U can do that with 5.3... my old 5.3 with cam long tubes and true dual did 375rwhp

Steve91T

Do you have the dyno graph? I'd love to see it. It might be easier to hit my goal. Seems like the LS1 is either too little or too much.

xdanny510x

Let me look for it as this was back like 7yrs ago

Steve91T

I really appreciate it.

DavidBoren

I like the 5.3 because it has thicker cylinder sleeves, and that, personally, gives me peace of mind in terms of longevity, durability, and the potential to add boost. Also, the 5.3 will be easier to keep within your class limitations. Any halfway decent headers/exhaust and an ls6 cam with the tbss/'10+ truck intake should put s junkyard 5.3 right in your target power range with a good tune. It will still have all the torque you can possibly have traction for, and should be plenty driveable with the stock ls6 cam.

Steve91T

Well I can say this, I will never have boost and the truck intake doesn't fit under the cowl of an Fbody. So I'm thinking a mild cam will put it where it needs to be.

But that's my guess. You could be right about the traction issue, but then again there's no such thing as too much torque.

DavidBoren

Fair enough. I am still a fan of the 5.3's thicker cylinder sleeves, even without boost. I also think that a 5.3 with a full compliment of ls6 stuff (heads, cam, intake) would be better suited for the job. Running a 5.3 with a headers and exhaust to reach your performance goals seems smarter than nerfing the performance of a 5.7 with restrictive manifolds to keep it from exceeding your class limits. This is a performance application, after all, so increasing the performance of a 300rwhp 5.3 up to 340rwhp with the benefits of headers and exhaust make more sense, to me at least, than de-tuning a 400rwhp 5.7 motor to 340rwhp.

onebadbowtie86

iTrader: (13)

If your limited to 345rwhp why not just put a stock ls1 in it? If it dumps a little low throw a better intake on it like a fast or ls6?

Steve91T

Because I need an average of 345 rwhp. I don't think a full bolt on LS1 will do it.

big hammer

The later ls6 cam gives you a very long range of peak or near peak hp. Would likely be good for what you're wanting to do.

Steve91T

Good to know. I'll check it out. Thank you.