ive been doing a lot of research and as many of you im sure have read, it looks like the LE2 package from elliottportworks is one of the best bang for your buck and reliable ways to get over 400rwhp on a stock bottom end LT1 motor. my question is this. If you are starting out with an LT4 instead of an LT1, how much higher do you think the rwhp would end up? I know Loyd has said that he can get the LT4 heads to flow damn near 300cfm on the intake which is the same as the highly respected AFR195 eliminators. obviously you would need a higher spinning cam to take full advantage of heads that flowed that well and i wonder if bottom end (under 2k rpms) might suffer a little with head chambers being so big. which brings me to my next question. my motor has a lot of miles on it. it still moves and screams like a raped ape but has accumulated a few miles over the years. a little over 150k to be more precise. I dont want to spin my motor up to 6500 or higher for fear of spinning a bearing, as well as the fact that i dont have forged internals or increased displacement so i dont want to lose much on the bottom end as well. i have pretty much all boltons right now including a full exhaust, CAI, TB, lightweight flywheel, new clutch, electric WP, ect. the only thing i dont have but would get at the same time is my intake ported and injectors and tuning. just curious if anyone here has or knows anyone that has sent off their LT4 heads and intake to LE for a LE1 or LE2 package with stock displacement and bottom end and what their results were. any input is welcome.

 

I thought the big advantage of the LT4 over the LT1 is the top end (heads, cam, and intake).

I'd imagine there wouldn't be a considerable improvement over doing the LE2 to the LT1, since they'd wind up with more similarities than differences after the mod.

 

Pretty sure the bottom end is the same.

 

Lloyd did an LE2 port job to my LT4 heads; they flowed 296 CFM when he was done and the intake ports came in at 210cc (stock LT4's start at 195cc, LT1 at 170cc). With one of his cams, my 383 LT4 made 450 RWHP. We talked considerably about doing these heads on a stock LT1/4 bottom end, and 400 RWHP is very doable, especially with a ported intake.

As far as a power increase, it depends on the entire combination, specifically the cam. If you have a stock bottom end and keep the revs under 6000, the LT1 heads might actually make the car faster, since you probably can't use added flow and the extra port volume will just hurt your bottom end power. Lloyd is a very nice guy and very willing to answer question. Email him and he will set you straight on what you do or don't need to reach your power goals.

 

Since you're starting out with the LT4, I would think that the package would put you really close to the 400 range. The crankshaft is different in the LT4 than the LT1. The major difference being that is cut differently to handle torsional vibration, thus allowing for the higher compression ratio and higher rev. (6200 redline)

What I have come to understand about the LT4 is that in it's original design, heads and cam, that the engine made 400 bhp. At this time GM Marketing said "you can't do that" so they added material to restrict head flow and put in a smaller cam. I think what is sold as the LT4 Hotcam, was actually the originally intended cam for the motor.

If you look up the grandsportregistry they have a little article entitled LT4 vs. LT1. This is a pretty detailed analysis of the differences between the two engines.

With your miles, however, while your heads are getting their makeover, it might be a good idea to have those bearings replaced. It's better to replace a worn bearing than a spun bearing, don't you think?

 

i have never taken the heads off of my LT4 but to the best of my knowledge, it takes a little more than that to get to the bearings in an LTX motor. i beleive to replace the bearings, i would have to take out the crankshaft. that makes it a hell of a lot bigger job than simply taking off my heads and intake especially if the motor is left in the car.

 

As with all SBC's, the rod bearings are going to fail before the main bearings, and you can absolutely do rod bearings without pulling the crank or taking the engine out of the car.

 

Yes, you are correct that it is a much bigger than job than pulling the heads. But it is a much smaller job than fixing a spun bearing, which from what I've read and personal experience is not uncommon LTx motors. The tolerances are pretty tight and combined with the fact that they run a little hotter makes them prone to this particular problem. A spun rod bearing will at least mean replacing the crank, at least the rod involved, possible machining of the block. And of course, the worse case scenario of killing your engine. I'm not saying it's something that is required, I'm just saying if/when I go to have my heads ported, I'd get new rod bearings too. I was just offering this as a suggestion when beefing up a high mileage LTx motor. No big deal, just saying.

 

LT4 bottom is improved for higher rpm operation....rings for example....LT1 rings have high blowby when you start going above 6000 rpm

So LT4 bottom doesn't really make more power than the LT1 until you get to about 6000 rpm and then the LT4 becomes both more reliable and efficient..

I now have the limiter on my stock bottom set at 6800rpm which I get to quickly as my power peak is about 6500 with my mods

 

Honestly i would sell your lt4 stuff and send the some cheaper lt1 heads off if you truly want the kit.150k is some mileage but if its always had good oil and not completly beat on your engine is more like 50k inside.Todays oils have done leaps and bounds over the older stuff and ive built several 4.6 dohc cobra motors from high mileage lincoln donars that were dd cars and i even done one with 310k!The inside of that motor was as good as some that had 100k-BUT it had been maitained and syn oil in it from day one.The timing chain failed,not the bearings,which were worn but was in spec!

Your not going to pick up any much more over the lt1 stuff he sells,because he is turning the lt1/4 heads into the same thing.Thats why id sell the lt4 heads.Would help pay for the work too.If you have unlimited funds and plan on keeping the car forever(and its in real good shape),dont trust the bottom end you might as well go 383 with those new bearings.You would be stupid to just do the rods and not the crank

If your going to do this its not that hard to pull a engine,you will find it makes the rest of your work(HEADS,ACC,CAM,BEARINGS) REAL EASY and actully take less time,take advantage of that clamshell hood!

 

Id be hesitant to spin a 150k mile bottom end up real high. COuld last a long time could bomb quickly, if it did it would probably destroy those heads. If you already have the LT4 heads Id keep them.
Typical LT4 ported intake heads with Hotcam runs pretty good but why not save up and stroke it, 383/396 would like a 210cc head much better than the 350. Just a thought.