I am sure that many of you are sick of this questions, but I need all the opinions and most important all the practical advise I can get for the swap for my 1989 Firebird. Here are the facts: I have a brand new 2007, o miles LM7 with the full harness from the factory and full intake with injectors, coil packs and fuel rails. I am missing the computer and the accessories. Along with that I have the ls-1 intake and the f-body oil pan and I have the added space that a ram air hood adds, so I can even keep the truck intake. I have also access to a rebuilt LT-1 30 over with all new internals, flat top forged pistons. Missing accessories opti and have a bare intake, no injectors or rails. I do have the harness and the ecm from a caprice that has been modified for stand alone operation. Currently I have a carburated 355 74 block, 69 camel hump heads with a t-5 attached. The current powertrain will go into an 1987 T/A that I "rescued" (this is the term I used for the wife) I would be very happy if I could got with a manual, which I know that with the LT-1 I can keep the t-5 until I get a t-56 (since I know the t-5 will not last) but with the LM7 due to cost I am going to have to swap to a 4L60, since I cannot keep the t-5 with the LM7 and take my time to look for a t-56. I understand that the LT-1 has better bottom end torque but the LM7 has the most potential, plus it is brand new. I guess both will need modifying the k-frame for the A/C compressor and that the LM7 will need motor mount adapters. Thank you in advance for all the input and most important your time

The LT1 has WAY more potential than the LM7.

Seeing the LM7 made the same, or more HP from the factory then the LT1, and the fact that it can use 99% of LS1 parts, and with a simple cam change, you can gain 35+ HP, id say the LM7 Has more potential.

Theres a book, where a CAI, Catback, 02+ LS6 Cam, and a bit of extra timing had the LM7 at 360hp, 350tq.

The LM7 is truely the more capable motor despite a 25ci setback. Also, when your car is setup for an LM7, the LS1/6/LQ4/9 will easily swap into its place.

Sheldon

And a CC306 cam would put the LT1 in the same range, the CI difference puts them on a similar level, it depends on a lot of things for how much you're going to spend and what trans you want to end up with. The reality of it is that either way you go, it's going to be fast, get good mileage, and respond well to mods.

LM7=

Lighter than the LT1
Better mileage than the LT1
Complete vs the missing parts LT1
No specs, but I'm betting more hp than the LT1. If not, spend the money just to finish the LT1, on speed parts for the LM7.

I'd say the LM7is a win-win choice.

Go LM7. LSx series motors are the new standard and Gen 1/2 sbc's just can't keep up with the engine design. You won't get the same drivability or potential in a Gen 2 motor. Plus you are missing so much out of that LT1 its not worth buying the missing stuff. Find a 4L60E or 4L80E would be easy.

Either one will require significant $$$ to do right but the LM7 has the greater potential.

Put a 4L60E behind the LM7 and put it into the firebird for your wife.

Finish putting together the LT1 and put that in your car.

Sell off the gas sucker carb'd engine.

I'd say go with the LM7. Lots of power can be had! Like sheldon said easy to swap and lsx later

Come on be a underdog go LT1!!!!!!!!

I vote LM7 the lt1 is great for alot of people but my personal choice is the new lsx style. the options for these just get better everyday

I really appreciate all the responses. I gathered from the responses that the gen III engine would be to my best interest being the most complete of the two that I have in my possession and I guess it is the one with the most potential.

The one trait of the LT-1 I like is the low end torque, which I think is unmatched by the LM7 but then again the LM7 is higher revving and more hp and better driveability Has anyone had any comparison experience?

I would think the LM7, being a truck motor, would have more torque. Lt1s are not know for their torque, but rather their higher rpm horsepower.

I do hafta retract one statement I made above. I forgot the LM7 is an iron block, not aluminum like the LS1, so there goes the weight advantage I spoke of.

LM7 295 HP / 330 TQ

LT1 300HP / 340 TQ

The LT1 is MAKES MORE TORQUE by far than the LM7. The LM7 is a TURD below 4,000 rpm in a truck. My dad owned one and I raced his previous L31 350 Vortec both stock and the L31 will walk away and wave bye bye (285 HP @ 5,600/320 TQ @ 4,000 vs. 255 HP @ 4,600 and 335 TQ @ 2,800) The LT1 made more stock HP than most LM7s did, with the ram air package they made 305 HP/340 TQ.

As far as the LT1 not being known for torque, it is true they don't make the torque of a TPI down low, but the LT1 is still a snappier engine than even the LS1 due to its STRONG low-end torque. Torque is going to give you the driveability you speak of. I could honestly care less what happens over 5,500 rpm. Torque is what propels the car from a stop and the LT1 excels in that department. It just needs some breathing help. The LT1 is typically going to gain more from bolt-ons than the LSx. I have seen a stock head, stock cam B-Body LT1 make 320 RWHP with bolt-ons. Keep in mind the B-car has a 191/196 @ .050" duration cam in it.

5hp & 10ft lbs.....I'd think of that as more of a varience in the dyno testing.....temperature/humidity differences/F-body intake & exhaust vs a truck intake & exhaust sytem, than actual differences.

A dyno test could be that different on a 60 degree day vs a 90degree day.

Thats not comparing one test to another, thats factory ratings, they take variances into account before rating something at a certain level. Both may test higher plenty, however according to factory ratings, the LT1 puts out more Horsepower and torque, stock.

And the factory claims tended to be on the high side, in the older years.....IE:LT1

In any case, 5/10 isn't enough for people to brag about "mine makes more power than yours"...

It is when you look at the overall dyno curve and the power UNDER peak. The LT1 takes the win there hands down. The curves I have seen put the LM7 over 25 ft/lbs under the LT1 at 2,500 ish RPM.

Sell it all and go with a regular ls1/2/3.. If the pocket book allows or you can save up, you will be better off doing it right the first time.

The only benefit to the LM7 would be the ability to go LSx later for more cubes and power. Not sure but it probably gets better mileage than the LT1.

I don't buy the arguments above since there aren't too many folks if any that have done a real side-by-side mod for mod argument for LM7 vs. LT1..

IMO the best advantage to any LSx is that you don't give up as much driveability and mileage for a given power level compared to old school small blocks..

...

uuuh...
Of course, being a 15 years old engine, it sure has more potential. Go LM7, stick a cam and call it done. Thats such a no brainer.

Why would you want to do that. It takes more to swap in a LM7 than it does a LT1. I cannot stand the gutless, put it on the floor and rev it above 4,000 rpm, just to accelerate decently 5.3.

I agree with Fast355 - the LT1 has more cubes and can be stroked even further. Ultimately, cubes will win when you get the right cam choice (something people keep overlooking). The cam will "shift" where the peak torque occurs but you ultimately get more torque "potential" by having more cubic inches in the first place. And a stroked LT1 will give you the most potential.

Lastly, when you get into modifying the LM7, remember the parts tend to be more expensive with less selection than the Gen 1/2 series. Lastly, tuning on the LT1 is far easier and cheaper which MUST be done if you want the true potential of any modern day fuel injected engine.

Add up ALL the costs of ALL options before you go either way. And then make sure you consider whether or not you may do any further modifications after that (and what modifications are even possible).

would the milage compensate for the increased cost(s) for the LM7 looking at todays gas prices the difference ( no matter how small) may become significant over the course of a year. another point to ponder

first off this is my first post on here as i was directed by a friend to join in on some of the 5.3 vs lt1 argument... we are currently under going the 5.3 swap on his 3rd gen..

i am enthusiest of most all modern day horsepower along with some old school muscle... but the argument goin on in here of the lt vs ls is almost comical

thats like sayin the lt-1 based f-body is just as strong running as the ls based f-bodys...

i may be a nooB to 3rd gens and this board but not so much as it pertains to the LS motors

whats funny is my 5.3 will out accelerate 90% of the 3rd gens and lt-1 f-bodys out there... but then again i will put nothing past an auto enthusiest because i know there is always someone out there with something faster than the next guy... i have plenty of low end torque and can top it off with some power to carry me through the big end

the ls1/2/3 is always ideal but money can restrict anything... seeing that he has the 5.3 already he might as well keep moving forward from there...

the z06 cam cam (204/218 551/547 @ 117lsa) is actually a relatively small cam to go into the 5.3 but anything over stock can have the potential to gain power where it is needed..

from what i have seen (my experience/opinion is not always correct) the ls1 has more power potential at doing less mods..

heres just a couple trucks that i know of with minimul power adders or motor combinations that are relatively cheap...


150 shot silverado squeaked into the 11's

http://www.youtube.com/watch?v=heuIT1n5Yy4
12 second all motor 5.3

i mean thats just a couple guys over on another board... i know there are fast lt-1 motors and there are fast ls-1 motors... but just the fact that there are "put it to floor and wait till 4k to make power comments" make me

boost can do amazing things on a stock 5.3 as im sure it can on an lt1... but putting 500 to the ground on 5-7 lbs of boost i just havent seen it done on an lt1...

well i got a little something for all of you guys, and i think its a no brainer, this is what i might go with and i cant see where you can go wrong, tell me what you think; thanks'.........http://www.carcraft.com/techarticles...ine/index.html

Because there is NOT NEARLY as much TORQUE as a HEALTHY LT1 from that little 5.3. I will repeat, I would MUCH RATHER have the LT1. I have seen 350 CID LT1s dyno over 415 RWHP through 4L60E transmissions.

i have owned,built, and helped out a lot of people with the good ol 5.3 in trucks. i have seen these engines with bolt ons and cams push heavy trucks to 12 second runs all day long with good tuning. the fact that the bottom end is way stronger to me it is the choice. remember-4.8-5.3-6.0-ls1-ls2-ls3-and ls6 all have interchangeable parts. my old ext cab truck with the 60e and weighing in at 4951 pounds with a full bolt on and cam went 13.7 off the gas and 12.7 on it. you have a brand new one. i say put in a cam and go to a truck board and start reading what they have done. the newer engines are even faster.

Well, not to offend anyone, but this is really a silly debate. (I used to argue against the new engines as well, calling them "trendy", etc. - but I finally looked at the design & came to my senses.) No one's arguing that the LT1* can't make decent power if built properly, but mod for mod, the new engines will beat the LT1 like an ugly stepchild 999 times out of 1000.

Why?? I believe that a large part of it is because of Moore's Law. If you're an engineer looking for better ways to design something, how much do you think it would help to be able to increase your computing power by 200% or more? Just for the sake of this discussion, let's say that it took GM three years to design each engine (I don't know how long it actually took, but that doesn't seem entirely unreasonable). Add an extra year to build them in the volume needed for production, which means that development of the LT1 would've started in 1988, & development of the LS1 would've started in 1994.

Now I'm sure that someone will correct me if my "scratch-pad" guesstimates are off, but in the six years between releases, Moore's Law would allow for a roughly 800% increase in transistor count per area, which roughly correlates to computing power. So, if your computer is eight times more powerful, then you can do a LOT more work/testing in the same amount of time, & thus, you can "zero in" on the most-efficient & least-expensive solutions for whatever you're trying to design! (Actually, it's probably more like 10 times more powerful or so, given related improvements in computer design like bus architecture, but whatever.)

In that time, the Gen-III/IV engines got improvements like 15-degree valve angles, hollow-core camshafts (to reduce reciprocating mass), etc. that have rocketed engine efficiency to levels that previous engines couldn't even have dreamed of!

So yeah, as you build power, the LT1 can hang with the newer engines for a while, but don't kid yourself into thinking that each engine's ultimate power potential is comparable - it's just not physically possible.

*(NOT LT-1, that's a totally different engine!)

I remember that article! That's part of the reason that I'd like to swap one of those into my wife's RS! And since you brought it up, this is the article that set me on the path to my L92 swap...

Looking to the future, Dart is going release an aftermarket block for the LTx that could let you build up to a 434 LT1. On the LS side, the 6L80E/6L90E might become more mainstream.

Wow never thought I'de see this back up here. I started to do the 5.3 swap over the LT1, IIRC about the time Sheldon done his (is he on 7 or 8 now?)but I could not find "deals" on the stuff needed so I stuck with what I had the LT1. Now when the LT1 gose south I plan on the 5.3 or the 6.0 and the hp per $$ is unreal on these LS motors.

There is a LOT of misinformation in this thread. I still laugh at the people that claim that low end torque is a requirement and that upper rpm power should be given up for it. It is truely funny to see that comment.

My last car was a cc306 cammed lt1 with a t56. I never got to see its true performance because of a LOT of problems and only drove it a few times. Most say that cam (230/244 .544/.596 112LSA I think) will give up a lot of low end and make the car very hard to drive. The funny thing was, the opti in my car was bad making the car run on 4 cylinders instead of 8. The car was also untuned which would make the drivability worse. Finally the car wa originally an auto and had 3.23 gears which would be terrible with a t56. Wanna know whats funny? The car drove JUST as easy my auto L98 in good running shape. So ask me how low end torque means jack squat for driving around town.

i think there can be arguments made for both engines. a properly specced lt1 or a 5.3 will run great. i believe that the 5.3 will prevail with the proper mods and tuning. the bottom ends are built better and the engines design all arund are better for the 5.3. i raced them from 1999 to 2004. and have built a few of them. loved them. i ran big cams in them with 2200 stalls. with a standard you can get away with bigger cams and no stall. with an auto it might feel slightly sluggish. i think like you mentioned it is going to better in the long run.

sorry can anyone tell me the bolt size for the back of the block trying to put my LM7 on a stand I bought 3/8 x4.5 long and i am not sure the thread size is correct..thanks dennis

I dont want to strip the bolt holes,,anyone please chime in.. thanks Dennis

I was looking at very similar swap options for my project car (keep in mind I have not done a swap and wont for a while yet). I was battling between doing a LT1 or a LSx swap. Both of these are good motors and both have endless potential given ones pocket book is deep enough(just like anyother project. A few downfalls to the lt1 are things like a very limited number of aftermarket head manufacurers, the optishit I mean Optispark is a pain in the butt. I friend of mine had a lt1 in his car and under hard exceleration it would loose oil pressure and it contiuned even after a aftermarket oversized oil pan with baffles was put in and aftermarket oil pick up. This cause 2 motors to go boom. I still maintain that the LT1 is a damn good motor despit some of these issues. The LSx motors are a great motor too and deserve all the respect in the world. It is my opinion that it is getting the "shinny new toy" affect and everyone wants to play with it. The fact is though you are getting new technology, one heck of a stronger lower end, a 5.3 which from what I understand revs for forever, and the LS series motors seem to make power easier then the LT1s. The down fall is that LS parts are more expensive, and the 5.3 will not just bolt right into your car.

Well good luck, keep us posted on what you end up doing, keep in mind that if you get ride of one of the motors, you will put you in a good step towards a t56 to bolt up behind it.

hah this thread makes me laugh. there is no question - the 5.3 is the easy choice. i'd really a hope a 350cid engine with 1 more point in compression would have more low end tq. however, comparing the lt1 and ls1 in low end tq is a toss up. those of you claiming the lt1 has more low end tq have not seen overlayed dynographs. the tq curve is almost identical in the lower rpms, but as the rpms rise the lsx carries the tq and obviously hp surpasses that of an lt1 basically off idle haha.

potential is still given to the lm7, in my opinion. the gen 3 heads are light years ahead of ltx heads. period. the gen 3 engines offer almost unmatched interchangability. no question - lm7 or die!

bump. let here some more.

Im picking up a 2004 5.3 out of a tahoe. just to sit in a corner or re-sale. or do heads/cam and use it. But the fact I have a boosted 383 lt1 already makes me think Id have to do to much to the 5.3 to = mt 383 lt1. (only reason I'm thinking keep my lt1 is its a bullet proof lower end already. see parts in sig.)

Id like to do a lsx style swap but would I really be making a step forward or backwards of what I have now?

Sell it and build a 6.0L

The 5.3 is a good engine, but much like 305 vs 350s comparisons, dollar for dollar the end is rather biased to the larger block

Since you're comparing it to your 383, it doesnt make any sense to drop over a liter of displacement and start from scratch to have an engine still limited by the smaller bore

Also of people finding this thread with a search, an 07 LM7 engine will be GEN IV. Its still LSx, but 90% of the tech in this forum, esp the wiring does not apply. Things like accessories, waterpump, intake ports etc can get tricky and the general rule of "use the Fbody stuff" doesnt always apply. Something to think on

ya, im thinking of just offing it and puting a t56 in my car. I mean I have callies dragonslayer crank and rods. JE pistons and ported heads. Cam etc.. with boost.
just running old school still. I dropped a msd distrib. in and running a 7730 with $59 code.

stepping upto a lsx style setup with boost would prob. be a night n day diff.

I re-read this thread today, and got a big kick out of some of the comparisons. Considering folks are comparing an LT-1 out of an F-car to a Truck motor as it is pulled out of a truck. The Truck motor will need a new Intake/injectors/Exhaust in order to be installed into our car. Just those items alone are going to put the 5.3 ahead in HP, and we're not even talking about using any bolt-on goodies,and we're assuming that we're using some kind of exh manifolds instead of headers. You put LT Headers on both motors and the 5.3 gains even more of a lead.


Since I have an LT-1 car, I've considered doing the swap and putting the drive train into my '91 RS, but I've listened to the advise given on this board and I'm building a 5.3 instead. One great thing is that if I want to bump the NA HP I can always pick up a 6.0 longblock in the future!

^^^ This is true, and that's why I put an $800 30,000 mile 5.3 in my camaro, I'm going to pick up an LS2 block tonight and getting it bored and stroked to a 427. Ever since I put the 5.3 motor in my car I have caught the LS fever and I'm wanting to put an LS based motor in my 79 Malibu now. You just can't beat the power and reliability these newer motors provide. Go LSX and NEVER look back!