Why the LT1?

[Stallion]

I see that it seems to be good to have an LT1 block in your Vette and I was just wondering what made it that much better than most small blocks (it's a small block, right? If I remember correctly it's a 350 ci?).

Thanks! :D

TR

[LT1Vettepilot]

Well everyone calls it a 350...technically its a 346...but hey, who's counting ;)

Depends on which LT1 you are refering to...wether it be the earlier LT1s from 1970-1972, or the newest version, the 1992-'96?

I'm not sure about all the details, but the earlier LT1s had solid lifters, allowing for a higher max RPM. There may be some more reason behind the earlier ones, but they are beyond my knowledge.

The new LT1s, from '92-'96, also have a raised redline over it predesessors, plus the big advantage is the reverse cooling. Meaning, coolant is routed to the heads first instead of the block. this permitted higher bore temperatures and reduced ring friction, and helped cooling around the valve seats and plug bosses.

This information came from the Corvette Black Book (and you just thought I was one smart cookie! :L)

I have some more information around here about the later LT1 and the LT4...just not sure where. I think it may go into a little more detail about the newer engines. Someone have more for the earlier ones??
:w

Oh, and yes it is a small block...

And just to get your mind off onto another tangent...the LS1 and LS6 improved upon the late generation LT1 significantly...that engine, however, is beyond much of my realm of knowledge!

[BigBrakeFuelie]

From what I understand and have learned is that it is a very high performance engine..
The LT1 combined Rat Like Muscle with nimble handling.Most Big Blocks because of the extra weight didn`t handle as well.The LT1 produced 370 BHP in 1970.That more than one HP per cubic inch.
Corvette equipped with the LT1 achieved a 50/50 front/rear weight balance.
The LT1 was spring off of the old Z28 engine.Both engines were solid lifter small blocks with High winding potential.
The 370 HP. arrived at 6,000rpm. max torque was 380ft.lbs. at 4,000 rpm.
Also Corvettes with the Lt1 came with a stiffer supension.Legend has it the Lt1 Corvette out HANDLED a Porsche 911E for MotorTrends comparision.

[Stallion]

Okay, thanks for the information and reply. So I guess that it's good to have an LT1. I'm looking at C3s, so I'm referring to the earlier ones.

>> And just to get your mind off onto another tangent...the LS1 and LS6 improved upon the late generation LT1 significantly... <<

But weren't these engines big blocks (454 ci)?

Thanks again! :D

TR

[LT1Vettepilot]

Yes, the earlier (C3) LS6 engines were big block 454s...I don't believe the LS1 designation was used until the 1997 Corvette came out with it. The LS1 and the newest LS6 (in the ZO6)are both still a small block 350s.

[DkBG]

As for your questions on the early LT-1 , it was based on a four bolt main block . It had 2.02" intake valves , which were the largest you could fit into smallblock heads . Along with the solid lifters it had a more radical cam . It was close or maybe the same as the Duntov 30-30 cam . It was factory fitted with a Holley 780 Dual feed carberator on an aluminum "cross-H' intake manifold . Down in the oilpan ,it had a windage tray to keep the crank from haveing to fight its way through extra oil that splashed up from the pan . The exhaust manifolds were slightly better than some of the other engines but not exclusive to the LT-1 . I don't remember for sure but it may have come with a factory dual point ignition . Thats all I remember now . Hope this helps . Cliff

[Stallion]

Hey, thanks a lot for all of those specs, Cliff. That does sound like a real nice block to have. ;) Maybe I'll be an owner of a C3 LT-1. :D

TR

[tonyk72]

HP figures for Corvette LT-1's
1970 has 370 HP gross
1971 has 330 HP gross/275 net
1972 has 255 net

Camaro LT-1's
1970 has 360 HP gross

"Zora picked the 302 small-block planned for use in the Z/28, made a few modifications and turned it into a legend, which debuted in 1970.
The LT-1 was a hybrid between the 302 and the 350, In essence, the engine was a 302 with a 350 crank."

all info found in Corvette & Chevy Trader Feb. 2001 issue

[LIRacer]

What did the 71 and 72 have different to reduce the HP to 255 net from 275 net?
Does any have performace numbers for the 3 years of the real LT-1?

[tonyk72]

Here's a link within this forum that goes into the differences between a '71 & '72. Basically, the '72's ignition & valve timing were retarded and the transistorized ignition was out the window...

http://www.corvetteactioncenter.com/forums/showthread.php?s=&threadid=7770

[jmp]

Well everyone calls it a 350...technically its a 346...but hey, who's counting

Just curious... where do you get that number from? The bore is 4.00, the stroke is 3.48... That equals 349.849 ci.

[69autoXr]

I think he's getting it confused with the LS-1/LS-6, tecnically those are 346 ci.

[Erik S. Klein]

I think the real reason I ended up with an LT-1 was the overall ballance of the car.

When I started looking for a Vette I knew I wanted a C3 and I was certain it had to have chrome on both ends. Initially I was pretty sure I was going to get into a 454 convertable but after doing a little research I realized that the 454, while a very strong engine, wasn't that much of a better performer then the LT-1. It does win in a straight line, of course, but because of the extra weight out front the handling and braking of the LT-1 is superior.

When I was shopping I was thinking of competing with the car (autocross, mostly) and felt that the handling would be a bigger factor then the acceleration.

In the end I never raced my car (unless I saw a mustang in need of a lesson) but I still enjoy having the extra power and quick winding of the LT-1 when I need it.

[Robert N]

Erik, nice car.

Mine is a NOM 1970. In the case of the 1970, the LT-1 is as fast or faster than the 454. HP rating was 390 for the 454 and 370 for the LT-1. The overall weight and distribution made up that gap very well.

[Erik S. Klein]

In 1972 the 454 was rated at 270 HP and the LT-1 at 255.

The big difference was where they reached their peaks. I don't have the numbers in front of me but I'm fairly certain that the LT-1 was pushing peak HP at a significantly higher RPM. The 454 also had more torque.

Still, the performance of the LT-1 was far more general purpose where the 454 was more of a straight-line runner.

[Stallion]

Originally posted by 69autoXr
I think he's getting it confused with the LS-1/LS-6, tecnically those are 346 ci.

Isn't the LS6 an engine option only offered in '71 which is a big block 454? 425bhp and pretty rare. I thought that the LS6 (as well as LS5) is a big block? Right?

TR

[69autoXr]

Yes, you are partially correct. The LS-6 designation was originally used in 70 and 71 for big block 454 engines, only offered in the Vette in 71. Chevy resurrected the LS-6 designation for the engines used in C5 ZO6's, and that is what I was referring to about the 346 ci. Chevy has reused old designations several times, not only with the LS-6 but also the LT-1, ZR-1, and of course the Z06 designations.

[Brett]

Erik, are you saying the '72 454 had more torque than the '70 454?

[Brett]

If I remember correctly, the the main difference in horsepower came from the compression ratios. I'm talking 1970 here.

The LT-1, while a smaller block, had a much higher compression ratio (12.5:1?) than the 454 (10.5:1?), hence the minimal difference of 370 to 390 horse between the two. They had originally planned on making a high output 454 as well, with something like 450 gross horsepower, but it was never released, which is a shame. However, not all of the LT-1's had 370 hp. There was also a lower compression LT-1 with 350 horse. You can see the trend, and that they obviously wanted four engines--high output versions of both. I would be interested to hear whatever happened to that hot 454.....

Anyway, the 370 hp LT-1 engine is much rarer than the other two, and worth a pretty penny.



Brett

[Robert N]

The LT-1 was only offered in 1970 as the 370 hp, 380 torque. The 350 hp was the L46 designation.

The 1970 LT-1 offered a solid lifter setup and 11:1 compression, high rise aluminum intake larger holley carb, larger exhaust (2 1/2) accounting for the power. By all true accounts, the 1970 LT-1 was closer to 425 gross hp. The LT-1 has run the 1/4 in 13 sec at over 105 mph supporting the claim.

The only common point with the L46 and the LT-1 was the the 11:1 compression.

[69autoXr]

The 70 L-46 and LT-1 also shared the same cylinder heads with 2.02" and 1.6" valves. They had the same valve covers, too.

[Brett]

Thanks for the correction, Robert. 350's can get jumbled up in your mind sometimes! I should have remembered they both weren't designated "LT-1's", otherwise, how could you tell them apart on paper, haha. :hb Although I swear the LT-1 had a higher compression ratio. You would know though, you know, owning one and all, haha.

And 425 gross? Wow. So the LT-1 was more powerful than the 454? I thought the ratings in 1970 were already gross, and '72 was the year they switched to bhp?

Also, do you know how to calculate bhp in the cars pre-1972? I have always wondered.



Brett

[Erik S. Klein]

Erik, are you saying the '72 454 had more torque than the '70 454?

I was just comparing the torque for the 72 LT-1 and 72 454 and saying that the 454 has more torque and, therefore, better straight line acceleration, all other things being equal.

I'm pretty sure that the big block cars of a given year tended to have more torque then their small block counterparts from the same year. In fact, I can't think of a single case where that rule was broken.

The paragraphs above relate to cars as-delivered only. I'm sure you could build up a 1972 LT-1 with a few performance parts and blow the doors off of a typical big-block from 1972.

Also, I am talking about two Vettes here so both cars are fast, it's just a question of which one is a little faster in stock configuration.

The 1970 454 would almost certainly have higher torque then the 1972 as Chevy steadily de-tuned the engines between those years to make Ralph Nadar and friends happy.

[Brett]

Ok, I thought you were comparing the 70's to 72's in that thread. And with the change in horsepower ratings (makes things confusing sometimes--you never know exactly what produced what...), I thought maybe you knew something I didn't in that the 72's were actually more powerful than the 70's.

And yeah, one thing displacement is going to give you is torque, hands down. There is no replacement.



Brett

[Robert N]

69AutoXr, you are correct on the heads and valve covers.

Brett, the 1970 454 was also more powerful than rated. Much of the difference in the cars also comes from where peak hp and torque are reached. Personally, I believe the LT-i is the faster of the 2, though the 454 will give more of a head-snapping rush when punched. As you pointed out, cubic inches will give you that. I am aware of at least one 1970 LT-1 owner that has won a few races against 454s.

Hp was gross rated in 1970, both gross and net in 71 and net in 72.

As to how they came up with the calcuations, I have no idea.

Part of this was insurance related. It is also why the numbers where listed conservatively.

[Brett]

I was looking around on this site, and the LT-1 option was almost twice as expensive as the 454 in '70 ($450 for the LT-1, to $290 for the 454). Very interesting, don't you think---the larger HP package being less expensive. To me, that is just more evidence pointing towards the originally planned high output 454. I have my dad's original owner's manual from his 1970 454, and they list the engine in there as one of the options to choose from. Maybe it didn't pass emissions regulations and they had to quickly cancel it.


That thing would have been a freakin' MONSTER.:BOW




Brett

[jmp]

Brett, I'm no expert, but I think it is a fairly accepted fact that the 70 'vette was supposed to have another 454 option -- the LS6. For whatever reason, Chevy delayed this engine until 71, where it was rated at 425 hp (gross) and $1221 (compared with $295 for the LS5 and $483 for the LT1). There's a (contentious) thread around abouts where a new vette owner was trying to determine if his 70 was an LS6, which would have made it one-of-a-kind.


People have been saying that a 70 LT1 was comparable to the 70 454, and there seems to be some question as to whether that was true in 72 as well. Well, according to a Motor Trend article (http://www.corvettearchive.com/images/1972/MTJun72/Mt672_5.gif) from 1972, the LT1 was comparable:

LT1 vs 454
HP: 255@5600 vs 270@4000
CR: 9:1 vs 8.5:1
0-30: 2.9 vs 3.8 (maybe this is a typo, as the base 350 went 0-30 in 3.1)
0-45: 4.8 vs 4.9
0-60: 6.9 vs 6.8
1/4 mile: 14.3@92mph vs 14.1@93mph
60-0: 116ft vs 122.9ft

The LT-1 in this test had 3.70 gearing, but I don't know 'bout the 454. The 454 was also an auto, which probably affected things.
The article also says that the LT-1 handled better, running 2-3 seconds faster in lap times over the 454.

The one thing I'm not sure about is the torque. The 72 LT-1 is rated at 280@4000 net or 360 gross. The 72 454, in this article, had a listed torque of 390@3200, but I don't know if this is net or gross. I would think gross, but it is kind of odd that the article would mix its measurements like that.

[Brett]

I know it is an accepted fact, I didn't mean to come off that way. I guess I was just trying to make the obvious point that it makes sense they intended to release it. I was kind of having a conversation with myself, haha. I was just hoping someone would know why the engine was canceled. It's a topic I'm very interested in, and no one seemed to be biting. Like I said, my 1970 owner's manual lists the engine as an option, so there is the proof right there. And it wasn't going to be called the LS6, it was the LS7. They are different engines. The LS6 had a 9.0:1 compression ratio. The planned LS7 was supposed to have a whopping 12.25:1 compression ratio, and rated at 465 hp! And just like the other engines, that was probably a very conservative number. None were produced from the factory. Oh what could have been.

I highly recommend the Corvette Tech Data posters, they are a wealth of information.




Brett

[jmp]

And it wasn't going to be called the LS6, it was the LS7.

Really? I'm basing most of my info on the following thread, in which everybody was calling the mystery 1970 engine an LS6.

Anyone ever hear of a 70 LS6? (http://corvetteactioncenter.com/forums/showthread.php?s=&threadid=18172)

I guess your manual says LS7? That is news! Now, does that mean there was supposed to be an LS6 and an LS7? Maybe we are talking about two different engines here! Ah, well, we'll probably never know.

What are the 'Corvette Tech Data posters'?

[jr9170]

I have owned many SHARK cars and various MID-YEARS,and driven many others including my friends 427/435 67 coupe and test drove a 70 LT-1 coupe that i almost bought.The 67 is a monster as far as power and torque goes,literally pinning you in your seat.The LT-1 is no slouch either.I was very impressed with its balance of power and handling.I say almost bought one,because i bought a 70 454 conv. instead.I currently own a 91 red/red ZR-1,and a 70 454 blue/blue T-Top(MY 2nd 454 ).I opted for the 454 instead of the LT-1 for the simple reason of the mystique of the big block vettes.But there is also some of that same mystique in owning a LT-1,that is one very impressive S.B. It pulls like a B.B.But as far a kick ass car neither can compare to the ZR-1.Compared to the Z neither one can compare.The ZR-1 has a balance of speed,power,accelaration,handling,braking that would impress any old school vette guy even if they dont like the newer cars....JMHO THANKS JERRY...BTW great website i will be hanging here more often.

[Robert N]

jr9170, you are correct in the fact that the modern ZR1s and Z06s are no comparison to the older vettes. It is amazing what increased aerodynamics and computer aided design can accomplish. All things considered, the fact that both the 70 LT-1 and the 454 can give most modern day cars a run for their money, I am impressed with the 32 year old technology. My LT-1 will be nodified slightly to take full advantage of everything the engine has to offer.

[Brett]

Sorry for the delay of my response--busy weekend.


Yes, the mystery 454 of '70 was dubbed the LS7. There was no LS6 in '70. This is coming from my original owner's manual. The manual lists 5 engines:

Base engine: 350 ci, 300 hp.
L-46: 350 ci, 350 hp.
LT-1: 350 ci, 370 hp.
LS-5: 454 ci, 390 hp.
LS-7: 454 ci, 465 hp.

I also have a Corvette tech data poster that lists the same exact stats. The Corvette Technical Data posters show every single year/model of Corvette, with all prices, specs, engines--you name it. All fitted onto a normal sized poster. Look for them on Ebay. Very nice quick little reference guides. Their info exactly matches my owner's manual, and it has been spot on with every other reference I have seen, so it is very reliable.

I have not read through that entire thread yet (it's long!), but the unreleased 454 of '70 was definitely named the LS-7.



Brett

[jr9170]

Brett,you are correct the LS-7 was to be a 1970 option and was even listed the 70 owners manual.The other motor that was to be produced but never was built was the LJ-2 that was to be a TRI-POWER 454,to be rated at 460 hp.....JERRY

[Brett]

Here's a Corvette tech data poster on Ebay right now:


http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2404913008&category=10076


The 2001 version is the most recent I have seen.




Brett

[jmp]

Originally posted by Brett
Here's a Corvette tech data poster on Ebay right now:


http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2404913008&category=10076


The 2001 version is the most recent I have seen.


Ah, yes, I've seen this poster before, at one of my local vette shops. I'm buying one of the ones on e-bay.... Thanks!