Talk:General Motors LT engine

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Some more stuff should be said of the LT1's reverse flow cooling. and a further expansion of ls1 stuff needs to be done. --Ultrapop1 01:48, Oct 3, 2004 (UTC)

First smallblock in 1970?[edit]

The first paragraph makes it sound like GM didn't have a smallblock before 1970. this needs to be corrected or clarified.--Pqdave 16:33, 11 Jan 2005 (UTC)

You're right. That was old junk text. What do you think now? --SFoskett 19:13, Jan 11, 2005 (UTC)

Much clearer, good job. --Pqdave 15:09, 12 Jan 2005 (UTC)


It looks like the GM Small-Block engine page and this one have a lot of overlap. The Small Block page is already as unwieldy as it is—can someone move the information over here and appropriately link in? --Milkmandan 22:51, 2005 Jan 26 (UTC)

I disagree. This page is for the Generation II small-block. That page is for the Generation I engine. The GM LS engine page is for the Generation III and IV. The overlap was intended to be a intro to this article. --SFoskett 23:31, Jan 26, 2005 (UTC)
Gotcha—I didn't realize that. Since the connection between the engines seems to be a complex one, maybe this should be stated more clearly in the introduction paragraph for each article? --Milkmandan 01:33, 2005 Jan 27 (UTC)
i am late to get on this band wagon seeing how the last post was in 2005. i am in favor of merging the Gen I and Gen II pages together. why is a simple question. Generation II engines are basically Generation I engines with some block mods in them. if you wanted to you could take the rotating assemble out of an LT1 and put it into a 95 or new 350 with ease. Gen IIs aren't that different from Gen Is, but more a further refinement of a Gen I. it's like having two different pages for the Gen III and IV engines, and all a Gen IV is just a further refinement of a Gen III. i have since reorganized the Gen I page so its very neat with good flow. if the merger were to be done it would be fairly easy to do. But that leaves only one question, what to name the merged page? the Gen III and Gen IV page is called LS-based series, so what you would you call a Gen I and Gen II page....Ed Cole series or classic SBC series?Gulielmi2002 (talk) 14:50, 26 October 2009 (UTC)

LT series engines respond well to modification[edit]

The LT1 and LT4 are readily modified to increase their horsepower, and many owners do so. I believe mention of this aspect would be beneficial, especially considering the rather thorough existing discussion of rated horsepower. The mention of the poorly designed intake and exhaust is true, but seems to detract from the performance aspects of the LT engine applications, and a counterpoint seems appropriate. But, I don't want to be too specific or off-topic. I think something like the below text is a good start, but I would appreciate feedback or editing clean-up, of course:

-- new text added... It has already been noted that the LT engine's reverse cooling system enables high compression, and the factory exhaust system and air inlet systems are not well optimized for performance. The intake manifolds and cylinder head castings are capable of supporting much higher horsepower than factory-equipped engines produced. Even more readily than the typical Gen 1 small block, these aspects of the LT1 and LT4 enable their horsepower to be significantly increased by the addition of high-performance air intake ducting and exhaust systems. Further, upgrading the cylinder head porting and camshaft design with appropriate supporting modifications can enable these engines to produce in excess of 400 naturally aspirated horsepower at the rear wheels, or about 500 horsepower at the flywheel. --

Sources: Various documented engine builds with dyno graphs and race timeslips were reviewed on discussion groups such as, and the unofficial Z28 forums. The 400 HP number is conservative, especially for the LT4. Drivetrain losses of 15 to 20% are commonly accepted, so with the conservative 400HP number, 500 HP at the crankshaft is a very feasable number.

Example engine build refrence for HP capability:

Example reference documenting factory cylinder head capability:

  • Hilarious. Why do you guys need all those litres? The standard 5.0L Ford block of the same era is also good for 400hp+ flywheel, normally aspirated, IF YOU DO THE RIGHT BUILD, i.e new bottom-end, pistons, heads. Heck a whole new engine is needed for either GM or Ford. Its not exactly a LT1 then is it? 16:23, 14 December 2006 (UTC)

Response to above comment from user User:|, for the purpose of addressing the discrediting nature of that comment:

I have a documented personal LT1 F body build with with measured, SAE corrected 417 HP AT THE WHEELS. The engine was built using a factory block and heads, so a 'whole new engine' is certainly not required with 'the right build' to achieve 400 flywheel HP from the LT1. Far from it. Porting the heads was required, but they are factory pieces.

last time i checked the 5.0L was dropped for the 4.6L in prelude to ford's fears about the Generation II engines and emissions. —Preceding unsigned comment added by Gulielmi2002 (talkcontribs) 21:55, 10 September 2009 (UTC)

LT5 connection to the 4.6L NorthStar[edit]

there should be something mentioned that the 4.6L NorthStar evolved from the LT5. i know that this is said in the 4.6L northstar section and perhapse something needs to be said about this in the LT5 section with some links.Gulielmi2002 (talk) 20:09, 25 September 2009 (UTC)

Absolutely! Could you add it? —Mrand TalkC 21:30, 25 September 2009 (UTC)

ok i have added the detail. i like it because it makes you aware that the LT5 wasn't just some one time thing that it infact lives on in basic design in the Northstar engines. i figured out how to do the links and it links directly to the development section of the Northstar engine series. Gulielmi2002 (talk) 16:26, 8 October 2009 (UTC)

I think it should be added here that one of the differences with gen 2 and gen one is that the gen one is a 2 piece rear main seal crank, and the gen 2 is a one piece rear main seal crank. mainly mark a bump up on the differences on the generations in the engines, also on trasnmistions since the gen 2 started getting electronic controled auto transmission for the 4l60e. derek v —Preceding unsigned comment added by (talk) 03:31, 25 December 2009 (UTC)

the Gen I's after 1986 were all one piece rear main seals. in fact the cranks used in the LT1 will fit nicely into an 1986 to 1996 Gen I 305's and 350's.Gulielmi2002 (talk) 15:09, 4 January 2010 (UTC)

LT5 and Northstar - again[edit]

There is absolutely no relationship between the LT5 and Northstar. If you have references please post. This 2nd undo is, in Wikipedia terms, a CHALLENGE to the facts of your post. Also notice the template at the top of the article "This article does not cite any references or sources."

Please see the Wikipedia article on citing sources thanks, Toneron2 (talk) 03:00, 21 January 2010 (UTC)

sourse has been posted. the problem is that it is mostly true. it's not that the northstar is a smaller version of the LT5 but does take much of its design from the LT5. it's like saying that the BBCs aren't related to SBCs. in the case of BBCs they share little from the SBCs besides distributors. but look at the history of the BBC you will see that they desend from the W engines which desend directly from the SBC. the W engines have characteristics that are of both SBCs and BBC and some that are unique to the W engines. in this way the SBCs are the ancestors to the BBCs. you can use the LS engine for an other example. looking that the LS engines and the SBCs you would think that they have little to nothing in common, but look a the history they do. the SBCs gave rise to the 90 degree V6 in this case the 4.3L V6 derived from the 350. in the late 80's and early 90's GM wanted to replace the 4.3L with an improved V6 but based on 4.3L with modern improvements. a swedish designer came up with this new protype engine name it the venture V6. the project was dropped but the design of the venture V6 lived on in the LS engines. looking at the blocks of the venture V6 and the LS engines, the LS engines look like the venture V6 with two added cyclinders (reference from an article from hot rod mag early 2000's). the point is GM rarely makes an engine from scratch. Cadilac did the same to the LT5. redused the size, made changes to make it cheaper to mass produce (cost effective), and added some modern improvements all these changes to fit their needs.Gulielmi2002 (talk) 15:47, 21 January 2010 (UTC)

Well those are the rules of Wikipedia, so I have to let it stand - however I know from personal experience that the Northstar design was done completely independent from the LT5. Sure they looked at it for inspiration - but they looked at every other DOHC V8 as well. They share absolutely no components and many [features are completely different.]
The problem comes down to semantics. Is the original 265 related to the LS3? In terms of design they have absolutely nothing in common. Is the original 348 related to the Vortec 8100? Again no appreciable design similarities.
However, the 265-LS3 engines have the same purpose - to power cars and trucks - from 4-door passenger cars, 3/4 ton work trucks, and eventually the Corvette. Same with the big block - to power heavier cars and trucks. Although both lines have pedestrian roots there were high performance and very limited edition variants.
Of course when GM designs engines it looks at existing designs - but remember they look at competitors designs perhaps even closer.
So you have a wide variety of small blocks in use for many different purposes. You have a wide variety of big blocks, again, used in many and varied applications. Therefore, although the designs vary dramatically within the "small" and "big" block groups, they share a common purpose - so correctly they should be grouped into one family through several generations. Same with the Rats. Common purpose: powering all types of vehicles as the V8 option.
This being said, that although the designs differ radically, there is a clear evolution within a common purpose. This is however not the case with the LT5 and Northstar. The LT5 shares no appreciable design elements with either mouse or rat which were in production at the same time and continued after the LT5 ceased - it had a different purpose. Same with the Northstar - it shares no appreciable design elements with either mouse or rat and has a different purpose as well.
Due to a) No common design and b) no common purpose, neither the Northstar nor the LT5 are considered to be in the same evolutionary chain as either the 265-LS3 or 348-8100. This is clear. I believe it is clear for the LT5 and Northstar as well. Based on component inspection, there are absolutely no common components between the two - and many design characteristics are not shared (see referenced discussion above). They are radically different. However, there are no parts that fit and no appreciable desig characteristics between the 265-LS3 or 348-8100. That leaves purpose to discuss.
The purpose of the small block has always been the same. The purpose of the big block has always been the same. The LT5 and the Northstar do not share a common purpose. Therefore, since purpose differentiates the LT5 and Northstar from small and big block evolutionary lines it must also separate the LT5 from the Northstar.
The LT5 was developed for a number of reasons. It was intended to be a technological "tour de force" which would place the ZR-1 optioned Corvette as the "king of the hill". It also served to "wake up call" GM powertrain engineering because there was no suitable powertrain engineering capability available. In some sense this led to the LS program. I know this from personal experience. The LT5 was never intended to power high-volume passenger cars - nor was it ever intended to be anything other than a very premium option on America's premier sports car. The purpose of the Northstar was radically different. Again, they looked at the LT5 but also every other design they could get their hands on.
The Northstar was developed, from the beginning, to be a high volume, luxury passenger car engine - with the intent of becoming the main powerplant for all Cadillac vehicles. Clearly a radically different purpose than the LT5. Another point is that the LT5 was developed by a very specialized team under the direction of Corvette engineering. The Northstar was developed corporately for the Cadillac marketing division.
On one hand, the small block, big block, Northstar, and LT5 were all GM V8s. As was the Oldsmobile V8 which arguably led to them all. Could one put the Oldsmobile at one end of the evolutionary chain and the LS9 at the other? In some sense of course - but it makes sense to further delineate the different iterations. All are pushrod engines (except the two in question). All are 90 degree. All were fitted to many production vehicles. It makes sense to differentiate them by releasing division. Beyond that what is left? Clearly designs differ - but that is a known variable. The only real way to differentiate engines from each other is purpose and then break them down from there. As you have done, bore size is an excellent way to break down the different variants within a particular "family". There are a few problems, although it seems to be the best approach.
Therefore, since beyond releasing division purpose is the key criteria for differentiation, the LT5 and Northstar must be differentiated from the small and big block engines, and from each other as well.Toneron2 (talk) 17:47, 21 January 2010 (UTC)
to say that there isn't a clear link from the 265 to 8100 vortec is missing the obvious. yes purpose is the reason why these engines are here and why they have certain design aspects, but the common point is design. compare the heads of a SBC, W engine, and BBC and you will see the progression of change from one to the other. if their parts as you are suggesting came from one an other then, their parts should be interchangable. this can be true but most often the case not. good example is the LT1 vs the Gen I 350. they share only pistons, rods, and crank. the heads aren't interchangable but the design is obviously similar if not the same, but for some key design aspects. are these key aspects enough to say that they are so different that they are unrelated, do some research on the net and will see just how close the 283, 327, and 348 are. i am not saying that the 348 is a gen I small block by no means but the w engine share a close relationship with the SBC and the BBC because they are the missing link between the two just look at the design. the same can be said about the Gen I's to LS engines dig deep enough and you will find this.
There is a clear link between all the GM V8s. The small block started as the 265 and the big block started as the 348. No dispute there - however just because an engine uses pressed rocker arms doesn't mean it is the same family. I never said their parts came from one another or were interchangeable. No need to go to the net for information - I've worked with Chevrolet and Oldsmobile engines for over 30 years. The Mark I (modern term Gen 1) wasn't "based on" the small block - it has some commonalities but that is very different. It was developed for a different purpose, powering the heavier cars and trucks, but I believe you agree. One could argue that the Mark I and Mark IV are not related - the former having a substantially different design characteristic (the combustion chamber in the block) that is only shared by one or two other designs globally (to my knowledge). But it does spawn a new purpose so under that purpose it is the progenitor of the big block.Toneron2 (talk) 01:06, 22 January 2010 (UTC)
the LT5 to northstar this isn't my doing. it was posted on the northstar section long long ago; however you can see there is too much a coincidence between the two. time when one was in production and when the other was in developement. you argrued that they would look at competitors....true but to say that they looked to ford's 4.6l as their design inspiration is ludicrous. why base your design on what your competitors with a similar design when you have a superior design in your pocket. one could argue convergent evolution, but why? why start from scratch having to fix problem on a design when you have already been solved in the LT5? and that it just it. i am not saying the Northstar is what the LT1 is to the Gen I; i am definding the fact that the LT5 is what the 283 is to the 348 for the northstar. if there wasn't an LT5, there wouldn't be a northstar as we know it today. why are the northstar different....purpose but does that mean that they don't share a close that line of thought would say that the LT4 has nothing in common with a SBC 400 which share nothing in common, but look at their histories and design similarities they do. you have a design that is proven to be a winner but because of some aspects of it, it is expensive. what do you do? modify the design to fit your needs which was done doing so doesn't make them 100% unrelated. i do it all the time at my job. i am given a design problem sometimes with a time limit. what do i do...the samething other engineers do, get an existing design and modify it for your needs.
Well that's called a circular reference and is not suitable for an encyclopedia. Wikipedia articles are supposed to be written by experts in their fields and supported by referenceable information from a credible source. Someone typing something in an another article is not a credible source. Neither is some non-automotive guy typing something into eHow. But those are the rules. I could type that the small-block was based on an experimental V2 into my blog and reference that here. That doesn't make it fact.
There is not enough coincidence between the two. They are completely different other than being DOHC V8s marketed by GM - and implemented for very different purposes. Engineers look at any similar design for inspiration. Period. It doesn't matter who when or what. Designers of the Quad 4 looked to Miller and Offenhauser designs from the 30s. The final design looks more like those engines than Cosworths and Lotuses of the '60s - although the did certainly look at those and I am sure Asian designs as well.
Your assumption that "if there wasn't an LT5, there wouldn't be a northstar" is completely false. They are unrelated designs created for unrelated purposes. The 265-LS3 and 348-8100 lines are similar designs with similar purposes as I described. The LT5 and Northstar are radically different designs with radically different purposes. They share nothing.
The LT4 and small block 400 are different, yes, but both members of the very diverse Chevrolet small block family due to their history.
What you explained about your job, the way you solved a problem by looking at the ways others solved the same problem, is the distinction that needs to be made. There is a big difference between evolving design for the same purpose and creating a new design for a different purpose - even if it shares some attributes - it is a different purpose. Do you look at competitive designs? You would be a fool if you didn't. A good example is the Ford flat-head V8 from 1932. The valve-in-block (or L-head) design obviously wasn't new - in fact it had known issues - however Ford used this old design for a particular purpose: to provide good tourque characteristics at a very low cost to manufacture. Chevrolet had a OHV V8 in 1918! This was actually a Scripps-Booth design but nonetheless featured OHV design. I am certain the designers of the flathead V8 looked at everything they could - including OHV and OHC (Miller/Offy) designs - and said "nope, that doesn't fit our purpose.Toneron2 (talk) 01:06, 22 January 2010 (UTC)
now i have followed the rule with sourcing the matterial and have admitted that it wasn't of my origin but was able to find a source that affirms the infomation. truly the only 100% source for this is a cad engineer to credit or discredit this, but for now this is what we got. i was doubtful too about this unit i saw the similarities in the heads and the block design.

Gulielmi2002 (talk) 23:09, 21 January 2010 (UTC)

I know you have followed the rule and I can't remove your contribution. There are also similarities with many other designs. This does not make them all the same family. I will have to do my homework to somehow document my knowledge and experience in the matter.Toneron2 (talk) 01:06, 22 January 2010 (UTC)

Another example. By your logic the engine in the Cosworth Vega led to the Quad 4 which led to the Ecotec - they are all GM DOHC inline-4 engines. This could not be further from the truth. The engine in the Cosworth Vega was a Vega engine topped by a Cosworth DOHC head - designed specifically for a particular, high-performance purpose, limited edition option. The Quad 4 was a completely clean-sheet design created as a higher performance but mass-market application. The Ecotec evolved from a Opel designed SOHC engine which debuted in 1979, again for mass market application. The Cosworth Vega has more similarities with the ZR-1 C4 in terms of purpose. The Quad 4 is a function more of politics - although a great engine. The Ecotec and Northstar have similar purposes (although one for compact & midsize cars vs. large luxury cars) but both intended for high volume production. The LT-5 (and Cosworth Vega) were never intended as such. Toneron2 (talk) 01:46, 22 January 2010 (UTC)

I am not insisting that they are of the same family by no means at all. I realize they aren't, but what I am insisting is that the LT5 gave rise to the northstar. the cosworth engine is a bad example too much time between the cosworth engine and the DOHC ecotecs like my example of the 400 to the LT4. the good example is the 265, 283, and the 348 (corrected had the 327 in the mix instead of the 265) during the w, x, y prototype program. i know that the 348 isn't a sbc but its history and design are intertwined with the 283 and the 265. the same program that gave rise to the 283 gave rise to the 348 two completely different engines. i know that the northstar isn't the same block as the LT5 one of the best ways to point this out is the bore spacing of the's different (i am not insisting that they are the same block). however the design of the northstar was heavily influenced by the LT5. just like the 348 design was heavily influensed by the 265. all of that is what i am advocating, one the design parent of the other. take what worked and what was best from one engine to the other and change what you need to fit your purpose.Gulielmi2002 (talk) 15:21, 22 January 2010 (UTC)
That is exactly what I am saying. Same company. Shared engineering resources. Similar characteristics - different purposes - therefore different families. This statement applies equally to 265->LS9, 348->8100, Quad4->Twincam, 20NE->LAF, LT5 program, and Northstar program. I yield at this time. I will get back to this when I have time. Thanks for your civility - it has been a pleasure. Perhaps someone else will chime in?Toneron2 (talk) 21:25, 22 January 2010 (UTC)
I'm impressed with the civil discussion. Except for the ehow article (which I do NOT believe is considered a reliable source), I can find no references anywhere that the Northstar was derived from the LT5, and actually found one write-up which explicitly said it was not. I actually had the mistaken understanding that there was a relationship, but upon further research, can not find any indication that is true. In fact, applying a bit of logic indicates there was little to no relationship to speak of: when designs morph or evolve, there are usually major hints of the previous design, but there does not appear to be any such hints when comparing the Northstar and LT5. That, combined with not being able to find such claims, leads me to believe that we should remove the statements from Wikipedia. Even if the Northstar was derived or evolved from the LT5 design, it was so different that I believe it would stretch the definition of either of those words to the breaking point. I vote to remove the statement. —Mrand TalkC 19:21, 23 January 2010 (UTC)
i am finding evidance for the relationship besides the ehow site. I do believe one of the best ways to find proof for a given topic is to find evidance against what you are claiming. i have found several websites for it. i have also looked at the physical specs of both engines and they are different in every spec from bore spacing, rod length, piston compression height, and probably deck height if i could find that on the northstar. but i keep on finding comments like this as i search: "Key LT5 features were incorporated in GM V8s of

today, such as the "Premium V8" series ("Northstar" and "Aurora") and the Gen IIIs." i think that the wording needs to be changed to reflect from all of the above. perhapse it needs to say that the LT5 was a major design influence for the Northstar.Gulielmi2002 (talk) 05:10, 24 January 2010 (UTC)