Tom400CFI

Not sure about that....I don't think any GM tooling was used to make the LT5. Motors were machined and assembled at Merc.

Never read anything about a "wider V angle" either. That would affect the balance negatively.

EDIT: Guess the bore centers has been covered.

glass slipper

Once again, exactly how many SBC engine blocks will the LT5 4V heads fit on?

The program originally started out to be just 4V heads for the SBC, the reason an all new engine block was done was so the 4V heads could be optimized.

glass slipper

When you answer my question, you will have all of the answers to your questions (of which most all of them are meaningless...FYI, it was not a $30K engine). I'll quote myself so you won't have to scroll back:

"What production line machinery would the LT5 engine block have in common with the small block Chevy 4.4" bore center? The LT5 cylinder liners are forged aluminum with a Nikasil coating, they are already bored/honed before installation. LT5 cylinder liners are then installed into the cylinder block with sealant. Gen I and II small block Chevys cylinders are bored/honed while Gen III and IV small block Chevys have cast in liners or pressed in liners that are honed in place."

In addition, there are many other block machining operations peculiar to the LT5...do you really think GM could have incorporated the assembly of the LT5 into any production line? And let's not even get into the machining operations for the heads...there is no way the LT5 could ever have been streamlined into any existing SBC production line. I stand by my "arbitrary and capricious" depiction of Midgley's decision, it was exactly that...there was no engineering reason driving the bore centers to 4.4", it was a clean sheet of paper design and could be whatever was needed.

Make a good case for your points and I'll listen, don't answer my question by asking a lot of senseless questions in an effort to deflect.

Dominic Sorresso

Tom,

Graham Behan has addressed the V angle several times in presentations. The original proposal to GM was for a wider V in the motor. Building the ZR-1 on the same line as the base Corvette required the motor to be installed from underneath. And so the compromise was to narrow the V allowing the motor to fit thru the frame rails.
Maybe if either Graham or Dave McLellan are at the Gathering in May, I'll ask them about the rationale for the insistence re: the bore spacing. Was it capricious?
At the time of the Midgeley decision, I would say bb62s explanation accurately describes the background for that decision.

Tom400CFI

Huh. I'm reading " Heart of the Beast" right now and I don't recall any mention of a V angle other than 90. There is no meaningful benefit to a wider V angle that I am aware of. What ever the case, I'm glad they stuck w/90*

glass slipper

Please explain to me why it was so important to have the same bore spacing for boring/honing on the same assembly line when there is no boring or honing done on the LT5 cylinder block. In fact, please tell me one single machining operation the LT5 shares with the SBC.

There is a reason Ford has a separate assembly line for it's 4V engines and it isn't because of different bore spacing.

Go back and read The Heart of the Beast, you'll see the exchange between Midgley and Rudd after Midgley stated the LT5 had to have the same bore spacing as the SBC. Rudd stated (IRT the SBC bore spacing): "That's got nothing to do with it. You're not going to make this block on the same production line as you make the small-block. It's a different thing altogether. It can be any bore center..."
Midgley said "No, no it can't."

That's about as arbitrary and capricious as you can get from the head of GM powertrain engineering...there wasn't a single technical reason given. Everything bb62 posted was nothing but superfluous "stuff" meant to deflect from the truth.

There were plenty of stupid decisions made by GM that were detrimental to the LT5, the bore spacing was just one of them. GM's insistence on a cast crank ranks right up there with the bore spacing decision. The hell of it is the crank was eventually forged, it just took a lot of development time and cost for Lotus to prove it to GM.

glass slipper

You're correct Tom, I never read or heard any mention of a V angle other than 90°. There was discussion about the valve angles that Lotus wanted but couldn't get due to the frame rail width but nothing else. I think a few people need to go back and read Heart of the Beast...

bb62

GS,

My answers (or questions rather) are not meant to deflect, they were meant for you to ponder how GM arrived at the LT5 and in what sequence. Part of your problem is that you do not understand how the process for engineering a new engine architecture works, who the stakeholders are, and the probable sequence of events as the LT5 was developed. Recognize that the questions I asked assumed certain knowledge that I, as a former OEM powertrain planning manager, know intimately, but may be out of your knowledge base (but not out of your capability to understand). The problem for me is how to condense 20 years of this experience into posts that would make sense without my writing a book.

Many of the technologies that you refer to, such as the cylinder liners used in the LT5, would be technologies decided upon well after other major decisions would be made (such as bore centers). That is why your question is irrelevant to me. Maybe I should describe the process in a bit more detail (at least from my perspective given that I worked for the guys across town – but with you recognizing that the process works the same way for any of the OEMs).

Key Stakeholders in any new Engine architecture (all of whom will have a say in the development of the engine – even an engine such as the LT5).
- Advanced Engine Engineering
- Base Engine Engineering (in the LT5’s case, this would include discussions with Lotus)
- Engine as Installed Engineering
- Powertrain Development Engineering
- Powertrain manufacturing Engineering
- Vehicle Engineering
- Vehicle manufacturing Engineering
- Vehicle Packaging (which today is not a big deal with the upgraded 3D computer technology, but was a bigger deal when the LT5 was being developed)
- Powertrain Finance
- Vehicle Finance
- Manufacturing Finance
- Cost Estimating
- Powertrain Product Planning (these guys lead programs from birth to start of production – this is what I did)
- Manufacturing Planning (these guys are the leads for any program from start of production to the end of the program – usually 10 years after the end of production)
- Vehicle Product Planning – for vehicle programs
- Vehicle Platform Planning – for vehicle platforms
- Marketing
- Parts and Service
- Purchasing
- Vehicle Cycle Planning (not a term used at GM – a Fordism of sorts – but it is where the major spending tradeoffs are made for review with the highest levels of the company)
- Program timing
- Emissions and Safety Planning
- Note that “Research” is highly involved in many of the upfront decisions – but they are not really stakeholders.

Each of these stakeholder positions report to an E-Roll (executive level) person. And these groups would ultimately report to at least 6 VP level people who need to sign-off on any program (Vehicle Program Office, Powertrain, Finance, Manufacturing, Purchasing, and Marketing). The point of showing the stakeholders is to give you a sense for both the complexity of the overall development process, but also that decisions like Midgeley’s do not occur in a vacuum. No decision is made capriciously or on a whim – certainly not at the level that Midgeley was at. Recognize that some stakeholders had more influence at certain points in the development cycle than others, but executive buy-in would still have been a key requirement.

Overall program milestones-
- Pre-SI activities (“Strategic Intent” is a term that Ford used at the time, doesn’t use now, but describes how the process worked in the 80s and 90s)
- SI Approval - generally 4 years before SoP
- SC (Strategic Confirmation) – 3 ½ years before SoP
- PA (Program Approval) – 3 years before SoP
- PC (Program Confirmation) – 2 years before SoP
- Production Readiness – usually 3 months before SoP
- Start of Production (SoP)

Keep in mind that a powertrain program from conception to start of production is actually longer than a vehicle program. This is why it is always difficult to develop a new vehicle and powertrain at the same time. The powertrain guys will always be asking what their engine needs to do before the vehicle guys even know what they want. The milestones are similar for vehicles, but just timed differently.

The development process would generally be about 4 ½ years before the start of production including the pre-SI activities by the various planning and finance groups. Usually Advanced Engineering in the pre-SI phase help the planners project what technologies are possible in what period of time. The overall program timing might be considerably compressed if the program is a modification of an existing engine architecture.

At an early stage (such as “Strategic Intent”) of a new engine architecture like the LT5, alternatives for manufacturing will be developed without any firm decisions being made. But the basic architecture will be determined – not to the extent of knowing details such as how the cylinder liners will be installed, but parameters such as bank angle, displacement, projected HP/ torque, head architecture (such as DOHC), fuel delivery, etc. General cost levels will be estimated for each of the manufacturing alternatives. Most papers at the “SI” level also project some level of buy-in for which vehicle platforms and vehicle programs would use the engine.

The problem for engineering (and to the consternation of Lotus for a program like the LT5) is that certain hard points like bore centers need to be decided upon before the manufacturing plans (which include long range estimates of how the engine architecture will be utilized and in what vehicles) get finalized. Manufacturing plans are always beholden to product planning and marketing estimates of utilization.

By the time that manufacturing plans are agreed (an iterative process sometimes not finalized until PA or Program Approval), much of the engine from CAD perspective will be designed, but not how the specifics of the parts themselves – like the engine block – will be sourced. For example, the tooling for the casting of an aluminum engine block will generally run either about $70K or about $250K. The difference is that the $70K tool will yield about 100K units of production versus about 1 million units for the more expensive tool (but reduced cost per unit). These low volume penalties abound in a low production engine. Your description of how the cylinders for the LT5 differed from the LS engines is precisely one of those later low volume manufacturing decisions that would be made long after the bore centers decisions was made. Had the decision been made to utilize the LT5 architecture in high volume applications, the block sourcing and manufacturing process would have changed so as to use existing GM assets (I was involved in a very similar decision with some of the engine architectures for which I was responsible – ask me sometime how union labor would affect how the heads of a DOHC engine could be designed).

Had the decision been made upfront that the LT5 would be a very low production effort, then you would be right that there was not “engineering” reason why the engine couldn’t have been totally unique – with the unique bore centers. But consider as I noted above that engineering is not the only voice in the approval process and that in the late 80s, all of GMs competitors were migrating to DOHC architectures (including Ford) and that studying the potential for manufacturing the engine in-house in high volume would have been a priority – and that demanded that GM keep their options open.

Fast Freddy

what years did the LT5 motor have a cast crank and what years did it have a forged crank?

USAZR1

LT5's all have forged cranks.

USAZR1

I could have sworn this thread was about LT5 cylinder heads?

Rkreigh

big valves aren't worth all that much because the increase rather than decrease shrouding. for sure don't go big valves unless you go with 4 or larger liners. I think 4.125 might be the sweet spot for big valves.

flow "quality" is more important that raw cfm. mixture velocity, swirl, tumble, fuel distribution and even mix, and yes high compression all contirbute to power from the basics

suck, squeeze, bang, blow

sounds simple, but clearly the 4 valve heads have some advantages from an engineering standpoint. the LS7 head flows a whopping 370 cfm out of the box which allows the rather plebian LS7 to make an underrated 505 hp. a similar displacement LT5 with WAY less CFM fllow can make more power due to superior cylinder filling.

but unfortunately getting to 370 cfm might be beyond the mighty LT5 due to the rather tiny port volume for both. so going after "quality" or using a billet cyl head with redesigned ports might be the only solution.

my work around is easier

instead of suck (intake stroke) add more blow

increase the cylinder filling through turbo charging. not cheap, but nothing on the LT5 is and you can use relatively mild cam timing (stock would be fine).

so in relative terms the LT5 has a "weak" cyl head flow.

take a look at the latest 'Engine masters" shootout

just to "show em" a small bore long stroke 408 or so "mod motor" made 720 hp of jam N/A

humbled a lot of the "big boys" with higher flowing heads, more compression and cam timing ect.....

like to see what those heads flowed but I'm betting Mr. Kasse won't be sharing that data or the cam timing. he experimented quite a bit.

as has Pete. he has clearly shown that a solid CNC port job, the proper cam timing, and optimizing the overall combination will produce similar power from a well sorted stock block LT5 as many of the strokers are making.

hopefully one day I can "modernize" the LT5

right now, I'm more focused on getting the bottom end knock out of a wheezy little LS6 motor. the heads on that one don't flow all that great either but those twin hairdryers make up for a variety of engineering deficiencies

Long live the ZR-1, still the only DOHC vette and only "stock block" FIA record holder. hopefully we'll see that record fall again soon. I kinda hate that VW has had it for so long.

but that as "little Adam" would say, is another story........

glass slipper

As stated already, all LT5s have forged cranks. Read my post again, in particular my last sentence where I stated at the end: "...it just took a lot of development time and cost for Lotus to prove it to GM." It's obvious from my statement the cast cranks never made it out of development.

z06scentair

Very nice process summary!

Would love to see that on the wall as a value stream map. That would require alot of sticky notes!

Tom400CFI

^That all makes sense, but I feel that based on the quote Glass Slipper cited, it seems like it's not relevant. Based on that quote, it would seem that they knew at that early stage that is was indeed a low volume engine, and that it was not going to be using any shared tooling. It would seem that they already knew things that would disqualify the LT5 from those "rules" or process.

tpepmeie

From my memory, the issue with loading the powertrain from underneath had more to do with the width of the engine at the cam covers. Because of that constraint, we ended up with smaller diameter cam sprockets than Lotus would otherwise have designed. Great for packaging, not so great for chain stress. The low wrap angle of the chain on the sprocket limits chain durability at higher RPMs.

I believe this was a 90 degree design from the very beginning. The bore spacing constraint limited the inlet valve size which could be fitted efficiently. With the bigger inlet valves, Lotus could have guaranteed the 400 bhp, but had to concede to Midgley and lower the goal.

Ron, with a big enough bore and associated valves, these heads will go 400+ on the intake. That alone won't make more power without other things being right. My valves are 39.5mm, the heads go >350cfm. That's about 92 cfm/sq in. Good, but not exceptional. Scale it up to a 42mm valve (a conservative 32% of a 4.125 bore), and see what you get.

Can we get this thread back on topic?

Todd

glass slipper

I appreciate your experience and everything but a lesson in how engine design by committee is accomplished is not what I consider to be an answer, just more deflection on your part. What you did accomplish is to show us how engine designs get so screwed up... Ford's modular V-8 program is a prime example, I'm sure you're familiar with it having worked at Ford. That engine was used in many different applications (as the name "modular" implies) and it ended up being "worst in class" in all of them. The Coyote engine they have now stands in stark contrast, it is a great performance engine because that was its singular design goal.

Your problem is ignoring the fact that the LT5 could never share a common production line with the SBC regardless of bore spacing. You keep dodging my one question: "What production line machinery would the LT5 engine block have in common with the small block Chevy 4.4" bore center?" The answer is none, zero, nada. Even if cast-in cast iron cylinder liners were used, Rudd's comment ("You're not going to make this block on the same production line as you make the small-block") is still true. You haven't presented one good engineering or non-engineering reason to have the bore spacing the same as the SBC, neither did Midgley. He arbitrarily set the bore spacing at 4.4" like the SBC and it was done with a known loss in performance, i.e. capriciously.

I think at this point we need to consider agreeing to disagree, I know what's stated in the book and I'm very familiar with machining processes so I'm sure the LT5 would never share a production line with the SBC regardless of bore spacing. You seem to be equally sure this was a management decision based on the desire one day in the future to possibly have an LT5 block going side-by-side down the same production line with the SBC for high volume production. This is how 16 lifter bores would end up in an engine block used in a DOHC application...engine design by a committee of management who knows nothing about engine design.

PS FYI, the engine block material was already accepted as aluminum as well as the forged aluminum nikasil coated cylinder liners before the 4.4" bore spacing edict was issued by Midgley. Of course the cylinder liners weren't written in stone but neither was the 4.4" bore spacing...you tell me which one is better to change given the fact that it makes no difference to the capability of going down the same production line. That one single decision cost a lot of HP down the road and effectively killed the LT5 before it even got off the drawing boards. With VVT, more displacement (think 7L), and direct injection, 650 HP would be easily achieved NA and have a much better power curve than the LS9 or upcoming LT4...the addition of a supercharger/intercooler system to the LS/LT series evens the weight and size disparity between the DOHC and OHV engines. More power under the curve gives the win to the DOHC engine.

bb62

Yes we will need to agree to disagree with a number of things.

1. The Modular engine was very successful for the vehicles it was designed for. The Mustang with a volume expectation of about 50K at the time was not one of them. It was primarily designed for truck applications – and there it had best in class cost and BSFC. It also had excellent torque for the low and mid-range – again for truck and large car applications (like Crown Vics/Grand Marquis/Town Cars which at the time were responsible for nearly half of all FoMoCo profits). The rest of the profits came from the F150 and variants where Ford sold over 750,000 units per year for a time. The quality and serviceability of the engines was also key. There are executive limo companies that regularly run more than 500,000 miles on many of their Modular engines without a major overhaul.

2. The problem with the Modular (like the LT5) is that it also had (has) constrained bore centers (for power applications). I agree that this was an unfortunate series of decisions given how things ultimately were borne out, but the thought at the time was that many vehicle lines using the Modular were going to go FWD. FWD applications needed to fit between the frame rails and so constrained the bore size available. The Lincoln Continental (off the Taurus platform) was a FWD application for the Modular, but it was the only such application.

3. Modular, the name, wasn’t meant so much as a description for an engine in many vehicles. It was meant to describe a common combustion cylinder and valvetrain design that could be used in a variety of configurations – like 60 degree V6s, 90 degree V8s, V10s, and even I4s. The concept was shelved years before the 1st engine was produced, but the name stayed.

4. By the way, the 5.4L Modular was a very successful engine both from a sales perspective and critically. And it was used in such varied products as the F250s and Ford GT.

5. You do realize that the Coyote engine is just another development of the Modular.

6. Yes I think that GM manufacturing management coupled with their marketing teams probably wanted the 4.4” bore center for the LT5 held because of what they thought of as the promise of DOHC engines. I can guarantee to you that internal GM engine planner/finance (with support from engineering) were looking at ways to bring the production in-house – and that would have required reusing existing assets.

7. You keep stating that I believe in the possibility of the SBC and the LT5 going down the same line – nonsense. I didn’t state that. But I did state that there are millions in assets that could be re-used for a “GM modified for high capacity LT5” design – a design that would replace the SBC engine if necessary – not built concurrently with the SBC. That would have meant a re-designed LT5 compared with what the Lotus guys were thinking – but I can nearly guarantee that it was studied. And yes, those studies probably held the LT5 back from its true potential. But it’s not really design by committee as much as it is those people taking a total corporate viewpoint. Worrying about volumes that were at best 2 to 3 thousand a year compared with application with maybe 250 times that volume are what drives the senior leadership in all these companies (even the ones overseas).

8. While I agree that the LT5 certainly had lots more power potential, I believe that it was also too tall for the C5. The hood line (coupled with the coming pedestrian safety standards) meant that the LT5 couldn’t be used in that application.

9. I don’t think the bore center decision killed the LT5. I think it was clearly killed by “not-invented-here”. In many ways not much different than the Yamaha designed and built Ford SHO engines for both North America and Europe. They were experiments in joint ventures and a way to transfer technology without any real expectation for the long term regardless of what we enthusiasts (as I also have a 95 ZR-1 with its stable mate 67 435HP coupe) would have preferred 25 years on.

Dominic Sorresso

"I don’t think the bore center decision killed the LT5. I think it was clearly killed by “not-invented-here”. In many ways not much different than the Yamaha designed and built Ford SHO engines for both North America and Europe. They were experiments in joint ventures and a way to transfer technology without any real expectation for the long term regardless of what we enthusiasts (as I also have a 95 ZR-1 with its stable mate 67 435HP coupe) would have preferred 25 years on."

Absolutely. Two great motors that I have owned. Word is GM Powertrain HQ doesn't even show a sample of the LT-5 as one in their historic line of engines.

combatdoc

GM powertrain was just pissed and they didn't want the LT5 to be so superior to the L98 and LT1. Thats why they don't display the motor, it wasn't their's. This is all my opinion BTW!