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dwightlooi

Why GM should NOT build a DOHC V8

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I know i've read somewhere about dohc SBC. I hope GM will also make some effort in looks department.

Yes, there were concepts of an over-under Dual In-Block Cam arrangement. The idea is to separate intake and exhaust valve control into two discrete camshafts. This involves a mess of pushrods and rockers at two different angles, but it permits dual independent VVT.

Personally, I am not impressed with the idea. It'll be much simpler and neater to simply use co-axial camshafts to achieve Dual VVT. Actually, this has already been implemented in the 2008+ Dodge Viper.

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hrdp_0908_15_z+variable_valve_timing_guide+.jpg

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I can see GM implementing this type of VVT in their future LS series (if future small block will be called LS series at all because all i've read is that for now is being called Gen V).

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I can see GM implementing this type of VVT in their future LS series (if future small block will be called LS series at all because all i've read is that for now is being called Gen V).

Collectively, the contemporary Small Blocks are called the "Gen IV" Small Block V8s. The LS series RPO is part of the Gen IV Small Block family, but the Gen IV includes more than the LS engines. They include:-

LS-series (cars): LS1, LS2, LS3, LS4, LS6, LS7, LS9, LSA, etc.

L + "Not S" + Number series (branded Vortec; for trucks): L96, LY6, LZ1, L20, LC9, LH9, LMF, LMG, L94, L9H, etc.

A few stragglers without "LS" RPO, but used in cars: L76, L99

Point of Note: All the RPOs in Red has VVT. As you can see, ALL of the truck engines -- the Vortecs -- have VVT. However, only one car engine (the L99) used in the Camaro SS has VVT.

If you ask me, that's WAY TOO MANY V8s (and we haven't counted the Northstars yet), I'll like to see the variants cut down to one architecture, two displacements and maybe four variants in all.

Perhaps these (all sharing the 103.25mm bore, but with either 82 or 92 mm strokes):-

  • 5.5 (420~432 hp, power optimized; DI/VVT/AFM) for performance cars
  • 5.5 (550~580 hp, Supercharged; DI/VVT) for really fast cars
  • 5.5 (375~385hp, torque optimized; DI/VVT/AFM) for big trucks
  • 6.2 (425~435hp, torque optimized; DI/VVT/AFM for bigger trucks

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reading on GMI that the northstar is toast in the STS to me makes me wonder if Caddy's lone V8 in the future won't be a small block now.

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reading on GMI that the northstar is toast in the STS to me makes me wonder if Caddy's lone V8 in the future won't be a small block now.

The Northstar is not a Small Block to begin with. In general, the term "Small Block" applies to GM Pushrod V8 engines with an 111.76 bore center spacing. The Northstar is 102mm. Despite the ~10mm narrower spacing, the Northstar is a longer, wider, taller engine which weighs more than the Small Blocks due to it's DOHC design. It also has worse reliability record, especially with head bolts that pull off causing the gaskets to fail. IMHO, I don't think the Northstar will be missed.

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The Northstar is not a Small Block to begin with. In general, the term "Small Block" applies to GM Pushrod V8 engines with an 111.76 bore center spacing. The Northstar is 102mm. Despite the ~10mm narrower spacing, the Northstar is a longer, wider, taller engine which weighs more than the Small Blocks due to it's DOHC design. It also has worse reliability record, especially with head bolts that pull off causing the gaskets to fail. IMHO, I don't think the Northstar will be missed.

I think by 'small block' the Reg was referring to the pushrod V8s in the Escalade and CTS-v.

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I think by 'small block' the Reg was referring to the pushrod V8s in the Escalade and CTS-v.

right. what has been called small block for quite awhile..the GM pushrod v8.

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>>"The Northstar is not a Small Block to begin with. In general, the term "Small Block" applies to GM Pushrod V8 engines with an 111.76 bore center spacing. "<<

Correction :: the term "small block" is a relative term to differentiate between 2 V-8s of markedly different external dimensions in the same marque. It has nothing "in general" to do with an internal dimension. Chevy, Buick, Olds, Ford, Merc, Plymouth, Dodge all had small blocks.... because they also had big blocks at the same time.

For the catalyst for the term, note than 'SBC' was not applied to the Chevy V-8 when it debuted for '55; it wasn't until the big block 348 showed up in '58 that the term was ever used.

However, in recent times, the term has become synonymous with the GM corporate V-8 that has decended / replaced the traditional SBC.

BTW, the BBC V-8 went out of production last year, IIRC, so by rights, the term 'SB' should fade out of use over time.

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>>"The Northstar is not a Small Block to begin with. In general, the term "Small Block" applies to GM Pushrod V8 engines with an 111.76 bore center spacing. "<<

Correction :: the term "small block" is a relative term to differentiate between 2 V-8s of markedly different external dimensions in the same marque. It has nothing "in general" to do with an internal dimension. Chevy, Buick, Olds, Ford, Merc, Plymouth, Dodge all had small blocks.... because they also had big blocks at the same time.

For the catalyst for the term, note than 'SBC' was not applied to the Chevy V-8 when it debuted for '55; it wasn't until the big block 348 showed up in '58 that the term was ever used.

However, in recent times, the term has become synonymous with the GM corporate V-8 that has decended / replaced the traditional SBC.

BTW, the BBC V-8 went out of production last year, IIRC, so by rights, the term 'SB' should fade out of use over time.

Thanks for the clarification. I use the term loosely because it has become synonymous in popular usage to refer to the 111.76 bore center GM pushrods of yore and contemporary times. But, yes, you are right.

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MAYBE if the 'SB' term DID pass out of usage, I could get past the association with Chevrolet & my unacceptance of said termed motor in a Cadillac. Still working to get past the 'Corporate engine' announcement. :wacko:

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could it be possible to make an engine block that can utilize both DOHC and CIB?

i do like CIB better mainly because it sounds stonger, pushrods sound powerful, while Cammers sound weezy until you get to AMG's or flat plane ferraris

Edited by CanadianBacon94

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It's been done. The GM 3.4 DOHC twincam comes to mind. The issues that engine is known for have more to do with packaging than the fact that it was based on a CIB engine.

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It's been done. The GM 3.4 DOHC twincam comes to mind. The issues that engine is known for have more to do with packaging than the fact that it was based on a CIB engine.

You can, but it usually does not amount to an optimized design. In particular, the cam drive section will be kinda messy. You'll probably end up with having to use an intermediate sprocket in the SBC's location. You then have try to enclose the rest of the chain drive to the heads or resort to belts. Given that the most complex and costly parts an engine design effort is in the heads and combustion control systems, the very act of reusing the block casting may not be worthwhile from a savings standpoint.

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You can, but it usually does not amount to an optimized design. In particular, the cam drive section will be kinda messy. You'll probably end up with having to use an intermediate sprocket in the SBC's location. You then have try to enclose the rest of the chain drive to the heads or resort to belts. Given that the most complex and costly parts an engine design effort is in the heads and combustion control systems, the very act of reusing the block casting may not be worthwhile from a savings standpoint.

Even with the cast-sharing between the pushrod and OHC block, did not the LQ1 still end up one of the most expensive engine designs for its time? I would think if the same idea could be used, it would have to be based on development of a new block designed to share the different valvetrains, and not from a design originally for one or the other. This, because the LQ1 ended up a bunch of fussy fixes to accommodate the change from pushrod to DOHC with oil sealer plugs and funky hoses for coolant channeling, etc. Being belt driven wasn't such a bad thing, at least helping to reduce noise levels; however I imagine it was more of a necessity than an exact thought.

I forget whether the fact that the 60 degree engine allowed for a tighter package to enable the cam alterations?

Edited by ShadowDog

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I have read somewhere that ultra V8 engine (which was cancelled) was finished before GM pull the plug on it. Now that engine was supposed to have Direct injection, VVT , Dohc heads, 4 valves per cylinder etc.

But GM didn't want to spend money for investing in engine plant necessary equipment etc. (or something like that).

Dwightlooi will probably now more about this.

I was thinking..if GM doesn't want to spend money needed to build that engine but they already developed it etc. maybe they could outsource some company to build that engine for them if there is need for let say cadillac with DOHC v8 (maybe cosworth, illmor, mclaren etc)

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ShadowDog ~ >>"Even with the cast-sharing between the pushrod and OHC block, did not the LQ1 still end up one of the most expensive engine designs for its time? I would think if the same idea could be used, it would have to be based on development of a new block designed to share the different valvetrains, and not from a design originally for one or the other. This, because the LQ1 ended up a bunch of fussy fixes to accommodate the change from pushrod to DOHC with oil sealer plugs and funky hoses for coolant channeling, etc. Being belt driven wasn't such a bad thing, at least helping to reduce noise levels; however I imagine it was more of a necessity than an exact thought."<<

Would like to delve into this much further.

Designed from scratch, a dual-capcity OHC / IBC engine should not be prohibitively expensive (some more CAD time, of course). But the space taken up by the cam in a IBC set-up is doing a lot of nothing in a OHC set-up.

Since perception has such a heavy thumb on this 'To Overhead, or Not To Overhead' discussion, a dual-capacity block would -decently utilized across a number of lines, seem on the surface to have the greatest chance of pleasing 'both sides' and costing the least. A chain-drive 'tensioner/sprocket' for the OHC set-up, and some chain covers are nickel/dime stuff compared to 2 different blocks. Then, with varied displacements AND both 'pushrod' and OHC heads, you have the greatest degree of differentiation across all the divisions using it.

Someone post some exploded views of a IBC V-8 and a OHC V-8 and let's get started designing this...

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I have read somewhere that ultra V8 engine (which was cancelled) was finished before GM pull the plug on it. Now that engine was supposed to have Direct injection, VVT , Dohc heads, 4 valves per cylinder etc.

But GM didn't want to spend money for investing in engine plant necessary equipment etc. (or something like that).

Dwightlooi will probably now more about this.

I was thinking..if GM doesn't want to spend money needed to build that engine but they already developed it etc. maybe they could outsource some company to build that engine for them if there is need for let say cadillac with DOHC v8 (maybe cosworth, illmor, mclaren etc)

I don't know if it is finished. But, even if it is, there is a huge chasm of investment difference between building an engine and vesting it for mass production. Creating a one off prototype or even a race engine is one thing. Getting it through qualification and investing in the tooling for mass production is another.

Personally, I won't try to build a DOHC V8. Instead, I think GM will be best served with DOHC I4s, DOHC V6es and Pushrod V8s -- all fortified with VVT and DI. I4s for displacement sensitive markets and simple single-turbo solutions. DOHC V6es for mainstream luxury. Pushrod V8s for maximum power density applications -- sport luxury and other performance cars. DOHC V8s are a waste of resources because it offers neither better performance, nor better economy, nor differentiation from the competition.

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Here is something from Mercedes.

New DOHC 5.5 l v8 engine with Twin turbo

I think that Gen V with DI, VVT , and supercharger (or maybe GM will start using turbochargers on their V8) could easily surpasse that number. This is around 100 hp/l. LS9 develops that much and i think GEN V could go even further (with flat torque curve :booyah: ).

So the top engine in Mercedes will soon be 5.5 l TT v8. And top engine in GM will also very soon be 5.5 l v8 (supercharged or turbocharged), if there isn't anything biger planned.

Can wait to see real spec. when top engine from GM come out.

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You know what would be a really funny picture.... the GM 5.5 sitting next to a MB 5.5....... just so we could see the size difference.I bet SMK would lawl all over it.

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The 5.5 liter AMG engine makes 660 lb=ft of torque, that is substantially better than the CTS-V's 6.2 liter engine can put out. As far as packaging size, the Merc engine is going to fit under the hood of the E-class, so I don't see how the future GM 5.5 liter pushrod taking up less space matters. And remember this isn't even Mercedes top end engine, they still have the BiTurbo V12.

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The 5.5 liter AMG engine makes 660 lb=ft of torque, that is substantially better than the CTS-V's 6.2 liter engine can put out. As far as packaging size, the Merc engine is going to fit under the hood of the E-class, so I don't see how the future GM 5.5 liter pushrod taking up less space matters. And remember this isn't even Mercedes top end engine, they still have the BiTurbo V12.

I assume the 5.5 will be in the C-class AMG as well (the current one has the 6.2 V8). Engine packaging is really only an issue with a FWD transverse setup where there are space constraints....if RWD compacts like the BMW 3-series and Merc C-class can fit a DOHC V8, then the space argument is moot..

What's funny is the truck fans always make an argument against OHC V8s, but Ford has built a lot of them for over a decade now...

Edited by Cubical-aka-Moltar

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I assume the 5.5 will be in the C-class AMG as well (the current one has the 6.2 V8). Engine packaging is really only an issue with a FWD transverse setup where there are space constraints....if RWD compacts like the BMW 3-series and Merc C-class can fit a DOHC V8, then the space argument is moot..

What's funny is the truck fans always make an argument against OHC V8s, but Ford has built a lot of them for over a decade now...

Anywhere you can put a DOHC V8 you can put a Pushrod V8 anywhere from 1 - 2 liter's greater displacement.

Ford's OHC <not DOHC, decent size difference there> has been the laggard of the bunch for years.

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Anywhere you can put a DOHC V8 you can put a Pushrod V8 anywhere from 1 - 2 liter's greater displacement.

Don't necessarily need more cubic inches. Cubic inches aren't the only way to make more power and/or torque.

Ford's OHC <not DOHC, decent size difference there> has been the laggard of the bunch for years.

They are still the top selling trucks, so obviously they aren't that much of a laggard.

Edited by Cubical-aka-Moltar

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So are the GM trucks if you scrape the badges off. Ford has gotten to claim "Best Selling Truck" for as long as it has only because GM spreads it's full size trucks over two name plates. I'm sure there are some years in the past 30 where the Chevy+GMC outsold the F-150.

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