Piston Weights?

[henris42]

Hi,

Its me again with my strange questions. Now, does anyone of you have spare pistons? Bad ones are OK!

I''m trying to find out on how much each model's pistons weigh.

This is important for potential engine mods - if you keep you existing crank and rods, you need also same weight pistons. Other dimesions are not then important to keep balanced system.

I'm hoping we could build a table here for different configurations!

 

[philw696]

Contact Matt at Sports Italia as he has had a couple of damaged engines in the workshop.

 

[spacecadet]

For which engine? The V6 engines starting with AM 490 (Racing) utilized a redesigned rotating assembly, with significant weight reductions. I have spare used pistons for the 2.0L engine but they are different then in the Biturbo engines.

 

[Mr S]

If its 4.2 related, i can help with weights. Drop me a message

 

[henris42]

It AM 475

 

[alpa]

Hi
Are you still looking for that ?
I've got several dismounted engines.

This is important for potential engine mods - if you keep you existing crank and rods, you need also same weight pistons. Other dimesions are not then important to keep balanced system.

Well that's not necessarily true on these odd-firing engines. Compare the 2.8 and 2.0 cranks : they weight the same, 2.0 pistons are 100gr lighter.
I looked into several combinations. My choice was: AM490 block, crank and conrods (same as on 3200), 2.5 sleeves, 24v heads (they are all the same), custom pistons.
In fact the most expensive to make custom are sleeves (and the crank of course). The rest is acceptable: rods 150$/item, pistons 250$/item.

 

[henris42]

I indeed am! I have a 2500 set around (tubes & pistons), I'm thinking I can use the piston tubes, with new custom pistons.. The compression would be all wrong with those ones.. I intend to increase compression as I do E85 fuel on these.

For balance it would be best to have same weight custom pistons, as the original 2.24v pistons.

 

[alpa]

There are lots of technical aspects to take into account. But the first question is : what do you want ? RPM, torque, power ? What usage ?
Did you have a look at the heads ? Did you measure the intake ports ? Isn't anything shoking you there ?
Do you want to stay with the AM475 block and crank ?
Do you know this discussion ?

Evolution moteur AM475 (2.24V) to AM490(RACING), AM496 - Maseratitude

It's in french but you should understand easily.
Then I can weight stock and custom made AM490 pistons. The 2.24 AM475 engine I have is fully assembled but there are numbers in the thread above.

Balance: it's a v6. A v6 is never completely balanced. Our is odd-firing, it's even worse. Many modern race engines don't have weight match between the crank and rod+pistons. And I actually suspect it's the same on our v6. If you go from 2.0 to 2.5 you can't keep the same piston weight unless you make them much shorter but this means longer rods. Unless you make a very short piston but this isn't very good on turbo engines. That's why my choice above.

 

[henris42]

Hi, great stuff on your thread! It stated weight of 0.500kg, but with the axle inside... I'd need the axle weight as well.

With our odd-fire engine, high RPM is not really possible, so you go for extra torque. I'm just building a daily driver, and I want to keep a "reasonable"* budget. So I want to keep my basic AM475 engine, no need to dismiss stuff that is ok (or ok enough).

Piston weight thing is not that simple as you describe, I'd get custom ones. Its possible to save weight here and there (look at the bottom of thoce Racing pistons). My current challenge is that I'm not going to disassemble my finally assembled engine to weigh a piston.. just too much work for this long project ! I think I'd need to get myself a busted piston etc to continue... Balance will never be "perfect", but I think it can be ok with keeping the 6250 redline...

What do you mean by intake ports? We did a full rebuild of the heads, and our expert said they're actually quite good for factory ones. Given my project constraints, he did not recommend any porting. Besides, you handle that with turbo pressure, right? I have new billet compressors with thinner shafts so I'm expecting much better boost.. (but no completely new turbos, as I said I try to keep the budget "reasonable") I also have set up Megasquirt MS3 with flex fuel and all new injectors and independent coils...

//HS

*) mods should not be more that car purchase price.
- Also doing the AS Motorsport suspension upgrade, and Galileo Engineering fusebox (that was brilliant)

 

[alpa]

There are no problems with high RPM on odd-firing engines. Ghibli have the rev limiter at 7200 but actually happily rev up to 8000.
V10 engine are all odd-firing, F1 3L v10 were revving up to 19k. Many race V6 engines were/are odd-firing because an odd firing crank is shorter and stronger. And a 90 degrees block is lower.
Group A biturbo (they were 2.5) were revving up to 8-9000 RPM.

The new Maserati MC20 v6 biturbo engine Nettuno is a 90 degrees odd-firing v6.
Medias say the following (the most detailed article is here https://www.autoblog.com/2021/02/17/maserati-nettuno-v6-deep-dive/)

What's more, the Nettuno is designed as two three-cylinder motors working off a common crank containing four main journals and three rod journals that each hold two pistons. As an even-fire engine, the crank experiences a firing event every 120 degrees. These principles could all have been lifted from the Alfa Romeo 690T.

This is a non-sense. A three rod journals 90 v6 crank means odd-firing.
The pictures below clearly show three main journals.
Red line is 8000 RPM.

https://s.aolcdn.com/dims-global/di..._Nettuno_Engine_Lab_Washing-of-crankshaft.jpg

https://s.aolcdn.com/dims-global/di...tuno_Engine_Lab_Positioning-of-crankshaft.jpg

If you just want a little more on a 224 it’s easy: put the SEM restrictors in the Ghibli 2.0 position, you’ll get 1 bar instead of stock 0.8 bar of boost. All distributor injection and ignition ECUs are mapped up to 1 bar boost. Stock 224 turbos are not much different from the Ghibli ones, the compressor is smaller but the turbine seems to be the same.
If you want more than a little more then you can change to MS3 and map up to 1.2 bars. I've never heard about the knock on these Fuel Injected v6.

Now about the balance and weights. Let’s have a look at the numbers.
Stock 2.0 24v AM475 (not forged): 500gr with pin (I don’t know how much for the pin, must be 90-100).

Stock 2.0 Ghibli/QP4 piston (forged): 340gr + 75gr pin = 415gr
Aftermarket (not CPS but Italian) 2.0 24v Ghibli/QP4: 367gr + 78 pin = 442gr

Stock 2.8 18v (not forged): 503gr + 156 = 659gr
CPS (aftermarket) 2.8 18/24v: 463 + 142 = 605gr

As you can see there is a huge difference between stock and aftermarket piston weights. People just put them into the engines, nobody seems to care about the weight.
There is no magic: you can NOT design 2.5/2.8 pistons for stock 2.0 conrods that weight the same as 2.0 pistons: the bore are 91.6 against 82 mm. It’s a huge difference.

My custom made 2.5 24v pistons for the Ghibli 2.0 conrods: 384gr + 92 = 476gr. They are actually very light for the size, they were made by Gibtec in the US: this people are good.
You might save more weight on pistons with longer conrods, but steel is heavier than aluminum so not sure the overall would be lighter. If you do radically short pistons you'll certainly save but you need to keep some top to ring distance for multiple reasons.

More facts:
All 18v, AM475 and 2.8 24v engines share the same 137.35mm long conrods, except for the pin diameter on 2.8 (25mm instead of 22mm on others).
Ghibli/QP4/Racing have longer 145.3mm conrods, but you can’t use them on the other crank: longer rods have 2mm smaller big ends (these are actually v8 conrods).
Stock rods are high quality.

All 2.0/2.5/2.8 blocks have the same block to deck height. Conclusion: short rod engines have pistons with a bigger compression height (distance between the pin and the top of the piston crown). That’s why their pistons are heavy: they are taller and there is nothing to do about this. Even worse: the 2.0 short rod engines have the biggest compression height and thus the tallest pistons, they are unnecessarily heavy. That’s why Maserati modified this on Racing/Ghibli engines (and used them on QP4 2.0).

All engines have unnecessarily low R/L: 0.244 on 2.8, 0.23 on short rod 2.0, 0.217 on long rod 2.0. The max piston acceleration is quite low on all of them.

There are several combinations: you can use a 2.8 crank with stock rods with a 2.0 block: you get a longer stroke 2.2. Or a 2.0 crank with a 2.8 block stock conrods: 2.6 engine.
All possible combinations are still hyper square: even the 2.8 is still 94x67. You’ll find such ratio on F1 engines, nowhere else. It’s useless on low reving engines. Except for the block that is more compact.
The best would be to have a longer stroke, but a custom made crank costs a fortune.

 

[alpa]

About the 24v heads
They are the same on all 24v 2.0 and 2.8 engines. There are slight differences between GT and not GT heads and may be the other versions, but they are all compatible.
24v heads are from Cosworth: one of the best head foundry and design company.
These heads are very good:

• They had a novel (probably inspired by F1) cooling flow: on the exit side (in the V) there is a collecting gallery with two exits to the pump, so that the flow inside the head can be balanced with external restrictors on the exit path.
• The intake seats are round-shaped like in F1 engines (not a 3-5 cut shape)
• Intake ports are straight, almost vertical, with a long separation wall between two ports

Very similar heads (except for the number of cylinders) were used on VW ABF/ABY/ABZ and few other VW/Audi engines, the most known is the 2L 16v on Golf GTI. VW heads had the same valve positioning and the same camshaft chain without chain tender (however the chain costs 20e and not 200e).
I initially wrote (and thought) they were also designed by Cosworth. They were obviously not.
Here is a detailed description of the GTI head cutaway:

https://clubgti.com/forums/index.php?threads/the-2-litre-16v-head-cutaway-and-maximum-porting-dimensions-thread.193826/

These heads have something special: exhaust valves are parallel to the piston top, like in diesel engines. I don’t know why, probably a packaging problem to make heads narrower.

When turbocharged the 2L GTI engine easily reaches 400hp with mild camshafts and a decent boost level (I think at 1.4 bars). With 8.5-9:1 CR.
Maserati v6 struggle to go above 400hp while it has 6 and not 4 pistons, means more breathing capacity (more valves) and less effort per piston.
Why ?
To me the Maserati heads have two problems:

• Too small intake valves
• Too narrow intake ports

There are no issues on the exhaust side.

Intake valves are 30 mm (not 33mm as stated in the biturbo workshop man, the QP4 is correct). Heads were designed for a 82 bore.
Surprise: VW GTI is also 82mm bore, however intake valves are 32mm.
Both engines have 27mm exhaust valves. Actually v6 valves are 27.5mm
Compare with GT-R RB26: 86mm bore, 34.5 intake, 30 exhaust.

Corrected here:
Narrow intake ports: there is a widely accepted rule of thumb about the ratio between the valve size and the diameter of the port (see Graham Bell's books). The rule states that on a good 4v head the port should be 81-83% of the valve external diameter.
For a 30mm valve this makes 30 * 0.81 = 24.3mm
What do we have ? 22mm, 19% of surface less ! It's actually even less because it's not round, you have to start with a 21.5mm reamer when you try to enlarge them.

Let’s check on the 18v (not Cos) head: valve 28.3, port: 25. -> 89%. And 18v camshafts have 1mm more lift. On these heads the valves are more shrouded, so it's too much.

To me all that indicates that even 2.0 24v engines are intake limited. Even worse for 2.8.
Don’t forget the ridiculously low 7.4-7.6:1 CR (means a low thermal efficiency). Initially such a low CR made sense: the engines had carburetors.
And to finish a ridiculously short stroke which means less torque and even less thermal efficiency (you’ll find good scientific papers that explain why over-scare engines have a low thermal efficiency).

So to me there are several mods to do:

• Increase the port diameter. I went from 22 to 23.5 (did not find bigger reamers)
• Increase the CR to 8.5-9:1: I'll go 8.5:1 and will run 1.2 bar boost (to save turbos). Today street turbo engines run 11:1 but they feature VVT.
• Would be good to increase intake valves to 32mm but I did not find valves.

Few years ago I also found how to adapt VAG chain tenders (cost 15e each). I’ll use them because I’m against paying 300e per chain that will last 100k km.

 

[Frog3200]

Hi Alpa, always great to read your in depth analysis and learn things..
So for a 2l 24v (like a racing ) we can swap the chains with vw 2l GTI?
Do you know if the 3,2 heads are similar (+2 pistons) design than the v6 24v? Again for the chains even if supposedly lasting forever on the v8..
Sorry a bit away from the original question

 

[alpa]

So for a 2l 24v (like a racing ) we can swap the chains with vw 2l GTI?

No you can't

 

[henris42]

Merry Xmas, and thanks for the comprehensive info!

For the time being, I'm doing MS3 with flex fuel, I also had the turbos enhanced with new shafts and billet compressors. I wonder if anyone else has tried E85? I assume I can run plenty more boost, at least 1.5?

Enlarging the engine is still an idea for the future as I have a set on 2.5 cans that look like they should fit to the block.
Probably best idea would be custom rods and pistons then, should be that 2.6 after the mod.

 

[A.S. Motorsport]

These are always valuable topic!
IMHO the first issue is the engine control, hence we're developing the conversion kits for 24V and 32V to modern ecus as that is the first massive step.

That would allow you to run much higher compression for example you'd easily go up to 8.5 without issues.
As a side project I'm looking into much better injectors and sensors to bolt in to existing BiTurbo engines to improve AFR and control. (for example the amount of data a BiTurbo ecu can process is very limited the trigger info supplied to it reflects that)

Regarding the conversion kits, we're planning to complete initial kit for Ghibli and QP IV style coil engines later this year. (I'm also looking in to testing modernization components for the late multi-rib cars (GT, QP EVO, etc)
In the planning 24v distributor engine is next, FYI we already have 3D printed the conversion boxes etc so the OE integration aspect is already taken care off.

 

[alpa]

Having a modern ECU replacement would be a very good thing for static ignition 4v engines (having to ajust in parallel two identical ECUs is a PITA). Especially if this comes with basic settings that allow starting the engine and even breaking it in with a min (mechanical) boost level.
Even just to be able to have a decent diagnostic report is already a high value. Although you may need to find mechanic shops that are intellectually capable to plug a laptop to a car.

For distributor engines the stock ECUs (injection + ignition) are OK. They need firmware updates, already done. But of course a modern replacement is better.

Injectors: Bosch 0280 155 759, plug&play. EV6 connector.
Already a few v6 18, v6 24 and v8 biturbo running with these cheap more recent injectors. Just need to lower the rail pressure on 18v and adjust richness on any of them.
There are more injectors but none of them are EV6. You need injectors in the 300-400cc/min range, not that many of them have the right dimension and spray pattern.

The biggest sensor problem is the APS MAP sensor of distributor versions. It's ****. But to replace it you need to adjust a parameter inside the ECU eprom because there is no p&p modern equivalent. Other sensors are good or not worse than modern ones (actually the sensors' quality went down over the time).
To replace the (impossible to find) TPS you (likely) need to adjust the eprom, again.
I know how to adjust the eprom.

For 4v heads 8.5 is for sure not that high.
On 18v a 9:1 may be a problem. May be not. I'm going to see how 2.8 18v works with CR 8:1 (Karif was supposed to be 7.8:1 but I don't believe that, this would imply special pistons or heads). The head's cooling is excellent but the chamber is very uneven with a side mounted spark plug. I mean it's certainly possible but with how much boost ? Is this worthwhile ? It may be more interesting to go a higher boost that can be I/C cooled and then compress less in the chamber. A better balanced two-stage compression scheme.

The other aspect is the inter-cylinder VE balance, this prevents from going to high CR. And this balance depends on the intake plenum design which is weird (I didn't say bad) on biturbo v6 engines, especially on 18v (carb heritage). The v6 plenums design is very uneven. It's good to spread the torque over rpm but not good in transients.
When Nascar went injection (less than 10 years ago I think) they had to adapt injectors on the stuff that was designed for a carburator's manifold (a spyder). Exactly like what we have on the 18v engines, the 24v plenum being closer to but still far from traditional intake plenums. They did lots of studies about how evenly was distributed the effective compression ratio (VE) and the fuel mixture over cylinders (on Nascar v8 engines all cylinders have different CR to counter-weight the uneven air distribution). They observed that cylinders were largely robbing mixture from each other, so in transients there was a high risk of a wrong richness. Nascar engines spend most of their time at 9000rpm, our engines rev much less and are odd-firing so this danger is even higher.

 

[Wally]

Bosch 0280 155 759 has too much flow compared to the original injectors. Surely there must be other EV6 that are more within flow-range?

 

[alpa]

Bosch 0280 155 759 has too much flow compared to the original injectors. Surely there must be other EV6 that are more within flow-range?

As I said there are now several 18 (2.0 and 2.8), 24 (2.0) and 32v (Shamal and QP4) cars using Bosch 0280 155 759. Tuned up with a gas analyzer.
It's a fact, not a guess.
There may be other compatible (and still available brand new) injectors but either at mucher higher price or with more flow difference. I've been looking for compatible injectors for years, this is all I found at an acceptable price.
These injectors are 10% more flow.
All biturbo fuel pressure regulators are adjustable. All biturbo ECUs have a CO level pot.
Static ignition engines run 3 and 3.5 bars fuel pressures, 18v engines run 2.5 bars fuel pressure. The minimal fuel pressure that regulators can provide is about 2.5 and 2.2 bars.
In most of case CO level adjustment was enough. In some cases the fuel pressure had to be lowered.

A reminder:
flow = sqrt(new_pressure / old_pressure)

If you wanted to go to a more precise discussion.
A one-to-one replacement does not exist or that would mean injector providers would have designed several identical injector references, financially speaking this does not make sense.
An injector is defined by its nominal flow (cc/min at a pressure) AND by the opening/closing time (depending on voltage). And the spray pattern but here I assume a compatible pattern.
So anyone who wants to substitute an injector by another should adjust the ECU to account for a new flow AND opening time.
Without such an adjustment only a test can tell you if an injector fits because the effect is non-linear. This is what I did on my cars and this is what someone who runs a Maserati garage did as well (now he proposes this replacement in his services).
Biturbo cars management is very imprecise especially in transients. So it's very resilient to the changes of components. My tests (with a wide band lambda on a 2.8 18v and v8 qp4) show that the impact of the substitution is invisible while engines are much more pleasant to drive compared to old original injectors.

 

[Wally]

You're right. Is positioning of this injector special in any way because of the spray-pattern? (When converting Alfa 24V from EV1 to EV6 it is...)

 

[Wattie]

Oops, saw “piston weights” and thought this was a new fitness thread involving wine.
Offski, byeee.