Ultimate N/A M20 racing engine?

[digger]

Yep, its always about the bhp/L number and VE , 120 bhp/L from a 2.9 L m20 with 84mm stroke needs 8500-9000 rpm, high duration cams, lightweight rods, custom lightweight pistons and pins. Of course 11.5 CR. A 3.1 L engine only needs 110bhp/L to achieve the same hp numbers.

A rule of thumb i use is 6500 rpm for 100 bhp/L for a high performance build

[Mooms]

i'm sorry, but no. for a top-notch head, the answer is Rebello.

I dumped almost $10k on a L30 stroker turbo motor from Rebello for my Datsun 280z only for it to arrive with oil all over it, no less than 8 fully stripped bolt holes all over the head (including 2 cam tower bolts), finger tight oil pan bolts, a destroyed timing cover because the installed the damper incorrectly (damper also destroyed), and it (still) leaks oil. I sent it back only to be stiffed by Dave on the agreed cost ($1100) to have Ignite Performance pull/reinstall the engine. PS..they had 2 other Rebello motors being sent back as well. I was yelled at, called a liar, and basically treated like shit because he has some monkey in a shop who shouldn’t be near a torque wrench. I will crush that damn car before I give that dipshit another $. Rebello is garbage.

[Rtalatief]

around 210CFM at max valve lift (probably atleast around 13mm) is actually enough if everything else is correct. A 2.7 or 2.8L might need need 8000-8500 rpm but a bigger stroke engine like >3L 7000-7500 is enough.

Yep, its always about the bhp/L number and VE , 120 bhp/L from a 2.9 L m20 with 84mm stroke needs 8500-9000 rpm, high duration cams, lightweight rods, custom lightweight pistons and pins. Of course 11.5 CR. A 3.1 L engine only needs 110bhp/L to achieve the same hp numbers.

[digger]

around 210CFM at max valve lift (probably atleast around 13mm) is actually enough if everything else is correct. A 2.7 or 2.8L might need need 8000-8500 rpm but a bigger stroke engine like >3L 7000-7500 is enough.

[Rtalatief]

350+ bhp is attainable IF you can get the head to flow at least 240 CFM. And 8500 rpms of course :)

[zaq123]

What are the realistic limits of an M20 ?

to sum this all good advice in this thread and to answer your question,,,,the realistic limits of an M20 are in a direct proportion to the realistic limit of your wallet.

To do this correctly, look for a shop with a "proper" flow bench and the engine dyno.
Bench needs to be able to see the velocity, swirl etc....not just the flow. Engine dyno is needed to match the head to your engine: best performer head on the bench doesn't mean that it would be such when bolted to your engine.

cha-ching


not affiliated but here is an example of a properly equipped shop you are looking for

https://www.youtube.com/watch?v=1JjFlK-oDjI

[ForcedFirebird]

I concur about the piston shape. Doesn't matter what MFGR you go with, the m20 highly benefits from the angular squish band. At TDC the design forces the combustion to the center of the dish in the piston, away from detonation prone area. There are several companies that have pistons mimicking the stock shape - just stay away from the generic flat top type pistons (or with a pent shape dome on top).

[digger]

The dome is a certain shape to create squish which means the piston squeezes the air fuel mixture against the head. This creates additional mixture motion resulting in a faster burn and better knock resistance. At lower rpm this is absolutely critical for reducing knock as the port speed is slow you need all the mixture motion you can.

A lot of custom pistons or off the shelf ones don’t achieve this. The m20 885 head is different to many other heads in that a flat top creates no squish it needs a specific dome like those racetep pistons which is a copy of the OE.

you want the 9.7:1 style dome not the 8.8 style which still won’t get you to 12:1 unless you deck the head but will be still pretty high

[hasa]

Thanks for the responses! For some reason I have forgot the "Racetep" as a source. So this is what you are talking about:

https://www.racetep.com/automaker/bm...-oemcrown.html

I've never thought that the combustion chamber at piston side would have a big effect to power (unless a huge dome prevents the proper ignition flame traversal).

Okay.. now I think I'd have a concept:
Racetep 86mm pistons
Early 84mm forged crank "C38"
= +2.9 litres of displacement

Ported head
RHD valvetrain
42mm ITB setup
suitable headers

end results depends much on the headwork

[digger]

If generic pistons from ”usual places” are no-go, what an average tuner can do? Nothing... I understand clearly your point digger, but I don’t have your contacts, engine design skills and cad-skills. I like the simple design of the M20, but also understand that staying away from S54 is not clever. Sent from my iPhone using Tapatalk

yeah i mean dont just get off the shelf pistons that dont suit the combustion chamber. the Mahle MS 2.9L suit the 885 head but they are 10:1 CR a fair bit lower than you stated that you want

Alternatively if you take the dome of a 9.7:1 OE B25 pistons and translate it to 86mm with 84mm stroke and proper squish the CR works out roughly 11.5:1 (11.3 with 85mm bore if you prefer OE gasket) depending on valve reliefs which depend on the cam. top end can do this, if you want a much higher CR they have a dome that retains the squish but much less dish which is what was used in the 14:1 CR 2.8L race engine on webers AFAIK.

[AWDBOB]

If generic pistons from ”usual places” are no-go, what an average tuner can do? Nothing... I understand clearly your point digger, but I don’t have your contacts, engine design skills and cad-skills. I like the simple design of the M20, but also understand that staying away from S54 is not clever. Sent from my iPhone using Tapatalk

He’s saying don’t buy off the shelf pistons that aren’t matched perfectly to your setup. “The ultimate racing engine” doesn’t come from off the shelf parts.

There is one set of really good off the shelf pistons that will get you close to where you want to be. Those are the 2.9L Mahle ultimate street pistons from IE, perfectly designed to work with an 885 head and m52 crank and rods.

An average joe can get custom pistons spec’d by a company like Top End Performance. They just made me custom 86mm pistons to work with a 731 head an S52 crank/rods, to whatever compression you desire. The same price as the off the shelf stuff and perfectly made to match your setup, had them here in a few weeks.

I would spend money on head work/ITBs and just use the ultimate street 2.9L IE pistons I mentioned above.

[hasa]

If generic pistons from ”usual places” are no-go, what an average tuner can do? Nothing... I understand clearly your point digger, but I don’t have your contacts, engine design skills and cad-skills. I like the simple design of the M20, but also understand that staying away from S54 is not clever. Sent from my iPhone using Tapatalk

[TobyB]

This is one of those things:
unless you HAVE to keep the 12v head for rules reasons,
why beat yourself up doing so?

Breaking the 300 hp level's not so hard that way.

t
why push it by hand if you can use wheels?

edit: would not race an E30 engine that came from that
workshop in Duarte without doing a thorough measurement
of it by myself beforehand. Because Furry Camel.

[digger]

Most forms of racing you see teams use biggest bore and shorter stroke length to achieve a given displacement. so a sub 3L will be better choice as you are limited in terms of power by the head. Please don’t use generic pistons from the “usual places” there’s a bit more to it than just finding something that has the right compression height and compression ratio.

[hasa]

the best wont come in "kit" form from the well known places. are you talking about a proper race only engine that never sees the street? or a street car you take to track on occasion?

Just pure racing. I know the absolute best comes only by deep knowledge and extensive development. But I would be happy to solve the basic choise between 3.1 and 2.9. 3.1 brings more torque, but does it bring problems due bad rod ratio or torsional vibrations etc. ? In my case the engine could operate in quite narrow powerband as I use race geared dogbox. So I think the mid-range torque is not so much important. Sent from my iPhone using Tapatalk