why would anyone build a 2.7 rather then 2.8?

[mrLEE30]

thinking about pulling the engine out of my scrap 325 chromie to have a play with it, and maybe build it upto a 2.7.... but then i read PBMW and it seems that a 2.8 is easier to build then a 2.7, so why would anyone build a 2.7 rather then a 2.8

am i right in saying i need:

325 block/head/pistons (which i have)
M52 crank, with a small amount of machining / and making the oil seal spacer (which i can find and make)
M20B20 con rods (which lie about all over the place)
zone chip??? (which type is recommended)

it seems so easy and no need to search around for a diesel or ETA crank as M52 engine are all over the place and even more importently no requirement to machine the head (bad i guess in my hot country)

can anyone please elaborate on what pbmw mean when they say you must machine the crank bolt

and finally what is the compression ratio (roughly) and does this engine run hot (whigh plugs to use) as this is an issue where i live in summer temps of 54C

cheers all

mrlee

[DaveD]

i would like to know too

[JazzMan]

me too! I had a look at both options briefly and 2.8 is the route I plan to take unless there's a massive pitfall somewhere!

[dazleeds]

not seen this article
but starting my 2.7 this week

will have to get hold of it and see the differences
will watch this closely also, maybe i can turn the sport engine into a 2.8 spare

but i somehow imagine theres more work to the 2.8

[oguz327]

Apparently the 2.8 makes very good torque but not high power due to it being square and not over or under square like the 2.7.
Please do not ask me to explain what that means as i am not that technically minded.

The 2.8 is a cheeper way of doing the conversion as the block needs no machining but from what i am told wont make big power.

One of the more clued up fellas on here may be able to explain better though!


Daz, hows yours coming along fella?

[dazleeds]

Daz, hows yours coming along fella?

all systems go as of this weekend mate

dropping block and head off to Iain on saturday

[oguz327]

Nice one Daz, glad its all kicking off dude!

what pistons are you going for?

[JazzMan]

So if your doing other stuff like cams / btb etc which move the power further up the rev range a 2.8 would counter that slightly due to it having more torque low down and less power at the top thus creating a more balanced/drivable engine - or am I talking out of my rear end?

[dazleeds]

Nice one Daz, glad its all kicking off dude!

what pistons are you going for?

errr pretty sure there late 325 jobbies
but im a s bad as you lol

leave that stuff to Iain

[DaveD]

where is ant when you want him

[oguz327]

So if your doing other stuff like cams / btb etc which move the power further up the rev range a 2.8 would counter that slightly due to it having more torque low down and less power at the top thus creating a more balanced/drivable engine - or am I talking out of my rear end?

lol, not sure Jazman, it was explained to me but i have a head like a siv when it come to technical engine stuff

[DRIFTBOY]

[quote="oguz327"]Apparently the 2.8 makes very good torque but not high power due to it being square and not over or under square like the 2.7.
Please do not ask me to explain what that means as i am not that technically minded.

quote]

A 'square' engine has the same crankshaft stroke (distance the piston travels basically) as the width of the cylinder bore.

An oversquare engine has a shorter crank stroke than the cylinder bore.
An undersquare engine has a longer stroke than the bore width.

Oversquare engines are - as a gerneral rule - more rev happy, undersquare is generally more torquey.

Both have good and bad points.

Try this link!
http://www.answers.com/topic/undersquare

Martin.

[mrLEE30]

so can anyone answer my question? its seems too good to be true, no machining of block and minimal fabrication work, and yes the stroke would be longer than a 2.7 but only by 100cc and that would be split over six cylinders so i cannot see that making such a huge amount of difference

[tomson]

surely if you want to go 2.8 dropping an M52 in would be quickest method???????

[JazzMan]

True, but if you already have tuning parts for the M20 and / or if you want to do it for the experience of rebuilding an engine? But then I supposed you could say a 2.7 is a more technically challenging build.

[maxfield]

People are saying 2.8s don't make loads of power?

Look at scots (player6)

I know he has had a done alot more to it but still i think he had more power than 2.7s without TBs etc

[oguz327]

People are saying 2.8s don't make loads of power?

Look at scots (player6)

I know he has had a done alot more to it but still i think he had more power than 2.7s without TBs etc

And how much did he spend to get that power Max?

[maxfield]

People are saying 2.8s don't make loads of power?

Look at scots (player6)

I know he has had a done alot more to it but still i think he had more power than 2.7s without TBs etc

And how much did he spend to get that power Max?

Alot but if you built a 2.7 and a 2.8 with the same spec engine ish i.e same cam manifold bbtb etc

then i would put my money on the 2.8

[mrLEE30]

surely if you want to go 2.8 dropping an M52 in would be quickest method???????

no as it requires different engine mounts /drive train and there is the OBC (OBC2) system to circumvent and the guages etc etc etc not a hard conversion but not easy either

my question was simple why build a 2.7 if a 2.8 is easier to build and parts are more common place and as Jazzman says i enjoy tinkering with engines but a 2.7 requires head skim which requires vernier pulley to be set up where as 2.8 seems straight forward.

[mrLEE30]

then i would put my money on the 2.8

do you earn any money, though child labour was reserved for this part pof the world

[maxfield]

then i would put my money on the 2.8

do you earn any money, though child labour was reserved for this part pof the world

Every known and again i earn a little money

[mrLEE30]

i wont ask by doing what!!!! down the docks is it!!

[oguz327]

People are saying 2.8s don't make loads of power?

Look at scots (player6)

I know he has had a done alot more to it but still i think he had more power than 2.7s without TBs etc

And how much did he spend to get that power Max?

Alot but if you built a 2.7 and a 2.8 with the same spec engine ish i.e same cam manifold bbtb etc

then i would put my money on the 2.8

Not from what i am told due to the engine being square but hey, i am no expert.

[Andyboy]

Look in the latest TBMW mag - 5 pages in explicit, mind numbing detail on how do do 2.7 and 2.8. PBMW doesn't say how it's done.

325i/525e block, 2.8 M52 crank, 2.0 or Eta 130mm rods, late 325i pistons which give 9.8:1 in a 2.8, machine the oil seal spacer from the unwanted M52 front pulley hub, M20 crank spigot bearing, M52 crank pully bolt, no block machining, job done. I did one of these 4-5 years ago. Spec for spec, a 2.8 will ALWAYS give a little bit more power and torque than a 2.7 because it has 100cc more - assuming of course that it's properly set up. There's no substitute for cubic inches.

[oguz327]

I stand corrected

[Jhonno]

2.7 will rev better, 2.8 produce more torque/power..

2.8 will be a better road engine more flexible etc

[JazzMan]

I've got a M52B28 block (with all the bits) on the way and a dbilas dynamic 282°/272° cam ready. Just need B20 conrods and make a call to Ant at some point for Megasquirt and we'll see what happens. This a long term project though so I probably wont get start until the weather goes bad after the summer! I want to get the Sportster on the road with the standard M20 first!

[march109]

2.7 will rev better, 2.8 produce more torque/power..

2.8 will be a better road engine more flexible etc

Why tho?

[Andyboy]

Why is a 323i better than a 320i? Same bore, same head, same manifolds, same throttle body, same injectors - but it's better. One has 125 bhp, the other 150. The more fuel and air an engine burns, the more power it makes, simple.

The other thing is that the 525e is now a dying breed and they won't be around forever. There are now increassing numbers of old shagged nikasil 2.8's floating about and these will take over fully one day.

[mrLEE30]

sorry typo i meant TBMW not PBMW!!

i can get hold of all the bits so really a 2.8 would be the easiest, it will be built in my garage anyway so time is not an issue as i will use my scrap car engine as a base (assuning its any good when i pull it apart.)

andy when you built yours i assume you ran with the 325 AMF/TB/inlet and 325 injectors, so did you use a different ignition chip or go for a different ignition system? would the ''zone'' chip be suitable for this 2.8 build?

can i run newer pistons in an older block as my donor 325 engine is a 1986 vintage and it seems to use the older pistons there may be some machining to be done to clear the webs

and last question it mentions a difference in the older and newer 2.8 cranks, can i used the newer one or should i only look for the older one?

cheers

[Simon13]

People are saying 2.8s don't make loads of power?

Look at scots (player6)

I know he has had a done alot more to it but still i think he had more power than 2.7s without TBs etc

yes but look at it this way Maxfield if i threw 10 grand at a 1.0 micra engine checkbook modding it (as Scott freely admits) i would be a tat pissed off it it didn't make any real power increases.

As a rough example off the top of my head to get a 200bhp,200lbs 2.5 route 2.7 M20 built it will cost you £3500

To get the same power from a 2.8 your looking at more money £4500, despite what everett says E30Adams car does not make the power it should with the mods and money thrown at it like a 2.7.

As said square engines are not the best

All my experiences and i'm not starting a fight!

Mr Lee the 2.8 will not give you the lazy real world torque a 2.7 can imo

[mrLEE30]

Mr Lee the 2.8 will not give you the lazy real world torque a 2.7 can imo

thanks all... i may build it anyway and see how it goes, only ever driven one 2.7 and it was tired so i have no real comparison and at the end of the day if i am pulling the older 2.5 motor apart anyway it would be silly not to rebuild it as a 2.8 as i can do it in my garage

i will let you know what happens if it happens

would still like to know the answer to my question of fuel - 235 TB/AFM/Inlet and a zone chip - ok??

mrlee

[topspark]

Why is a 323i better than a 320i? Same bore, same head, same manifolds, same throttle body, same injectors - but it's better. One has 125 bhp, the other 150. The more fuel and air an engine burns, the more power it makes, simple.

Andyboy, the cam in the 323i was better profile than 320i. 252 for the 320 and 260 for the 323. Also the 320 was detuned to fall in with tax laws or summat.??
But basically i agree more cc's = more power / torque.

lee

[Geoffsco]

Anyone had experience with engines larger than 2.8? Ireland Engineering have kits for 2.9, 3.0 and 3.2.

[reggid]

E30Adams car does not make the power it should with the mods and money thrown at it like a 2.7.

Therefor all 2.8 will make less power.........not likely. 1 example doesn't mean much there are plenty of average 2.7;s around aswell

As said square engines are not the best

All my experiences and i'm not starting a fight!

where is your proof of this? Its a neglibile effect in this case.

Mr Lee the 2.8 will not give you the lazy real world torque a 2.7 can imo

i know it will give you more......lol. but seriously what are your opinions based on?

i have a m20B31 and know some one with a M20B28 and it makes atleast as much torque if not more at low rpm than mine. Yes my car is more heavily cammed and had port work and so makes more topend but subtle details such as cams, headwork can strongly affect both torque and power characteristics. another example is Player6 car makes probably less peak torque than a 2.7 but thast becasue the torque has been shifted to the upper rpm band to give power.