2.7i Pros and Cons

[stormtrooper15]

I currently have a 89 325i with the m20b25 and aftermarket cam of which I do not know the specs. The rod bearings and possibly more are worn out. I may have the opportunity to pick up a 2.7 bottom end (block, crank, bearings, pistons, etc) and I am curious to know what benefits I would reap and what I would lose? I have been reading some and seems with the I head and 2.7 bottom end I would gain low end torque and lose hp. How would the aftermarket cam affect that guessing that it is a 288/288?

Any advice would be great, thanks!!!

[ak-]

The benefits are that once you turbo the car, it's going to make an ass load of more torque. e.g. Me.

The cons are you're probably not going to turbo your car.

[crappycoco]

So an 2.7 with low boost would be the tits?

[EatsHondas]

So an 2.7 with low boost would be the tits?

Yeah you could say that!

2.7 Turbo Acceleration

[whitebulat22]

A standard 2.7i can be expected to make the same 2.5 power with a bit more torque, custom tuning will make a great all around package. In your situation i'd consider a 2.8 stroker with m52 crank, 2.7 rods and 2.5 pistons, reason being that the higher displacement and compression will work better with your cam. Or turbo the 2.7, it'll go and sound like a plane before takeoff.

[george graves]

I'm all for building up a motor - that's awesome. But there are times "upgrading" to different motor just makes sense.

There are so many factors that go into picking a motor or even building a motor. No one can tell you what's right for you. Fuel economy? Boost potential? Budget? Old school vs new school? Do you have a small or large budget? How's your skills? So many of those you've got to figure out. Or at least post up so we can put our 2 cents in.

[stormtrooper15]

The priority currently is a small budget while I'm still in school. Since the car is not currently running properly I am looking to get it running with reliability (N/A). I came across a deal where it would be cost efficient to buy the 2.7 bottom end package instead of risk the current 2.5 crank or cylinders being scored. However is the 2.7 bottom end is not beneficial then I would simply rebuild and possibly have the 2.5 machined if it is that bad.

[stormtrooper15]

This car is a project car for my senior year of college so as far as skills and time wise, I will figure out how to do as much as possible by myself.

[stormtrooper15]

The benefits are that once you turbo the car, it's going to make an ass load of more torque. e.g. Me.

The cons are you're probably not going to turbo your car.

I would absolutely love to boost the car but unfortunately small college kid budget. For now anyways.

[stormtrooper15]

Would it be more beneficial to get a new 2.5 bottom end than a 2.7 bottom end if everything was the same price?

[IronFreak]

Yeah you could say that!

2.7 Turbo Acceleration

You do realize that motor in that video was probably 700+hp.....

The car was then wrecked I believe but the heart was saved and it turned into this.......

The Blue Monster

Little fun fact.

[redsubdivisions]

when you 2.7i and boost it later on, you will thank the torque gods.

[jalopi]

Since the car is not currently running properly

is it knocking? what makes you say the rod bearings are worn out? how exactly is it not running right?

without more details we can't know whether you're blowing a small issue out of proportion into an engine swap

[IronFreak]

It also depends on the 2.7, if its from a E-model you're going to loose compression which will drop the HP but you'll see some tq like everyone said. If its a 2.7 seta.....well it'll be more fun.

If you can verify the condition of the 2.7 is in good shape I'd go that route over rebuilding the 2.5. you'll be in it less time and money.

[nando]

when you 2.7i and boost it later on, you will thank the torque gods.

it's only 0.2l of displacement - it doesn't really even make that much difference.

if you already have an eta, fine, slapping a B25 head on makes some sense. Pros: it's cheap.

Cons: If you started with a B25, putting in the B27 block is hardly worth the effort. I collected a ton of 2.7i dyno graphs and most of them made the same or less power as a stock B25. They peaked torque a little earlier but really didn't make much more torque (often less) either. The displacement gains are mostly lost in the fact that the pistons don't match the shape of the 885 combustion chamber and you lose almost a full point in compression ratio.

The lower CR for boost doesn't even really make any difference either because the B25 already has a fairly low CR and it works great for boost out of the box. it's going to make what, 10ft/lbs more at 15psi? what's an "assload" of torque? blunt? :p