Turbo b25 here, worth the "pain" to swap to 2.7i?

[roads]

You might ask "why not swap to 24v for ez 300hp" but I already have a ms and good setup for m20 fi so it's a bigger investment to redo all the fi stuff for m50 (ecu, headers, exhaust, etc. etc. etc.)
I just barely got my turbo m20b25 running about a month ago but I burn oil on aggressive gear shifts so I rebuilt the turbo (got it balanced at a local shop too ) but I still blow blue smoke.
Now I have the car up on jacks again to hunt for oil leaks cause she was weepin like a mother, so I'm in the process of redo'ing the oil pan gasket (gonna just say f it and drop the subframe).
ANYWAYS, I think the reason for burnt oil is leaking valve stem seals meaning another head rebuild .
This got me thinking, why not build a 2.7i to get more displacement and lower compression for the ultimate boost experience.
I've never rebuilt an engine before but wanna get the experience.
I want to push like 350hp by the end of it reliably and *hopefully* cheaply (the turbo has shown me otherwise LOL)

TLDR
For a boosted m20, is a 2.7i an upgrade compared to 2.5?
With this next rebuild I might as well build it nice so here's what I'll do:
fairly aggressive cam (280? I know nothing about this so give me ya opinion)
Upgraded rockers, valves, and springs
O ring block
Some fancy headgasket (MLS?)
ARP studs (cant forget these, but already got em)

I want to keep it budget friendly in the end, not trying to go all out here
I also want the 2.7 to be pretty freely revving and be able to go up to 7k rpms

If I do all this, is it worth it to build a 2.7 block, crank, and rods with an "I" (2.5) head and pistons, or just keep my stock m20b25 and just upgrade the head on that?


heres a little bonus of the the bad gal sorry about 2001 quality

[varg]

If you're going to do a 2.7 don't lower the compression ratio, keep it at B25 level or higher and definitely don't do it without B25 pistons. Plus aggressive cam and low compression ratio doen't mix, it'll be a dog off boost. MLS and O ringing are mutually exclusive. As for 7,000rpm, upgrade the rockers and get the bottom end balanced well and all will be fine.

[roads]

If you're going to do a 2.7 don't lower the compression ratio, keep it at B25 level or higher and definitely don't do it without B25 pistons. Plus aggressive cam and low compression ratio doen't mix, it'll be a dog off boost. MLS and O ringing are mutually exclusive. As for 7,000rpm, upgrade the rockers and get the bottom end balanced well and all will be fine.

How would I maintain a higher compression ratio (8.8 like the stock 2.5) while using the B25 pistons? On e30tech I found that using the B25 head and pistons with B27 crank rods and block lowered it to like 8.1.
I also hear that a lower CR is good for FI, but I guess that only matters when you're in the boost.

[varg]

You do it by machining the block. There is no reason to lower the compression ratio vs a stock B25, people boost the hell of of them with the stock compression ratio and those who tune them well never seem have any issues with the engine itself. 8:1 will just make for an engine that is a dog off boost and that makes it feel excessively laggy.

[citizen_insane]

Have you confirmed the oil is coming from the head and not the turbo? The seals on any turbo are dynamic and they will never be 100% sealed, they rely on the pressure differential between the housings and the oil core to prevent blow by. You can confirm if the oil is coming from the turbo by pulling the comp outlet piping and checking for oil. If there's a lot of oil in there (and also in your intercooler typically), you probably have issues with oil draining properly. If you flood the oil core of the turbo with too much oil you'll always have issues with pulling oil into the comp stage, especially during transients and high rpm cruise. What size is your oil drain? It should be big (15mm ID) and straight to the oil pan with no loops or kinks.

[roads]

Have you confirmed the oil is coming from the head and not the turbo? The seals on any turbo are dynamic and they will never be 100% sealed, they rely on the pressure differential between the housings and the oil core to prevent blow by. You can confirm if the oil is coming from the turbo by pulling the comp outlet piping and checking for oil. If there's a lot of oil in there (and also in your intercooler typically), you probably have issues with oil draining properly. If you flood the oil core of the turbo with too much oil you'll always have issues with pulling oil into the comp stage, especially during transients and high rpm cruise. What size is your oil drain? It should be big (15mm ID) and straight to the oil pan with no loops or kinks.

There was oil in the outlet piping before I rebuilt the turbo, that's how I narrowed it down there. You could be right with me flooding the turbo but my drain is pretty good. See the attached image. It's directly straight from the bottom of the turbo in -10an to a (i think) 60deg fitting.

[roads]

You do it by machining the block. There is no reason to lower the compression ratio vs a stock B25, people boost the hell of of them with the stock compression ratio and those who tune them well never seem have any issues with the engine itself. 8:1 will just make for an engine that is a dog off boost and that makes it feel excessively laggy.

Do you have any place I can find the specs to machine the head to?

[varg]

That drain is fine. Mine is nearly identical. The head is not the proper thing to machine for a good compression ratio in this case because you have to take way too much off, you're better off machining a cheap as chips eta block than a cylinder head anyway. Do not quote me on it but I think it's 2mm. It has been posted on this forum and I'm sure a search for 2.7 stroker builds would yield it. The other option is custom pistons, unless a ready made aftermarket piston is available to achieve this end. It's probably cheaper to have the block machined but I don't know the piston options; hopefully someone who has done it will chime in The low compression ratio though, you don't want that in a street car making modest power like this.

Here are some of the search results for 2.7 stroker block machining:

https://www.r3vlimited.com/board/for...87#post6752687
https://www.r3vlimited.com/board/for...02#post5636702
https://www.r3vlimited.com/board/for...piston-choices

[ForcedFirebird]

Machining 2mm and stroker typically is the budget stroker. That using the b25 pistons, b27 rods/crank and shave the block 2mm to get the deck height back. This also increases compression to 9.4. You aren't going to take enough off the head to make a significant difference - the hemi chambers get exponentially smaller as you shave more off.

885 head on an eta block is 8.4:1 and is poor for power delivery. Only time it's a good thing is if you have an eta and want a little more power - the 2.7i is a step backwards from a stock 2.5.

[mikey.antonakakis]

My turbo 2.7i is a 885 head (resurfaced) with eta crank, rods, and pistons, and Enem Z45 turbo cam (280/280). Can confirm it's a dog off boost, plus I live and drive between 5500 and 6500 feet above sea level, so even worse. Makes great power in boost and above 4000rpm though! I have a spare 2.5i short block, so at some point I'll probably pull the pistons out and clean them up, and deck the block to get compression ratio up.

[ForcedFirebird]

My turbo 2.7i is a 885 head (resurfaced) with eta crank, rods, and pistons, and Enem Z45 turbo cam (280/280). Can confirm it's a dog off boost, plus I live and drive between 5500 and 6500 feet above sea level, so even worse. Makes great power in boost and above 4000rpm though! I have a spare 2.5i short block, so at some point I'll probably pull the pistons out and clean them up, and deck the block to get compression ratio up.

At your altitude, you can go ahead and figure 20% loss on KPA. That means you can easily add 3psi gauge pressure and your engine will act like it does here at 14' altitude - or go ahead and add a whole bar and it will be like 10psi here. 10psi (absolute) equates ot about 290whp/300wtq on a super 60 or equivalent. Even the eBay copies produce similar results. The m20 is impervious to 10psi, even with a lackluster tune, stock head bolts, and gasket.

[mikey.antonakakis]

At your altitude, you can go ahead and figure 20% loss on KPA. That means you can easily add 3psi gauge pressure and your engine will act like it does here at 14' altitude - or go ahead and add a whole bar and it will be like 10psi here. 10psi (absolute) equates ot about 290whp/300wtq on a super 60 or equivalent. Even the eBay copies produce similar results. The m20 is impervious to 10psi, even with a lackluster tune, stock head bolts, and gasket.

Yup, 80kPa baro pretty consistently. Of course it fluctuates a bit here in the mountains (500ft climb from the entry to my subdivision to my house, for instance, in a little over a mile). Running ~155kPa absolute at the moment (just got the car running again a couple weeks ago - check out my thread in the FI section for details - VGT content).

If you get a chance to check the spark/fuel map thread, I'd greatly appreciate it! Guesstimating ~270whp at 155kPa absolute (made an Excel spreadsheet that calculates power based on speed Delta over time based on datalogs, includes aero drag, have checked dozens of data points and it's pretty accurate. Won't be getting to a dyno any time soon with covid situation). Planning to bump the boost up to ~200kPa absolute once I'm comfortable with the current tune.

[mikey.antonakakis]

Glitch - double post

[ForcedFirebird]

Yup, 80kPa baro pretty consistently. Of course it fluctuates a bit here in the mountains (500ft climb from the entry to my subdivision to my house, for instance, in a little over a mile). Running ~155kPa absolute at the moment (just got the car running again a couple weeks ago - check out my thread in the FI section for details - VGT content).

If you get a chance to check the spark/fuel map thread, I'd greatly appreciate it! Guesstimating ~270whp at 155kPa absolute (made an Excel spreadsheet that calculates power based on speed Delta over time based on datalogs, includes aero drag, have checked dozens of data points and it's pretty accurate. Won't be getting to a dyno any time soon with covid situation). Planning to bump the boost up to ~200kPa absolute once I'm comfortable with the current tune.

Sounds about right as far as power. I have been reading your thread since the day you posted it, just haven't replied in it - you are kinda new here and didn't realize you were the OP when typing that last post haha. I have installed a lot of Super 60's, to4e's, hx35's etc and they all behave similarly up to about 10-14psi. The common 10-12psi build have pretty consistently been 275-300whp mark and all over 300wtq. Once did a t4 Precision 6266, but it was really - really - laggy, then BOOM 520whp at 6500 rpm and slipping clutch. :/ Curious how the VGT power-under-curve looks in comparison.

[roads]

Machining 2mm and stroker typically is the budget stroker. That using the b25 pistons, b27 rods/crank and shave the block 2mm to get the deck height back. This also increases compression to 9.4. You aren't going to take enough off the head to make a significant difference - the hemi chambers get exponentially smaller as you shave more off.

885 head on an eta block is 8.4:1 and is poor for power delivery. Only time it's a good thing is if you have an eta and want a little more power - the 2.7i is a step backwards from a stock 2.5.

Even if I use the 885 head and pistons and machine the block, the 2.7i would be a step backwards? I would think that the higher CR and higher displacement would be better for power, especially turbo'd.

Thanks for the info FF & varg, I think if I end up going the route of a stroker its gonna be between a 2.7i build or a 2.8 with a m52 crank (I think the 2.8 is gonna cost more in the machine shop due to clearancing the counterweights

ALSO, offtopic but is there like a massive shortage on billet camshafts rn? Bimmerheads and IE are out of all billet ones. VAC cams are the only ones I can find right now. Also looked for the ppf z45 turbo cam but that's out also. Gonna need to do more research to find the one I want anyways