Topic: 2.5L Bored out

[Schmitty]

is it worth it to bore out a 2.5? i just blew the motor in my 1990 wrangler and im looking for a used 2.5, that runs, but i wanna rebuild it. but i have heard of people boring out the 2.5 and i was wondering if anything else is needed besides pistons and rings. and is there a good power increase with a bored 4 banger?

[chardrc]

if i remember correctly someone here did a 2.5buildup and they bored it (.060 over?) did a cam and used pistons and connecting rods from a Chevy 305(?) (something about having longer connecting rods transferring more power to use). the thread should be around here somewhere... or you can wait tell one of the more knowledgeable members reply.

if / when i rebuild my 2.5l i would bore it out a bit

[chardrc]

i found the thread i was talking about. he did allot of other work on the motor but the results where great..



http://4bangerjp.com/forums/index.php?topic=314.0

[Mr_Random]

Well, tearing apart my replacement engine I have found it has .030 over pistons... it seemed to have ran for probably 25K on them before the jeep was bought as a donor (4.10 axles), we thought it had 200K on it, but it was rebuilt and upgraded! I feel blessed... haha...

anyways, as I continue disassembly I'll report on what other things may be different...

[jason 00 tj]

I'm also very intrested in building a bored out 2.5l but dose anyone have some dyno reports to show what rpm the HorsePower and torque are being made at? What about emissions? Can you just change your injector size to work with bigger displacement or dose the computer need to be remapped?  thanks

[chardrc]

i was reading up of yjmechanics thread, and it looked like it was doing good with stock ecm.... he may have gotten a chip (but i don't think it was required).. and i think he ended up using 19# injectors although he hadn't initially. but i still can't find the build list anywhere...

[Mr_Random]

JUST boring it in any case wont net much difference in displacement or power, the stock ECM will work just fine (even the old TBI Renix that mine was used in).

Someone did a stroker 2.5 a while ago, I'm researching it right now...

[Jeffy]

I've only heard of ONE striker ever and he was using a custom crank for his JeepSpeed XJ.

I think you'd be better off with a mild bore and switching over to MPFI.  You'll see a real big gain with MPFI.  A real 10HP increase over the TBI.  Torque is also up as well.

[jason 00 tj]

So i want to do a 2.5l stroker and have found some very complete kits : http://www.flatlanderracing.com/rebuildkitsamc.html and http://www.rpmmachine.com/engine-rebuild-kits-amc-4cyl.shtml
But will i get the same power YJ mech. got by using one of these kits? I'm figureing on .60 over but what should i do the bearing at?
While I'm at it should i install roller rockers http://www.quadratec.com/products/51103_501.htm
Should i get the motor blueprinted and balanced or am I wasteing money
What type of head work ie: 3 angle valve job ? port and polish?
What about the cam that is included in the rebuild kit should i use it ,could i have it reground ?
Thanks for the help.

[chardrc]

from reading yjmechanic's build it sounded like he credited allot to balancing the motor and its parts... so that power wouldn't be lost in unnecessary vibrations and movements.

[countryboy514]

when you do the math...stock bore of 3.88in equals 150 cubic inch displacement.....0.060in over bore 3.94in bore equates to 154 cubic inches. my guess is you wouldn't notice a diffence from the enlarge bore, but it would feel stronger due to the total rebuild

[oakey]

I fixing to rebuild my 91 4cyl....  We have decided to bore it .60 over and mill .20 off the head....  This should give it a little more go.... 

l8r,

Oakey