sven911t

Hello all,

I just joined and already i am seeing that this forum is a tremendous asset to Yota owners. Thanks to all for all the great info!

I recently purchased a 95 4Runner that was oil starved, engine pulled and left for dead. The machine shop is telling me that we will likely need to go .030 over to get the cylinders cleaned up.

Will this change my compression ratio, and should I be concerned about additional fuel/air flow to cover the increase in cylinder volume?

Thanks for any help.

1stgen4gunner

ooh, that dont sound like fun, if you bore it .030 to get it cleaned up there are a couple things that will happen, you will have a bit more power at the foot, however you will be sacrificing gas mileage, but dont worry not by much, gas flow should stay the same you might have to get a bigger spark, but nothing serious, if the garage knows what there doing than there should be no problem. I dont know about the compression ratio, but i assume since the volume of the cylinder is larger it would change a little bit. Im guessing the engine is seized and seized engines are never fun.

1stgen4gunner

wait scratch what I said about gas up above if you have fuel injection instead of a carburetor, in that case you may have to increase the gas flow.

sven911t

That's what I was afraid of. I am trying to keep this build as stock as possible and oversize injectors add expense that i don't want. I agree with you, I think the additional volume will cause a lean run condition unless I get more fuel in there.
As far as the compression ratio, I think it would remain the same since the amount of air brought in, is the same amount being compressed, just more!

mastacox

The engine's ECU has an oxygen sensor and will automatically increase fuel delivery to stay at or close to stoichiometric AFR. Boring .030 over isn't much, so you should be fine.

MonsterMaxx

You would be a fool to rebuild the 3.turd, for the $ you'll spend rebuilding it you could have swapped in a 3.4 and really have something to work with.

sven911t

I couldn't agree more on the 3.4 swap. I am sure there are many posts on here about doing just that, but don't you think that I would be well over $1600 for a low mileage donor?

sven911t

Thanks Mastacox!

MonsterMaxx

You will NOT be able to rebuild a 3.turd for $1600. Not going to happen. You might find some used bone yard engine for that, but why bother.
I just DIY'd mine last year. I already had all the good crap, all it needed was the enginblder full kit (it cracked a piston), machining and labor. I figured it's nutz to do a full rebuild w/o doing a valve job, so I added enginblder's OS valves which added $60 to the build.

I DIY everything but the machining and shortblock assy (R&I, full dissassembly, assembly of the engine, etc) and spent $2200.

If you don't have the abilities I have to do much of that work, you can just add more $$ to the job.

There's several reports of people getting a 3.4 swap FINISHED for $2k.
I'm still kicking myself for not tossing the 3.turd in the trash and going 3.4

JonnyBoy

To add to this, if you go .030 over on a 390 Ford engine(not apples to apples, but bear with me, it's what I have lots of experience rebuilding), you only gain roughly 6 cubic inches. That's a 6.4l, so the math roughly figures a 3.0 is 183 ci. Even if you gain 3 ci from an .030 bore change, you're only making it a 3.04 liter. Not enough for fuel system changes, IMO, unless you're going hi-po and increasing compression, bigger cam, whatnot else. I do agree that since you're at a point to do a swap, why not? There's more performance products available, and from what I've heard, people usually get better fuel mileage outta the 3.4 too. More power, more fuel mileage...win win?

sven911t

Thanks MonsterMaxx and JonnyBoy, I think I'll stew on it for a bit and see if I come across a good donor truck. Any suggestions or threads that would give me a good synopsis of the hardware required for the changeover?

ozziesironmanoffroad

cherry picker, tools, know how, soldering gun, electrical knowledge, adapters. i think thats about it. oh, and yotatech for reference.

mmcpeck

I agree completely with the 3.4 swap, even if you spend $500 extra, it's worth it.

I had my '91 3.slow (or 3.turd as it's being called here) rebuilt, but it was by Toyota under the head gasket recall, I was hoping for a new short block, but they tore it down and did a rebuild instead, since nothing was wrong with the block. It was free so that was cool, but if I was paying, I would have put a 3.4 in in a second, no question.

My 3slow gets about 15mpg after the rebuild, still a dog, not sure how much over they went, but I have to assume it was .030 over, that is pretty standard for a rebuild.

rdharper

As an exercise, I calculated compression ratio for a 0.03 bore increase on the 3.0L engine. Assuming the head is stock... I get a change from 9.00 to 9.16.

This assumes the volume at TDC is unchanged by the bore increase which should be a valid assumption if the head is stock. Not having actually seen the head design.... makes this an assumption.

1stgen4gunner

yup I agree with everyone else, if my engine was burned i'd get the 3.4 it's got more power and it's better on gas, you cant lose.