What kind of gains could one expect after having their engine bored out, buying new pistons, etc. Since I do not know much about this, what are all the costs associated with doing this? Modifying the engine like this usually yields big hp gains right?

Btw, I understand gains are different for every engine, but I'm just asking relative gains. Guesstimate

 

WIthout changing the CR gains can be viewed roughly on a linear basis; increase displacement 5% increase power output 5%

Changing CR changes everything

and one also must consider wether the heads, IM, TB can flow enough air to make use of the extra displacement

 

Boring the motor will VERY MARGINALLY increase displacement and VERY MARGINALLY increase power. Typical bore on this car seems to be about .020" larger. In other words, "20 over." The VQ35 is 213 cubic inches. A 350 Chevy bored over .030 comes to about a 355 ci motor. Using this ratio, a VQ bored over .020 becomes about 215 ci. That is a .01% gain in displacement. So power will increase almost 3 HP by simply overboring .020. Worth it?

Ben is right about needing the motor to be modified to take advantage of increased displacement. However, do you think the motor needs to be modified to take advantage of the extra 2 ci?

In order to affect output by a displacement increase and keep the same block, you need to bore AND stroke the motor. This involves a crankshaft and connecting rods making the stroke of the pistons in the cylinder walls longer. This will enable an increase of displacement up to the area of even .5 liters or 30 ci. That seems much more worthy. However worthy, is it worth it?

All else equal, lengthening stroke decreases RPM potential. To illustrate, put your arm straight out. Now move your hand up and down about one inch over and over as fast as you can. Ok. Now stop. Now, move your arm up and down about 3 feet as fast as you can. Which range of motion do you think you will be able to do more overall times in 10 seconds? The shorter movement, of course. That is how stroke length affects Rotation Per Minute. Now, ANY motor can be made to handle MAD RPMs. But that is, of course, expensive. Anyways, less RPMs means less HP potential. RPMs are the only replacement for displacement. They are the only thing a smaller short stroke motor has over a big lumbering powerhouse. RPMs multiply torque output. This means more RPMs make more power. So does displacement.

This goes back to the old adage, focus on what you are good at. Our motor will easily make more power with RPMs than it will with a bump in displacement and since it will be easier, it will most likely be cheaper.

So, yes, increasing displacement will make more power. But not nearly enough to justify the cost. My recommendation is to build the heads to take some RPMs and let time do the work instead of your pocketbook. Not saying it will be cheap to do, but compared to boring, it sure will be. Bore the cylinders if you find yourself inside the motor and you are in a "might as well" situation. Don't do it just to do it. Just my 2.

 

I say give it more compression, airflow (cams; life & duration) and fuel that should yield more power, and only if it's tuned well. Just boring it out won't yield much power like the other fellas say.

 

Fly By Z

very informative, thank you

 

What kind of gains with 11.x compression pistons?

 

All I could do is offer a guess. Things like boring, raising compression, porting the heads, etc. are almost always done with other mods. No one in their right mind goes into a motor and does only one specific thing. I would venture to say raising compression from 10.5 to 11.5 would be worth about 15-20 HP. However, to truly take advantage of compression that high you would really want some 104 or more octane fuel. Timing would have to be backed way off on pump gas to avoid ping.

 

If only this were true

Honestly, the power of ANY engine is in the heads, not in the bottom end...the bottom end needs to stay together, that's all. Altering the displacement might shift the power band around a bit, but nothing dramatic at all.

I would think you might very well get away with 11.5:1 on 94 octane..its not unheard of at all. Thing is, the stock ecu wou,d definitely not be able to cope with that...you would need some form of true programmable engine management and a good tuner to truly take advanatge of the increased compression.

Adam

 

When you raise the compression, you'd do well to replace the cams, springs, and retainers as well.

Phile -

I think the stroker kit for the Z brings it to around 3.8 liters. Fly By Z is right that it doesn't really justify the costs.

If you are going to build a motor though, figure out what you want it for. A stroker kit might be better for everyday driving than an engine built to make its power peak at 8k rpm. Like Fly By Z said, there is only one replacement for displacement. But it works both ways. It depends on where you want to make the power.

Either way, it won't be cheap.

Dan

 

I basically drive it in the warmer weather months. It's a daily driver then, but it doesn't have to be really. What I really want to do, before I make any major mods, is to put it on the track. To learn how to properly use the power I already have...THEN make it super fast It's too bad that a good supercharger kit costs $6K+ install...that's pretty hefty all at once.

 

It's def. a great idea to get some track time and if possible, instruction. Then you can really enjoy what your car can do. Hey man, don't sweat the 6K. I was calculating up what I've spent so far in the past 10 months or so of modding my car (I got it last Feb.). It's over 10K. I thought I promised myself no mods on this car when I bought it. Well, I stumbled upon this website and the rest is history. I still have 15K to go I estimate. I recommend you just plunge headfirst into the mods!

Z1 is right that the main function of the bottom end is to just take the abusive massive power you generate with the top end. At least that's the idea.

 

Ah I hope you don't beat yourself up too much, 25k when you're done isn't that much over the "no mods" promise you made to yourself....*COUGH* heheheh

Btw what do you think of that tilton 8lb flywheel. I'm wodering how much of a performance advantage it will have over the JWT hp wise? Actually, have you dynoed your Z with the JWT flywheel?

 

No, I'll dyno my Z with all the NA mods done to it which will be finished by the end of Feb. Then about 6 months later, if everything lines up, I will go FI on top of the NA mods. Then dyno again.

I think that the Tilton is not streetable even in the slightest hint of the idea. I think someone said that the JWT has the effect of 7.5 HP of so. Of course it doesn't make any HP itself just being what it is but it may show that to the dyno. If you drive around on the street even a little I would get the JWT.

 

I would get the Tilton just so I know for a fact nobody else but me could drive my car. Ofcourse that's a big sacrifice in drivability for me, but I'd get used to it. And it might actually be a theft deterrent to a degree. What gangbanger thug is gonna be able to drive that?

 

I don't think a gangbanger thug is going to be able to steal the Z in stock form anyways. Isn't it a pretty theft deterrent car?

 

The promise that seems to be always broken

 

What could be done to the heads? Are you talking about strenthining so that you can take more than the normal boost if you go fi?

What kind of hp benefit would come from head work?

 

I bet you can get 15 HP from the bottom end and 75 from the top end. The top end is where all the air flows. In from the intake and out to the exhaust. The faster it can get in and out and the more of it than can get in and out, the more power you will make.

 

75hp, that's alot, modifying the heads you say?

 

Are the heads the top end? Would that be the same as boring out the intake and exaust on the engine, or are you talking about replacing something? I'm afraid your assuming I know more than I do about the top of the engine. I have studied alot recently, but I am relativly new to this whole car modding sceen.