Natural Asperation

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What are the pros and cons of increasing the natural asperation of my 4.6 mustang? i want to work on that soon, but need to know as much as possible. thank you

posted by  Carlos Traveria

:banghead: :banghead: :banghead: :banghead:


Increasing the displacement, you mean?

pro = more power
con = pre detonation problems on larger compression ratio
.........Gas Guzzler
.........Need a lot up upgrades for larger stroker kits

Is it worth it? Well, that's up to you. for mean, i find easier,faster and cheaper ways to make more power out of a mustang than a stroker kit. 5 liters is enough as it is.

posted by  Godlaus

Naturally aspirated simply means no turbo...or all motor...I think all motor is great and the most reliable out of either NA or FI (forced induction). Sure FI can be reliable but to go fast...it's hard

All motor can be fast...there are some big blocks that are fast, there are small blocks that are fast, there are V12's and V10's that are all motor and are fast as hell...some 4 cylinders are fast too like the Integra Type R motor...so all motor for me...means streetable and liveable

posted by  NISSANSPDR

...and the bonus of a NA car is (to me) the coolness factor. its totally sick when you see an all motor car hittings 11's or faster.

posted by  Import-tuner

How do you automatically equate increased dispalcement with increased compression? Are you implying that a 7.0L engine with 7:1 compression would be more likely to detonate than a 5.0L engine with 10:1 compression? It sure sounds like it. Explain yourself.

posted by  vwhobo

N/A or blown, the production engineering and effort is still substantial. It's a buzz hurling any car down the track regardless of times and the type of engine. But I don't think car companies are particularly interested in mass producing cars that are made for ┬╝mile purpose.


I think what Carlos is asking is the whys and wherefores of reducing intake air losses and increasing VE e.g. better intake pipe arrangement, better throttle body, better plenum, better intake runners, better porting and better bowls.

posted by  Wally

Well, the explanation was rather poor (i.e. nonexistant), I am actually on your side on this one. But here's what I think he was going for. If you have a motor with X displacement and all you do is increase the stroke (assume we shortened the rods as well), but you still maintain the same pistons and head, and therefore the same combustion volume; you will increase the static compression ratio.

To the original poster: What were you hoping to gain from this post? I have no clue what information to try and convey to you or what information you're actually looking for. Wally, you may be right, but it still seems like a vague post.

posted by  Bino

Huh? Did you know that in the real world, if you stroke your engine you run pistons with a different pin height or rod length? Did you know that as long as you're performing mods you can change all sorts of dimensions such as deck height, combustion chamber CC's, piston dome/dish/relief CC's and head gasket thickness? You're assuming that you would only change one thing in this theoretical engine which is fine, but... I don't build theories.

posted by  vwhobo

Well, you'll have to excuse my sense of knowing what a stroker kit does. To my knowledge, it raises the stroke depth, and because of that, the compression ratio will generally rise.

I haven't done very many performance upgrades on very many cars. Hence, things like stroker kits/turbos/any form of power, is all put together in my mind.


That's generally how I think out these problems, simply changing the stroke, and nothing else.

Still, I'm halfway right in my 'speculation' that the compression ratio would rise.

I've explained myself, can you see it from my point of view now?

posted by  Godlaus

yeah its a trap for the uninitiated. When you stroke, its pretty uncommon to use the same rods and pistons because the head has a nasty habit of stopping full travel. So the compression height of the piston is shortened and the rod length often increased to maintain good angles (and acceleration).

posted by  Wally

Woooow. Is that why everybody doesn't have a 383 stroker with a 13:1 compression ratio. I'll be damned Mearle you here what this here fella's sayin' huh huh.

Obviously people change everything. I merely stated his logic, which was correct logic. But it's not the correct way to build the engine. Thanks once again for the ill tempered post which was totally unnecessary.

posted by  Bino

yes this is right if you leave everything the same.

But if you increase an engines displacement, does the top-end horsepower get weaker because low torque increase right?
On BIG displacement engines like mustangs, like redline at like 6000RPM and their torque curve go down earlier than like a small displacement Honda where they redline at like 7000-8000RPM and their torque curve is constant and goes down only a little at hight RPM.

So does displacement effect the redline and powercurve of an engien?

posted by  CarEXPERT

Torque curves have more to do with cam shafts and valve timing than piston displacement. And if you put a crank with a longer stroke in an engine and shorten the con rods without changing the pistons to a higher wrist pin height wouldn't you be pulling the pistons out of the bottom of the cylender?

posted by  srober32

How can you possibly speak for what his logic was? Have you done a Vulcan mind meld? Maybe you have a crystal ball.

If you change nothing other than the crank, you're only going to be able to increase the stroke MAYBE .020" before the pistons start colliding with the heads. That is not a stroker engine in anyone's book although it would be as a pure technicality.

By the way, thank you for appointing yourself as the official forum "identifier of the unnecessary. Please ad your post to the list.

posted by  vwhobo

A) I said I "think" this was his logic, which was an attempt to help. Much unlike any portion of your post.
B) I said we shortened the rod (I.E. we used a shorter rod). Read the thread (as you've stated a billion times)
C) You're welcome, anything I can do to help

posted by  Bino

Shortening the rod is an odd thing to do. As srober32 posted you risk sending the piston skirts too far down the bores losing stability and posing possible confllict with the crankshaft. Your BDC rod angle will also be quite acute and may foul the piston skirt, plus you need more power to overcome the lateral tendancy.

A good way to cancel out some of power gains from stroking really.

posted by  Wally

That does not change that fact that it can be and is done on certain stroker kits (I agree it's much better to avoid this route). I completely agree that the best way to retain a decent rod/stroke ratio is to use longer rods and move the pin on the piston as far upward as possible (custom pistons, perhaps custom rods). But you can only move it so far before you start compromising the integrity of the piston. At a certain height you have to make a compromise as to whether you want to set your rev-limiter lower or risk grenading a piston. I know on high boost motors this is especially a concern.

I'd have to say (In my opinion) that if you're losing a noticable amount of power due to the rod angle coming off BDC then you're beyond an angle that you should be working with anyway, moving the pin up a little may not even solve the problem. Enough friction off the piston to actually lose power will eat the piston in no time flat.

posted by  Bino

You can get some pretty decent pistons these days that take some pretty decent abuse. I don't see how stroking a stock production car engine would present a problem with elongated rods and shortened comp height pistons? If it was a hipo to start with then obviously things may be different.

posted by  Wally

I didn't say there was a problem with using elongated rods and raised height pistons. I said there was a limit to how much you can do either. And you are correct, piston technology has come a long way and there are some great products on the market, but there's still a limit to how far you can raise the pin before it compromises the piston, not matter how great the pistons are.

posted by  Bino

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