deep thoughts on VE

so, im probably mind berkeleying myself here, but wanted to bounce this off you guys.

my daily is a DOHC neon ACR. consistently getting upper 20's, lower 30's. this is driving it with the thought of "a redline a day keeps oil consumption away"....

anyway, im currently porting a stock intake manifold. nothing too drastic, just making the air flow smoother with less disruption. not really enlarging ports or anything, but smooting whats there out to make it flow better.

this got me to thinking. which is probably dangerous.

an engine makes power, and burns fuel, based off of effeciency. the more air it can get, the more power it can make. the more power it makes, the more fuel it will use (unless it uses the same fuel more efficiently, which is more in combustion chanmber design and quench area).

with all other things being equal (no PCM changes, no cam changes, no driving changes) will less restricted airflow in and out of the engine (ported intake manifold, bigger throttle body, ported head, long tube header, high flow cat, stock exhaust) increase efficiency? IE, more power when the skinny pedal is whacked, and more fuel economy when its being treated nicely?

and taking this a little further, since id have to pull the head for porting anyway, is bumpung the compression. id mill the head slightly, remove the head gasket shim, and try to bump it from the 9.5:1 it has now to 10.5:1 do i could still run on premium pump (aluminum head). this would reduce the quench area, and encourage a more complete burn for the same amount of fuel, therefore allowing higher efficiency.

does this make sense? or am i on the wrong though train here? it makes sense in my head, and would seem to be the best of both worlds. stock enough for reliability, peppy enough for autocross domination, efficient enough for daily usage in mky 600 mile a week rounds.

what say y'all?

Michael

Also interested in the response from the hive mind.

Can you really go from 9.5/1 to 10.5/1 with just some head milling and headgasket tomfoolery? Seems like a big jump in my non-scientific opinion.

Can I pull the age old saying I STILL CONSISTENTLY hear from the Magnum crowd, that is completely false, that "They require backpressure to run the best."?

It is still air in=air out plus some fuel and spark to make some power. Eliminate the restrictions and you gain power from increased efficiency.

As long as you aren't detonating, the increase of compression is a huge jump in power and throttle response. Although it isn't cheap, a true flat top piston is a good way to gain power with the pent roof chamber.

Just my plugged nickel of opinion from a lack of morning caffeine.

Yes, less restricted airflow into and out of the engine does increase efficiency because you will have less pumping losses. It takes a lot of power to suck in and blow out all of that air, so anything you can do to reduce the needed power will increase efficiency.

Of course, there are also issues of ideal air velocity in the intake for optimal cylinder filling (don't go too big on intake ports) and other things to consider that could fill an entire text book, but if you're just smoothing out casting lines etc then you can increase efficiency and power at the same time.

Hmmmmm sounds like a little experiment I've done with Grunt... my All-Trac Corolla........

AE95 All-Trac Corolla runs a 1st gen 4AFE..... The 4AFE is the work horse cousin to the better known 4AGE.

I did some EXTENSIVE porting on the 4AFE so all the exhaust ports would flow equally........ http://www.hachiroku.net/forums/showthread.php?t=24099

I never had her on a dyno before the rebuild, but she does have more power* now, I also managed (manifold replacement) to move the torque peak 2000 rpm lower in the rpm band.

I did extensive searches for 4AFE 4wd dyno figures... I found zero. Next I searched for 4AFE 2wd dyno figures. I did manage to find a few of these... the highest I found was 78 whp in 2wd configuration. My car in 4wd configuration makes 73hp... my 4wd drivetrain loss is far steeper then fwd drivetrain.

The other dyno 4AFE's I found made LESS then 73 hp.

The peak torque output was the most significant change.... on an engine dyno(NOT @ the wheels), the 1st gen 4afe made 100hp, and 101#/ft. In my 4wd drivetrain, my wheel hp is 73, my wheel torque is nearly 78#/ft. Far more torque is being generated.

Oh... what all did I change? bumped compression 1/2 point (9.5 to 10), ported head, swapped intake manifold. No other changes... and that includes retaining the stock 4AFE crappy exhaust manifold

Oh... I neglected to report gas mileage...

The EPA for the All-Trac Corolla "estimated" 25city 28highway , "adjusted" 25 city 25 highway My mileage going from Portland to Bend averaging about 70 mph... 29 mpg.

this is pretty much what im talking about, oldskewl. you did almost exactly what im doing.

factory exhaust is 2.25 mandrel bent, sho we should be good there.

im also concerned about torque production in the midrange which is where this car lives. highway cruising (2 lane) is right at 3k, so 2-4k is where im looking for the increase primarily.

on my intake manifold, im really just smooting all the lumps, taking ff the sharp lines, reducing lumps that i can, and blending it all in. much like this, only without the JB weld, port enlargement, etc. http://www.angelfire.com/space/neon/porting.html

so, im just about done with the grinding and cutting. next is the sanding rolls and smothing my cutter marks.

the inside of the manifold is pretty rough cast. should i smooth it all out, or is it not worth it? i could polish it to mirror if it would elp, but i read the rougher surfaces create a tumbling effect that actually speeds up and flows more air. but i never found what kind of surface texture this actually requires.....

so, what should my next step be? 1. smooth out what ive done with some 60 grits on my dremel, and be done? 2. smooth out all the rough cast, and leave it at 60 grit? 3. mirror polish the whole works?

this is step one, doing teh manifold. step 2 will be grabbing another head to rework.

sjould i polish the inside of the throttle body? cut down the half shaft? its a 52mm throttle body, already upgrading from a 48. dont want to lose too much velocity...

and when i get a mimute, ill post some pictures so you guys can see what im going.

michael

Actually, the rough texture is for homogenizing the incoming air for the squirted in fuel at the cylinder head port/valve. The idea is if you can get the air to "tumble" into the cylinder, you can expose more fuel to the spark for a more complete burn.

I don't think I would polish it mirror smooth, but a few quick hits from a tootsie roll wouldn't hurt.

so, do the plenum, but leave the runners? do it down to say 60 grit?

Takes me back many years when I did a similar thing on my Goliath/Hansa 1100. went from 45 hp to 50 hp. Never got around to put the dual carbs on it.

I didn't touch the replacement intake manifold at all, just took it from a slightly newer model...

Concerning smoothness... you will get all kinds of arguments... from all kinds of porters... BUT I've found that TBI, or carb pretty much requires a textured surface to help keep the fuel from collecting on the port walls/runners. MPI... matters far less since the injector is directly above the valves(usually)

Shorter Runners = Power Higher in the powerband... correct?

so in other words, dont overthink the surface texture. smooth what ive goy and can get to easily to ease transistion, and be done. right?

wont work on it anymore tonight. parts came in for camry so i can get it fixed and sold.

Autolex wrote: Shorter Runners = Power Higher in the powerband... correct?

Theoretically

Dusterbd13 wrote: anyway, im currently porting a stock intake manifold. nothing too drastic, just making the air flow smoother with less disruption. not really enlarging ports or anything, but smooting whats there out to make it flow better.

Partially, yes. You do want some texture on the walls in theory. Let's say you have two ports of exact same construction and volume, but one has an as-cast finish and the other is polished mirror smooth. In theory, the as-cast port will flow more mass although it may require greater velocity to achieve it. Here is why. The rough casting causes localized turbulence against the walls; often times called a boundary layer or laminar layer. That turbulent air lets the bulk of the mass flow scoot by with very little friction since its air-on-air. If the casting is too rough, the layer is thicker and can restrict flow. If the port is polished too much, there is almost no boundary layer and flow can suffer. Figuring out how much grit to leave is splitting hairs, but suffice it to say that if you leave it with anything rougher than about a 100-grit finish you'll be fine.

an engine makes power, and burns fuel, based off of effeciency. the more air it can get, the more power it can make. the more power it makes, the more fuel it will use (unless it uses the same fuel more efficiently, which is more in combustion chanmber design and quench area).

Before we get too much further, let's delineate between thermal efficiency (or combustion efficiency) and fuel efficiency. Thermal efficiency relates to how much of the energy in the fuel can be translated to force on the piston. Fuel efficiency is a whole different critter. It is safe to say that increasing combustion efficiency often translates to increased fuel efficiency, but not always.

with all other things being equal (no PCM changes, no cam changes, no driving changes) will less restricted airflow in and out of the engine (ported intake manifold, bigger throttle body, ported head, long tube header, high flow cat, stock exhaust) increase efficiency? IE, more power when the skinny pedal is whacked, and more fuel economy when its being treated nicely?

Rarely do things work out that way, but its possible. This is the root of the "backpressure" myth, but I'll attempt to explain it a little deeper. As you increase the flow potential of these pathways, you often decrease the velocity of the mass flowing through them. This does two important things: 1) reduces the inertia of the mass, and 2) shifts the hp peak up in the RPM band. To make an extreme example, let's say you double the cross-section of the ports with some major porting. The RPM at which the mass flowing through those reaches its peak velocity (and therefore peak inertia) has increased significantly. This inertia is very valuable both on the intake side and exhaust side (except in turbo applications when dealing with exhaust) As the intake charge is being drawn in past the valve(s) it carries with it inertia. Once the piston reaches BDC, this inertia tends to continue the flow of air into the cylinder even after the piston has started its upward travel. If you increase port volume (and therefore decrease the velocity) you must rev to a higher RPM where that affect is maximized.

The same is true for the exhaust. The rising piston expels spent charge at a certain velocity. The inertia of that exiting stuff tends to create a low pressure in the chamber when the intake valve is already starting to open, thus drawing in some intake charge before the piston begins its downward stroke. If you increase exhaust size you can make it such that the RPMs required to achieve that scavenging effect will be higher.

So, you can see how the backpressure myth got started. non-VE-speaking people looked at the raw data - huge exhaust causes a loss of torque - and they translated it into requiring backpressure.

Again, we're somewhat splitting hairs, but the point is that it all has to match. Adding a ton more flow on both sides (which you aren't doing, but we're talking theory here) should require more cam, more RPMs, more compression, etc.

What you are doing is kinda the best of both worlds. You are adding flow with a proportionally smaller increase in port volume. 10% more flow with only 4% more volume. That's a win-win.

and taking this a little further, since id have to pull the head for porting anyway, is bumpung the compression. id mill the head slightly, remove the head gasket shim, and try to bump it from the 9.5:1 it has now to 10.5:1 do i could still run on premium pump (aluminum head). this would reduce the quench area, and encourage a more complete burn for the same amount of fuel, therefore allowing higher efficiency.

Yes, you should be fine with 91 octane. But, you won't see the difference in your pocket. You will be increasing combustion efficiency (getting more of the stored BTUs out of the fuel and into motion) but if you see any increase in MPGs it won't offset the additional cost of the fuel. What I might attempt is to polish the chambers. Just like porting it doesn't really remove much material but it pays off big time in detonation resistance. Bummer is that it will almost definitely require a valve job.

i ahd planned on a valve job anyway, so thats already built in. along with stem seals, decking, etc.

and your post was great!! very educational, and much better phrased than any rambling, incoherent drivel that would have come out of my head.

im glad to know that im on the right path.

the dohc neon motor pings on premium from the factory with the ACR ECM due tio the hot spots in the chamber. so im thinking with some careful polishing and blending in the chamber, thereby reducing the detonation inducing hotspots, ill be safe with the higher compression.

why would the higher compression NOT get better gas milage? other than the human factor of sticking your foot in it more? the cost per mile with premium is already there, so its a matter of finding a way to make it more efficient.

will the areas that are as-cast versus the areas that are 60 grit finish dirupt the boundary layer dramatically? im not sure that i can get the whole length of the runners to get them to 60 grit after looking at it tonight.

Dusterbd13 wrote: why would the higher compression NOT get better gas milage? other than the human factor of sticking your foot in it more? the cost per mile with premium is already there, so its a matter of finding a way to make it more efficient.

It potentially takes some prodigious tuning to get it right. Just raising compression without adapting timing curves means that you might be wasting a ton of that energy on "kickback" or cylinder pressures rising too high before TDC. You also can't necessarily account for how much of that extra heat you're releasing is going to the piston and how much is going to the water jackets/oil. Just because you are releasing it from the fuel doesn't mean any of it is making a net increase on piston force. There is also a crossover of thermal efficiency with flame front speeds. Efficient chambers have faster flame fronts. An inefficient chamber tends to waste more of that released energy into the water jackets for a couple reasons. 1) inefficient chambers require more ignition lead which means more of the energy is spent prior to the critical first 25 degrees of the power stroke, and 2) the increased amount of time that combustion spends during piston dwell means that more of the heat has time to go into the water jackets.

There are a few thousand other reasons like piston construction, placement of the spark plug, 2v or 4v heads (since 4v chambers tend to have less surface area against the water jackets), dome- dish- or flat pistons, cam overlap, etc...

Suffice it to say that its rare for increased compression to reduce MPG, but if things aren't properly tuned to take advantage of it I can see how it could reduce MPG.

will the areas that are as-cast versus the areas that are 60 grit finish dirupt the boundary layer dramatically? im not sure that i can get the whole length of the runners to get them to 60 grit after looking at it tonight.

Hmmm... that's a good question. I do know that fluid flow (including gaseous flow) doesn't like to change, but I do know that its very common for people to "gasket match" ports and leave the runners alone. Think of it like an airplane wing. An airplane wing works because the air flowing over it is sticking to the wing. If you increase the angle of the wing too much, the air on top de-laminates much like cavitating. The air's tendency to not stick to the wing is greater than atmospheric pressure and the wing stalls and the plane crashes into the side of a mountain in the Andes where they're rescued by the Brazilian Ski Team in bikinis. (that has nothing to do with airflow, just a little fantasy of mine.)

I would say that I don't know the finer points of transitioning from 60-grit to as-cast, but I will say that it is common practice in performance building so go for it.

Autolex wrote: Shorter Runners = Power Higher in the powerband... correct?

Yes. This was a much larger deal with wet flow intakes (e.g. carb or TBI fuel systems) but with dry flow its a very small effect. For instance the 92-97 LT1 is a low-rpm motor with a mild cam, but the intake has a large-plenum, short-runner design with little or no impact on torque/power production.

In reply to curtis73:

To kind of go with this- always look back at the basics of combustion- fuel, air, spark.

Most of the discussion has been getting the air in and out 'better'. Fuel- you do need to tune that so that you don't have too much (which is generally a waste, but sometimes has it's benefits), or too little (99% of the problems of too little is just basic bad combustion that you feel- the 1% more is when you are WOT, too lean, and bad things happen- not always, but can). You should tune that.

Spark is a big discussion- as Curtis pointed out- too early is bad since it gives you more pressure on the up stroke. But too late is really bad in terms of efficiency- it's amazing to see data where retarding spark drops power/tq off so quickly. That's ALL about combustion efficeincy. Where higher compression causes problems is if it introduces knock- which then requires that you retard spark to prevent it. So if best spark is at 20 BTDC with good fuel, and the fuel you run only can run 10 without knock- the increase of efficeincy due to the compression ratio is more than offset by the decrease of efficeincy due to spark.

Not sure if that helps or not.

So if best spark is at 20 BTDC with good fuel, and the fuel you run only can run 10 without knock- the increase of efficeincy due to the compression ratio is more than offset by the decrease of efficeincy due to spark. Not sure if that helps or not.

I like that explanation. Its spot on.

hmm.....

y'all are making me ponder a full 1 point increase in compression. maybe a .5 increase whould be the better bet, as im am unable to tune the ECU in this car, and must retain it for NC inspection. i could go megasquirt, but again, inspection, autocross classing, etc.

this is the kind of discussion i love. mnakes me do lots of research to learn more, and expand my knowledge basis. ill be doing that on combustion chamber effeciency vs spark lead tonight, with a little bit of boundary layer theory thrown in.

so, now that im rethinking compression, in also rething header/exhaust.

what ive always been told is that the scavenging effects of a longtube are much greater than the effects of a short tube, which are only slightly better than a stock manifold. after looking at stock manifolds for this particular engine, i cant see how a short tube is not a major improvement. with the short tube, the primaries are not the same length, or even anywhere close. the transition into the collector is also a jumbled mess looking at it. with the long tubes, the collector design is much better, the primaries are almost the exact same length, and the air is a much smoother, easier flowing path. but from what i understand, the SHIORTER primaries produce more low end rpm range, while the longer favor higher rpm. i know a lot of this depends on diameter of the primaries as well, but so far i have been unable to locate the data on ID of the headers. we are assuming OBX ebay pieces for this, as they are the most cost effective solution. the other alternative is to use a stock exhaust maifold that has been ported. this has more equal length runners than the short tube eader, but of an unkown ID, unknown consistency, very poor merge at the collector, and very necked down. i could port match it, and open up the neck a little bit, but again, were working with variables insode the runners that i cannot see or do anything about. but externally, theres quite a lot of variance, ut like 1/2 inch or so.

after this comes the exhaust factory gave me a mandrel bent 2.25 id exhaust, with a ok flowing muffler. i have a 2.5 inch mandrel bent pipe, and could end that with a single inlet, single outlet dynomax super turbo muffler. this would be freer flowing than the factory, sound pretty nice, look a lot better. but would the increase in diameter, and therefore decrease in velocity, move the effectove RPM range highr again?

again, most of my driving is in the 2k-4k range on the street. ill wail this thing the whole way to the rev limiter on track, and on the street on occasion. thats 7400rpm. but where id like my gains to be centered upon is the 2k-4k range. broader would be better, like 2k-6k, but i believe that to get the gains at 6k, id be loosing more than i gain at 2.5k

does this sound right?

Can't speak to other heads... but in a 4AGE head... to reduce the chance for knock/ping removing the factory machining marks goes a loooong way...

curtis73 wrote:

So if best spark is at 20 BTDC with good fuel, and the fuel you run only can run 10 without knock- the increase of efficeincy due to the compression ratio is more than offset by the decrease of efficeincy due to spark. Not sure if that helps or not.

I like that explanation. Its spot on.

I thought of something else to add to this...

As Alfadriver said, most engines will run best with certain parameters. Some are obvious, like A/F ratio, cam LSA, etc. What is not always obvious is that most engines also run best with a certain amount of spark advance. I've read a ton of back-to-back tests on engines where they compare compression ratios, cams, heads, etc, and they always seem to make peak power (with each combo) at the same BTDC total spark lead regardless of the combo.

I've built some engines that weren't ideally matched and had to crutch it by taking one of those parameters out of spec. For instance, i built a 454 with 8.5:1 compression and used a cam that was on the larger side of optimal. To get peak drivability out of it I had to advance the spark about 4 degrees from optimal. What I should have done is gone for 9.5:1 and shelled out for the mid-grade gas.

In reply to curtis73:

IMHO, the reason Spark kind of gets not looked at as closely- it's not the easiest thing to calibrate- to do it right takes a considerable amount of development.

fuel is pretty easy- peak power- about 12-13:1- depending...

Spark- it takes dedicated experimentation for each engine and a knowledge of fuel that will be used to do it. And that's to do a bang up job with fully digital spark. Trying to set an advance curve with a distributor to the edge- ouch.

It's a tough subject to calibrate without time and some good resources. But it's easy to get it totally wrong for FE, that's for sure.

In reply to Dusterbd13:

You could run a PT exhaust manifold. It'll bolt right up and is supposed to be at least a little more free flowing.

I'm using a pacesetter mid-length header, but will be modifying it a bit. Its got a 3" collector, but the ball/socket type connection on it cuts down to about 2.25". Plan is to cut that off, weld up a freer flowing cat, then a flex joint to the rest of the exhaust, which will be 2.5"

On the computer, can you get a hold of a Mopar Performance ECU in your budget? I'm pretty sure they are CARB-legal, so should be legit in your state.