Forced Induction vs. High Compresssion

[admiralturbo]

A thought, I have been thinking about this recently.will a high compression ratio (like 13-1 plus) give the same gains as a turbo or a supercharger?since they both only increase cylender pressure.What would the differences be ;turbos make most pressure at high end blowers are more pronounced at lower rpm and high compression is always present.I would think thgat as long as you arrive at the same cylender psi at TDC yor HP will be the samei dont know what a, say 8-71 blower turns your compression ratio in to running 15 -20 psi boost. the 7.5-1 in my Beetle equates to about 120 psi.In this case would that mean that every 16 psi in boost will give a 1 increase in comp.ratio? I think it would be great if an engine could be built with enough compression to match a blower.

[Torque1st]

Moved to proper forum.

[FTE Herman]

Eric moves it but doesn't answer it. It is the mass of the fuel air charge that will make more power, you cannot acheive that with cylinder pressure alone.

[admiralturbo]

Where forced induction comes in,packing more air fuel mixture in correct?So giving blowers the power advantage?

[frederic]

Naturally aspirated engines "suck in" whatever air they can, depending on the opening of the throttle plates and atmospheric pressure. A N/A engine can never suck more in than atmospheric pressure.

A forced induction enigne has a turbine which pressurizes the air going in, so you can go over atmospheric pressure, in some cases many times over. By doing so, you lopside the amount of air over fuel, and need to compensate by adding more fuel, which you can do in with EFI every easily - squirt more.

You can increase the compression ratio as much as you deem practical, however you can never suck in more air volume than the size of the chamber, with the piston all the way down.

I've done quite a bit of testing, and have discovered that one can make significnatly more power with a ridiculously low compression ratio, with insane amounts of boost, with no detonation as compared to the other way around - low boost, higher compression.

[BigF350]

one can make significnatly more power with a ridiculously low compression ratio, with insane amounts of boost, with no detonation as compared to the other way around - low boost, higher compression.

Spot on, drivability won't be great, but you will have lots of power thats for sure.

[FTE Herman]

I think I'll have to mildly disagree with Frederic here. Due to the elasticity of air molecules, intake velocity, and cam overlap, it is possible to acheive volumetric efficiencies in excess of 100% in a normally aspiriated engine. You're not going to get 1ATM mind you, but perhaps the equivalent of 1 or 2 psi boost.

[BigF350]

Yes, that is possible with the use of correctly tuned variable intake runners and valve overlap (with VVT to maximise rpm effectiveness), but the results aren't going to be remotely close to something with 10psi of boost.

[frederic]

Originally Posted by hkiefus

molecules, intake velocity, and cam overlap, it is possible to acheive volumetric efficiencies in excess of 100% in a normally aspiriated engine.

I'll agree with you based on the scientific merits of your comments, I don't think it's practical or desirable for a daily driver, especially a heavy, bloated vehicle like a pickup truck. Those techniques are more often found on limited RPM range racing applications where maximum horsepower is required in the narrower RPM range, and very often why the SCCA guys "bang gears" in the 4000-6500 RPM range, and the Nascar guys stay in the 7000-9000 RPM range (typically). They are sacrificing lower RPM performance, for higher RPM performance, because that is what they need - top end.

Totally difference scenario than a guy driving a truck to and from work, passing imports along the way with a huge trailer attached. Humor aside, this is the context in which my comments are based on - real world, daily driving of a pickup.

Originally Posted by BigF350

Spot on, drivability won't be great, but you will have lots of power thats for sure.

If one were to lower the physical compression ratio by itself, and change nothing else then the drivability would absolutely suck. No question about it!

But the engine is part of a system, and one can adjust different parameters of the system to achieve something more specific than the manufacturer's intentions. Much like hkiefus stated earlier - one can tune and achieve more than 100% vol efficiencies but the question is, can you use it on the street day in and day out. Maybe, I'll let hkiefus and others take that question if they want to, but I've driven cars that were clearly overbuilt for the street - too much overlap, too much lift, and too much focus on high RPMs whereas daily driving absolutely sucked. This is not what I for one want to build my truck to. And here is why...

I may or may not be different, but in the last year I paid very close attention to my driving habits with my F350 crewcab. I've never hit redline, and I rarely even approach it. I typically shift between 3000 and 3500 rpm with no or a negligable load, and maybe 200 or 300 rpm higher with a significant load. I don't really consider these high rpms, by todays standards.

Then I did some math, using standard formulas, to calculate out what rpms I am hitting under normal driving speeds, since I don't have a tach in my truck.

mph = (rpm x tire diameter) / (diff ratio * trans ratio * 336)
65 mph = ( rpm x 31 ) / ( 3.55 * .76 * 336 )
65 mph = (rpm * 31) / 906.528
65 mph = rpm / 29.284
65 mph = 1903 rpm

Using the same formula, 85 mph requires 2489 rpm.

Again, very low RPMs. So it became obvious to me that if I build up the powertrain of my truck, I should be focusing more on lower rpm ranges, than mid and high, mostly based on my driving habits.

Does anyone see the similarity in used RPM range to diesel engines? Yeah, my truck should be a turbo diesel, but it's not, and the state I live in does not allow that swap no matter how clever I do paperwork. I pursued this avenue for about eight months before I became frustrated enough to throw my hands up. Originally, I wanted to swap in a turbo cummins with a NV5600...

Anyway, I'm almost done building a 460 based, 500 cid stroker, which will have a 6.5:1 physical compession ratio. As is, tossing it into the truck, will result in unpleasant drivability as the compression ratio is very low. Because the engine is massive in size, there is some compensation for that, but certainly not enough to make it fun to drive. Maybe, tolerable at best. So, I'll be applying forced induction, using a pair of hybrid turbos. The intake side is T4, and the exhaust side has the T3 mounting flanges, but is sized somewhat in the middle of the T3 and T4 standard garrett turbos... so based on tons and tons of math, discussion with others, and experiments, I've concluded at idle, I'll have a small amount of boost. Very small, probably not too noticable, however once I tap the throttle, the boost will spool way up very quickly. On the flip side, the turbos that I've chosen will certainly max out early, probably around 4200 RPM again based on tons of math, discussions with others, and experimentation. But if you look at my driving habits above, you'll see that maxing out at 4200 RPM won't really be a problem for me - I'm doing that now with a high mileage, very tired 351W. So that kinda works out from where I sit.

There are some other advantages of building a forced induction motor this way... the most obvious is longetivity of an engine running lower RPMs. As you know, the force of the pistons changing direction at BDC and TDC are based on the square of the RPMs, so the force diference bewteen 5000 RPM and 6000 RPM is extreme. This is why the higher up the RPM range you intend to play in, the lighter, and more exotic the materials have to be, and the more precise the workmanship has to be. Lightweight/exotic materials, and machinist precision costs significant money, as anyone who has built a racing engine can tell you. And, they really don't last because of the forces involved. Ask John Force how often his engines are rebuilt by his crew. I bet they don't measure reliability in miles Another thing to note in regards to this is adding a fair amount of boost at a lower RPM doesn't "hurt" engine parts the same way as increasing the RPMs. Corky Bell's book and the McInnas book both state this several times, and based on what my experiments have shown so far, I'd easily agree with their statements.

Another advantage I see in building a lower RPM, lower compression, high boost big block is emissions. The higher the compression ratio, typically it's more difficult to get through emissions without the plethora of EGR, cats, and so forth. Certainly not in every case because there are a ton of variables here, but at least based on the current testing that goes on here in NJ, I firmly believe my combination will breeze right through. Why? Because 5-6 years ago I lived in Connecticut, which had adopted emissions standards similar to California, and I managed to get a twin-turbo '75 Dodge pickup through it's last emissions test of its life (due to age), this way. No cats, no funky vacuum hoses, no EGR - nothing. It registered high on the emissions dyno machine of course, but not high enough to fail. Hydrocarbons were notably higher. In fact, when the testing facility tried to run it on the dyno the first time, the truck "leaped off" the rollers because of the significant boosted power that was not expected by the dyno testing person.

So, put all that together, and you'll see why I'm building my engine this way. I've certainly left off a ton of math and about 30 pages of explaination, but what I've typed should give enough information to provide some of the concepts. Is this the way to build an forced induction engine for every application? Of course not. Does it fit my needs, my driving style, and my vehicle? Yes, and that's why I'm doing it this way. This is my fourth forced induction project, and I've learned a ton from the other three based on real-world driving experiences. This is absolutely NOT how I'd build for the track or racing applications, but for a 7000lb crewcab, I totally believe this is the right way to go.

Assuming "Desktop Dyno" has any accuracy to it whatsoever, based on the parts I have put together, I should have about 800 HP and 966 ft/lbs of torque, all well below 3500 RPM. I'll have to see it to believe it of course, as I imagine you guys would, but this is at least what the software gave me, which I consider a crude ballpark. The aforementioned dodge truck shredded several transmissions as well as the rear twice, and I could smoke the tires in 1st, 2nd and 3rd. 4th they'd spin and churp. A far cry from the original 2bbl 318cid V8 that was in there, and I didn't build that engine anywhere near what I am doing with this one - it was a bit smaller (451cid) and the boost was lower (never went above 18lbs) and the c/r was higher, 7.6:1 or 7.8:1 or something along those lines.

The power of a diesel, with the convienence and availability of gasoline.

Well, back to body work.

[BigF350]

Originally Posted by frederic

I'll agree with you based on the scientific merits of your comments, I don't think it's practical or desirable for a daily driver, especially a heavy, bloated vehicle like a pickup truck. Those techniques are more often found on limited RPM range racing applications where maximum horsepower is required in the narrower RPM range, and very often why the SCCA guys "bang gears" in the 4000-6500 RPM range, and the Nascar guys stay in the 7000-9000 RPM range (typically). They are sacrificing lower RPM performance, for higher RPM performance, because that is what they need - top end.

This is where Variable Valve Timing comes into its own.
The first wave of them (Accord VTiR etc.) had crude versions, low and mid range was acceptable, top end was nothing short of ballistic.
Nowadays, driveability can be had at lower rpms while still maintaining greater volumetric efficiency than 100% at higher rpms.
There are some limitations, but the later systems can vary timing AND lift...
I got the chance to go for a short ride in a current Porsche 911 GT3 around a race track, the driver placed it in 6th gear, while it was spinning at 1500rpm (remember this car has a 8200rpm redline!!!), planted his foot, and the thing still had quite amazing acceleration. Admitedly that is out of the price range for most of us (well me anyway), but that is what we will have in our Fords soon...

Forgot to add, your project sounds great, and has me hugely interested.

[frederic]

Originally Posted by BigF350

Nowadays, driveability can be had at lower rpms while still maintaining greater volumetric efficiency than 100% at higher rpms.

Yep, Vtec is one example, and I believe the Taurus SHO with the yamahaha engine had something along those lines, manipulating intake runner length. I could be wrong though, but it sounds familiar.

But alas, how would one affordably build an engine like that for a Ford pickup?

Actually, I have an answer if someone would like to put the money and effort into improving a design I and two friends put together about 5 years ago...

What we did was extend the length of a timing chain, and slapped it on the front of a Buick V6, then pinched the slack with two small gears, which were firmly mounted on a sliding bar and track. A double pneumatic cylinder controlled the position of the two gears, thus moving the slack to the left and right of the engine, thus controlling which side of the timing gears the extra length of chain was on - thus directly controlling the timing relationship between the cam and the crank. We had interesting results, and it worked pretty well considering it was a homemade pile of junk - for about 10 minutes or so until it started to pull apart from the loads the timing chain experiences under hard acceleration and rude decceleration - and it fell apart and the engine of course committed suicide. We also operated the pneumatic actuator using ball valves off shop air, so we didn't have any way of controlling the timing relationship in a more variable sense... it was either "full left" or "full right", but it was a start. This was a diversion from the reasons why we were working together with Buick V6's in the first place, so when it disintegrated we simply put the broken bits in the "junk pile" and went back to forced induction experiments.

Feel free to try and make that work. I will someday, but not in the near future.

While Vtec and various other systems play with lift, timing, and intake runner length, they are not easily grafted to something "old school" like a 460, which is the foundation of my 500cid stroker.

And, all the forced induction experiments demonstrated to me, that in the rpm ranges I'm talking about here (certainly not in Gt3 8.2K redline range!), the intake runner length matters less and less as the boost goes up. In fact, the last Buick V6 we slapped on the dyno had no intake runners, other than the runners that are part of the cylinder heads. The homemade intake manifold was essentially a tig welded aluminum box, that was bolted right onto the heads covering the lifter valley. No runners at all. And you know what? It didn't seem to matter much in the output of the engine and making an intake shaped like a box is by far easier than welding in runners and all that stuff. This won't work well for naturally aspirated engines of course, but for high boost, it worked out well. We also brazed in an aluminum intercooler in the "box", and fed that well water for the experiments, playing with intake charge temperature and intercoolers. These aren't useful experiments in the sense of practical application because I've yet to see an F350 with a 50 mile hose pumping 38 degree well water through it's intercooler

My project is about power, and cheap. The block was dirt cheap, the EFI bits were dirt cheap, I made a homemade dual-throttle body plenum for this thing to attach to the 460 gooseneck like so:



$10 worth of steel, and about 15 hours of my time. Cheap!

The crank is a 460 crank that the journals were reground and moved out, the rods are either big-block buick or slant six, I forget what I sent to my machinest friend for "adjustment" of rod lenght, and the pistons are custom wisecos, and about the most expensive thing in the engine, actually. Everything else was scrounged. Even the heads are interesting pieces... they are "industrial" heads rather than car or truck heads, and all that means is larger valves than the truck engines, bigger exhaust ports like the F500/F700 429 big truck motors, but more importantly, they have the small truck EFI patterns on the intake side - which means the EFI intake and related parts I have will bolt on with minimal port mismatching, thus significantly cutting my time using a dremel.

Originally Posted by BigF350

Forgot to add, your project sounds great, and has me hugely interested.

Thank you... it's been going slow since my wife and I have a newborn in the house. Also, I was distracted by cutting rust off my truck bed, which resulted in repairing frame rust when I took the bed off and saw how bad it was, which resulted in reworking the shock mounts since one of the upper shock brackets was so rotted the shock on that side was *missing*. Been one of those months

Here is the bed/frame repair adventure. I have more pictures to put up, just haven't gotten around to scaling them and slapping them online yet. I take pictures with my video camera, then download the video, then pick the best "frames" to convert to jpegs, rescale, then watermark:

http://www.midimonkey.com/~frederic/f350/bedrepair.html

My problem is I start too many projects at the same time... aside from the body work (which isn't turning out to my satisfaction), and the twin turbo stroker project, I recently completed a full rebuild of the BBF ZF sitting on a dolly in the garage, I've rewired the truck using Ford connectors so I can add AC, power windows, power locks, power seat connectors, an ignition controleld PC, a power sliding rear window, audio, air suspension all around, digital dash, etc. Also partially constructed a homemade dashboard, which needs to be completed because I'm tired of driving with a cluster on my lap, and tons of crap hanging out of the dash.

At least I did get the tilt-wheel column in over the winter, fixed both gas tanks this year, and built superbumper last year.

http://www.midimonkey.com/~frederic/...perbumper.html

I just need 30 hour days and I'll get some more done.

[BigF350]

Good point about making it difficult for someone to build...
My car doesn't even have VVT, and I am a Mechanical engineer, and am fortunate enough to have connections to find out this kind of info... But I threw that idea in the too hard basket, despite the fact I could use a lot of off the shelf items (the 3V 5.4 runs VCT)

Some awesome pictures there, and I hate to head off-topic slightly, but the "super bumper" has me going, why?
Looks? safety? How much does it weigh?

[frederic]

"Superbumper" was an accident... I had a chrome bumper that was poked with a forklift fork, and while I hammered it back and did an "okay" repair, I needed to replace the bumper brackets because mine pretty much were paper thing from rust. So while driving around for a week without any bumper at all, I spied a tow truck with a bumper shaped much like what I built. I liked the look of it, and measured the tow truck bumper right in a parking lot, wrote the measurements on a cardboard box I had in the bed, and used up all the 1/4" plate I had lying around with an addition of a couple of smaller pieces. Superbumper was born.

I really wasn't looking to make a bumper from scratch, however I had to make some thick-wall exhaust manifolds and I wanted to be sure that I could get good penetration in thicker materials with my welder, so the superbumper project was a good "welding test" project. I didn't mean for it to be so large, heavy, and unweildy at 240lbs in its current state. In fact, I didn't intend to leave it on the truck more than a few months, then make new chrome bumper mounts, put the stock bumper back on, and cut this up for other projects. But it grew on me so I've kept it there.

I'm not an engineer or a professional welder, or even a mechanic. I just like making stuff, hence some of my more bizarre projects. When I was learning to mig weld aluminum, I decided for 'giggles' to make an aluminum birdhouse. It came out pretty good and it's hanging in my cousin's yard, as he really liked it. But, because it absorbs so much heat from the sun, no birds have used it as of yet. But, it was fun to make.

Everything I make ends up being really functional, and terribly ugly. For example, the last few days I've been cutting off rust, welding in patch panels, priming and painting. Everything was fine until the painting stage, where I used "official body shop paint" that was a three part acrylic enamel. Never shot that kind of paint before, and it came out awful. While I ran out of play time for this project and the bed is going on the truck as-is, I will have to address this later, resand, repaint, and cross my fingers.

The sad thing is the red rustoleum stripes on the bottom of the bed came out 200% better than the official car paint

[BigF350]

240lbs!!! Wow...

[frederic]

It's honda proof