Modifying a motor for maximum fuel economy while gaining a bit of performance 1

[yoshimitsuspeed]

I specialize in performance parts and tuning for the Toyota 4A-GE. I would like to come up with a kit that will maximize fuel economy while bringing performance up to a more modern level.
Here are the technical specs on the various 4A generations.

http://club4ag.com/faq_and_tech_pages/4A-GE_technical_specifications.htm

The big differences in the motor are the heads. 1984-89 used the largeport head. This is by far the most common in the US. It used TVIS with 8 runners of equal length. Next they made the smallport which had smaller intake ports and no TVIS. Then there were the 20 valve silvertop and blacktop which had 20 valves and ITBs.
My main focus now would be for the largeport but I wold also like to discuss general theory that would apply to all of them and other similar motors.

My biggest question is on cams. Running the most compression possible on the cams will make the most power, have the lowest BSFC and should therefore get the best gas mileage but I would like to know a lot more about what cam characteristics I would be looking for.
Bigger cams can allow you to run more compression but they move the peak cylinder filling up in the RPM band. On the bright side at cruise this would require you to use more throttle which could reduce pumping losses.
Would it work to use a larger cam that gave you very strong top end power while maximizing efficiency down low? Or would there be notable gains in economy by staying with a smaller cam that put peak cylinder filling closer to cruising RPM?
How would duration, overlap and cam timing be the same or different than they would in a performance based cam?
The largeport 4AGE had 9.4:1 compression so just increasing that can get some notable gains in performance and economy.
It put out about 115 CHP from the factory. I have customers making over 150 WHP on the stock ECU with 11:1 compression and 264 cams. I would love to target a design that could hit similar numbers while focusing more specifically on gas mileage.

Then there is the emissions aspect. I would love to have a design that did all of the above things while passing emissions as well or maybe even better than stock.

And finally how much could be done on the stock ECU and what could be done if someone were to run aftermarket engine management? Would this greatly effect the design of the internals?

 

[Lou Scannon]

Normally in a factory tune there is some performance and fuel economy left on the table because they absolutely must meet emissions legislation including degradation factors, and they also like to have plenty of stress, knock, thermal and durability margin.
To eke out what they have left on the table, especially without expensive base engine hardware changes such as compression ratio, camshaft, and port optimization via manual or CNC machining/grinding, requires knowing what your doing, and probably a lot of trial and error on top of that.
There is no pat answer to your questions. In order to explore the possibilities with a particular engine such as the one you reference, you really need a validated simulation model with detailed and accurate representation of the subsystems you intend to optimize. This is very difficult unless you are the engine manufacturer, or a very capable consultant, such as Ricardo or FEV. The other approach is cut and try, but you can really chase your tail unless you have flow bench and dyno resources that you know how to use to get statistically valid results.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[Tmoose]

I think when Chevy developed their Vortec head for small block V8s the improvement in low lift flow and chamber shape made them quite suitable for trucks (low rpm service) but (perhaps accidentally) made them outperform the various "fuelie" heads from just a few years before, even exensively modified by folks that seemingly know how. One symptom of how good the Vortec heads are is requiring significantly less ignition advance.

//If// those early Toyota heads philosophically resemble fuelie heads then maybe adopting the right late model head would be the low hanging fruit.

 

[yoshimitsuspeed]

Hemi I definitely get your points. Unfortunately advanced simulation is not something currently available to me.
I do have an engine dyno I have purchased but I still need to build a dyno room and I don't know how soon that will happen. Once it does my capability will definitely be much greater.
I was hoping to discuss some general theory here that would get me started in the right direction.
Common cam tuning theory of lift, duration and overlap is always related to performance. If MPG becomes the priority with power being an important second thought does anyone know if and how the general theories might change?

Would it be possible to use cam timing to reduce pumping losses in a way that was actually able to increase efficiency?

Or like Tmoose mentioned making mods that allow less ignition advance.
More advance can create more power loss from the piston compressing against the combustion right?
Could it be better to run more compression and less timing?


Tmoose the smallport and largeport 16v both ran essentially identical combustion chambers. Very basic pentroof design.

https://encrypted-tbn3.gstatic.com/...I6SkjaQRg_w_z6Jkw4yn3drjkw4wpJm53D-l8Czd_c_QQ

Like you said about Accidentally made they used very horizontal intake and exhaust ports because at the time they believed that was the best geometry for performance.

The 20v heads are a lot more complex and have a lot more advanced design including gen 1 VVT. They weren't brought into the US in production vehicles. Quite a few people import them and run them but I would prefer to focus on the 16 valve which is more common and legal in the US.
I would be interested to hear about any general theory about combustion chamber, intake and exhaust port design or to hear if anyone has any input specific to the 4AGE.
There are a lot of pictures here for reference.

http://www.billzilla.org/4agstock2.htm

http://www.billzilla.org/4agstock.htm

 

[Lou Scannon]

Valve timing to reduce pumping losses, taken to its logical extreme, is known as VVT.
When discussing ignition advance and negative work, you should really be thinking about combustion phasing, heat release rate and effective expansion ratio. Within the limits of a given fuel and engine combination, for maximum efficiency, you want the majority of the heat release to occur as quickly as possible after TDC. There is a NOx penalty with this recipe, however. Other limitations will be imposed by the flame travel speed (normal combustion), maximum permissible cylinder pressure, and abnormal combustion, i.e. knock.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[JackAction]

Bigger cams can allow you to run more compression but they move the peak cylinder filling up in the RPM band. On the bright side at cruise this would require you to use more throttle which could reduce pumping losses.

If you mean that you will need more throttle because you will be at a higher rpm during cruise, this has the drawback of also increasing the friction losses (fmep). Intuitively, I would guess that it would completely counteract the gain in pumping losses, maybe even more.

As for the «ideal» cam you are looking for, it's not that simple. There is no cam geometry that acts the same in every engine. The valve events works hand in hand with intake and exhaust designs. You can put a large cam in a 60's-70's US car all you want, it won't work because they have a log-type exhaust manifold as shown below; You absolutely need a header - and the right one - for it to work. Even the stock intake manifold design will affect your cam's performance. (It has to do with pressure waves going back and forth into the manifolds)

This is why you will never find a universal cam recipe such as: Set X° for intake duration and Y° for exhaust duration, with Z° of overlap, and you will get this result.

Learning about pressure waves is your best bet (and it is complicated).

 

[inline6]

if you want a camshaft with more duration then you err on wider side of lobe separation to keep overlap manageable but it needs a compression bump to cope with the later valve closing. this still provides improved performance but without affecting economcy much, however it leaves performance on the table compared to the same duration with more overlap. too much overlap is a great way to kill the fuel economy

 

[140Airpower]

Yoshimitsu, what you want is what everybody wants and usually can't get, more power AND better economy. The manufacturer already worked hard to get the power and economy performance the engines have. Normally to get more of one you will have less of the other. The only help you have is, as was mentioned, relief from emissions requirements -IF you are in fact not obligated to meet these engines' standards.

But, if you can employ some measures not included in these engines designs you may be able to get some of what you want.

If the two intake valves are activated by individual cam lobes you can get some swirl by having different profiles on each lobe. This should allow somewhat higher compression.
Chamber and piston top coatings will reduce heat transfer to the cooling system and this should definitely show up as improved efficiency, -better power AND economy. However, note that coatings effectively increase the octane requirement due to higher combustion temperatures, so this measure may be incompatible with increasing compression.

Already suggested is low restriction exhaust headers. Anything done to reduce exhaust back pressure increases power without hurting economy "much" or at all. However, headers tend to reduce exhaust temperatures and may hurt catalytic converter performance and it's even much worse if there is a thermactor that gets eliminated by going to headers. Larger exhaust tubing from the cat back also usually helps power and economy without affecting emissions.

But, if you are free from emissions standards, eliminating a thermactor and catalytic converters make a big difference in power and economy.

Any significant changers probably require reprogramming the computer.

 

[PackardV8]

All the suggestions above are valid and should result in more power or improved economy or both. However, none of them, including the OP, address the cost/benefit/payback factor.

I, too, build custom engines. When a customer wants us to "Modify(ing) a motor for maximum fuel economy while gaining a bit of performance," I just smile, agree and give him a cost estimate and a timeline. In the rare instance when there is a demand for specific economy improvement guarantees, usually the sale is lost. Once he does the math, he'll never live long enough or drive the vehicle enough miles to ever pay back the costs of a custom engine versus an OEM rebuild.

Coated pistons, thinner rings, custom exhaust/cam grinds/head work, dyno carb/injection/ignition tuning, higher compression, different/more gears, et al, are known techniques. They just cost more to add on aftermarket than they'll ever return in lower fuel costs.

As has been stated, the OEM engineers were experienced, talented men who knew where they were aiming with cost/benefit crossover targets. I know some who work in the diesel pickup area and the claims made for "tuners" assume the factory engineers could have given the buyer much more (40% more power!) and (20% better mileage!) with the same reliability; they just stupidly chose not to. Then, the buyer of this "tune" destroys a $6,000-10,000 engine and is often frantically trying to remove and hide the evidence before having his truck flatbedded to the dealership service department for warranty service.

Bottom line is the bottom line and yes, it's fun to find improvements; just be careful when to cost-justifying them to the customer with hard numbers and warranties.

jack vines

 

[gruntguru]

A few ideas.
1. The best economy gains are in the tuning. Most tuners are fixed on the rules for race engine durability -
"don't run lean", "don't over-advance". Unfortunately both of these rules are bad for economy. Best part load economy occurs at lambda 1.2 - 1.4 but you will need lots of ign' advance, some squish and a very good ignition system. You will not meet NOx emission regs at this mixture. Pre-cat NOx will probably be lower than stock but the cat won't improve the number (may even make it worse). Don't be afraid to run 0.9 - 0.95 at full power either (NA only of course). If the power doesn't decrease, you are not hurting the engine.

2. Concentrate on exhaust port flow. Increase exhaust valve size if economy is crucial.

3. Late inlet valve closing (Atkinson, Miller etc) will improve part load economy especially if CR is further increased (which is usually possible with LIVC). How late you go depends on how much bottom end torque you are willing to sacrifice.

You will need need aftermarket ECU or piggy-back to do this properly. Running leaner than 1.0 will require operating open loop which may be difficult with a piggy-back. The leaning and LIVC will both contribute to lower manifold vacuum at cruise and therefore lower pumping losses. The leaning improves economy of itself (regardless of pumping-loss improvement)

Engineering is the art of creating things you need, from things you can get.