348 throttle body porting

Interesting comments about TB's in general, but taken in the context of the 348 intake, probably not on point. Your comments are certainly informative, however. The 348 engine is a great unit, built in theory like 2 1.7 liter in-line 4's joined by a crank. The intake sides run independently most of the time, except when the center butterfly opens. It is pretty obvious that the capacity of the upper plenum is restrictive. The engine is capable of better efficiency, witnessed by racecar upgrades that do just this - increaase the amount of air in and ot of the motor.

So, this has been the ultimate goal of the Stooges in seperate programs. We are each trying to find some way to increase the engine's efficiency at moving air through it. for now we have been looking at normally aspirated systems, trying to make the most of what's already there.

For me and goth, we have been looking at using as much of the stock stuff as possible, keeping the cars smog legal in CA (no small challenge). Our focus has been to clean up the air flow in and the exhaust flow out of the engine. So we have the goth exhaust system with cats (heh heh Ernie, I got 200 cell HE versions now, you dog!) on the bottom and a variety of upper modifications. Some of these work (in our opinion) and some might not. TB's have been bored, spacers added to the plenum to increase its capacity, the runners were hogged out (by quite alot), porting and polishing the inner surfaces, and generally improving air flow through the upper intake plenum.

We have flow sheets so we know we are getting better air flow into and out of the engine. We are making more power across the rev range, both torque and HP so we know our efforts have positive results. It is difficult to cite exactly what is doing what, however, but it was fun doing it and we have no regrets.

Still we feel there is more to be done. For one, no one has cracked the ECU's to mod them for the upgrades we have made. There is some potential there. We know that at some point we are going to surpass the duty cycle of the injectors, but so far it does not appear that we are there yet. We are strill running stock fuel pressure - race cars have high capacity injectors and higher pressure fuel systems - at least ours does.

It still looks obvious to us that the top end of the engine is too restrictive. We are pretty sure that we have cleaned up the exhaust side as much as possible while remaining legal - cats, etc. So the quest is for greater input. The question is how much more can we use. At some point there could be too much, so where is the balance for these engines? We are curious about redesigning the upper intake system along the lines of the Steve Maxwell car or the 360 Modena intake. Unfortunately, it takes cash and mine is in short supply right now for taking flyers down these investigatvie paths, not that I don't want to.

Or, there is Plan B - low pressure forced induction.

 

Based on my CFD work on an F355 motor, there is 3X as much power to be found in the top end (air intake) as to be found in the headers/exhasust end of the 'motor'.

I did find the nominal 10HP plus in the headers and another 5HP dollop in the exhaust end of things, but completely new airbox found 35 HP all by itself. Along with a broader bower band. Slightly different length velocity stacks with more modern 'bell' shapes will help a bit, but a resonator per velocity stack is what realy made my simulations come alive. Getting this resonator to resonate with the air box was truely an exasperating trick. But once you get it working it is just marvelous.

All of this was done with std cams at std cam timing and no change in the engine rev limit. The CFD similator says I can get 425 HP from the F335 motor at 8200 PMS. When I put in the measured stock airbox, measured stock velocity stacks, and measured stock headers this drops to 380 HP. By tweeking over lots (several thousand) of simulation runs, I was able to even have better power below 3500 RPMs than the stock system. All gain.

 

WOOT! Can you do a sim on the 348 engine?

 

But Mitch don't you need more fuel? What do we do for a nice robust piggy back fuel controler? There is so much cr@p out there that works for a little while but fails when you need it.

 

At some point thats true, you are going to need more gas. We have some overhead capacity in the map and injectors, but we have yet to detemine how high is it? The on-line injector calculators suggest that the 348 versions are "safe" up to about 330HP at 7500 rpm or so. Beyond that the duty cycle exceeds the safe limit of 80%. This leads (reportedly) to injector overheating and possible failure. Whatever. I use these guidelines since I am not an engineer.

If we wanted to exceed the 330HP, then we are supposed to either increase injector capacity or up the fuel pressure or even both. For example if we wanted 400Hp out of the engine (assuming it could be made to do it), the injectors need to be 24lb versions (we have something just over 18 lb models) and fuel pressure could stay at 50-55 psi.

Allegedly. We still play with it. As I mentioned we are just trying to see how far we can take it in the most stock-like configuration.

Now, the 355 injectors have a greater capacity than our 348 models. Too bad they don't retrofit.

 

Well I hear you but you still have to tune it and iirc the dyno sheets had A/F ratios on them that showed that the 348's could use more fuel. But I could be wrong on that.

 

Mitch,

What does your simulated air box look like? Anything like the GruppeM with the cone type K&N filters? I have the GruppeM and I know of other 355 owners that got 17rwhp from the box. My dyno guy never tested the GruppeM by flowing air into the air vents while on the dyno, but he though 20rwhp was likely.

 

Given 200-1000 hours to do the required sims, yes.

I have offered to help Earnie a cuple of months ago with this..........

 

The fuel injectors become iffy around 415HP. That is the fuel necessary to achieve stoichometric mixtures at 85% injector timing corresponds to 415 HP.

Alternative A) raise the fuel line pressure by 2-3 PSI.
Alternative B) use slightly larger injectors.

 

You are actually talking about the air FILTER box. The 'air box' sits right on top of the throttle bodies.

My Air Box is pretty close to the F355 factory box, but the velocity stacks are shorter (by 12mm) and the bell is shaped* somewhat differently. The important thnig is that each velocity stack sits inside its own resonator (think of a quart jar with a velocity stack inside it and a properly shaped mouth.) Four of these VS+Res sit inside an airbox that is dimensionally close to the F355 box. So there are two sets of resonate functions going on. This alone was worth 15 HP over the standard 4 velocity stacks in an air box. This also cost me at least 500 hours to figure out how to make both sets of resonances work with each other. 500 hours is MY time, the computer had thousands (5-6) of simulations hours doing the number crunching.

(*) Google up "best Bells" Blair

 

With the sims are you basically playing with helmholtz frequencies optimizing for WOT for max HP? What does that do to the driveability over the range or its relationship to torque? Are there simple things that can be or should be done to a generic airbox when racecars are forced to use a restrictor plates which I imagine would change all this too? I don't really understand this stuff. I'm like a kid who has learned a few new words. Sometimes they are used in the wrong context.

 

Mitch,

Sounds like you put in some serious work.

The jury is still out on "correct bell shape" and what we find is that it makes little difference between what intuitively looks like a huge change . Best way is to test some SLA (3D printed) parts which are cheap and quick to produce (about $100 each).
As you may already know, the inlets increase the discharge coefficient (0 bad, 1 excellent) which in turn decreases the pressure delta across the blade. This of course is only useful at high throttle angles since your throttle blade is causing the majority of the pressure drop which is its exact purpose.
For instance, at low blade angles, you may see 60 kPa across the blade. No matter what you do, there is no way you can force more air past the throttle blade since you're at sonic velocity (choked or Mach 1) as it is. As the throttle opens, the delta pressure across the blade approaches zero but never gets there so a discharge coefficient of 1 (100% efficient) is impossible. What you're trying to do is get it closer to 1.

Bob brings up a good point however. Your curve must and will adjust negatively if you concentrate on top end only. Ferrari calibrate their vehicles for drivability and performance over a wide RPM and load band hence the Variable Inlet Manifold Valves but I don't think that concerns you since you're looking at top end HP's. Good luck and I too am looking forward to seeing some pics.

 

My sims have throttle plates at the correct points, and I have done the throttle experiments from, 5% to 100% in 5% increments. Makes for some interesting TQ and HP graphs. There is one little range where the motor makes about 4% less power at WOT than at 80% throttle over about 300 RPMs, and in this range, more throttle leads to less power.

Although the simulator is capable of doing the time domain acceleration stuff, I have not devled down into that time comsuming endeavour.

In my sims, I have maintained the 78mm MAF path from the air filter box to the air box. Although to be fair, I have not simulated the ducting from the window to the air filter box.

 

Yes, I did find 1-2% stuff in the shape of the velocity stack, but what realy floored me was the shape of the mouth of the individual cylinder resonator. A 1mm change in the profile of the mouth of this helmholtz resonator made 6 HP show up rather magically; adding a little more made it all go away.

Yes, we plan to "print" parts that can fit inside the factory airbox in place of the velocity stacks.

As I discussed above, I have the throttle plates inthe simulations, and have run simus using these plates at various angles (after I found the optimal WOT tune).

I have never, in particular, concentrated on peak HP, I have, instead, concentrated on the shape, the smoothness, and breadth of the TQ curve; under the assumtions that the peak RPMs will not be raised, not the cams changed, not the ports seriously modified. {Although I do know what happens when you put in big valves, and big cams.}

In my work with headers, most of this concentrated on extending the header performance from 4500 RPMs down to 2700 RPMs, find those parameters that had a nice smooth positive TQ advantage in the cruising part of the power band. And this was done without sacrificing one iota of top end. Likewise in the air inlet stuff, I concentrated on extending the breadth of the TQ curve down as far as it would go so as to end up with a big broad, smooth tall TQ curve.

The real trick, in my opinion, is to get all the parameters sorted out so that the air inlet and the exhaust outlet both "sign off" at the same time, which just happens to be about 9000 RPMs. You can't use any power up in this range anyways, so you want to adjust everything so all the power that is in there is found in useable RPM ranges.

In fact many of the nuance details lead to more power up top that I then have to add length to the headers or velocity stacks to move the found power back into the acceptable power band.

 

Rob,
Your mailbox is full, so I'm posting this here.

Are you still doing throttle bodies?
I would like to have you do the same 57mm upgrade as you did to Ernie's?

Thanks

 

Cool deal this will help

 

Arrrrgh. That's a shame.

 

Can you expound about the radius made in the plenum entrance. What was removed ? What changes were made ? Any Pix ? Any info would help. Andy

 

That was the piece of the puzzle that was missing. Thank You. This is going to be fun.

 

Only a few years late to the game (lol); great thread with even better information. Excited to hear more:

Any update,, Mitch.