Individual Throttle Bodies and Improved Airflow

[dynomatt]

I'm not sure about Tony's rules, but I definitely can't modify the bonnet (hood Harvey? shame on you).

Here's another question...if I run ITB's, ram tubes and socks under the bonnet, with no cold air source or plenum, whilst not ideal, what will the gains be over the standard setup? My guess is I'll get a fair benefit. Remember, webers and ramtubes with socks was the norm for a long time...

My gut feeling is yes there will be...but by what, I don't know.

I find myself interested in sensible gains...if $1 is a 10% improvement, but $5 is a 20% improvement and $1000 is an 80% improvement...I'll focus my efforts on the $5 improvement.

[dynomatt]

Harvey, on your IRIS thing...take a look at my dyno graph. See anything interesting?

[Dessertrunner]

Matt I purchased a research paper about intake designs on the Honda 4 cylinder race engine. Even though they had a restrictor by redesigning the plenum, while they are a bit short on the finer detail they make a couple of points. They managed in the redesign to increase peak power by 18%, the average power increase was 11% over the rev range.
The big point they make is that there is major power to be gained by seperating cyclinders that are close together in firing order. They aimed to put opposites together aiming for 360 degree difference.
So on that bases alone we will get more by changing the throttle body. What interested me was that I read an other different articale were they increased power by 20% by changing to individual throttle bodies.
Tony

[oab_au]

Originally Posted by dynomatt

Harvey, on your IRIS thing...take a look at my dyno graph. See anything interesting?

I remember talking to you about it at the time. My opinion has not changed. Looking at the torque curve, there are three peaks. The first at 3600, is the Inertia effect in the manifold, without the valve being closed. The second at 4700, is the results of the resonate wave action, and the third at 5800, is the cam timing working.

The torque curve is the result of the cylinder filling, so we can see that this increases at 4700 when the resonate pressures increase. It also increases at 5800 when the engine speed rises to suit the valve timing. As these two peaks are arriving at different rpms, they don't combine to give a total increase in the torque. If the inlet tract resonate length was shortened so that it resonated at the same rpm as the cams, the torque would rise to around 300nm at 5800, and the power would be peaking at around 7000.

The rpm that the resonate peak is tuned to is set by the length of the inlet track, from the valve to the atmosphere. This is set in the standard manifold for about 4800/5000. If it is to be raised to about 6000, the tract has to be shortened. Fitting throttle bodies, and ram tubes of the right length can provide this length.
The problems that I outlined can be overcome if the whole inlet manifold is removed, and replaced by the inlet tubes curving up over the engine, on each side towards the middle of the engine. The ends of the tubes could then enter a common air box, that is fed from the original air supply, and filter.
As the vacuum is below the throttle plates, the air box could be made from any material, sheet metal, plastic (or titanium carbon fiber for the Bling value)
The throttle plate vacuum could be connected from each side, for the brake booster, Auxiliary air valve, fuel reg, purge, etc.
What do you think?

Harvey.

[Dessertrunner]

Harvey,
A lot has changed for Matt and I because they changed the rules and we are allowed to changet he inlet and outlet manifiods finally. So what you say sounds like a plan. By make these changes and nothing else, eg inlet and exhaust I would expect major power increases given what Matt & RallyBob found on the flow benches.

I sort of have a question with a statment which means I am sort of answer my own question but not sure if answer is right. I am really good friends with the Subaru workshop manger here were I live and they tell me that when they take the intake & injector part of the manifold off on most Subaru the inside is coked (not sure if right word) up. Its all black from the exhaust. What I didn't get but think I do now is how the hell the exhaust end up on the intake. Am I right to assume that its due to one cylinder sucking exhaust back out before the inlet on an other closes? If this was the case then you would have to assume that changing trottle bodies has some big gains to be made.
Tony

[oab_au]

Originally Posted by Dessertrunner

Harvey,
A lot has changed for Matt and I because they changed the rules and we are allowed to changet he inlet and outlet manifiods finally. So what you say sounds like a plan. By make these changes and nothing else, eg inlet and exhaust I would expect major power increases given what Matt & RallyBob found on the flow benches.

I sort of have a question with a statment which means I am sort of answer my own question but not sure if answer is right. I am really good friends with the Subaru workshop manger here were I live and they tell me that when they take the intake & injector part of the manifold off on most Subaru the inside is coked (not sure if right word) up. Its all black from the exhaust. What I didn't get but think I do now is how the hell the exhaust end up on the intake. Am I right to assume that its due to one cylinder sucking exhaust back out before the inlet on an other closes? If this was the case then you would have to assume that changing trottle bodies has some big gains to be made.
Tony

Matt having to use the std manifolds is the erasion that it did not produce the goods. With both manifolds set for a higher rpm, that problem should be overcome.

I would expect major power increases given what Matt & RallyBob found on the flow benches.

I would not place too much importance on flow bench testing. It is not the same conditions that the engine has when it is running. For a N/A engine 9mm lift is about the limit, the gains over this are small, and the loses in torque spread are greater. 10/11mm is OK for a forced induction, but we only have atmospheric pressure to do the job.

I understand about the coking in the inlet tracts on other 4 cylinder Subaru engines, as they have a firing order that has No 2 exhaust valve opening, while the No 1 exhaust valve is still open on overlap. The exhaust pressure from No 2 pushes back into No 1. This won't happen on the 6 cylinder as it fires each side alternatively. It is only when a longer exhaust duration is used, that one cylinder can push into the next cylinder on overlap, but longer branches on the exhaust manifold will prevent this.

Any gains that are made by fitting throttle bodies has to be looked at against what the engine conditions were before. Our engine is allready filling the cylinder to 106%, it is pretty hard to make it take more air in. If the engine runs to a higher rpm, the resonate pressures will increase to get to about 110%. So our gains will come from trying to maintaining that VE at higher rpms.

Harvey.

[dynomatt]

Does anybody know how far it is from the face of the head to the valve?

And Harvey, what are your thoughts on inlet lengths (ie valve to atmosphere)? I don't believe I will go for a shared plenum initially as I have no need for vacuum sources (but obviously do have a need for cold air) and due to cost. My ram tubes will just be hanging in free hot air behind the alternator.

A plenum will come later for sure, but not initially.

Matt

[oab_au]

What cam is this engine using?

Harvey.

[dynomatt]

My original ones...I'll chase down the specs

[oab_au]

Originally Posted by dynomatt

My original ones...I'll chase down the specs

These are the specs that you gave me before.

The cams are 240 degrees at 0.50 inlet and 232 degrees at 050 for exhaust…lift is 10.4 and 10mm respectively (I think).

Installed centerlines were 105 I think.

Ok I work it out on these.

Harvey.

[dynomatt]

This from my cams post

Originally Posted by dynomatt

The intake cams have 10.0mm lift, with 230 degrees duration at .050.

The exhaust cams have 10.5mm lift with 236 degrees duration at .050.

[oab_au]

It would be good to know what the timing figures were for them. Probable about 260* seat to seat.
I would try for 340mm/15.5", valve to atmosphere end.

Yes get it going then build a air box, to feed them. May be a couple of boxes from a three cylinder Triumph, a three cylinder stroker, Kawa, Suzi.

Harvey.

[RallyBob]

Originally Posted by oab_au

I would not place too much importance on flow bench testing. It is not the same conditions that the engine has when it is running. For a N/A engine 9mm lift is about the limit, the gains over this are small, and the loses in torque spread are greater. 10/11mm is OK for a forced induction, but we only have atmospheric pressure to do the job.

I question the validity of this statement only because the largest gains I've seen were from higher lift cams (about 11 mm) and modest inlet porting/more aggressive exhaust porting. 71 whp is nothing to sneeze at! No other singular modification had this large an effect on the engine's performance.

In fact the heads showed huge flow gains at higher lift, about 35% more than with the standard valve lift. Frank Aragona commented on the same thing, that this engine 'loved valve lift', and he ended up with .550" peak lift (just under 14mm) on his last cam grinds.

Regards,
Bob

[Trevor]

Originally Posted by RallyBob

I question the validity of this statement only because the largest gains I've seen were from higher lift cams (about 11 mm) and modest inlet porting/more aggressive exhaust porting. 71 whp is nothing to sneeze at! No other singular modification had this large an effect on the engine's performance.

In fact the heads showed huge flow gains at higher lift, about 35% more than with the standard valve lift. Frank Aragona commented on the same thing, that this engine 'loved valve lift', and he ended up with .550" peak lift (just under 14mm) on his last cam grinds.

Regards,
Bob

Kia ora Bob,

I agree.

Flow bench testing is an acknowledged science, is applicable, and it is logical that the SVX engine should be particularly receptive in respect of increased valve lift. It is significant that as designed, the engine was rendered safe against cam belt breakage.

Trevor.

[oab_au]

Originally Posted by RallyBob

I question the validity of this statement only because the largest gains I've seen were from higher lift cams (about 11 mm) and modest inlet porting/more aggressive exhaust porting. 71 whp is nothing to sneeze at! No other singular modification had this large an effect on the engine's performance.

In fact the heads showed huge flow gains at higher lift, about 35% more than with the standard valve lift. Frank Aragona commented on the same thing, that this engine 'loved valve lift', and he ended up with .550" peak lift (just under 14mm) on his last cam grinds.

Regards,
Bob

Bob I don't want to get this thread off topic, but I made these statements it context of what these two engines are going to be used for. Tony's has to run a 5 day trial on the wet slippery roads of Tasmania. Matt's has to run on loose gravel roads. Neither need the max HP that can be obtained for straight line work. They need a wide strong torque curve that will make the car drivable in the conditions. I don't think Frank's engine would make a good example, for the conditions.
Yes we use 13mm lift on the similar Ducati cylinder, but it is delivering torque at 8000 rpm, not what we need.

Harvey.