Quad throttles - why bother?

[Sam_Q]

ok I tried a search for this in the old forum and I came up with heaps of stuff that wasnt relevant, and the search gave an error in this one, so I ask this:

anyone that has tuned a engine with quad thottles knows that its partually a guessing game as to what load the engine is at at the time, unless they run an air flow meter.

So I really want to know why do we keep them, I mean sound aside, if a silvertop set of throttles is lined up against a custom manifold on a 4ag with a simular intake length and bellmouths what would the difference really be in performance?

This might make a few people foam at the mouth but if I make a nice manfold with a generous plenum and single throttle (XF or something) I could get a nice solid vacume signal and have a much simpler and more compact setup.

I know that the shorter path means they are meant to have better response but what is it like in the real world?

[takai]

Having the shorter path certainly helps with the response, even with a plenum stuck on the end of it all. Also it is far easier to tune the runner length with a quad throttle setup than with a post-TB plenum.
Tuning them is just as easy as you can retroactively tune to some degree. Insert X amount of fuel here, get Y AFR therefore Z amount of air is going into the manifold.

[Lench]

edit: nevermind

[Billzilla]

It can be worth quite a bit. More so as the engine makes more power.
The inlet length for Hemholtz tuning isn't really a factor as the end of the runners can be made exactly the same for both types of manifold.
The real difference comes with even airflow into each cylinder. With a plenum, it can be very difficult to get the same airflow into all the pots.
All things being equal, an engine will always make more power with indiviual runners.
There's also the problem (Harmonics? Not 100% sure) of using big cams with a plenum inlet, as typically the engine will not idle well or run smoothly at low revs. With individual runners you can use rather large cams and still get the engine to idle at close to normal revs fairly smoothly.

Measuring load isn't a problem at all - All you need it revs Vs throttle position and enough load points to make it work around the idle & low throttle/revs areas. Higher revs/throttle doesn't need much resolution.

Oh, and they sound much cooler.

[1jzracing]

I have used both on the same engine and there was slightly increased power with the multi set up once i put some longer runners on it particuarly in the mid range and response, before the long runners it actually lost power over the factory intake, it was on a 325 BM and just used TPS as load sensor, GLORIUS sound on a six

at the end of the day its marginal but you only need to look at what uses each, all M3's and atmo racing engines will always have multis, but honda S200 also considered one of the most high performance production engines uses a plenim!

[psychofox]

I was also under the impression that the "Pumping Losses" were less with ITBs as you are not making the cylinders work against the vaccuum in the plenum chamber.

TODA make a ITB kit for the S2000 - big $$$, but apparently there are gains to be made - even on the F20C.

[Sam_Q]

I guess I forgot to mention I meant a direct comparasin to where the intakes are the same length, and both have an airbox/plenum.


Takai: I am not quite sure what you mean about the tuning. Heres how I understand how they work: The ECU senses TPS and then compares it to the rpm, compensated with the air temp and then decides what load its under, looks up that load rating in the map and gives a certain amount of fuel. The problem is that using TPS alone isnt a real effective guide on load and hence a richer mixture needs to be used to be on the safe side. Does this sound right?

I was told the way to go is to run a combined map to TPS switching and then make it a bit on the rich side.


Bill: My engine would inherit the airflow problem either way because I am using an airbox so that rules that option out. With the big cams thing, I have heard that also, and to be honest I dont get it. I see it like this: under full throttle you have 4 pipes with open throttles and a box or 4 pipes and a throttle somewhere else, I really dont see a difference. Well unless its under partial throttle and theres a reversion wave off the thottles under partial opening that somehow effects the idle, I really cant see this being of any good though.

Also I thought that high load didnt need to be that precise, i was thinking about mid throttle openings (like on an average hill) where the vacume has dropped to zero and the fuel would probably head towards 13 to 10:1 to allow for fluctuations in possible load.

I have fuel economy in mind as well as power and I correct me if I am wrong but I think if i had a single throttle manifold I would have a better sensing of the load and therefore better fuel control (hence better economy).



1Jman: I did notice that the S2000 engine has a plenum, thats one of the reasons I am so interested in this.


Psychofox: I heard that a factory S2000 has a pleum thats too small and is this way to do tight polution control, so perhaps the thottles help a restriction more than anything else. A comparasin to an oversided plenum would be interesting indeed.


If I was to convert my 20V to having a single thottle I think I would have a well designed plenum and have it a real decent size, maybe 2 to 3L or something

[Ben Wilson]

Massive selected quote time:

I guess I forgot to mention I meant a direct comparasin to where the intakes are the same length, and both have an airbox/plenum.

You might well make more peak power, but you will lose throttle response.

Takai: I am not quite sure what you mean about the tuning. Heres how I understand how they work: The ECU senses TPS and then compares it to the rpm, compensated with the air temp and then decides what load its under, looks up that load rating in the map and gives a certain amount of fuel. The problem is that using TPS alone isnt a real effective guide on load and hence a richer mixture needs to be used to be on the safe side. Does this sound right?

I was told the way to go is to run a combined map to TPS switching and then make it a bit on the rich side.

It really comes down to cam size, I ran my silvertop using pure MAP sensing and it worked fine and got good fuel economy. I know of people who are running PP rotaries on MAP sensing successfully and they have SFA vacuum at idle - a lot comes down to the individual ECU and the tuner.

Bill: My engine would inherit the airflow problem either way because I am using an airbox so that rules that option out. With the big cams thing, I have heard that also, and to be honest I dont get it. I see it like this: under full throttle you have 4 pipes with open throttles and a box or 4 pipes and a throttle somewhere else, I really dont see a difference. Well unless its under partial throttle and theres a reversion wave off the thottles under partial opening that somehow effects the idle, I really cant see this being of any good though.

Once again, it's down to cam size, with big cams quad throttles idle better - I'll admin to not being 100% sure why.

OK - I'm tired of individual quotes here

To put it in it's most simple form, plenums are really hard to design. A plenum too small will cause mixture variations, and one too big will cause massive throttle lag. If you've got quad throttles, you can make the airbox as big as you like without having any problems with response.

[takai]

My 4A still idles at 1100rpm perfectly, and could idle lower but i was having issues with stalling it off the line if i stuffed up my launch. I think it is because there is a much smaller volume of air post-throttle than with a plenum design. So at idle you dont get the massive lumpy idle where it sucks out the plenum and then replenishes it.

[minorobsession]

I am not sure why everyone say that quad throttles are guess work when it comes to tuning its not that bad! If tuning was so difficult with quad throttles how did Toyota achieve it and meet all the polution laws!

I am using a Megasquirt EFI (inbuilt map sensor) with an Innovate wide band sensor on a 4age blacktop and I have been able to achieve a pretty good all round tune. The biggest problem is finding somewhere that I can drive full throttle repeatedly, will have to invest in some dyno time.

My suspicion is that lot of people are replacing the long factory ram tubes and with the short after market ones, destroying any Helmholtz effect that may have existed. The orginal long ram tube setup could be compared to the long runner plenum design of the earlier models. I have seen dyno results for a 1275 mini engine drawing air through a single ram tube, the idea length for best results throughout the rpm range was 18inches long! Helmholtz's theory will suport this if you do the math.

The other thing is that when drawing air directly from the engine bay the inlet temp varies significantly from day to day and for different types of driving.

[myne]

The closer to the ports you can move that much needed 14.7psi air, the quicker response you get.
Rev 2 otherwise identical engines - one with a single throttle and a plenum, and one with quads.
The quads should rev up and down quicker - particularly at the higher revs.

Like any supply chain, it's crucial to have the goods delivered in a manner that best suits.

Quads are like having a big warehouse out the back that has a constantly replenished stock level - if a big order comes in, it can be filled immediately.

Single TB has a big warehouse too, but the incoming supply is regulated, so the warehouse isnt always full. If a big order comes in, it takes time to build the stock levels before they're sent off.

Obviously these events are much much faster on an engine, and often can make about 3/10ths of fuckall difference, but sometimes there is a need, and if that is what you need, that is what you must have.

Quads are for response, and to a lesser extent for tuning.

[Celica RA45]

and they will also make more power when you use big cams and it also depends on what size will suit your motor. i have tried 45mm 48mm and 50mm and the 50mm makes the most power in my engine and also the most torque as well and the best thing is it still idles at 750 rpm

[xero]

what about angle of the ITB?

would ITBs that are 90degees to the block be better than ITBs at say 110-120degrees to the block?

eg: =B or ``B

[gianttomato]

Ideally you want as straight a line as possible from bell mouth to the valve seat. Practically that just means you follow the port out of the head.

[xero]

thanks gianttomato...

thats what i thought like the old hemi engines the air flows through the ports in a straight-ish line...