ITB's Vs TB + Plenum

volospian

volospian

volospian

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I'm thinking about how I'm going to play with the Stag engine. I was looking at a set of ITB's on a custom manifold from AlTiSS engineering, similar to these but I've got a couple of considerations.

1. I may want to supercharge the car later (in which case it would probably be centrifugal with the blower before the TB's) and I think the cost of ITB's would be a bit of a waste if I went that route as I assume they would not provide much/any extra over a single TB in a FI environment. However, as long as ITB's won't cause actual problems with a blower, I may still be OK with a "two stage" approach. Blowing is only an idea at the moment if I still feel the Stag is sluggish after EFI. I'm probably only aiming for around 200hp, which should be do-able in the Stag engine without the need for FI.

2. I think ITB's would only be a real benefit if I fiddled with the cams, which is difficult as nobody makes Stag cams, so I'd need some reground (which, although I'm not familair with, I assume would only be able to provide a limited effect) or manufactured specifically. Hmm, sounds expensive!

So, I'm thinking that maybe ITB's is a bit of a waste of effort and I may be better having a plenum made with a single (or maybe dual) TB and seperate injectors. It would also then be easy enough to add a centrifugal blower or maybe TT setup later.



Or... I could just say nuts to it and have a manifold made for a twin screw or rootes from day one, at least then cams would be less of an issue:D

lol, I think I've kind of answered my own questions anyway, but any advice/experience/ideas would be worth throwing into the mix
 
Dunno if it helps but fitting ITBs to an S2000 makes no more peak power. Just as evidence that a single TB isn't exactly a compromise.

If your gonna go FI then a single definately makes mroe sense.

Although ITBs NA do sounds amazing :D
 
.....because the casting alone will cost more than a decent LS6/7, shipped from the States? ;) :p

I don't think supercharging the Stag holds much potential. The narrow crank mains and bearings probably won't support much boost, I know a twin turbo one that was run with much success but there was never a known power figure for it so I suspect, in reality, that route wasn't worth it. It suffered from blow by as well, with the mixture being forced past the rings, although, IIRC, not badly enough to cause any problems.

Also, this may sound terribly 'concours' but it seems that blowing the Stag lump might 'ruin' it with regards to it's noise and eagerness....

Like I say, if you get the engine built right point blank you can get 210 out of it - if you were to look at ITBs, which would give you similar flow to a set of quad Dellortos, and got Cosworth or similar to make some pistons (not as expensive as you might think), you may be able to nudge it towards the 250 area, if not a little more :)

If you do go ITBs though, later blowing will probably neccessitate the need for a bulky bonnet bulge due to the plenums.

You can adapt the Rover Flapper/Hotwire injection manifold to fit the Stag, giving you a single plenum, single throttle body manifold with fairly good distribution and 1 injector per cylinder :)

Just thought I'd add that into the mix.

Interesting ideas all the same...
 
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saitrix said:
Why don't you have a bash at fitting the Sprint head to the Stag? :p Mmm a 32v Stag engine.
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lol, been down that discussion a few times :D

Lashout_UK said:
.....because the casting alone will cost more than a decent LS6/7, shipped from the States?

I don't think supercharging the Stag holds much potential. The narrow crank mains and bearings probably won't support much boost, I know a twin turbo one that was run with much success but there was never a known power figure for it so I suspect, in reality, that route wasn't worth it. It suffered from blow by as well, with the mixture being forced past the rings, although, IIRC, not badly enough to cause any problems.
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Yeah, but I probably wouldn't go for much boost anyway. I'm not after huge power figures for the Stag, I was just thinking of boost as a way to reach the higher end of 200 as I'm concerned about the cost/power ratio.

Also, this may sound terribly 'concours' but it seems that blowing the Stag lump might 'ruin' it with regards to it's noise and eagerness....
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Meh, not worried about that too much :D

Like I say, if you get the engine built right point blank you can get 210 out of it - if you were to look at ITBs, which would give you similar flow to a set of quad Dellortos, and got Cosworth or similar to make some pistons (not as expensive as you might think), you may be able to nudge it towards the 250 area, if not a little more
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I was wondering if any other pistons may fit, I think the Stag bore is 86mm. There may already be pistons somewhere that would be suitable, but I think I'd be happy with 210 at the moment.

If you do go ITBs though, later blowing will probably neccessitate the need for a bulky bonnet bulge due to the plenums.

You can adapt the Rover Flapper/Hotwire injection manifold to fit the Stag, giving you a single plenum, single throttle body manifold with fairly good distribution and 1 injector per cylinder

Just thought I'd add that into the mix.

Interesting ideas all the same...
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Yeah, I'd thought about the need for a bulky plenum if I charged it, and I had also already thought about the rover plenum too :D
 
There is zero advantage to having ITBs in a forced induction setup.

What matters in a n/a application is throttle area. Simon - do you know the diameter of the stock TB and the replacement ITBs?

What is the budget? You could always go bike ITBs/Jag M62 blower/7psi/slimline plenums...

*n
 
penski said:
There is zero advantage to having ITBs in a forced induction setup.

What matters in a n/a application is throttle area. Simon - do you know the diameter of the stock TB and the replacement ITBs?

What is the budget? You could always go bike ITBs/Jag M62 blower/7psi/slimline plenums...

*n
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62mm stock i believe.

ITBs vary from 40 to 60mm, heres a thread i found. http://www.s2ki.com/forums/index.php?showtopic=436322

Note the massive midrange gains. All depends on where the restriction is in the engine. I guess most engines inlet systems are no where near as good as the Honda ones
 
penski said:
There is zero advantage to having ITBs in a forced induction setup.

What matters in a n/a application is throttle area. Simon - do you know the diameter of the stock TB and the replacement ITBs?

What is the budget? You could always go bike ITBs/Jag M62 blower/7psi/slimline plenums...

*n
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Yeah, that's what I was thinking, but I'm not convinced I'll go blown anyway, hence the ITB possible starting point.

I'm thinking of cbr 600 bodies but I forget what size they are.
 
Plus we're getting into the whole fluid dynamics thing if we start talking about one big TB vs. one smaller one per cylinder...area vs. diameter and all that jazz.

For what its worth, were I in your position I would use bike TBs on a decent manifold designed to be able to fit a plenum easily in the future. It will futureproof you against future forced induction and won't be a hinderance. Win/win ;)

What are you using ECU-wise?

*n
 
penski said:
Plus we're getting into the whole fluid dynamics thing if we start talking about one big TB vs. one smaller one per cylinder...area vs. diameter and all that jazz.

For what its worth, were I in your position I would use bike TBs on a decent manifold designed to be able to fit a plenum easily in the future. It will futureproof you against future forced induction and won't be a hinderance. Win/win ;)

What are you using ECU-wise?

*n
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That's pretty much my plan, but it will be an expense, hence the "is it worth one large TB instead" route as, as Lashout suggested, I could modify the RV8 plenum and it would probably be cheaper, but I still like the idea of ITB's and a plenum if I need it.

I was thinking of emerald for the ECU, I think it gives me everything I may require, and Dave Walker seems to know what he's doing if I get stuck anywhere :)
 
penski said:
CBR600 TBs = 40mm each. :D

Sexy TIG'd crossover manifold for the win.

*n
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Yeah, I'll have to have a flick through the writings of Mr A Graham Bell later and look up the throttle bits, see what would be the best size, but I'd imagine 40mm will be ok. It's only 375cc's per pot
 
ITBs sound lovely, but wouldn't bother personally if you go down the FI route as it's not worth the cash.
 
Ev0 said:
ITBs sound lovely, but wouldn't bother personally if you go down the FI route as it's not worth the cash.
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Yeah, I know, but I won't know whether I want to blow until I see how well it does on efi. A single tb on a plenum makes more sense if I was sure I'd go FI, but I think ITB's could make enough power as it is.

This isn't aimed at silly power so a blower isn't necessarily a definate, I'm only looking for around 200hp (preferably the right side of that figure ;)) but the Stag is still going to be my "leisure" car. I intend to use it for long weekends away and stuff. It's more of a play around than any attempt to get serious power from it. However, if I struggle to get a decent power output, then a blower would be next.... or if I get fed up with ~200hp after a while :D

I still have plans for an LS1 engined... erm.... something or other... to be the beast :)
 
I'd love to get a decent ITB setup on the Clio, but currently it involves cutting the slam panel out and removing the aircon. Although a new design is coming to market soon that has redesigned bracketry that allows the retention of aircon and no cutting :)

Won't be cheap though, I reckon 4k+ for a reliable setup.

But then when it goes like this who cares :)
 
Ev0 said:
I'd love to get a decent ITB setup on the Clio, but currently it involves cutting the slam panel out and removing the aircon. Although a new design is coming to market soon that has redesigned bracketry that allows the retention of aircon and no cutting :)

Won't be cheap though, I reckon 4k+ for a reliable setup.

But then when it goes like this who cares :)
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Bike TBs, Megasquirt'n'spark...About a grand?

*n
 
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