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Evening all,

I know with other engines (i.e. SR20) you can get larger throttle bodies (single...not quads!!) for some gains, for single TB's on MX5's is there such a mod?

just more a general question really!
cheers,
Chris

Yes, Skunk2 makes one.

They are not popular with MX5 crowds because people who want to go fast for cheap are attracted to NA/NB chassis cars and TB's just dont do anything.

Dann

EDIT: the skunk2 was developed to fix snapped throttle shafts not for HP.

Ok cool, so really no gains to be had in any form unless throttle shafts snapped.

you can get power gains with them paired with a new intake manifold but you really need to be pushing big power for it to be effective.

otherwise i am pretty sure on lower powered cars you will actually lose power.

i am sure waz and dann could confirm that though.

100%.

The people who can benefit from them typically have ITBs already.

Pats car made the 325whp with a completely stock inlet side save for porting.

55mm stock TB

Dann

NitroDann wrote:100%.

The people who can benefit from them typically have ITBs already.

Pats car made the 325whp with a completely stock inlet side save for porting.

55mm stock TB

Dann

Boosted though, so even if it was a restriction, increased pressure and flow is compensating.

Obviously when NA a less restrictive intake helps, but you need to be in a situation where the TB is the restriction. Only in rare case would it be, and most cases it would be very negligible. Like all things, it is a balance between WOT conditions and transient. For the 1.6 engine, the stock TB is in the sweet spot for that balance. Larger would only likely favour a lower set of conditions making other things worse (like transitions).

...allow the designer to use a sufficiently large throttle body bore that rarely limits engine performance to a measurable degree. It follows that enlarging the original throttle body will only make a useful gain when other aspects of the engine have been changed to substantially increase the power output. The most likely change due to a larger throttle body, if any, on an otherwise standard engine is a car that goes slower round corners due to lack of fine throttle control for the driver. At best, there may be a slight improvement in response (see below).

It helps to understand the relationship between size and output to consider that a 2L Formula 3 engine produces 200+BHP through a 26mm (531 mm2) restrictor and a 75mm throttle body is eight times larger at 4,418 mm2! Similarly, in an experiment to curb the power of 270 BHP touring car engines, we reduced the size of the single throttle body to less than 44mm (1520 mm2) before there was any noticeable reduction. A 75mm body has three times the flow.

From http://www.jenvey.co.uk/jenvey/why-not-just-use-a-big-single-throttle-body

I put a skunk 2 on my race car, no so much for performance but more for reliability, I had 2 stock throttle body's fail so figured this might help, not cheap but a really nice bit of gear.

& if you're still running the NA8 MAF, from memory, it's narrower than the NA8 TB.

93_Clubman wrote:& if you're still running the NA8 MAF, from memory, it's narrower than the NA8 TB.

That's a good example of where the restriction (by design) is needed to increase flow so that the sensor works better over a range of conditions (slow air cruise vs fast air at WOT).

If you change the fueling solution (ie non-stock ECU) you can then remove the restrictive MAF and get a small increase in performance - note that you can't do this with just the MAF being replaced for a bigger MAF as you'll end up wrecking the slow cruise fueling and make transition bad.

G

gslender wrote:note that you can't do this with just the MAF being replaced for a bigger MAF as you'll end up wrecking the slow cruise fueling and make transition bad.

G

Thanks for that, G. I think you've just saved me some more work. I've played with bigger MAFs on an NA8. You do get more power at WOT but it's at the cost of lousy transition at around 4000rpm at part throttle. I was going to go back and play with fuel maps for it again. Now I'll just leave it and stay with the stock MAF.