81mm or 84mm - Better Response

[Johnny_9]

81mm or 84mm - Which has better response?

Which B-series bore size (81mm or 84mm) engines got better response?

Assume both engines are high-compression pistons with racing cams

Why?

Thanks

 

[hattech-v]

no replacement for displacement.

 

[shiroitenshi]

more displacement - more torque. More torque, can accelerate faster/carry more weight.

No replacement for displacement.. :P

The only reason why you want to limit displacement is for racing regulations, or engine registration issues. 1.3->1.8 no issues.. 1.3->2.0 = more issues with jpj registration.

 

[Johnny_9]

I was looking at a BMI video - MINES GTR - the Mines boss said that the kep the bore standard as he wanted good engine / throotle response.

Of couse 2.0 liter (84mm) got more more than 1.8 litre (81mm) - but which got better throttle / engine response.

Lets do a test on the road - both engine at 3rd gear 3500 rpm

50% throttle to WOT - which one got better response ?

 

[J101]

this question is just too vague.

use quad throttle is you want fast response, 1.6 or 2.0, the air travel faster than the normal intake manifold. the closer the valve to the throttle opening the better.

allot of fine tuning needed to make an engine responsive. it can either be small or big displacement.

im answering based on engine responsiveness only.

ps. the mines GTR was built for the tracks. it can either be big or small tracks. if they were to go to saltlake city, the response would die on the salt as they dont have much top end power like the jun akira supra or smokey top secret r34

 

[shiroitenshi]

actually for all rounder applications.. still big displacement, because the higher displacement usually means big wide torque bands.

Small displacement will always suffer from narrow torque bands or less torque, due to the fact that they have to be tuned for wide torque band at the expense of peak power, or for fatter torque at the higher rev ranges, but at the expense of narrow torque band.

Which is why supercars are constantly over the 3.5L displacement, so they can get the 'responsiveness'.

Like J101 says, if you're talking about throttle response.. it's all about tuning.. but a big cc car will always feel more 'responsive' than a small cc car in terms of feel or throttle input. More go with less throttle %, I mean.. :P

Big TBs also make the car feel more responsive, but it doesn't really increase the power, unless it was being a restriction to your engine performance.

Standard bore is probably a concern for lastability, as thin bores usually compromise strength for high rpm applications... I don't think any non-sleeved 86mm B20B setups can last a few secounds of true 9K rpm at high loads without breaking.