28 replies to this topic

[LC-GTR-1969]

It certainly is an interesting thread... Air speed is one of my personal interests areas in engine technology...

 

As a side note- my old irving head had quite small port volume and port area was very conservative. From memory the round inlet ports were 1.5 inches in diameter and the port volume was about 140cc. The head flowed about 340hp at .600 thou from memory (I have the flow sheets round here somewhere) but stayed strong right up to .800" lift. 

 

With this head, the port area was relatively small but obviously as it was an efficient port it flowed quite good cfm. As this was a very stable port, in theory you could run quite high airspeed through the port before it would back up on itself and stall. The flow was not necessarily huge- say when compared to a ported JZED head, but it was very stable. The string in port trick showed very stable air. I've head of some very good 9 ports flowing similar cfm- but the efficient port of the irving would help to improve the volumetric efficiency of the engine across a relatively wide rpm range- whereas the 9 port would make good volumetric efficiency at a peak but drop off before and after the peak more considerably..

 

Hence, an irving headed engine may produce only a little more hp than an excellent 9 port (say 325hp at the fly) but I can guarantee the average hp- or the hp across the curve would definitely be a lot better and it would produce a much better torque curve. A member on here, Thomastorana runs my old irving head on his race car and the thing is a torque machine- he really gives much higher hp cars (like ls engined race cars, and turboed imports in IPRA) a run for their money. Makes great watching- google/ youtube LJ IPRA thomas racing... some great footage... 

 

In theory, 2 engines, one a strong 9 port making say 300hp and an irving headed engine making the same 300hp- both would run similar mph numbers in a drag race, but put them on a circuit and the irving headed engine would be 2 car lengths further after every corner due to the improved torque spread. 

 

At least that is my understanding and my wife thinks i'm an idiot on most days, so take what you will from this information 

Edited by LC-GTR-1969, 22 December 2017 - 08:37 AM.

[nzxu1]

Talking about air speed , probably about  25 years ago  l replaced the  factory 1.5 strombergs  on my 186 august 71 XU1  with a  genuine set of  1.75's  from an LJ  XU1  . With the original 1.5's plus  HX  cam and  original XU1 head  the car was very snatchy and jerky as you would expect .  l  really fitted  the 1.75's  just as a trial to see what they would be like  fully expecting them to be too big for the 186  and was pleasantly suprised at jut how much  smoother and more driveable  they made the car ,  proving  ( at least to me  ) that  bigger carbs don't nessacarily mean poorer drivability 

[warrenm]

Talking about air speed , probably about  25 years ago  l replaced the  factory 1.5 strombergs  on my 186 august 71 XU1  with a  genuine set of  1.75's  from an LJ  XU1  . With the original 1.5's plus  HX  cam and  original XU1 head  the car was very snatchy and jerky as you would expect .  l  really fitted  the 1.75's  just as a trial to see what they would be like  fully expecting them to be too big for the 186  and was pleasantly suprised at jut how much  smoother and more driveable  they made the car ,  proving  ( at least to me  ) that  bigger carbs don't nessacarily mean poorer drivability 

 

And the 2" SU's would be another leap forward.