Delorto DHLA you say?...
And what if it were to be a low rpm/high torque motor like an A15 stroked to A17?

What about using Reed valves after the SU's? My grandfather used to believe in them heart and soul for his L20B

My father and brother both vouch that the 38's work best for the motor, but his little A14 has 40mmx34mm(I think) oval ports, modified L16 intake valves and a 273deg camshaft. Hell if they can work for his A14, I might just source me an A12GX, stroke it with a 1400 crank, and jet the 46's for it. Can't be worse than 38's if correctly jetted can it? I mean we have the 46's here and if they provide even a slight improvement. . . .
Maybe I'm just too fussy, but I find the SU's a lot more attractive. Webers seem to make the engine appear to be more than it is

Hey Guys,
I read 46mm SU's are too much for 4 cylinder engines. Why is that? I've seen Webers on nearly every second A-series motor and they have a 40/45mm butterfly for each intake port. how is it that a one 46mm carb can be too much for four intake ports? My little brother's playing with an A14 on an engine stand and I'd like to offer some older brotherly advice. We aren't sure what we're going to strap the motor in yet, but instead of ordering a set of webers, I thought he could use the two 46mm SU's lying around.

Just discussed the subject with my father and he just laughed...
He reminded of a little experiment we did nearly 2 decades ago when he started teaching me about engines - I was 6 or 7 years old, and I asked this very same question. My father took 5 liter plastic bottle that he modified with a lighter's ignition, a fuel line and tap, and glued the cap on. He squirted lighter gas in through the line and closed the tap, after which he ignited it. When evrything settled, I noticed the bottle had pulled into itself having less air inside it.

And so I never asked again. . .until now.

HAHAHAHAHA!!!

Ok, I'd settle for that answer.

D I wasn't second guessing you any of what you said. In fact, I don't believe those Japs' engineering degrees were bought like here in SA. I was simply curious as to there reasons, and as you've explained, they were power oriented.

Thanks Guys for all the input

Nah, I was just contemplating that instead of making both bigger, use the available space and bring the exhaust valve size up to par and spend the rest of your cash on having the perfect camshaft cut.

Ok so what if the intake valve was still a bit bigger but not as significantly and the space utilized for a bit larger exhaust valve? I.E. - custom camshaft to be cut - what if instead of 40/35 you size them more like 38/37 and rather increase the ex. duration just a little more? I mean as D said, if you already have an adequate intake valve, why not bring the exhaust valve up to par and just manipulate the cam timing?

I learned quite a bit from that link!

I'm still curious though: intake air is either pushed in via Forced Induction, or sucked by the downward motion of the piston. Either case requires that the flow is simply improved. That coupled with the fact that exhaust gas pressure and temperature is so much higher than intake pressure and temp already, shouldn't the exhaust gasses flow more quickly from an identically sized valve even before the piston pushes the rest out? That being said, once again shouldn't the exhaust then be the one requiring the improved flow?

Hey,
I was just reading through some of the articles in the Tech Wiki and wondered:
Why the intake valve is significantly larger? I understand the principle of a larger intake valve means air for power is more readily available, but take this FIGURATIVE example:
40mm carb throat - 40mm intake throat - 40mm intake valve, but on the opposite end, 40mm header runners - 40mm exhaust throat - 35mm exhaust valve. I know I'm not quite the sharpest pencil, but I thought the pressurized exhaust gasses need the larger valve for a quicker and smoother escape? Even in boost applications, an enormous intake pressure of 2 bar still doesn't have the flow and thermobaric need of the exhaust gasses after a compression ratio of 8.5bar.

And if this works so well, why do DOHC head use symmetrical valves? I'm just reeeaaally curious and I'd love to learn from you gentlemen.

Btw, anyone try symmetrical valves?

Thank You ddgonzal. I'm honestly very pleased to read this. I was afraid I might have had to cut out the tunnel out and duplicate an auto one for this to work. To be totally honest, I'm still exploring options with ratio's and reliability. I scarcely find info on how much abuse gearboxes themselves take. I realize the 63A is quite a bit heavier from the bakkie's 60-series, but I'm afraid the 60 won't last under the abuse I'll put it through. I am definitely going to supercharge the A15 once I've had enough fun with it in N/A form.
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On the subject of abuse, do you perhaps know if there's a way I can use the original H145 diff? I keep reading the original diff won't hold up, then again, others say not to underestimate it. I thought of ordering a new gear set and rebuilding it, maybe incorporating shims to even out the grab and wear on the CW&P. Apart from the fact that I'm struggling to find an H165 in good condition locally, the H145 is 10kg lighter, and significantly smaller.
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Thanks once again. Your input is taken with High regard