Stock exhaust valves vs over sized exhaust valves




#1
i'm trying to gain some info on the benefits or downfalls of using stock size intake valves, but with over sized valves(+1mm) on the exhaust side only (ported head of course) Has anyone experimented with this setup before and can share details of the issues or gains that they experienced? Answers can be based off of either Gen Hayabusa, experience, scientific or hypothetical.

Is this type of head setup primarily for turbo applications?

Would this type of setup help or hurt a naturally aspirated combination?

If it works well with NA motors, what would be the minimum recommended displacement?

If used on a naturally aspirated setup, say 1397-1507, what would be the recommended exhause cam profile? (broad range of displacements, i know)

Thanks in advance for sharing your knowledge! Also, please let me know if i should post this is the Engine and Performance Mods section. I couldn't decide, but chose here since i'm leaning more towards seeing answers from NA motor guys.
 
#2
I've been looking/searching for this "specific" type of head setup, but it seems the majority either uses all stock size valves on intake and exhaust or all oversized on both intake and exhaust.

I've also been curious to know if anyone has played/ported a head that has one intake port/valve larger than the other(one for volume and the other for velocity within the same cylinder) Is it possible that the smaller velocity port would help pull air into the cylinder through the larger valve on the downstroke?

Searches (even google and bing) so far haven't come up with answer to the above inquiries, possibly because i'm looking for such specific info. Maybe someone will chime in.
(By the way, I've been a forum stalker for quite some time. Here, SuzukiHayabusa, Psychobike, Fireblade, etc., but usually no need to post because I find the answers that I seek)
 

Jacobs

OEM Parts/Accessory guy
Donating Member
Registered
#3
I was told that going to over-sized on a stock bore motor is a complete waste of time, at least on the Gen II. This question is probably better suited for the guys on Psychobike
 
#5
Goldenchild has played with alot of combos send him a PM
Thanks, i'll hit him up. If i have his name right, i see him posting up stuff for sale all of time on a Facebook page. May check with him there.

As for the the bore/engine size, i'm particularly interested in the effects on engine sizes from 1441 up to 1507. I think i'll stick to building a 1441 since i typically see 10-11,000 miles a year and live a humid/rather high temp area(Northwest Alabama). My stock motor may be modified over time for turbo use while i'm rocking the new, bigger one. The larger exhaust valves seem that they would be a good idea. Since tons more air is being sucked in when increasing bore and stroke, larger valves should be able to get more of the hot gases out, but not all theories or good ideas work out as expected.

I picked up a head that has all bronze seats, but the exhaust side is increased +1. I may just give it a try since i plan to order another head with different characteristics some time later. (maybe sooner if don't like the outcome of this one).

Thanks for the replies gentlemen and i hope to become a bit more involved with fellow members than i have in the past!:beerchug:
 
#6
Goldenchild has played with alot of combos send him a PM
Thanks, i'll hit him up. If i have his name right, i see him posting up stuff for sale all of time on a Facebook page. May check with him there.

As for the the bore/engine size, i'm particularly interested in the effects on engine sizes from 1441 up to 1507. I think i'll stick to building a 1441 since i typically see 10-11,000 miles a year and live a humid/rather high temp area(Northwest Alabama). My stock motor may be modified over time for turbo use while i'm rocking the new, bigger one. The larger exhaust valves seem that they would be a good idea. Since tons more air is being sucked in when increasing bore and stroke, larger valves should be able to get more of the hot gases out, but not all theories or good ideas work out as expected.

I picked up a head that has all bronze seats, but the exhaust side is increased +1. I may just give it a try since i plan to order another head with different characteristics some time later. (maybe sooner if don't like the outcome of this one).

Thanks for the replies gentlemen and i hope to become a bit more involved with fellow members than i have in the past!:beerchug:
 
#7
Goldenchild has played with alot of combos send him a PM
Thanks. I sent him a facebook message. I mostly sign on to the forums while at work, but the security on those computers is so restrictive that I cannot complete registration at psychobike. I'll have to do that later
.
I picked up a head with the larger exhaust valve seats because it was a great deal. All bronze seats on both sides and pressed guides also. I figured I could least see what it makes on the dyno and how it performs and if it doesn't work out, i'll just order something different. It would seem to be beneficial to have larger exhaust valves because with a bored and stroked engine, you'll be sucking tons more air. Then you would need to for the hot exhaust gases to escape in order to bring in the fresh, cooler air and fuel. Of course, not all theories and good ideas work out so well.

Thanks for the replies gentlemen.
 

Similar threads




Top