| Author | Topic |
|---|
Location:
Sydney, Australia
Registered:
May 2002
|
 4AGE Bigport v Smallport heads
|
Wed, 17 July 2002 00:48
|
 |
Hi All,
My 100kW conversion is at a bit of a crossroad at the moment, trying to determine which is the better head to use before I go spending any more money. My motor currently has the standard small port head on it.
Now folklore has it that the bigport head with a 100kW bottom end is the combo to have. I suspect this is true for someone with an 86kW and is after more compression/stronger bottom end, but the question is, is it worth scrapping the smallport head for a bigport one? Has anyone ever run a smallport head on a 86kW bottom end to prove the theory? Or is it a case of it just belonging to the "bigger is always better" law, which doesnt always hold true. The motor is planned to stay N/A and may end up with some cams and quad throttle bodies at some point in the (distant) future.
I'd like to hear from anyone who has experience with different 4AGE combos to help me deside which is the best way to go, or what compromises I can look forward to.
thanks heaps fellow toymodders
rgrds
sam
|
|
|
Toymods Board Member
I supported Toymods
Location:
Turramurra, Sydney.
Registered:
May 2002
|
|
Re: 4AGE Bigport v Smallport heads
|
Wed, 17 July 2002 06:06
|
|
There's a thread on this exact topic on the www.club4ag.com forums, with some interesting reading.
I doubt it would really be worth it if you have a 100Kw head in good nick.
|
|
|
Club Member
Location:
sydney
Registered:
May 2002
|
|
Re: 4AGE Bigport v Smallport heads
|
Wed, 17 July 2002 08:38
|
|
Bigger ports = more potential flow, particularly if you are thinking of cams later, on the other hand a small port may have increased air flow speed into the chamber because of the design of its inlets.
I have never seen anyone try to run the smallport head on a 3 rib block but doubt it would be any better than using the 7 rib which has a higher C/R.
the only benefit I could see in using the 3 rib block is that it runs a 40mm main bearing and at high rpm (8000-10000rpm) it is likely that there is less frictional load around the bearings.
|
|
|
Location:
Sydney, Australia
Registered:
May 2002
|
|
Re: 4AGE Bigport v Smallport heads
|
Wed, 17 July 2002 22:44
|
|
Of course I don't recommend a 3rib block over a 7rib one... that was my point, that nobody (to my knowledge) has actually replaced a big port head with a small port one to see if it actually produced more power or less, given no other changes (which might be a bit hard with the different manifolds).
I checked out the thread on the club4ag forums, thanks for that Joel, it is very interesting, the general consensus seems to be that the small port head is the way to go.
I think I have read somewhere that the small port head also has smaller valves as well... so maybe theres some gains to be made there also.
So the question is, how big is big enough, is the small port head big enough and what is to be gained by going bigger. My feeling at the moment is to stick with the small port head, it would be interesting to do some proper testing and check the differences.
rgrds
sam
|
|
|
