1.8 inlet too big?

[HighLiner]

I have a HPI 54-58mm throttle body with 1.8" intake ports. Is 1.8" too big for 10.5:1 103" in a bagger? Heads will be ported to match!

[HighLiner]

I know it's going to favor the upper end but my 259e cam doesnt wake up til 3000rpm anyhow. I just don't want a pig out of the hole!

[DBChoppers]

I don't think you will like that set up for a bagger unless your blasting light to light.
Try a 1.6" port diameter throttle body with the same size intake port on the heads and the bike won't be too soft down low.
Also use another cam, the 259 is a poor choice for what you are trying to accomplish.

[nw_guy4_fun]

No, it is fine, alot depends on what proportions the rest of the port have. I change the late models to 1.71 and 1.8 when I know the manifold matches that size

[HighLiner]

I think they offer 1.71, 1.73, and 1.76 manifold if need be.

I'm pretty sure the S/E 58mm is a 1.76 and they include that on their stage 4 103".

[HighLiner]

Originally Posted by nw_guy4_fun

No, it is fine, alot depends on what proportions the rest of the port have. I change the late models to 1.71 and 1.8 when I know the manifold matches that size

Even on a little 103?

[INDEPENDENT 1]

I don't think it will be a problem either on a fuel injection bike. With a good tune and the right port work it could bring the torque in earlier and make it hang on longer.

[KingofCubes]

We have used the 1.800" port heads on many 95" and 98" bikes with great success. The difference from our R&R Stage 4- 1.675" port to our R&R Stage 5- 1.800" port is the torque coming on 600-800 later but there is more of it (10 ft. lbs.) so the difference was un-noticable.

[HDWRENCH]

Well what does port to match mean?? Are we talking the welded stage 4 rr or the new cast raised port 5.. or a set that where done in some guys garage??

Being clear on what the head will entail would be much more helpful... Can you run a 103 with a big port yes however you may have give up a tad of low end for more mid and upper.. Cam selection is going to be very important as well..

I ran a stage 5 cast HP head with a 1.800 and a 58/62 FBW( HPI) crane 296 cam and a zilla pipe, it made 100 tq @ 2500 peak numbers 121 tq and 124 hp.. Comp level 10.8 run on 91 pump gas in our heat.. Now is my set up the BEST low end type bike.. I would say not really however it pulls extremely hard with those head and the rest of a matched kit..

I tried 6 or 7 cams , 3 air cleaners, 2 pipes, 2 FBW t/b's and a partridge in a pear tree

DB is correct based on what you have given for info as well King of Cubes.. Is not one item but a complete matched set.. Trying to run bone stock Heads and run a large port may end up getting you into trouble..

Please keep us posted,

[HighLiner]

The heads are yet to be ported or a head porter selected.

[nw_guy4_fun]

Once again the port opening out of the context of the rest of the build and the head sizing is not significant and it is difficult to talk benefits or possible cons. Cam choice, compression, pipe, valve sizes and other factors can have a 1.8 port head act very civil or fall flat on its face in the low end. The term "1.8" port" is used very loosely, consider a 1.8" port where the cross sectional area of the port is not changed just the port opening enlarged at the mouth. Or a port proportionally opened up to compliment the port opening. Two different animals.

When somebody calls me up we have a conversation about how they ride, what the payload is and what their goals are then these decisions are made.
The whole package, not just one measurement.

Sometimes builds go sideways when the parts are not working in sync. This is common and the bike owners spends good money on good parts and the result is underwhelming.

FWIW
My 07 Bagger ran a 107" with a 1.8" port, 10.7:1 with an HQ600 cam and that same manifold before it was ever ridden by me stock. It was very civil and fast until I had a little nikasil issue.

[torqueinc]

If all you have to change is the manifold maybe HPI will swap you out or exchange somehow

If doing a bagger build a 1.7-1.725 intake/manifold opening will flow more than enough air to make enough power to keep you happy and not be soggy anywhere and carry it thru

Based on head/manifold combo alone

Cam pipes and tune will be the rest of it

[petew]

Trust me, I find that with my SE stage IV, it too having the 259E cams, when U want to ride normal instead of light to light it has more tq everywhere than my stock 103 ever had anywhere!!!!! To me it is like the 110 when driven normaly and when the light to light urge happens, it feels like a stage IV 103 that is very powerful.
I used to buy into the belief that everything moved to the right on the tach. And lugging it was all but impossible... Just such a wrong impression, it is a much more powerful machine at every level, much more fun to ride as well. I cannot imagine anyone not being happy with this change done to their motor....