2 short stack/bellmouth questions

[Jscobey]

I recall someone doing a dyno run with two short and two long a while back. You can surely find it if you search. IIRC, the shorts gave no real advantage on top but had slight losses in the low and mids. The two long were practically identical at peak, but gave small but noticeable gains along the way.

see thats what i was afraid of. the loss of low and mid range power gives the illusion that your gaining top end. do you know if the bikes were correctly jetted for each set up?

so then what your saying is with two long stacks you dont loose any top end but you do gain a little mid range all the way up?

were these 2 OEM shorts and 2 OEM longs if you remember?

[lloydie]

To use two short you really need hot cams and a full system to make the most of it all

[mik_str]

Not sure if the test bike had been re-jetted, but the trumpets used were the OEM units. FWIW, the best reuslts for a "stock" engine seem to be the long HPower (ie. Dr Honda) stacks. I recall that Markus (aka Tweety) tried them on his dyno back when we had the first batch made and reported no loss in top-end but a significant boost in the lower and mids (up to 5 hp at some points IIRC)......

[VTRDark]

TBH mate I don't think there are many gains to be had from installing different stacks on a standard engine, maybe seat of the pants/placebo, but along with some engine work and correct jetting there would be genuine improvements. I'm also not sure if any gains would show up so well on a dyno as they would being out on the road/track. When I installed the two long OEM stacks there was a definite low/mid increase seat of the pants feel. Quite a bit more Oomph than when I installed stick coils if that gives you an idea.

From what I gather and have read two OEM long equal more low/mid at the sacrifice of top and two OEM short equal more mid/top at the sacrifice of low. The one long one short OEM as Honda intended is either an average across the rev range or the long works better at low end and the short better at high. Two Billet style like Dr Honda (HRC) apparently give more across the range, I suspect more like the OEM long and short but a bit more than average, but as said this comes into play more along with engine work. I have no idea how the mori billets stacks compare against the Dr Honda's but they are more like a billet version of the OEM long and short but more extreme.

Since going from two OEM long to Dr Honda's I have not noticed a vast improvement if any as I have got used to the two OEM long. There is definitely more induction noise with them and it had a greater effect on my jetting which required leaning off. But as far as far as seat of the pants goes, not much difference.

If you want more gains in top end then there are other paths you can take, but remember that one thing is usually a compromise somewhere else. You can then do something else that may even counteract that or add to it. It depends on what other mods and engine work has been done or have planned. All these things have to work in conjunction with each other to produce an end result we want. Whether that be more or less low or more or less high or an average across the board. Then there is the longevity of wear and tear and stress on an engine to compare versus reliability and rideability issues.

(:-})

[Stephan]

Since going from two OEM long to Dr Honda's I have not noticed a vast improvement if any as I have got used to the two OEM long. There is definitely more induction noise with them and it had a greater effect on my jetting which required leaning off. But as far as far as seat of the pants goes, not much difference.

I did exactly the same, and noticed gain in midrange. Sure it depends on actual jetting of each bike, but for me Dr Honda stacks worth every penny.

[lloydie]

To use two short you really need hot cams and a full system to make the most of it all

[tony.mon]

I recall someone doing a dyno run with two short and two long a while back. You can surely find it if you search. IIRC, the shorts gave no real advantage on top but had slight losses in the low and mids. The two long were practically identical at peak, but gave small but noticeable gains along the way.

That would be me, and I posted the back-to-back runs on here, some years back. in Workshop.

Tried two short, two long, and one of each, IIRC.

Doesn't matter about other mods, as it;'s the comparison between the variables, not the comparison to another person's bike or another dyno.

[VTRDark]

It's a bit more complicated than that depending on other mods/engine work. Don't forget possible porting in that to accommodate more airflow Lloyd. And as there is more airflow, with that you may want more fuel and then add oversize valves to accommodate the increase

Playing with the cams alone could give you a bit more top end at the sacrifice of low. Move the torque band around and advance or retard either or both cams. Slot cam sprockets and retard the cams a couple of degrees for more high end or advance for low end. Better still install aftermarket cams designed for a specific job. You could even fit an ignition retarder to give more high end or balance things out from either or both changing cam/cam position and/or fitting Hi comps. Maybe things are beginning to run too hot or burn to fast, so one could fit a larger oil cooler change spark plug temperature etc etc. It's never ending

Exhaust....this could either be a 2 into 1 or even fit shorter end cans, change the state of tune to suit and dial in to everything else. But as I said earlier all these things work in conjunction with each other. One needs to know what they want and which direction to go in, otherwise one just ends up doing things for the sake of doing it without actually knowing what effect it's having by itself or with other changes. For example you could fit short stacks to get a bit more top end and then go and fit an ignition advancer that gives a bit more low...depending on the state of play with everything else, you could end up going around in circles and chasing your tail.

Maybe it would be far simpler to just change the gearing.

(:-})

[Jscobey]

Yea I here you Carl, I deffinatly don't wanna counter one mod with another and work against myself and my wallet. That's why I ask so many questions. I think eventually like distant future, I'd like to go with Mori cams, pistons, valve springs, etc and get a little more out of the top. But I'll start Saving my dimes for all that. I can spare the cash for some HPower stacks though, and also some dyno/tuning time. I don't know how we'll it was set up by the PO with the hindle pipes. So it's a good time to get in there and make some adjustments to get the optimum performance for the stacks.

The HPower stacks which correct me if I'm wrong are similar to the Dr. Hondas. One is the same length as the longer OEM and the and the other is a little longer. Bill from HPower gave me some good info on the stacks and the VtR in general. He certainly knows what he's talking about. He said with proper tuning the longer stacks won't give any measurable loss of top end but provide a few bhp the rest of the way up.

Anyways I won't install them until I get to the dyno and can sort things out properly.

[Stephan]

Jscobey: both Dr Honda stack are the same lenght. By heart it is about 7.5 cm, longer oem has about 8.5-9 cm

[Jscobey]

Jscobey: both Dr Honda stack are the same lenght. By heart it is about 7.5 cm, longer oem has about 8.5-9 cm

how similar are the HPower's to Dr. Honda's? i thought i read they are the same? after re-reading emails with Bill from Hpower, he states "The stacks are both the same length and longer than the longest OEM which are CNC machined from solid"

he also told me that There is no measurable power drop off on the top end on the dyno, even though both stacks are longer than the longest of the two OEM units, but a gain in bhp in the low to upper mid range power

This seems like the best of both worlds. gain in the mid without really loosing anywhere else. one thing that always rings true with bikes is that mods are always trad off's. you gain here but you loose there. you help this but you hurt that. The HPowers give a nice boost in the usuable mid range power without any sacrifice to the top end when jetted properly.

i sprang on a pair so i will let you know how things go. my bikes going off for some dyno/tuning soon as well as having my shock rebuilt and forks refreshed.

[VTRDark]

i sprang on a pair so i will let you know how things go. my bikes going off for some dyno/tuning soon as well as having my shock rebuilt and forks refreshed.

Dr Honda's or HPower? Pics

+1 on Dr Honda's being equal height to each other and slightly shorter than OEM long as Stephen said.

I'm a little confused as I also thought the Dr Honda's are a copy of the HPower stacks. I also thought the HPower stacks are a copy of HRC, therefore they are all basically HRC stacks. Maybe I'm wrong though, it's been so long since I read all the info on them. I expect there may be a few discrepancies between the different brands and they are not an exact clone of each other, especially when it comes to the mounting plate, but the height, doughnut (don't know what else to call the curve around the top) bellmouth maybe! and angle leading down to the carbs should essentially be the same if done on CAD. Maybe mik could shed some light here.

For some reason in my mind I thought there where only ever two styles of billet stacks for the VTR. Moriwaki and HRC.

(:-})

[tony.mon]

It's a bit more complicated than that depending on other mods/engine work. Don't forget possible porting in that to accommodate more airflow Lloyd. And as there is more airflow, with that you may want more fuel and then add oversize valves to accommodate the increase

Playing with the cams alone could give you a bit more top end at the sacrifice of low. Move the torque band around and advance or retard either or both cams. Slot cam sprockets and retard the cams a couple of degrees for more high end or advance for low end. Better still install aftermarket cams designed for a specific job. You could even fit an ignition retarder to give more high end or balance things out from either or both changing cam/cam position and/or fitting Hi comps. Maybe things are beginning to run too hot or burn to fast, so one could fit a larger oil cooler change spark plug temperature etc etc. It's never ending



Maybe it would be far simpler to just change the gearing.

(:-})

That's my bike, pretty much, plus a few other things.
However the engine that's currently in it is standard, which is ok but a little boring, so I've just ordered the high comps and will rebuild the engine the way |I like it.
Only about 120 php, but lots more torque, and useful on the street rather than a track missile.

(and I've changed the gearing as well, but it'll be back to standard gearing once the engine is rebuilt, it pulls like a standard one does when the standard one has lowered gearing due to the extra torque)

[Jscobey]

We'll I'll be able to post more about the dimensions once the HPower sacks arrive. Ill post up dyno results to as well as a few other combos of OEM stacks (2 short, 2long) and also with the HPowers.

[mik_str]

Dr Honda are exact replicas of the long HPower stacks. Far as I know, HPower also made some short ones too, designed for top-end....