98.8 HP, but need help

[jmmmrm]

OK. I finally got my bike up and running and recently got it dyno'd in. However, I am having a problem and need some help.

My bike is a 1995 900ss, converted to FI (1999 900ss ecu), 3 mm bore, 2mm stroke, ST2 cams at 108 lobe centers, Guy Martin full heads, open airbox, power commander. The first dyno is from when I first got it converted to FI with the ST2 cams and power commander. No head work and stock ECU. As you can see, it pulls to 8300 rpm with a hp of 92.4.




The second dyno is with Guy's heads and a remapped ECU. Run 008 is a full d&d 2 into 2 with no cross over and dyno 015 is with a spaghetti header and termi slip ons. It stops dropping power after 7800 rpm.



Why the drop? I am assuming that it has something to due to the flashed ECU. Sugestions? Also, anyone have a spare ecu (the sandwich type) that I can borrow/buy to narrow this issue down?

Thanks

Mike

[chris steedman]

So the engine has been bored out 2mm and stroked 2mm giving around a 1000cc engine ?

Are you asking why the power falls away at 7800 rpm ?

[jmmmrm]

3mm bore, 2mm stroke, but yeah, about a 1000cc. And yes. In the first dyno, it is pulling out to 8000rpm. Now, with the only difference being head work and computer flash, it really drops off after 7800 rpm.


Mike

[chris steedman]

This is how i understand it.

Your first dyno made approx 90hp at 8000rpm. The second version after the head work - flows more air and obviously seeing the torque peak is higher and earlier in the rev range the heads also have a much better gas velocity speed .

even though the power falls at 8000rpm with the new head it still has over 90hp wich is more than the original at 8000rpm .


If you want the power band to be extended - wich i would also want you have a few options to try .

To maintain VE you can retard the intake cams. The second thing would be to shorten the intake tracts by removing the airbox .

If the 2 obove things dont give the powerband you require then the intake port needs to be enlarged to cope with the engines larger capacity.

[jmmmrm]

The cams are st2 ones set at 108 and the intake manifolds are also made by Guy to match the heads.

I do not think that it is an air issue, but I will remove the airbox and see if that helps.

I really need to get a stock ecu and try that also. I have a feeling that when it got flashed it had too much retardation.

Mike

[jmmmrm]

Well, just got my bike back today. I removed the airbox and installed some pod filters. Here is the result.



It does help out on the top end but I am still getting a steep drop after 8200 rpm. I was also told that I am getting detonation b/w 4500-5500 and on the top end. I guess I will have to have the ECU reflashed after all.

I think it is interesting however that b/w 0-6600 rpm there is no difference b/w an open airbox and the pod filters.

Anyway, broke the 100 mark with 103.

[brad black]

try retarding the cams 5 or so degrees. it'll reduce the pinging and will show if the top end drop is cam related. maybe getting rid of the extra inlet length of the airbox rubber boots helped as well. it's just a case of the next weakest link.

[FunkZ]

Congrats! That is quite an achievement, nearly 50% over stock.

[chris steedman]

Did you fit bell mouths inside the pod filters ? As brad says retard the cam timing 5 degrees . It will reduce the detonation and may give a couple more on top. Any ideas what the compression is with that long stroke ?

[jmmmrm]

Bellmouths were installed in the pod filters and I trimmed the rubber boots that connect them to the throttle bodies. I am going to try to get the pods as close to the injectors as I can next.

I guess I am still in the dark a little bit as to reatarding the cams. I thought that setting the lobe centers at 108 was doing that?

What lobe center should I be looking for then?

I have not checked compression as of yet b/c it still starts easy enough.

Thanks

[chris steedman]

A 966 kit with your added stroke will definatly boost the compression to the high zone. I would stop messing with the tuning and sort the detonation out before you end up re-building the whole engine.

I would change the lobe center to 112 degreed with belts at 10 on the old tension guage scale or 180hz on the new tension guage. When setting belt tension make sure the belt your working on is set at tdc with both valves closed . Otherwise the spring resistance gives a false reading. Are you running 98 octane fuel as well ?

If the cams were degreed to 108 with belts at running tension the engines centerline when running will actually be around 104.

[jmmmrm]

Thanks for the reply. There was no mention as to tension setting in Chris's write up. I did not make it running tight, but snug.

Fuel was 91, no ethanol. I was hoping that I could still use pump gas in the end.

I am going on vacation in the next couple of days, when I get back I will change the cam timing.

Thanks for all the help.

Mike

[chris steedman]

Belt tension must be equal on both cylinders when degreeing the cams otherwise there will be some extra error between cylinders.

The error between tight belts and snug is around 4-5 degrees and very loose 5-7 degrees .

If you degreed them to 108 with snug belts there more like 104 when the bike is hot and running . Fine for a 944 but a 966 with a longer stroke (much higher compression) unless the bulder milled some from the pistons ? 104 centerline MIGHT BE ? to far advanced . I would try 112 with tight belts - it may hit the sweet spot killing your detonation problem and releasing some top end with minimal mid range loss . Its not gospel but its worked for me on some very hi compression 4v engines. When an engine is in detonation it causes a power loss.

[brad black]

without wishing to undermine anything chris has said:

i use running tension when doing 2v cam timing as the first one i did years ago was with V2 cams and that's how they told me to do it. so it's just my convention. overtightening the belts retards the timing, ime about 2 degrees from the running tension setting. certainly on a 4v motor the difference between 3 and 11.5 on the gauge is 1.5 - 2 degrees. i don't have the adaptor kit for the tool to suit 2v motors, but similarly the difference between running and "tight" i've found is about 2 degrees. so my setting of 106 say i'd expect would be 108 overtight.

given i'm sitting in the office having lunch i've just had a look in a few 2v manuals - 900m 95, 99 and 01. the 95 book has a reference to offset keys if required, but no mention of how to check. the 99 and 01 books say to tighten belts to 11.5 on the tool (overtight) and check the timing that way then adj as required, 99 with offset keys, 01 with the std adj pullies.

but with std comp you can usually advance a long way and not get pinging issues at all. my 600m at the std 115 inlet c/l was fine, but 107 inlet c/l was rough at lower revs - the 600 has 11:1 comp std so that's why.

as chris says, i'd retard the cams until it stops pinging. i'd actually do it to see what it does to the top end - it'd be the first place i looked for my missing power. actually, it'd be the second - i'd do runs with lessened ignition advance first, but then i have stuff to do that and you don't so it's not something you can do. unless you can get the ecu reflashed with less ignition advance, which is a better idea in theory, but not so in practice maybe. cam timing is just a setting that you make based on lots of other stuff, and more comp has a clear effect on what you can or should run.

as an example of applications and bad ones thereof - years ago we did a 900ss for a customer with some minor porting and v2 210 torque cams. had a real nice midrange, but fell off quickly. we then sold it to someone else who wanted a 944 kit as part of the deal. the reports below show it all, and what can go wrong when you have high comp and midrange based cam timing.

BikeBoy.org - 900SS CARB WITH SOME VEE TWO CAMS
BikeBoy.org - 900SS CARB WITH 944 KIT

this graph shows my std comp 750 with big vavles and 900 cams, green is 107 inlet c/l, red 119. big difference, 119 not better anywhere http://www.bikeboy.org/graphs/750mg8.gif

this graph shows my high comp 750 motor - green is 113, red 107. as you can see, the 113 has a top end advantge, more so possibly in the shape of the torque curve than actual number, but the shape is the important part. http://www.bikeboy.org/graphs/750mg16.gif

that's why we are saying retard them. we don't know for sure it'll change the shape of power curve, but it's a logical step for the two issues you have. and because no one has built that engine before that we know of, no one knows for sure. it's all suck it and see at this level (then tell us about it so we know too).

think i'd better get back to work.

[jmmmrm]

Thanks for all of the info. When I get back, I will set the cams at 112 and see where that leads me. I would rather do that then haul it 5 hours to have Doug remap the ecu. Will keep you posted.

Thanks again

Mike

[chris steedman]

Brad

No undermining or offence taken

I just checked my file for a 900ss from 2 months ago where i first tested how large the error really was . The error is not as large as i first implied . See below. So it seems the error between very tight and very loose is 5-6 degrees wich ties inline with your snug/running tension vs tight at 2-3 degrees

2v cam timing test 900ssie 18/5/2009
overtight as 12 on guage set to 23/75 = 116 lobe center .
Loosen belt to zero on guage = 28/68 or 110 lc

[908SSP]

Originally Posted by jmmmrm

Thanks for all of the info. When I get back, I will set the cams at 112 and see where that leads me. I would rather do that then haul it 5 hours to have Doug remap the ecu. Will keep you posted.

Thanks again

Mike

If you want to get the most from that motor take it to Doug.

With carbs mine pulled strong 10k. Sorry I can't remember where I timed the cams. I did use variably pulleys and took a lot of time checking it I just can't recall for sure what number I used. I did about 30 dyno runs and remember getting the most power with stock timing specs.

[jmmmrm]

Well I finally got my bike back today.

Changes made were:

1) Switched from dpr9ea to dr9ea plugs
2) Stock manifolds
3) Cams at 112.5

It stopped the detonation which I was looking for. Also, the drop off at the end is not as severe, so it is in my opinion definately a cam thing. (see first post)

I think I will stop here for now until winter comes around. Thanks for all of the suggestions.

[sideways]

We just bought a DS1000SS engine here in Indy. Looking to get over 100HP with a 1080, DP cams, and 2mm over intakes. I rode the last 100+HP S2RS we built and the only problem with the bike was that I didn't own it. This thread is good stuff.

[chris steedman]

[quote=jmmmrm;574955]Well I finally got my bike back today.

Changes made were:

1) Switched from dpr9ea to dr9ea plugs
2) Stock manifolds
3) Cams at 112.5

It stopped the detonation which I was looking for. Also, the drop off at the end is not as severe, so it is in my opinion definately a cam thing. (see first post)

I think I will stop here for now until winter comes around. Thanks for all of the suggestions.



Well done you got the result