imago Posted August 23, 2023 Share Posted August 23, 2023 What's the accepted wisdom for cams on turbo'd engines? The Upperton engine didn't come with cams so I'm using stock ones to run then top end in. That means I have the choice of anything really as I'll need to get a pair no matter what. Engine spec is sorted/checked and welded bottom end, 1168 Wiseco in the middle and a flowed Kat head with larger (EF) exhaust valves. Sat on that will be the draw through turbo with a HSR42 (probably). I'm not going for anything extreme boost/power wise, but I'd imagine a comfortable 175 ish with a maximum of 200 so that it doesn't grenade itself. It'll be road use with occasional pissing about, I don't intend using it for anything else. So my question based on the above is what cams (or cam profiles if I have a set ground) would the experienced boost collective suggest? Quote Link to comment
Paulm Posted August 23, 2023 Share Posted August 23, 2023 Mine has stock bandit cams with adjustable cam wheels Larry,stock ones with no adjustment work fine as well though. 2 Quote Link to comment
Gixer1460 Posted August 23, 2023 Share Posted August 23, 2023 Few builds feature 'turbo' specific cams and at the power level you want, just stick with std ones set with 110 LCs which seems to help with blown engines 2 Quote Link to comment
imago Posted August 23, 2023 Author Share Posted August 23, 2023 I'd have thought they'd run longer duration on the exhaust and a bit more lift on the inlet at least. Still, it does make sense that at low boost there's not much need I suppose. Bonus being it'll save a few bob. 1 Quote Link to comment
Arttu Posted August 25, 2023 Share Posted August 25, 2023 Cam selection depends also on turbo and other parts of the system. If the turbo is relatively big and efficient and therefore exhaust pressure low compared to boost then the cam works pretty much like on a N/A engine. But if the exhaust pressure is higher then cams with shorter duration and especially shorter overlap work better. In practise stock cams are usually a good choice unless you really need something else and know what you are doing. 2 Quote Link to comment
Reinhoud Posted August 25, 2023 Share Posted August 25, 2023 I've got 1mm more lift in my GS1000. My experience is, use the stock timing, everything else creates a poorer / sluggish throttle respomse, and on boost there's no / hardly any difference. What I also know from experience; Say, the GS1000 with "hot" (284 dgrees IIRC) cams won't work on a stock CR, it makes it actually slower/sluggish. How this works with a turbo I have no idea, but probably not well. So, probably best, keep it stock, or close to. 1 Quote Link to comment
imago Posted August 25, 2023 Author Share Posted August 25, 2023 Thanks for the info gents, every day's a school day. In terms of the head, valves and cams then it's turbo ready. I just need to look into the compression ratio now, as it's currently running Wiseco 1168 pistons which they list as 10.25:1. I think it'll be worth getting an accurate measure before I do anything as the changes to the valves may have included a skim. Once I know for sure what I have I can look at the best way to drop it a touch. The info I have read suggests for the relatively low boost I'll be using 9:1 is about right. Quote Link to comment
Gixer1460 Posted August 25, 2023 Share Posted August 25, 2023 From my own experience #1 with a suck thro 1186 kit, 12.5:1 pistons and decomp plate and #2 draw thro EFI 1460 kit with 9.5 CR, the forged pistons can be quite forgiving in terms of higher CR with higher boost. With #1 it got abused with 9:1 CR 10lbs boost and 35 deg timing, #2 equally has had maybe 25-28psi forced in without any issues. If you keep the boost 'sensible' say in the 7-8psi range and maybe give the cams some overlap, you probably won't need to change the CR which also has the bonus of a nice engine off boost. Just my personal opinion - others may disagree! 2 Quote Link to comment
imago Posted September 16, 2023 Author Share Posted September 16, 2023 Just to follow up on this FYI. I had a chat with Dave at FBM to have some questions answered prior to taking it over. Pretty much as above (1168 forged pistons, stock cams with slotted gears) going to check/measure the actual CR and then if it needs lowering a touch a shim for the base gasket tot the required thickness. One other thing came up, and that's to use a standard head rather than the Upperton big valve ported head. Basically it brings bugger all to the turbo party so it will be saved for a NA engine. Quote Link to comment
Gixer1460 Posted September 16, 2023 Share Posted September 16, 2023 I remember Sean @ BigCC had a Dom Trickett EFE head done with equal sized inlet and exhaust valves, fully ported both sides as he figured getting the exhaust out was maybe more important whilst the intake was forced in. As far as I know it lasted barely a few dyno pulls as it just didn't work so got off'd into the pile of failed experiments LOL! Conversely, a big valve will pay off if running big boost if only to minimise ANY potential airflow restriction. 1 Quote Link to comment
imago Posted September 16, 2023 Author Share Posted September 16, 2023 5 minutes ago, Gixer1460 said: I remember Sean @ BigCC had a Dom Trickett EFE head done with equal sized inlet and exhaust valves, fully ported both sides as he figured getting the exhaust out was maybe more important whilst the intake was forced in. As far as I know it lasted barely a few dyno pulls as it just didn't work so got off'd into the pile of failed experiments LOL! Conversely, a big valve will pay off if running big boost if only to minimise ANY potential airflow restriction. That's pretty much the thinking as it'll be running fairly low boost into a bit less than 1200 cc. So although the turbo is capable of providing way more than the engine can handle, getting the (relatively) modest increased huff and puff through won't be an issue on stock cams and valves. Double win really as the draw through is a goer and I'll still have what would be a very expensive to have done head as part of a package to get the most from a NA engine. Quote Link to comment
Reinhoud Posted September 17, 2023 Share Posted September 17, 2023 (edited) 17 hours ago, imago said: One other thing came up, and that's to use a standard head rather than the Upperton big valve ported head. Basically it brings bugger all to the turbo party so it will be saved for a NA engine. Ported / gasflowed defenitly makes a difference! At least, that's my experience.. My gasflowed head gives a way more agressive throttle response, over a ported head. Edited September 17, 2023 by Reinhoud 1 Quote Link to comment
imago Posted September 17, 2023 Author Share Posted September 17, 2023 13 minutes ago, Reinhoud said: Ported / gasflowed defenitly makes a difference! At least, that's my experience.. My gasflowed head gives a way more agressive throttle response, over a ported head. If you're chasing big power then I guess everything you can do is worth it and makes a difference. This is for an air cooled, roller crank, low boost, draw through road bike. So Based on the wisdom of others who've built and ridden way more turbo stuff than me, the maximum advisable safe limit is 200 hp. The thinking being that a ported/flowed head wouldn't give any advantage until you're going above that sort of power. In which case I'll save the head for a normally aspirated air cooled engine where I can use it and a few other bits to get some additional gains over the stock output. Quote Link to comment
clivegto Posted September 17, 2023 Share Posted September 17, 2023 My big valve flowed heads on my turbo bikes make more power than the standard heads. The better these engines can breath the better in my opinion (air cooled & oil cooled) . Your only looking to make 200hp so just turn the boost up Quote Link to comment
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