The Bullet Board

Ok GHG, I understand the idea. Is there a downside to this? I guess 1 tooth isn't a whole bunch on the cam wheel, but if all other things are equal, why didn't this become the factory timing to begin with? By any chance did you dyno the impact of just this 1 change?

No , I didn't dyno it ... that costs money !! Hahaha ! I save that for the REAL Cams that Scooterbob and me grind ! Haha ! But you tend to get a seance of of things over time . The only down side ... or POTENTIAL down side , is too much cylinder pressure , or possible piston to valve contact. Advancing the intake cam will move the valve and piston closer together at TDC. And I say this ONLY because every bike coming out of that factory MIGHT have some differences in deck height .... Or how deep the piston is down in the cylinder at TDC. BUT... from what I have seen , with the very meek valve lift on these stock cams .... or how deep the the valve goes into the combustion chamber. And with the deck height I have seen on these bike's. It should not be a problem . And yes , I have done this with the stock valve lift. BUT.. it is always a good idea to double check. Too much cylinder pressure over time can wear things out... like your crank pin or your big end bearing or main bearings . Generally speaking , under 200 psi is what you shoot for to keep the motor alive at a static test. I have found that around 165-170 is about the best. Valve timing and compression ratio kind of play together, but that's another thing.

A bone stock motor ... with that worthless auto decompresser removed from the exhaust cam .... will show about 170 psi doing a compression test. So by adding that 20 psi , your still "OK" . But I would run High test. Ideally... you want to match your Cam to your compression ratio, and get back to that lower psi number... but we are cheating things here to get a bit more power .

Why they didn't do it at the factory ? Because they just wanted to design a slow bike and meet emission standards. Over lap , or the amount of time that both valves are open effect emissions. Because you will get some amount of exhaust gases flowing back into the intake. The more overlap the more a motor can pollute. By tightening up the lobe centers on the cams... like advancing the intake.... can pollute . The lobe center's determine the amount of overlap. These bikes from what I have seen , have any ware from from 109-114 degrees of lobe seperation.. depending on things like how the wear is on the cam spindles or how they are adjusted. Anyway ... That is a pretty wide lobe separation for a motorcycle trying to make power. But you will even see that or higher lobe separations in Car cams now a days for emissions, and to keep the EFI sytems happy. More over lap or tighter lobe separation angles can make the air in the intake a bit unstable . Those intakes have a MAP sensor in them , which rely's on smooth air readings. BUT.... as long as you have something on your bike that will automatically tune around the effects of what that MAP sensor is seeing and getting your air fuel ratio to where you want it to be ?........

Thanks for the explanation, Doctor! Sounds like that's getting into potentially scary territory in terms of piston/valve clearances, elevated compression etc. I understand how that translates into more power, but... sounds like that might be getting into places that could compromise reliability. Keeping in mind this is a humble thumper I probably don't need to go there, although I understand the quest for power can be addicting.

I'll get the other mods in place sequentially and see how I feel about it. Honestly just the PC-V with the gutted silencer is making me pretty happy at the moment, so if the new pipe, UNI filter and autotune all work out, I'm hoping to declare victory with that. Which I don't think would compromise any aspect of the ol' UCE design.

Doctor .... Pfffff. I'm just a pipe fitter Swamp , I don't know nuttin' ! Not a huge risk , and easy to do , but yeah just things to consider. One thing ALWAYS effects the other as you know. Your also getting more air in and out of that motor to compress with your intake and exhaust mods. And I agree... one step at a time with the mod's, and stop when your happy. Until you get bored again that is ... Hahaha !

This is a good read Swamp , if your interested. Motorcycle engine or 350 small block V 8 type thing ? . It apply's...

http://www.superchevy.com/how-to/81679- ... mpression/

Interesting indeed! I've never got into cam swapping, but I always thought higher performance cams were really just to improve breathing - higher lift, open a little longer to better match head capabilities. Never gave consideration to the compression impact. Interesting the article points out putting 1.6 rockers on a small block - my 92 year old dad gave me his original owner '84 Corvette as he can't drive it anymore. These were relative dogs (205 HP) due to emission era crap. Part of it was the crossfire intake manifold ports were about 2/3 the opening size of those on the head. I've just finishing port matching the manifold to the head. And also have some 1.6 rockers to put on while I'm at it! Easy cheap mods.

Back to the original issue... received the copper gaskets from Tim, and happy to report the pipe/head sealed right up with one. As it turned out there was a very flat fibre gasket still in the port which came out with some screwdriver prying. But it was beat and obviously not sufficient. Anyway, the pipe looks good and the map that's loaded in the PC-V currently seemed compatible with it - no obnoxious behavior, nice linear response. Will probably get the auto tune wideband sensor put in as the next mod.

Yeah , I kinda figured there would be some of that old gasket still baked in there. Good deal .

Your Fathers Vette is gonna move now ! Hahaha ! Yup easy mods. The 1.6 rocker ratio will shove the valve deeper into the hole.... more lift ! More air ! More duration under the curve. Easy way to get more power , instead of changing the Cam. By comparison , our Enfield's have a rocker ratio of about 1.28 ... Hahaha ! Not a lot of lift from the rockers , so we grind it into the Cams. But.... I DO have some experimental 1.5 rocker's in my hot rod bike and holding up well. Muhahaha ! Made by a friend of mine down in Oz and myself. Yeah ... Cams are EVERYTHING to a motor. HUGE impact on cylinder pressure... as much as compression ratio. You can have a motor with a super high compression ratio and a cam with too much duration ... and have shyte cylinder pressure. The gas pedal might feel like stepping on a wet fish. Haha ! Until the RPM's come UP ! All about overlap and mostly when that intake valve closes.

You can only go so far with intake and exhaust mods to improve breathing ... they do help. But your always stuck with the Cams that are in the motor unless they change . Cams are ALL about how and where and when the motor breaths, and where the power is made . The Stock Cams in these bikes have a very short duration... like you might find in a truck, Hahaha ! , and low lift. That is good for bottom end power. If they just had more LIFT, they would have power in the same area, but more of it. If the duration of the cams were longer... or the amount of time the valve is open ... more mid range and top end power. .. More top speed. It's all a bit of a trade off here and there. When you look at these bikes, you can tell exactly what they were doing and shooting for when you see the Intake , the Cams and valve timing , the compression ratio , and the exhaust. Even when you do a compression test and see that reading ... The motors are very conservative, but they nailed it with what they were shooting for I believe. They are not dumb...


Just as a fun comparison between that Vette motor and the Enfield motor... hahaha !

That Vette motor has a compression ratio of 9.5:1... The Enfield is ABOUT 8.5:1

That Vette motor has a shortish intake duration 202 degrees... and a lobe separation of a whopping 115 degrees. Remember, wide lobe separation and less overlap for emissions ? Cam lift is .269 " or total valve lift of .403" into the chamber at a 1.5 rocker ratio. .430 at a 1.6 rocker ratio. That's a good gain, but be mindful of piston to valve clearance... not sure if that is a concern in that motor or not? But overall , that's probably why that motor may be down on HP. It makes good torque down low with the short duration Cam, but it cant make higher peak HP numbers with the shortish duration. A longer duration cam , would make more HP higher up in the rev's. And the wide lobe separation spreads out the power for the street... but less peak HP. Scavenging works better at Higher RPM's. Not getting much help from the Exhaust Cam either , with only four more degrees of duration I think .

The Enfield motor has a REALLY short Intake duration of only 196 degree's. And a wide-ish lobe separation of lets say 111. Cam lift of .289 or .370 total valve lift at a 1.28 rocker ratio. So the valve is not open very long , and the they do not go into the chamber very deeply. Less air to compress and light off. So ... you get a better picture of why these bikes are slow . Hahaha !

Yeah the L83 vette motor was a dog in a lot of ways - wimpy cam, restricted heads. But the manifold is ridiculous and is the first pinch point in having the motor breathe much above 4000 rpm. In the pic, left port is stock, the right is one I was in the process of opening up. So they're all done now, I think it'll help!

With that said, the car is reasonably fun to drive stock due to the low end torque. I don't really "need" to mod it any more than I "need" to mod the Enfield, truth be told. I spend a lot more time accelerating through the gears to "reasonable" speeds than I do with top end runs - whether it's a car or a bike. With the mods so far, the bike just feels happier - less constrained and more snappy than it used to, but hasn't given up any of the low end pull. I really don't want to lose that character. But if I can have it run stronger for longer, well I guess that's the main idea...

WOW !! You ain't kidding swamp... It really IS restricted ?! Whelp, makes sense they put that small-ish stock cam in there then . Those rocker's should certainly help. Nice work BTW !

swamp2 wrote: ↑Wed Mar 18, 2020 11:24 pm Oh, it's likely just the tip of the iceberg. I actually was considering the 7" LED headlight since I was in there but they're out of stock? Also looked like they got a little pricier than I recalled...

The LED headlight kits are back in stock if you are still interested.