I'm planning an L61 engine build, an this popped into my head. I'm building the engine to run NA, but eventually plan to go boost. My plans are forged bottom end, an overbore (not sure how far I can go with this), 10:1 pistons, port and polished heads, aftermarket valvetrain to handle ~7400rpm and a nice cam, cam will be a turbo grind, LE5 Intake manifold, bigger TB, and an LSJ exhaust manifold and LSJ Injectors until the time for boost comes along.

Register Log In BritBike Forum Forums The Competition Forum T140V or T140 E Performance Heads. Passed on a copy of an article done in 'MotorCycle' Feb 1993 quoting Roland Pike on BSA development of their twin carb racing A7 and found a single large carb did as well with less trouble than with twin carbs. The ad to inspect the bike.

For tuning, I'm planning on using HPT. Can the fuel maps from an LSJ be used for the L61 build to get a baseline tune? I'd just like a rough tune to get the car running and moveable to get it to a dyno or to someone who can take it from there and give it a proper tune. 2002 Cavalier 'LS Sport'. Z yaaaa wrote: i cant remember why eactly but compression goes UP when boring the cylinders.

I actually got into a huge argument with brian speed racer z about this awhile ago on here. When you over bore a cylinder you increase the displacement, slightly but it does go up. When it is compressed into the same space as a stock engine would be (stock head) you are increasing the compression ratio.

Just random numbers for comparasion. 25cc cylinder displacement into a 5 cc head results in a 5 to 1 ratio.

30cc cylinder displacement into a 5 cc head results in a 6 to 1 ratio. And so on and so forth, boring changes a lil bit but changin the stroke adds a whole new world of fun to the math. So whats the final word here, does it go up or down? My way of thinking would lead me to believe that pushing more air/fuel it into the stock head would raise the CR, but the piston doesn't go the whole way to the top of the cylinder wally(I think this is called the deck?), so there is actually more space in the top of the cylinder where the mix is being compressed so there really shouldn't be much of an increase on a.10 or.20 overbore right? Maybe.5 at.20 tops? I'm not pretending to answer the question and know everything lol I am just interested and would like somebody to explain this better so I can understand it.

Whalesac wrote: It was already explained. The head volume does not change (unless you modify the chamber or use flat vs undercut valves). Static compression ratio increases with increased displacement. So, scr increases.

Erd commander 6.5 torrent. This was the part I didn't understand. 'SCR increases with displacement.'

I could see how this would explain an increase via adding stroke. Im still not understanding why its going up with a bore. If the top of the piston went clear to the deck and was only compressing the mix into the head, I could easily understand why it would go up.

You are GAINING space in the top of the cylinder by boreing it, and the engine can only take in as much air/fuel as the valves/cam allow. So here your probably going to get a stronger pulse of fuel via the computer. The volume of the mix shouldn't change because the car can't ADD air, only fuel right? Like I said, i'm not one of those know it all people. This is just the way i'm thinking and if its wrong i'd like to know why, and details on how. How this subject applies to me: eventually i'd like to bore a 2.4LD9. I noticed awhile back that when Quad 4 went to twin cam in 96, the bore went from 3.6in to 3.5in(stroke went up).