The bug project...

[Merlin]

The exhaust...

Yes, I know it's in Advice too.

Still need to get some tabs welded on for the tinware, and have them shortened [J-pipes]...mistakes during manufacture.



N.

[Tony Z]

nothing wrong with that pipe. I used one very similar, just with a different silencer system and it supported 94hp no problem

[Merlin]

Sweet.

Calooker reckons we'll be in that region, more or less. No confirmed specs yet.

How do you know what a pipe is good for? IE: What makes one better for this than for that, and if, as an example, this is good for 40 Hp or 400 Hp?

Clue up the clueless here.

N.

[Tony Z]

the air from the cylinders has to get out. If the design leads to the air coming out easily, you will make more power. Look at the dragsters, with very short pipes, air goes straight out. If the exhaust looks like the first one, the box where the pipes come together doesnt promote flow, but looks like it will try to push exhaust from one pipe up another one instead of out, so it will limit flow, hense power. But that exhaust for a stock engine does increase torque thru the rev range.

Having the pipes come together like yours... one exh pulse moving out, helps to draw the next pulse out
The 4 pipes coming together not only helps draw the next pulse out, but increases the torque thru the rev range.
Longer primary pipes = lower rev for max torque
shorter primary pipes = higher rev for max torque
equal length primary pipes = flatter torque curve.
Too small (dia) pipes limits air flow, hense less power
Too big dia reduces air speed hense does not help the next pulse, so less torque with a spikey power and torque curve

thats about it in very simple terms. Look at the pipes and imagine trying to get air out.
Remember air out = air in (into cylinders), more air and fuel in = more max power.

[Merlin]

Thanks. That definately helps.

...so a bigger diameter pipe is going to produce higher revs for more power but less torque? *scratches head*

...and my setup should then have a relatively flat curve, or do I fail Exhaust 101?

N.

[Tony Z]

almost. A bigger pipe will allow the engine to rev higher if the engine is capable of doing so. If its too big, the velocity of the exhaust gas will slow down, which limits the amount it "helps" the other cylinders to exhausts and almost needs to be pushed out, that reduces your torque.

A pipe that is too small in diameter will have great torque down low because of the exhaust gas velocity which will help the other cylinders to exhaust. Think of it as when the gas passes the merged section, it flies out of its tube and into the silencer, leaving a small vacuum in the merge which sucks the next cylinders exhaust out. But you get to the point where the size limits the amount of gas that can be exhausted (friction goes up by the cube of velocity so to double the speed, you increase the friction by 8, or to triple the speed, friction increases by 27 times) so if you max out the speed of the gas, (high rpm, full throttle), the gas is still trying to get thru the merged section when the next one arrives and this causes a backup in gas, which drops the power very suddenly - feels kinda like a car hitting a flat spot, it screams up to that rpm then just stops accelerating even though you know it can go further.....

understand???

[Merlin]

...parts of it.

Figured my powerband would be below max revs already though. Will get the shift points and redline shown on a dyno, and then make a plan from there. Driving by feel is sweet by me, and I'm not pedantic about exact shifts but it'll be interesting to know.

Thanks for the lesson. Will have to save it.

Cheers, N.

[Tony Z]

that exhaust will work fine for your car

[Merlin]

Shot.

The '66 is running one too, same as mine, 'cept flanged.

The 4-2 I showed earlier in the Advice forum was the old one on there, and the same my bee-baa currently has...sounds muuuuch nicer.

N.

[Merlin]

Inside of casing cleared to accommodate No 3 & 4 con rods.

Casing has been refaced and a fresh line-bore done to it.







Al 4 cylinders OEM have been machined 1mm oversize (86.5mm) and honed to take new rings and pistons.



Sleeves prior to painting.



Sleeves painted with 1 coat of heat resistant paint, since taking the pic have received a second coat.



Push rod tubes with 1 coat of heat resistant paint, since takingthe pic have received a second coat.



Rods cleared and polish done to clean the rough edges.









Cam followers taken in for refacing. Will then be hardened and parkarised.

Thanks to Calooker for the info, because all of that went right over my head.

[Tony Z]

sweet, looks like fun

[ZeroAxe]

Those rods are not polished! We have been ripped off!

I am not saying that this hasnt been taken into account, I am purely asking. Have the rods been modified to weigh the same? Otherwise you would have an unbalanced rotating mass. Also, have each individual rod been balanced? Imagine themm mounted on the crankshaft, and then the gudion(sp?) pin end, resting on a digital scale. The weight should be almost excatly the same....

[Merlin]

I have absolutely NO idea what that means, so best I let Calooker rock up here and drop his 0.02

[calooker]

Rods are not fully polished, and will not be either, a complete waist of time doing that for this application, the grinding leaves some ugly rough bits that has been cleaned up (polished) with a lap wheel. The rods are far from all being the same at the moment the whole rotating mass will be going in for a full ballance, this is the early stages of the build, they will be within a gram of each other when done, they have each lost about 30 grams, thanks to the grinding, watch this space.

[Merlin]

R 700 for 4 short braided hoses I'm having made up

If they look real nice, I may suffer and get some more for the engine hoses in the future.

N.