How To Improve Bottom End Without Cam/Head Swap

[bugguy1967]

I built a 1915 longblock a few years ago for a guy. He brought me a 1776 with a CB cam similar to the W125. The 1776 had a worn top end. The engine had 40x35 welded/ported heads, that while they looked to have an excellent finish on the ports and chambers, they also had a very large port volume. Think DRD L7 ports. IIRC, they were 42mm on the long-side of the oval port and 38mm on the narrow side (100% of valve size). The cross section "looked" to be concentric. I assumed they were full race heads with moderate compression chambers.

So I proposed to work with his very tight repair budget by increasing the ccs from 1776 to 1915. Hopefully that would improve the bottom end power for his 65 Bug.

Final specs:
69 DMS crank
Rimco Super Rods
AA 94mm pistons
Rebuilt his heads
Clay Smith CS35, I think. Very similar to a W125.
1.1:1 rockers
44 IDFs 55/135/200/F11, 36mm vents
Welded/ported to match manifolds (short 5 1/2" A-RPM)
1 5/8 header

He finally got it in his car and running a few weeks ago. He took it to a shop and got the carbs dialed a bit. The idle was erratic. It needed to be brought up to 1500 rpm.

He's happy with the drivability. He says the bottom end is so-so. Like a 1500cc. After 4000 rpm, he says it keeps pulling, almost endlessly. His one complaint is that he feels like the engine seems like it will cut off if he were to let friends or his girlfriend drive it. He wants something a little easier for anyone to be able to operate. I'm looking for inexpensive ideas on how to tame it down, without a cam and head swap. I was thinkng:

32-34mm vents
1 1/2" header w/02 bung
Re-jet

Will these help the erratic idle, and improve off-idle acceleration?

[[email protected]]

[DeathBySnuSnu]

Put a heavy flywheel on it.
Should make it easier to let out the clutch without buzzing it up so high first.

Just a thought. No direct experience on that one. I am so light if there was a way to not have a flywheel I would.

[mark tucker]

cb big beef intakes, more cr. .035 piston to head clearance. 1.34 rocker arms., distributor tuned to the motor( recurved or a cb magnespork dist kit)platinum sparking bolts.
if he still needs more. add a 84 mm stroke crank and 5.5 rods. no cam or head swap.

[UK Luke 72]

Advance the cam
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[bugguy1967]

Good stuff. I did think about taller intake manifolds. I think the beefs are 8" tall vs the 5 1/2" ones he has now. It should aid the bottom end some. As for the flywheel, I never considered that, but it would improve idle stability. Not sure about takeoff, unless he revved the engine up before releasing the clutch...

The deck right now is .050". It could use some more cr too. 9.5:1 was too safe of a setting. If I'd done it all over again, I would have upped ot to at least 10.0:1. With 1.25s, maybe a little more.

Seems like more work than I was prepared to do. Readjust deck, maybe flycut the heads a bit more, use ratios, and re-do geometry. It would suck if after all that, it just became more of a cranky beast.

[bugguy1967]

Oh, as for the ignition, it'll all just basic stuff. He only had like $900 to refresh his top end at the time, so I reused whatever I could. He even has basic W8ACs. I told him about a better plug in his range.

Here's the engine before I worked on it:

[MURZI]

More's law.... bigger is better.😀😀. A nice set of 49cc 40x35's and a 1.5 inch exhaust is the cure.....
_________________
62 vert
2276
Tim’s welded heads
45 Dells
A1 sidewinder
Fk44 cam

[Brian_e]

You said you didn't want to swap the cam or heads, so I will suggest tossing a 84mm crank in there.

The only thing that's gonna help a huge port volume and a big cam is way more displacement.

A set of panchitos would also solve all your problems. Do you think his heads are sell-able?

Brian

[vwracerdave]

Stop fooling yourself. The only thing that is going to tame that engine down is a cam & head swap. Changing the manifolds and flywheel will only alter the working RPM range 100-200 RPM. Adding a 84mm crank would help a lot more, but with the cost & additional machine work it'd end up being the same as changing the cam & heads. You can sell your old heads so it won't cost as much as you think.
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[Alstrup]

[Dan Ruddock]

X3 I thinks heads alone should be enough. Dan

[modok]

[Slow 1200]

I don't know that cam but I'm surprised it won't idle under 1500rpm, are you sure there's nothing wrong otherwise with the engine? are all 4 cylinders hitting at idle?

[modok]

I notice cams with seat duration over 300 the idle starts to degrade.
Since different cam companies rate the "seat timing" slightly different ways, and have different ramp designs, where that point is varies from one brand to another.
It might be possible to modify the exhaust system to help matters but many would say its more work than swapping the heads. YES, I think changing intake and exhaust manifolds could help a lot but it sure makes more sense and works better to make the heads right. Exhaust ports may be to blame also, if they are too big. Jam some 1 3/8 tubing slices in the exhaust ports. Tell me what happens. I dare you.

[Alstrup]

[FreeBug]

Not the best idea, but when I put some hogged-out heads from a 1.9 back onto a 1.6, I epoxied up the walls on the intakes, and re-ported them smaller. It held.