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What engine spec for under 18s?

Posted: Mon Mar 13, 2017 2:43 pm
by atlime
Hi All,

I have been busy building an engine over the past few months and got the bug now. Then I noticed BWA and thought I'd like a good at that!!

My question is what sort of spec is usually needed to get under 18s ?

I know it's all down to engine build etc. But a rough idea would help.

I've yet to test my engine as once I'd built and fitted, found the steering on my bus is shocking so I'm now working on that.

Current engine spec below but have been wondering on ripping it out and upgrading various parts.

It's primarily for road use at weekends etc. But don't mind it running a bit rough at low revs if it makes good power high up.

90.5 pistons (1955cc)
76mm crank
Engle 110 cam
1.25 scathe rockers
Lightened balanced flywheel
Twin 40 idf webers
009 dizzy

Re: What engine spec for under 18s?

Posted: Mon Mar 13, 2017 5:10 pm
by vwJim
Depending on the weight of the bus and the CR / heads used, that engine should just about do it. Some very mild 2007cc engines have managed it in the past.

Re: What engine spec for under 18s?

Posted: Mon Mar 13, 2017 10:59 pm
by atlime
CR is mid 8's but was mid 9's. I fitted some copper shims to rule out it running rough (turned out to be carb related)
Heads are new CB 044 so bigger valves but haven't been ported.

Do you think I should be whipping the heads off to be ported and remove the shims to raise the CR?

There's not a lot in the bus other than a rock n roll bed.

Re: What engine spec for under 18s?

Posted: Tue Mar 14, 2017 8:07 am
by vwJim
Personally I'd not use a lightened flywheel and set the CR for road use.

Re: What engine spec for under 18s?

Posted: Tue Mar 14, 2017 8:14 am
by atlime
It seems to drive fine from what ive used it for so far. When I do drop it I'll give an OG flywheel a try to compare.

What's to high CR when it comes to road use?

Re: What engine spec for under 18s?

Posted: Tue Mar 14, 2017 12:45 pm
by vwJim
If it's been built properly in the past, the flywheel should be balanced and paired with the crank etc etc. So swapping it effects the balance of the rotating mass.

CAM's have a preferred CR range, so I'd stick within that range.

Re: What engine spec for under 18s?

Posted: Tue Mar 14, 2017 6:07 pm
by henk
Don't think a w110 will do it for what you want.

Henk!!!

Re: What engine spec for under 18s?

Posted: Tue Mar 14, 2017 7:33 pm
by atlime
Great, thanks guys. Something to think about then. May do a rebuild with 94s and work from there.

Re: What engine spec for under 18s?

Posted: Wed Mar 15, 2017 9:39 am
by orb
There are so many different combos that it's hard to say but as a generalisation you need a minimum of 125hp to run a sub 18 in my experience :wink:

Orb

Re: What engine spec for under 18s?

Posted: Wed Mar 15, 2017 7:29 pm
by atlime
Thanks Orb, soon as the steering is sorted ill be off to the rolling road for final tune and see what is making.

Then I'll be stripping it and starting again! Good job I enjoy it :D