How much extra gain with a flowed bottom end 31k?

[marrcel]

There is a big ridge between barrel and crankcase at the ports. The shape of the bottom end can be much better.
Apart from different tuning what can be expected? I m not looking for HP above 10krpm.
Thx in advance.

[marrcel]

Any specialist tuners with advice?
Or is my question not clear enough? You can see the shape and size on the gasket. I think it is obvious to dremmel that away. Correct me if i am wrong please?

[dusty350]

It's a good question. I know that if you plan to fit Athena barrels and head, it's worth matching the cases to the barrels for better flow. As I understand it, you lay the Athena base gasket on the crankcase and that shows you how much ally to Dremmel away. Jonw shows a pic in his build thread on his web page. I don't know what difference it makes in performance terms - either standard or big bore. I'm sure Mutts would know

Dusty

[ypvs400]

Its difficult to put a exact figure on the gain but yes matching the cases to the cylinders and making sure the gasket is shaped to suit will improve matters, like all mass produced engines you will find poor alignment and casting shapes causing poor flow.

[Tobyjugs]

The easy way is to get some better gaskets. I have some siamese gaskets. If you like you can try them and send some feedback via pm if i have the correct thickness you need.

[tsa]

Flowing the cases to match the cylinders does very little for power but may benefit initial pickup ie throttle response. It will also make your crankcase compression slightly lower. Is it a good thing to do well yes removing steps where flow is needed is always a good thing as long as it doesnt slow gas speed down by making the passageways to large. It is a balancing act when porting an engine bigger isnt always better. The other thing to consider is that the gasket can become very thin on the outer edges and can leak.

[bare]

Finally :-) Some decent advise.
IF it makes you feel better?
By all means cut the gaskets and Gouge out the cases to match the Cyls.. IF it pleases you/fits into your world views.
Differences ..Maybe ?...only detectable with a seriously sophisticated (expensive) dyno) though

[4l04ever]

I would turn the gasket around before you start matching the cylinder to the shape of the gasket... ;-)

My 31K gaskets are already matched to the cylinders.

[markhoopy]

Jun 12, 2018 14:54:54 GMT 1 4l04ever said:

I would turn the gasket around before you start matching the cylinder to the shape of the gasket... ;-)

I'd turn it over

[muttsnuts]

Kenny has hit the nail on the head, the differences are hardly detectable, and in some cases can have a detrimental affect, it is a balance, if you are careful and just smooth/blend the crank case carefully to the match the barrel it does help flow, but you want to be removing as little metal as possible and be aware of the gasket face on the crankcase getting very thin for the gasket to seat/seal against

the smoother gas flow does help throttle response and if tuning for mid rnage does help, I've not detected any noticeable gains at the top end of the RPM range in terms of BHP or torque, so if you are doing it, don;t expect to gain loads of BHP, its simply doesn't work that way and too big a transfer area is a bad thing

HTH

[LC_BOTT]

So is it a good idea for the Athena/Cub etc barrels, as mentioned above, or not necessary to do it for them either?

[headcoats]

I'm about to get my Athena kit and a bit 50/50 on what to do now as you mention , it makes that gasket surface even thinner !

[muttsnuts]

I tend to smooth the edges and try and make the crankcases and barrels a good transition between the 2 without going daft, I always put the gasket on the crankcases and mark with a felt tip pen, then look at how much material need to be removed and what will be left, if I think its going to leave too little surface for the gasket, then I tend to stop short of the lines I've made

If anybody needs any Athena kits then I have them in stock BTW