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Post by Mr Kipling on Feb 4, 2023 11:47:02 GMT 1
Hi all , Q for those that run long rod ypvs motors
Does the cylinder head need modding to run with the retuned barrells or do you just use the std head.
Many thxs Mr K
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Post by jon on Feb 4, 2023 11:59:35 GMT 1
The head needs modifying. I’ll get a picture of mine later if you want? Ideally cylinders need the ports dropped too. Strangely Mick Abbey lowered my transfers 2mm but not the exhaust as he said it was better for some reason.
Jon
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Post by Mr Kipling on Feb 4, 2023 12:12:57 GMT 1
The head needs modifying. I’ll get a picture of mine later if you want? Ideally cylinders need the ports dropped too. Strangely Mick Abbey lowered my transfers 2mm but not the exhaust as he said it was better for some reason. Jon Thxs Jon that,ll be great , mick abbey says he can retune the barrells but not the head... |
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Post by midlifecrisisrd on Feb 4, 2023 12:13:01 GMT 1
Yes, as Jon said head needs recutting
Exhaust port on mine was dropped as well
No head gasket, head o ringed
Extra 2mm stroke means piston crown comes out the top of the barrel but stops short of the top ring
Steve
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Post by midlifecrisisrd on Feb 4, 2023 12:14:46 GMT 1
Mutts should be able to do the head as he has oringed a standard stroke one for me so just cutting the chamber deeper
Mick did the porting of mine to slingers map
Steve
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Post by jon on Feb 4, 2023 12:20:04 GMT 1
Mutts should be able to do the head as he has oringed a standard stroke one for me so just cutting the chamber deeper Mick did the porting of mine to slingers map Steve Yes, Dave did mine. Jon |
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Post by jon on Feb 4, 2023 12:21:00 GMT 1
Mutts should be able to do the head as he has oringed a standard stroke one for me so just cutting the chamber deeper Mick did the porting of mine to slingers map Steve My exhaust port was lowered, but not by 2mm on Mick’s suggestion. Jon |
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Post by midlifecrisisrd on Feb 4, 2023 12:26:10 GMT 1
Here's my head Water jacket is sealed with a smear of rtv Steve  |
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Post by jon on Feb 4, 2023 12:32:38 GMT 1
Just to be clear with the title of this thread “long rod YPVS 385 tuning”, the long rod is nothing to do with the fact the cubic capacity is increased to 385cc (with 0.5mm over pistons). It’s the +4mm of stroke. You could have a +4mm stroke crank with standard length rods. Long rods and ideally lower crown height pistons has the advantage of reduced piston side thrust and so less wear and friction(heat).
Jon
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Post by davecroucher57v on Feb 6, 2023 16:49:55 GMT 1
The head needs modifying. I’ll get a picture of mine later if you want? Ideally cylinders need the ports dropped too. Strangely Mick Abbey lowered my transfers 2mm but not the exhaust as he said it was better for some reason. Jon keeping the heat off the front of the piston. |
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Post by jon on Feb 6, 2023 17:52:14 GMT 1
The head needs modifying. I’ll get a picture of mine later if you want? Ideally cylinders need the ports dropped too. Strangely Mick Abbey lowered my transfers 2mm but not the exhaust as he said it was better for some reason. Jon keeping the heat off the front of the piston. |
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Post by jon on Feb 6, 2023 18:00:04 GMT 1
Who knows? At first it sounded perfectly feasible not allowing hot gasses not to be blown across the entire area of the dome. Then I thought this back pressure occurs when the piston is covering some/most of the exhaust port.
Jon
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Post by Tobyjugs on Feb 6, 2023 19:41:21 GMT 1
The tuner I use did some serious development work to make a high power 50cc engine. He always tried to explain everything to me, but sometimes it would go in one ear and out the other. One of the things he learned was at a certain state of tune he could get more power by raising the bottom of the exhaust port higher.
They were aiming for 27pk I think the most they manage to get was 26pk but not constantly.
They could only get 24pk constantly.
I once watched a video of a young Dutch lad racing in the freetech class. His bike is making 20pk. He mentioned this in the video and in the comments below there was so many negative remarks by so called experts telling him he was a dreamer and it wasn't possible.
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Post by muttsnuts on Feb 6, 2023 21:21:37 GMT 1
depends on the porting you are doing and what BTA (Blowdown Time Area) you are aiming for, sometimes the only way to get the BTA you want is to leave the exhaust port higher than BDC, its not detrimental to performance and can under certain states of tune as people have mentioned improve it.
I tend to floor my ports but that's to get the BTA I want, although I am always playing with different setups, just need more time to play with them and get them tested on the dyno to know which is best/better, if at all
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Post by jon on Feb 6, 2023 21:54:29 GMT 1
I’m pretty sure once you’ve gone to the trouble of bigger carbs, expansions, longer stroke, optimised squish/volume and porting there is not going to be as much difference between the choices as there will be over the stock setup. We will see?
Even the same engine can make different power on different days purely down to the weather.
Jon
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Post by Tobyjugs on Feb 7, 2023 3:04:26 GMT 1
Well one of my engines with modifications and jetted correctly made 48pk with standard pipes, it was nice to ride long distances on the motorway.
The same engine fitted with TSA's and jetted to suit made 60pk no other changes. Not so nice on the motorway but great fun on the A roads.
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Post by midlifecrisisrd on Feb 7, 2023 8:57:14 GMT 1
Tony's point above I'd an important one
Peak hp is one thing but drivability is another
The biggest benefit I see from a 385 is midrange torque
Yes you can get 80hp out if them but make sure it's not at the expense of drivability in normal use
Steve
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Post by jon on Feb 7, 2023 19:00:30 GMT 1
Tony's point above I'd an important one Peak hp is one thing but drivability is another The biggest benefit I see from a 385 is midrange torque Yes you can get 80hp out if them but make sure it's not at the expense of drivability in normal use Steve I couldn’t agree more. The measure of a bikes performance/power is not the peak HP, its the amount of area below the curve. I’ve heard of scooters built for bragging rights giving maximum peak HP. Great dyno printouts, be crap on the road. Steve’s reason is also mine for putting together a 385. Jon |
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Post by Mr Kipling on Feb 7, 2023 19:47:58 GMT 1
The vertex pistons i,m using dont come outta the barrells they sit flush with only the domes sitting proud above like standard pistons....
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Post by muttsnuts on Feb 7, 2023 20:07:17 GMT 1
The vertex pistons i,m using dont come outta the barrells they sit flush with only the domes sitting proud above like standard pistons.... that's interesting, either you've got some odd pistons (what's the part number on the vertex pistons and I can check), or the crank you have is an old hotrod 4mm stroked with 110mm rods, which they don't do anymore, was a great crank as it meant you could fit stock pistons. The only crank you can get now with 4mm stroke for these engines is the 4111 crank, which has the 5mm longer rods fitted Is the crank a new one, or as it been overhauled? The only only option is if you've got 2mm spacer fitted underneath the barrels ? Any photos you have might help, but sounds odd |
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Post by Mr Kipling on Feb 7, 2023 20:12:32 GMT 1
Hi Dave the crank is new, i,ll check the part number out tomorrow same with the pistons and i,ll dig out my crankcases an take some pics of it all together...
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Post by Mr Kipling on Feb 8, 2023 14:49:38 GMT 1
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Post by jon on Feb 8, 2023 19:18:15 GMT 1
Yes that looks about right. Send your head to Dave and he can sort it (assuming he has time right now?).
Jon
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Post by muttsnuts on Feb 9, 2023 19:59:42 GMT 1
yes that's correct, measure the distance between the barrel and the edge of the piston (with a base gasket fitted and the barrels held firmly by the fixing nuts) and let me know what it is if you send the head, then I can machine the squish to exactly 1.2mm or tighter if you want tighter
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Post by jon on Feb 9, 2023 20:23:06 GMT 1
If you do as above torque the cylinders down first. I notice they have no nuts at all at present.
Jon
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