It's amazing what just this can do. Nearly half of your cfm improvement can come from a four angle valve job.barnett468 said:
Porting with flow check or DIY?
- Thread starter Finnigan
- Start date
Get books by Vizard and or AG Bell and read about port shapes and what needs to be done and what should be avoided. Frances (Barnett) included some good points, but there is a lot more to port design that can be fitted into a short reply. I know a little (there you go DOHC) about porting but our GT750 went from 48hp to 78 and one of our CB160 from 11hp to 21.
My comment to Finnigan that DOHC chose to cut for his personal amusement, addresses the fact that the OP has to decide what he is trying to achieve and what his budget it. He can go with Henning/Wiseco pistons and welded and re-machined ports and lumpy cams and have a really sweet relatively high HP bike or he can chose to spend a truck load less cash with a less radical approach.
If it were mine I would go with the mildest megacyclce cam, higher compression and cleaned up ports. Clean up any obvious bumps and what they used to call dingleberries. Match the inlet rubber to the port and clean up the port just behind the seat. Use stock valves, but you can slim/shorten the guides and guide boss. Take your valves and head to an auto machinist with a Serdi machine and do not lap the valves after that. Do not radius cut the seats because they don't flow as well as a series of 15 degree changes.
If you have the cash to get it ported properly and tested, you have the opportunity to correct the whole intake port shape. Short turn radius on intake and exhaust are too small on that head. You can add Devcon F to the intake floor and widen it to maintain area. The exhaust need to be welded and raised, but that is not cheap so focus on the seat and change flow direction to the roof and focus on that.
A good porting guy will have pitot tube probes or smoke probes to test for velocity gradients. Really good shops have swirl meters as well, but that is the exception rather than the rule outside of professional race shops. Once you have the flow readings you can work out the cam that would work best. If for example low lift flow is good but it fails to keep rising, a cam with less lift but more sudden opening would work better than a slow opening cam. It comes down to matching cam and ports. But that isn't necessary unless you are after every HP that there is to be squeezed out and hence my earlier comment about not knowing what you are looking for.
My comment to Finnigan that DOHC chose to cut for his personal amusement, addresses the fact that the OP has to decide what he is trying to achieve and what his budget it. He can go with Henning/Wiseco pistons and welded and re-machined ports and lumpy cams and have a really sweet relatively high HP bike or he can chose to spend a truck load less cash with a less radical approach.
If it were mine I would go with the mildest megacyclce cam, higher compression and cleaned up ports. Clean up any obvious bumps and what they used to call dingleberries. Match the inlet rubber to the port and clean up the port just behind the seat. Use stock valves, but you can slim/shorten the guides and guide boss. Take your valves and head to an auto machinist with a Serdi machine and do not lap the valves after that. Do not radius cut the seats because they don't flow as well as a series of 15 degree changes.
If you have the cash to get it ported properly and tested, you have the opportunity to correct the whole intake port shape. Short turn radius on intake and exhaust are too small on that head. You can add Devcon F to the intake floor and widen it to maintain area. The exhaust need to be welded and raised, but that is not cheap so focus on the seat and change flow direction to the roof and focus on that.
A good porting guy will have pitot tube probes or smoke probes to test for velocity gradients. Really good shops have swirl meters as well, but that is the exception rather than the rule outside of professional race shops. Once you have the flow readings you can work out the cam that would work best. If for example low lift flow is good but it fails to keep rising, a cam with less lift but more sudden opening would work better than a slow opening cam. It comes down to matching cam and ports. But that isn't necessary unless you are after every HP that there is to be squeezed out and hence my earlier comment about not knowing what you are looking for.
barnett468
Coast to Coast
deviant said:
yes and also back cutting the intake valve as i mentioned which is reasy to do . . just doing the intake valve alone will make a noticeable improvement on the flow bench at low lift numbers . . once it is fully opened, the effect is less.
if one has a head that doesn't flow well on the exhaust side, they can compensate for it to some degree by increasing the exhaust duration on the cam.
barnett468
Coast to Coast
Finnigan said:
in general, if you modify an engine with a "bigger" cam, it will have less bottom and and more top end . . there is always a trade off . . if you already have a header, and you want noticeably more top end rpm and power, you must change the cam no matter what else you do.
i also hate vacuum carbs even though they can be made to perform decent for a non racing bike.
just changing carbs will not get you what you want . . if you are on a budget, i would do these things in the following order and stop when it ran how i wanted.
1. get compression up if it is low.
2. exhaust system.
3. small cam upgrade.
4. port head.
5. bigger carbs.
as far as what carb to get, i would like to see people start putting carbs with fuel pumps on, otherwise the standard upgrade is a mikuni vm carb....and a lot of time jetting
lookinif
DohcBikes
Fuck You.
Going back to the original question. Actual port work, not just arbitrary grinding, absolutely requires a flowbench. Period.
90% of gains in port flow are realized within one inch of the valve seat. After a multi angle valve job, you will rarely gain any significant horsepower on an engine your size, regardless of extra port work.
Cfm is less important than velocity. Every increase in flow must maintain port velocity or the work is counterproductive.
As mentioned, polish is bad. Even the wings of a plane are not smooth. Smooth surfaces create a boundary layer which slows flow, and as mentioned allows the fuel to deatomize and drop to the floor of the port.
A professional porter worth his salt will often add as much material as he removes.
Knowing the jargon does not mean you know what you're talking about. It just means you know how to repeat info whether it be good or bad. I find it completely sensless and quite honestly irresponsible to recommend any porting technique that you have not performed yourself. This is a DIY vs. Pro thread. There is no such thing as DIY porting, only DIY grinding ports... You're kidding yourselves.
90% of gains in port flow are realized within one inch of the valve seat. After a multi angle valve job, you will rarely gain any significant horsepower on an engine your size, regardless of extra port work.
Cfm is less important than velocity. Every increase in flow must maintain port velocity or the work is counterproductive.
As mentioned, polish is bad. Even the wings of a plane are not smooth. Smooth surfaces create a boundary layer which slows flow, and as mentioned allows the fuel to deatomize and drop to the floor of the port.
A professional porter worth his salt will often add as much material as he removes.
Knowing the jargon does not mean you know what you're talking about. It just means you know how to repeat info whether it be good or bad. I find it completely sensless and quite honestly irresponsible to recommend any porting technique that you have not performed yourself. This is a DIY vs. Pro thread. There is no such thing as DIY porting, only DIY grinding ports... You're kidding yourselves.
Tune-A-Fish
BOTM LOSER Proudly Deplorable
Nice! I hope everyone is tuned in and learning from the wealth of knowledge, but if not you too can Google it 
crazypj
Split personality, I fake being smart
From what I remember, the entire intake port isn't the best shape to begin with plus it's oversize even for a 460 motor. (which is why they get welded up and re-positioned)
The exhaust port is a little small so needs work, valve size is fine for a lot more power though
The area directly under valve head/seat can be re-profiled for better flow at high rpm with a small loss at low rpm, (using stock cam)
short side turn is way too steep but not a lot can be done about it without pretty major expense.
This actually works really well and will, (to a degree), show where the air is going to be flowing.
You will find area's that need filling to improve flow and port velocity though
The exhaust port is a little small so needs work, valve size is fine for a lot more power though
The area directly under valve head/seat can be re-profiled for better flow at high rpm with a small loss at low rpm, (using stock cam)
short side turn is way too steep but not a lot can be done about it without pretty major expense.
Sonreir said:
This actually works really well and will, (to a degree), show where the air is going to be flowing.
You will find area's that need filling to improve flow and port velocity though
Tune-A-Fish
BOTM LOSER Proudly Deplorable
Find a CRF450 motor and shohorn that puppy in... now you have POWER hahaha!
Tune-A-Fish
BOTM LOSER Proudly Deplorable
crazypj said:
The X is lighting friendly ;D
Interesting read..I usually start off with some calculations to try and come up with intake port flow numbers the motor needs..Jam the head on the flowbench and see what I have and work from there...Cheap evaluation of your head will save you money in the end...People who port heads without knowledge and a flowbench remind me of people who set timing without a timing light..
barnett468
Coast to Coast
motorguy said:
An experienced person can set the timing and the advance curve without a lite, especially on an automotive engine.
Tune-A-Fish
BOTM LOSER Proudly Deplorable
barnett468 said:
I call Bull Shit... Most human ears are retarded a degree or 4
You can set it by vacuum, which is actually better especially for longer duration/higher lift cams that needs 12 or more degrees of idle advance.Tune-A-Fish said:I call Bull Shit... Most human ears are retarded a degree or 4
