Want a 50% horsepower increase over stock in your XS650/750 street bike? Or 65% for a race engine?
The secret ingredient is the porting. Everything else is easily available – cams, 750 kits, carbs, exhaust – proven components that are only a phone call and a credit card away. But, how do you know the porting modifications will actually increase flow across the board and allow the engine’s other components to work as their designers intended?
Harry Lillie ported the XS750 (650) cylinder heads of bikes ridden by AMA Champion Steve Eklund (see Steve and his Lillie-built XS750 winning the Peoria TT in the photo at the right), Scott Pearson, Ricky Graham, and others. That head’s porting is now available in a CNC copy that is accurate to .004” or less. And, it works perfectly on the street!
Fully built, ultra-trick versions of this head have been sold for as much as $1800. You don’t need the scarce, one-off unobtainium bits (or their cost!) for that last tiny race advantage, but you can have the exact same porting for your bike. Mild or wild, the porting is perfect for a hot street bike or an all-out race engine.
The head will support power up to 75 RWHP, at which point the cases and other components will begin to break. It’s just too much for a lower end designed to put up with much less power. On the other hand, when limited to 70 RWHP your engine will be reliable if properly inspected, assembled and tuned.
A stock XS650 engine typically puts out about 42.5 rear wheel horsepower (RWHP). With optimized porting, a 750 kit, decent carbs, an upgraded cam, and a free flowing exhaust, that same street engine will deliver 64 RWHP, an almost 51% increase! The same engine prepared to racing specs will generate 69 - 73 RWHP, a 65% increase!
Even if you are still running 650cc, the head, when coupled with an upgraded cam, free flowing exhaust and decent tuning, will generate about 55 RWHP, an increase of almost 30%!
Yeah, yeah, I hear you saying, but how much does it cost? The answer is $595, which is an absolute steal. And it's guaranteed to flow these numbers:
COMPARATIVE FLOW NUMBERS: STOCK vs. PORTED XS650/750 HEADS
The stock head was not modified in any way and was bead blasted to ensure the ports were clean. Stock valves were fitted. The modified head is the Harry Lillie modified “master” used for modeling the CNC porting program and has approximately 1mm oversize valves.
The results are expressed as a percentage difference at each valve lift increment. I am not sending out the flow numbers because your flow numbers will be different on another bench, and I don’t want to get into discussions comparing apples to oranges.
However, you should see virtually identical improvement over stock (castings do differ) with your CNC head. As you can see, the modified IN ports really begin to kick in at .300” lift, while the EX porting becomes effective between .150” and .200”. The EX porting focuses upon achieving a balance of increased cfm and reduced turbulence, and is sufficient to support up to 75 rear wheel horsepower.
Flow difference from stock head:
VALVE LIFT IN EX
.050” 0% +12%
.100” 0% 4%
.150” +2% 3%
.200” 6% 18%
.250” 6% 22%
.300” 9% 22%
.350” 19% 27%
.400” 37% 25%
.450” 46% 24%
.500” 56% 23%
The stock and Lillie modified cylinder heads were compared in September, 2008 by Competition CNC on their Super Flow 600 flow bench. The tests were conducted within a half hour of one another by the same operator, utilizing the same fixtures and equipment. Both were tested at 28” pressure.
REALITY CHECK: This head was in multiple engines that won in AMA-level flat track competition. There were a few tuners who developed heads with equivalent effectiveness (Jerry Branch, C.R. Axtell, etc.), but nobody ever did it better. These exceptional engines put out 72 - 75 RWHP. That was the limit. Not only could the casting not flow more, but the XS650 cases would begin failing and forming cracks. In 28 years of AFM and AHRMA road racing with this cylinder head porting never once did another XS650-based bike pass me on a straight, where it's all about horsepower.
When some guy says he has a XS650/750 world beater with 80 RWHP, or a head that flows like the OU750 race casting, I'm reminded of the old saying, "When the green flag drops, the BS stops." This porting is the real deal. It offers smooth and linear power delivery, and is a tested and proven winner at the highest levels of competition. (Plus, it works great on the street, as I can personally attest.)
Instructions for Having Your Cylinder Head Ported
► So there is no confusion, you ONLY send the part of the head with the ports in it. You do NOT send the cover, which has the rocker arms in it.
DO NOT SEND A DAMAGED OR MODIFIED HEAD. CASTING CRACKS OR CRACKS AROUND THE VALVE SEATS ARE BAD – BROKEN FINS OR COSMETIC DAMAGE IS OK. THE HEAD MUST BE UNMODIFIED. IF MATERIAL HAS BEEN REMOVED OR ADDED TO THE PORTS OR COMBUSTION CHAMBER, OR THE HEAD HAS BEEN AGGRESSIVELY SURFACED DO NOT SEND THE HEAD. IT WILL BE REJECTED AND RETURNED TO YOU AT YOUR OWN EXPENSE.
1) The full payment of $595 USD must be received before you ship you head.
2) You must pay via PayPal. If you are unfamiliar with the process, you go to paypal.com and click "send" at the top of the page. Then, on the second screen, click "make a payment." It will ask you for my email, which is email@example.com, and then ask for the details needed to make the payment.
If you don’t have a PayPal account it is easy to setup. You can use your bank account, your Visa, MasterCard, Discover, or American Express card or, if you have a PayPal Cash account, you can also use your balance.
3) The total price is $595 USD plus shipping. Terms are full payment up front, and it’s your responsibility to carefully pack up the head and ship it to the CNC shop. Then, when the head is done, you will be notified of the shipping cost, and once that is paid your head will be on its way. It can be sent to you, or the machine shop of your choice for the guides to be installed and the valve job to be performed. An experienced machinist who is extremely familiar with the XS engine and has a complete machine shop is Roger Johnson in Princeton, Kansas. His telephone number is (563) 340-2837.
[NOTE: If your head is rejected and can not be ported, I will refund your $595, but you must pay for return shipping. Once that is received, the head will be on its way back to you.]
1) Call or email me if you have any questions or concerns before you ship.
Craig Weeks - Cell: (510)915-0529 Email: firstname.lastname@example.org
2) To ensure the head isn’t damaged, you will need to inspect it. Carb cleaner, Gunk, bead blasting, brass brush, etc. Whatever works. Then inspect carefully for cracks or damage or evidence of prior modification. As noted above, if there is damage, or the head has been modified, it will be rejected.
3) Send the head “bare.” That is to say, everything is removed but the guides. Springs, valves, etc. must come off. If shipped, they will not be returned, There is no way to keep track of extra components.
4) The head must be packed in a box that will resist shipping damage. A small wooden box is best, accompanied with lots of bubblewrap or other impact absorbing material. If your head arrives in a damaged box, you will be charged for both a new box and shipping. Your local FedEx or UPS outlet can help.
5) Look for the number that is stamped on the head between the EX ports. This number is unique to your head and will be used to keep your head separate from others at CompetitionCNC. When you pack your head in the box, include a piece of paper with your name, address, contact information, and the number you found between the EX ports. Put the piece of paper in a plastic baggie in case the box gets wet. You must do this in case the box is damaged or defaced and your information on the outside of the box becomes unreadable.
6) We recommend you insure the head for at least enough money to replace it if it is lost in shipping. That may mean having to buy a whole new engine, so take that into consideration.
7) When you are informed your head has been completed, you can specify whether you want the head shipped back to you or, if you don’t have a local machinist, it can be shipped directly to Gary Hoos at Hoos Racing or to whomever you have selected to install your guides and do your valve job.
Where to ship your head:
Competition CNC, 130 AP Thompson Road, Longs, SC 29568
Their phone number is (843)390-0031 and their website is competitioncnc.com.
What you get:
1) CompetitionCNC is a busy shop, so you will have a wait. Typically 3 – 4 weeks before your head is done and you are informed it is ready to return.
2) Your head will be shipped to you cleaned, fully ported, and with the old guides removed. If you are building a cruiser, you will probably want to install OEM guides (which last longer) or, if you are building a higher performance engine, the Kibblewhite bronze guides.
3) While you do have the option of reinstalling your stock components, we strongly recommend you use new valve train components, especially a higher performance cam and the 1mm oversize Kibblewhite valves.
4) All purchasers will be provided specs and data to assist your machine shop perform the valve job properly. Additionally, you will receive a writeup of engine build suggestions and initial tuning settings.