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Cams and Rockers cont. from questions and support

7K views 21 replies 3 participants last post by  Silver F 
#1 ·
thank you to everyone who was Helping me with my last post. I intended for it to be a simple question on whether or not anyone had heard of "David E" or steal rockers. But it turned in to way more. I'm glad that it did, cause now I can get down to some class work and do some learning. lol I know a bit more than the average Joe about engines, but the more I learn the more I see I am far from knowing it all. I was asked by Ironmk if I planed to do all the work. I intend to do what I can. But when it comes to machine work that will have to be done by a shop. Preakish asked me about the de-stroke I mentioned and how it would lower my compression. I was hoping that Domed pistons would help to make up for this. I'm hoping to achieve somewhere between 8k and 9k rpms. At this range piston speed gets faster than what you find in an F-1 race car. I have been told that the X can handle it, but I'm not so sure. Thus the thoughts on de-stroking it. There is a lot more I'd like to bring up and ask but i have to go to work. Ill continue when I get off work. thanks again yall.
 
#3 ·
Why so much RPM? There's no need. Look at NHRA cars, they're turning 8k on the limiter at most (not talking top fuel, here).. Nascar engines are turning 9k but are built bullet proof to get there. The reason they do it isn't because they want to, it's because they're displacement limited and need more RPM to get more power. Power is a function of flow. Flow is a function of displacement and rpm. If you get capped on displacement, the only place you can go to is RPM. The VTX is not short on displacement!

If you de-stroke, it's not a compression issue. If you de-stroke and use stock pistons it is, but why do that? Custom taller pistons will make up the compression, but now you're slinging more weight - you've just negated the entire reason to destroke. If you want a light piston, you want a short piston, which means a longer rod. If you're going to spend the money on a custom crank, then you've got the budget for custom billet rods too. Rods are steel though, so they increase their weight significantly more than the piston does as you make it longer... see where I'm going? Not to mention that adding bore to get some displacement back...

You want to start with a short throw engine to begin with if you really want to minimize stroke and maximize RPM. The 1800 is not that engine. Heck, you'd be hitting close to 100 mph with the stock gearing in second gear!

Now, going back to reality, what do you want the engine to do? You can build something streetable that's brutal or build something completely bonkers that's race-only. Revving high sounds awesome, but isn't needed for big power. Maximize port flow, punch out the valves, ramp up the compression, go for moderate duration, maximize valve lift and get some decent valve springs into it, massive intake with plenty of runner volume to feed the heads and direct it all through a 'microsquirt' fuel injection setup and you can realize some great potential. All of this can happen at less than 7k rpm, and the engine can live at those revs if your rotating assembly is properly balanced. It'll probably even do it on stock rods and pistons.

The engines on these really are stout. The decompression lobe is a weak spot, but guys have run these bikes with turbos, super chargers, big bore kits, and though things DO break (always do when racing) it's always at ludicrous power levels and there's rarely any one part that gives up consistently.
 
#4 ·
To be honest I have this ludicrous dream that may never come true considering my current financial status. But I see no reason not to plan and try to work towards it. I want to run it at Bonneville some day. See how it would do as an non-streamlined, naturally aspired, twin cam, V-twin under 2,000cc's. I believe that it could get better speeds than the Confederate Motors Hell Cat. Even though it is over 2k cc's and is a push rod engine. " http://thekneeslider.com/confederate-x132-hellcat-combat-sets-bonneville-record/ ". Hence my attempt to keep the displacement from getting to big. I was hoping to get away with doing it a little at a time. But the more I read the comments the more I realize that a project like this cant't be done in such a way. But If I were to make the attempt. Where should I start? Top end or Bottom end? BTW 100 mph in second gear sounds pretty F-N cool. lol Oh update on my latest race. Got my a$$ handed to me by a Porsche 911 Turbo. It was fun though.
 
#5 ·
So I guess, going by what your telling me Preakish, I should start by 1. Boring out the intake and exhaust ports on my heads and going with Valves to match using stiffer springs. ( spring to reduce the chance for floating valves. I would assume.)? 2. custom cams with larger lobes to increase the rocker lift which translates to maximizing valve lift? 3. Adjust the cam timing to increase compression.? and 3. tougher rockers???? 4. A stand alone fuel system which leads to the need for better airflow (intake and exhaust) then 4. ignition system (power commander). ???? Am I correct? or have I misunderstood you. If I have misunderstood, I'm sorry.
 
#6 ·
power commander just re-program the stock Honda computer. and mainly add time the injectors are open for more fuel....and does not do much to the ignition timing... new computer for injection system and another for electronic Ignition. unless there is a racing one that does both (I do not know)

rockers need to be matched to camshaft. and the cylinder head.. as over rotating the rocker arm can hit the stem casting in the head.. or slip off the valve tip...

the springs do 2 things.... keep the valve closed when needed AND keep the rocker arm in contact with the camshaft.. as rpm's increase the stronger the spring need to be to do its job... and the stronger the springs are the more power from the engine is needed to fight against the spring pressure.

7,000 can be done with out lots of money.. but over that it gets real expensive.. regardless of brand of engine.

do a search on Honda motorcycle racing engine.. a 125 cc 6 cylinder... 4 stroke... I think 22,000 rpms and holds the record ... late 1960's I seem to remember...
 
#7 ·
Silver is right, keeping the RPM to 7 keeps the budget from going into orbit.

Bonneville is a worthy goal and on a shoestring budget can be even more impressive than a well funded race crew -- saftey not withstanding.
The hellcat is neat, but horsepower wise I think you're right: the X can beat its pants off.

Let's look at revs:
Primary reduction 1.571
1st 2.353
2nd 1.478
3rd 1.111
4th 0.871
5th 0.697
Final reduction 3.091

The Hellcat hit 172 mph. The VTX1800 runs a stock tire size of ~27". So at 172mph the tire needs to turn 2141rpm, which means the driveshaft needs to turn 6618rpm, which in 5th equates to 7247 rpm. So we're in the realm of possibility with stock gears - that's good. A taller tire wouldn't hurt, and with the relatively low gearing of these bikes it's not going to hurt too much, but you'll want to choose wisely to keep your rotating mass down. Also, that height figure does NOT take into account the growth of the tire at speeds in excess of 100mph. Some rigorous investigation is in order to determine such things!

The hellcat did it with 150ft lbs and 135hp. The higher torque than HP indicates to me that the engine isn't a heavy breather. Typically when you have a high winding engine, you make significantly more HP than torque, but 'truck' engines make gobs of torque and will usually fall just under the peak torque with their HP. Also, since HP = (rpm*torque)/5252, an engine always makes the same torque and horsepower at 5,252 rpm. This indicates that the hellcat makes it's peak HP under 5,252rpm.

The VTX will make ~80hp at the wheel stock, with about the same or upwards of 90ft-lbs of torque. So we've got a good starting point, but need to basically double the output.

Stock cams are about 240/240 duration. We can push that into 280 territory without losing too much low end grunt. Lift stock is under .400 from what I can find, but I can't find solid numbers. You could probably stick with stock rockers for this kind of build no problem. Eliminate the decompression lobe and spend all the money in heads and pistons.

Webcams lists .460 lift on their bigger cam for the VTX, which leads me to believe that this is near the limit for a stock engine. Getting upwards of .550 or more would be a benefit, but will begin to require clearancing work on the piston tops.

Speaking of pistons, stock compression is near 9:1 if I remember correctly. If going for a bonneville run, are you going to limit yourself to pump gas or are we looking at C10, C16 or C20? If so, we can look at compression ratios in the 14:1 range. If not, we're probably stuck around 11.5:1 max, maybe a tad more depending on where the cam really ends up. The chambers on these heads are wedge shaped with little quench, so good power will come from a domed piston to help turbulate the flow and will require significant design effort and well designed valve clearances. It can be done though, it's not new but it also isn't cheap since the machining is more complex.

In order to take advantage of big lift and long duration, we'll want huge valves. Stock are 36/45mm, or 1.42/1.77, but we have two intake valves so we have a valve area for the intake equivalent to ~1.90 (rough number). I can't find an off the shelf larger valve, but looking at combustion chamber pictures it seems we could get larger valves in there. Probably close to 3mm larger on the intake and 3-5mm on the exhaust.

The next issue is feeding the two intake valves. It's a single runner into two valves. This is where it will get tricky. The runner doesn't have much meat to really open it up, but with a bit of welding and some re-engineering to attach the manifold it could be made to really move some air. Even without welding it can be improved significantly. That said, if you go so far as to cut for better springs, change valve sizes and port it, there's no reason to stop short here.

That takes us to the intake manifold itself. V-twins are challenging because there's so much to pack in so little space. Torque will depend on how much volume you can get into the manifold (plenum size) and horsepower will depend on how much flow can be moved through it. Since these cranks are dual-pin with an effective 180 offset, we're not looking at huge scavenging increases since the pulses are as far apart as can be, but with proper cam design it can be maximized to good effect. Probably. 130-150cc effective runner volume should work and we'll want to have as large a size as possible. Since we're already working with port fuel injection, we don't need to worry so much about port velocity until the actual injector entry point, so the manifold should be as big as possible before the injector. To be able to take advantage of any scavenging the cam designer can build-in, we'll want a common volume, but also want to minimize the turning angles needed by the flow. I imagine two throttle bodies will be needed, with a cross-over tube between the cylinders, but one TB pointed forward (rear cylinder) and one pointed aft (front cylinder). Both should be fed filtered air by a large volume air box. Close to or a fraction of the engine displacement and should be as clean air as possible. This means running SOME ducting to the front of the bike, but it need not be any kind of 'streamliner' work. Look at the snorkels on the Vmax, they'd be a decent place to start. Ram air will definitely help beyond 50mph, and with top speeds in excess of 150mph it will definitely help!

So, all of this would use stock rods, crank, trans and final drive. All should be in absolutely 100% condition if you want to live. Custom pistons, custom work to the heads, custom valves, custom cam, custom springs, with stock rockers and brand new timing chain components.

Then it needs to run. There are standalone systems out there which are affordable and very adaptable. I would ditch the entire stock ECU, ignition and fuel, and run it standalone. The stock stuff can be tweaked with add-on computers, but they won't give you the granular tuning ability that a dedicated system will. Large enough injectors, ignition components, and sensors can be had from the junkyard and the sensors on the engine can be used as well. Getting it all mapped up on the dyno would yield best results, or lots of data logging at the 1/4 -- LVMS does weekend racing to keep the street racers off the streets.

This Link
describes a standalone EFI conversion of a '68 charger and does a great job of illustrating what it takes to run a standalone EFI/ignition system. Lots to learn.

You can piece together some of this. Personally, if I were broke (I am) and I were you (I'm not) but really had a hard-on to do this, I'd start with the standalone EFI. You could blow $10k on all the changes and machine work and then burn it all down with an accidental tweak of the software. You'd be far ahead of the curve to have tuning mastered BEFORE spending your life savings on head work. If I were still you (I'm still not) I'd then move onto the heads or intake manifold. In stock trim the heads out flow the intake, so you could see some gains and put your tuning to use there, and still not have to tear the engine apart. You could design up a system based on mandrel bent tubing and learn to weld (assuming you don't already know) and work on some designs and begin scavenging parts from the junkyard to make them work. After that, you can move onto the heads. I'd pick up a set off ebay and do lots of measuring and investigation. Make friends with local machine shops -- the track is a great place to do this! If you show up with a laptop and standalone system running your bike, I'm betting you'll meet plenty of good contacts in short order. Once you show up with a fabricated intake, you'll definitely get some attention.

Go in stages with the heads. Have them flowed stock. Then open up the valve sizes and pockets and have it flowed. Then work on the ports and runners and have it flowed. Once you break 280 at ~.500 lift you're getting there. Ask lots of questions from the dude doing the flow work too and make sure to use a tube on the cylinder side that is as close to your bore as possible (4", typical for big block motors so it shouldn't be a problem). You'll want good flow at all lift ranges, so if you're at 190 cfm at .400 but 280 at .500 you have an issue... You want max flow at all lift ranges. You'll have to look around at ported head flow #'s for comparable output engines. High power small block V8's will flow upwards of 350 cfm on the intake side with a 2.20 intake valve, FWIW. Once you have your two heads matched, all the cc's match on the chamber and runners, and your valves are ground and seal and your flow #'s coincide with your power goals, find a camshaft place that does custom grinds. Talk to them about what you want and what it means. They'll have to set the camshaft events up to accomplish what you want. Compression, stroke, bore, runner volumes, single-plane intake, it all matters for them so you'll want to have detailed notes on everything. Fast engines aren't black magic, they're science, act accordingly.
 
#8 ·
I think this POST needs a sticky.. LOTS of very useful information for others .. needing this type of information.


Mr. Phreakish again your are very good at describing a very technical area.. Thank You.
 
#12 ·
So I just picked up a back up vehicle, so my wife can keep the 2014 Camry while I'm at work and the X is down. It is a 97 Mazda Miata that I paid $1k for. problem is it wont pass smog. It needs an EGR valve P0400 and is misfiring P0300. So I just spent $200.00 for a new EGR Valve, Plugs, Plug wires and new wiper blades. I had my 16 year old son "help" change the plugs and wires. By help I mean that he did about 90% of the work while I drank a beer and supervised. I showed him how to inspect the plugs for bad singes like excessive oil, corrosion or physical damage and what each of those things might mean. I also taught him how NOT to over tighten the plugs and told him what could happen if they were over tightened. He hopes that one day the Miata will be his lol. I told him he had to help work on it if he wants it some time in the future. He's also going to have to fight his mom for it lol. When we finished with the plugs and wires, I let him start it up. I told him to goose the throttle a bit. lol He taped the pedal and the engine hit maybe 2k rpm's. I chuckled and told him "you can do better than that!". He floored it right up to 6k before backing off. haha chip off the old block. He then proceeded to do it again and again. I thought I was going to have to drag him out of the car to get him to stop lol. The EGR valve will get done this Thursday when I don't have to work. Only one plug gave me any concern. There was a bit to much fresh oil on it. This came from cylinder one. I will also be doing a compression test on Thursday for cylinder one. If it comes back bad. I'm looking at having to dump a bit of money in to it. Either for heads, valves, piston rings or God knows what. My toes are crossed (I can't cross my fingers. I only have two.) that it was just a fluke and I can get away with just replacing the EGR Valve and the Coil Pack.
 
#15 ·
P0300 often times comes back to O2 sensors in my experience. Not always, but it's worth keeping on the radar. I also once had a customer with a chevy pickup that went through multiple sets of plugs, wires, o2 sensors, EVERYTHING you could imagine chasing a P0300 and a notable misfire at part throttle. 2 years and trying EVERY brand of plugs we had or could order and 3x sets of all 6 o2 sensors (header, pre/post cats) AND a whole new exhaust, and we found it was his MAF sensor. cleaned it with MAF cleaner and the problem disappeared for good.

Just a few other things to keep an eye on if the codes and emissions issues persist.
 
#16 ·
Thank you Phreakish and Silver. I went ahead and did the compression test with my son. I only did the dry. I will do the wet after I do some clean up on the carbon deposits. It is a little promising with the engine having 110K miles on it. The results are in order 1-4. 160, 150, 150, 145. The shop manual states that it should have 190 though. I also said that the tolerance in difference is 28 psi. The engine is definitely old, but I don't think its fatal yet. I will check on everything mentioned by the two of you and I may make a new off topic post just for this. The fact is that I'm getting more help here than I am on either of the two Miata forums that I joined. Thanks again, cause I can't start anything on the X, not even the valve adjustment, till the car is reliable and passes smog.
 
#17 ·
Those results wouldn't bug me. If #1 is the one that showed oil, but is the highest compression that also makes sense: the oil is helping to seal that cylinder. With those comp #s, it's probably valve seals and not rings. Though I'm sure the rings are worn, they're not toast just yet. I could also be entirely wrong, but it's still something to keep in mind.

Unfortunately, those engines are cam-over-bucket, so to change the seals is quite a chore. You need to remove the cams and timing sprockets to do it. This also requires setting the cam timing up afterwards, which is the job I hate most in OHC engines.

This video and this video will give you a good idea of what it takes to get to the stem seal, and there's quite a few of them. You need something to hold the valves 'up' while you do the work. You can use compressed air in the cylinder if you have a compressor, or feed rope into the spark plug hole (as shown in the 2nd vid) and rotate the cylinder you're working on up to TDC.

You could also just leave it alone, and hopefully get other parts in good enough shape to pass the smog check. Oil makes it tough to get a clean burn, but I've had cars pass which I never would have thought would. The NV emissions check really isn't too terrible, but is certainly worse than what I'm used to from rural AZ (none!).
 
#18 ·
You are good Phreakish. The number one cylinder is the one that had oil on the plug. I'm hoping its just bad valve seats from carbon build up. And this can sometimes be fixed with oil and fuel additives. I'm going to pick some up on my way to work. I still haven't checked the PCV Valve, on the account of it being past dark when I get off work. I'll check that on Thursday when I change the EGR Valve.
 
#20 ·
I always liked to run synthetic oil, as I found that if nothing else it would wash away all the gunk in the engine. To overcome the high cost, I typically ran it longer between changes (but with regular filter changes). The first few fills it would turn black/brown rather quickly. Within a day or two. By the third or fourth oil change it would stay honey colored for several thousand miles!
 
#22 ·
for what's it worth..(no pun).... I have been using synthetic oil.. Since 1974... Amsoil or Mobil 1.. in everything....car/truck/lawn tractor/generator...MOTORCYCLE, wife's car

oil changes once a year... tractor 2 years.
 
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