Stroking an Evo

[friscofrankie]

So, I've just got this '97 Evo softail. But all my friends ride twinkies. The performance difference is not all that great between the two, but I want to make greater.

I have tried to balance the costs, considered a big bore/stroke combination and have semi-decided to go with a simple stock bore stroker. The only logical stroke for this bike is 4.625.

My build parameters:
Screaming Eagle heads (72cc combustion chamber)
9.5:1 CR
4.625 stroke
.040 quench clearance (squish)
Stock CV card with a dynojet Thunderslide kit
I've looked at several camshaft numbers and have a few in mind, am looking for a broad, flat torque curve so will be going wit a cam with a duration of about 240 - 250 and about .500 - .530 lift. for a 89" motor, larger motor, more lift.

Will be replacing the lifters, bearings, bushings, etc in the bottom end; a complete blueprinted <-(vague term, I know) build.

The problem I am having is locating dished, flat top, FORGED stroker pistons for stock bores. The piston is gong to require a fairly deep dish to meet my CR criteria. I want the dish to match the small SE combustion chamber or even be a bit smaller than the chamber. My rudimentary calculations tell me I need about 7.8 cc dish. Moving the piston .005 further from the head would make it 7.0 cc I think the extra .005 would be better spent squishing the mixture into the chamber.

I've crossed S&S off my list although they did answer the email it was a basic "we don;t have what you want" response.

I prefer to go with Truett & Osborne Flywheels but am flexible, I had thought of Jims but they haven;t answered my email and I am not overly fond of the idea of pressed Flywheel assemblies, but could use their pistons if there was enough meat on 'em to dish. Is there anyone with experience with dished pistons like this or know of a shop or vendor that can provide a piston configuration like this that will live?

While I am asking questions; I originally intended to go with Axtell cast Iron 3.8125 barrels, but decided against it due to all the horror stories about Evo Cases; thought the stock bore stroke would be a better idea. I open the thing up I can takes some measurements and decide for my self, build the stroker and get a top end /case combination for later. From what I understand; I've got about the best set of cases going for an Evo, the question of spigot thickness is one that seems to not have a clear answer available anywhere 've looked. (I've read the thread on this forum, and while quite informative it also is vague on the spigot thickness/model year issue). Does anyone have experience with big bore kits like this in stock late model cases? I could sell this '97 and pick up a '99. Right now, I know of two that I can get, if that makes a difference. I would prefer to start from the strongest base I can and build up as pocket book and time allow.

Due to my location, cases and a cylinder kit would probably cost me over $3000 US. Add in the stroker flywheel assembly and the motor starts to eat my Suspension, brake, wheel & tire upgrades; these ,in my opinion, are equal in importance to adding Torque and HP. Where I live there ain't that many straights and you never know when there will be an elephant around the next bend. I figure I can stroke it for half that (S.E. heads are a given no matter what the configuration), then maybe next year I can add the cases and bore kit. but If I could get by without the cases, I could then reduce the stroke (or not) and go with a top end kit.

I've contacted a lot of vendors via email and got very few responses, the folks at T&O have been helpful but have no answer, S&S and KB at least got back to me. I don't mind staying up and calling the U.S. if I've got to go through a list of vendors as long as my arm long transpacific calls can ring up the telephone bill and there goes those flanders #2 bars I've got my eye on...

[econnor]

The 89" stroker EVO engine (4 5/8" x 3 1/2") does not require new cylinders and your cases will be fine. Most shops that do head work can set your SE heads up. It would be easier, less costly and probably yeild better results to sell those SE heads, buy a set of OE heads and have one of this sites sponsors work over the heads. An 89" Evo can be made to run very strong, but by locking into those SE heads you are making things unnecessarily hard.

[route66paul]

If you really want a twinkie, there are twinkie cases that have evo mounts. That way, you could build a 124, have your cake and eat it, too.

TTC has many different engine combos. The evo platform can be had much cheaper than TC engines, and many cases are very strong. You can get an EVO with 120hp in and evo aftermarket engine for about the same money as doing a big bore, heads and throttle body(just top end). That engine would have a limited gaurentee and would be stronger also.


Good luck.

[friscofrankie]

^^Actually wandered a bit there the cases are for the over size bore second phase just kind of lost the plot there been through so man iterations with this plan.

Getting head work done would mean a trip to the US and back in again (for the heads) the paper work involved so that it returned as repaired item instead of imported item. I've only used branch flowmetrics before and would use them again (despite the name change) their Evo heads have a similar small chamber design that would end up with the same compression issues; but yeah they wold breathe a helluva lot better

Anyway, dished pistons, huh?

[friscofrankie]

Originally Posted by route66paul

If you really want a twinkie, there are twinkie cases that have evo mounts. That way, you could build a 124, have your cake and eat it, too.

TTC has many different engine combos. The evo platform can be had much cheaper than TC engines, and many cases are very strong. You can get an EVO with 120hp in and evo aftermarket engine for about the same money as doing a big bore, heads and throttle body(just top end). That engine would have a limited gaurentee and would be stronger also.


Good luck.

Have a twinkie, ya wanna buy it?

My idea is BUILD a motor, flat top dished pistons. This give me the advantage of having a nice, turbulent Ball of Air/fuel without ridges to climb or slides to go down. I want a max of 9.5:1 CR with the best possible Chamber shape I can get.

I've looked at Edelbrock, STD, S&S and some of the Branch options. For my money I like the SE heads. They all have similar chamber sizes If I were to have a set of heads 'done' it would be these, anyway, although the slightly larger chambers put out by S&S make an attractive "compromise." STD & Edelbrock want too much for their heads although they probably breathe better.

I want the extra inches for he extra torque it will give me wherever I choose to put it. it's no real trouble, just need to find dished pistons or pistons I can machine myself if I can get a piston that can handle the loss of maybe an eighth of an inch from the middle of it's top. The other option is to settle for less and stick with a stock displacement. just not in me. I've been out of the loop and am familiarizing myself with the current market. Seems like so far I've hit a marketing barricade at every turn.

Either way I go to get the inches, bore or stroke, I am gong to need dished pistons to get the quench tight as I want with the compression I want.

Just one lousy set of Dished Pistons! Axtell sells 'em for big bore strokers, I tried them via email; still waiting on that one. Hell , their dished, big bore, stroker pistons even come with an 8cc dish I could live with, if it came in a stock bore! I'm just lookin for options here. I fire another email off in a day or two, stay up late and give them a call maybe that'll work. I have experience with their stuff from waaay back. I trust their quality.

An 89" motor set up right, with 9.5:1 & good breathing gear is going to live like a stocker, and give me 1.1 ft lbs where I want it and a flat curve across the entire power band. I don;t want to enter Dyno shootouts I want to take my laptop, camera equipment a few days of clothes and ride around the mountains in northern Thailand and pass the odd elephant in the middle of hte road.

it is virtually impossible to find premium gasoline in many of the places I ride. Many joints here still are set up in bamboo shacks with hand cranked lift pumps and gravity nozzles. You pump ten liters into the clear tank and pour that into your tank. You change your fuel filter, often. On a lonely stretch of Hiway along the Burmese border yuo take what you can get. It's been a few years since I designed a configuration for a Vee-twin. I am positive my config will do as I ask it. Now it's a matter of finding the hardware. I've given myself some options, but they all seem to involve a dished piston.

I posted this in the Evo Engine mod forum because I want to Mod my engine, not buy someone else's idea of what I should ride.

[route66paul]

cool. Can you put the heads in a lathe and do an inside bevel to open up the compression area? That should allow you to use flattops, you just make the combustion chamber larger another way. I am not sure about evo heads, but TC heads can have this done.

[ripsass]

Try contacting some bigger machine shops and asking if any of them have ultra-sonic tested any of the common pistons for thickness. Then get then fly cut a few thousandths.

I did it once to get .040" for valve clearance with S&S pistons on a stroker. But those were domes though.

[dog155]

Originally Posted by route66paul

cool. Can you put the heads in a lathe and do an inside bevel to open up the compression area? That should allow you to use flattops, you just make the combustion chamber larger another way. I am not sure about evo heads, but TC heads can have this done.

Given your having to cross the ocean and it's costs,this sounds like the best alternative.Getting cr right with the 4.625 stroke will put a smile on your face.Good Luck

[friscofrankie]

Can you put the heads in a lathe and do an inside bevel to open up the compression area?

It's an alternative I've considered. We've got a five axis CNC machine and a program called solid works. The chamber shape is kinda pear shaped and the quench bands are narrow already, this is the main reason for Buying SE heads; those dual quench bands, ya know? but it's doable and might be practical. Id rather dig some material out of the pistons rather than mess with the heads, but it's been pinned as a last resort.

Try contacting some bigger machine shops and asking if any of them have ultra-sonic tested any of the common pistons for thickness. Then get then fly cut a few thousandths.

Yeah, even a mike and a measured rod would do for my application. I've actually asked a couple shops to do this (via email) I'm beginning to think most shops don;t read their email and it looks like I'll be calling across the ocean to get answers. This is the approach I though the best all round, One vendor did get back to me with a dome thickness on their forged pistons of .160". This, I thought a bit too thin to go digging into. it's going to be quite a few thousandths (think hundredths).

Axtell sells blank top domed pistons. They sell dished pistons for big bore strokers. They seem like the shop to deal with, but... Waiting to hear from them (again that email vs phone thing I think). I imagine there's not enough metal for a dish in the dome blanks, things would weigh a ton if there was, but worth looking into further.

The shop that comes up with answers will get the job of providing the wheels, rods and pistons, and probably all the other bits and pieces that go with a build like this.

Getting cr right with the 4.625 stroke will put a smile on your face.Good Luck

YEAH MAN.

[Hillside]

If looking for a BIG bang for the dollar, you may want to consider an Axtell Mountain Motor cylinder kit. Brings 'em to 97", with your stock stroke.
Even with a Wood 6, or Andrews 27 cam, OE carb, and Cycle Shack slip-on mufflers, they'll hover at 95-100 hp and 105-110 ft/lbs over a very broad band.
Fuel economy will be VERY good as well.
Scott

[route66paul]

He has to be able to burn the cheap stuff. This can add unique problems, if you are building for a single consistancy of fuel, that is EZ, but designing an engine to run on many different qualities and have performance is much harder.

Octane is not everything, there can be fuel that has gotten old, fuel that wasn't cracked correctly(well head gasoline), and the like. Add to that the requirements of a high performance air cooled motor and you can have many problems.


Good luck with your build. loosing a few ponies for dependability isn't a bad thing.

[friscofrankie]

If looking for a BIG bang for the dollar, you may want to consider an Axtell Mountain Motor cylinder kit. Brings 'em to 97", with your stock stroke

.

Gotta agree with this, In fact it is one I have on my list. Add in a 4.5" stroke and now we got a motor! my favorite of all the possibilities I've looked at. As I briefly touched on in my Original post, my concern is the cases. 97" sounds better than 89" to me, for sure. Still will always come back to them dished pistons though, ya know?

I'm hoping to hear from some shops or bike owners with experience boring '97 or later cases to, what is it, 4.005" - 4.10" diameter? and then keeping them together. If I could get some real world experiences from some folks I'd love to go this way. the dish would then need to be 12cc but I think Axtell might be able to accommodate that in their listed dished pistons (would know if they responded to email, wouldn't I?) I can bore the cases myself. Stroking would be slightly cheaper but as you said Bang for Buck the Axtell kit would be a higher ROI.

And I believe you to be 100% spot on with your power estimate. Think I'd add an SE 44mm CV though, similar cam timing but more lift for that many inches I think. This motor would be as tractable as stock IMO and live just as long as any motor with that much temptation built in. It all boils down to a 9.5:1 limit with .040 'squish' (+/-), I might fudge a point up or down on that but not much more. A good tight squish creating a highly turbulent chamber mixture is going to make things easier fuel quality-wise combined with that Main Idea, 9.5:1 MAX CR.

If I change the config go big bore or big bore stroker; what I need is dished pistons to use the SE heads. With stock heads and combustion chambers? Not an issue. but then the motor is down for a month. and I am losing what I think is an important design parameter. Guess I'm gong to have to send a second email to Jims and Axtell then back it up with a call... Oh yeah contacted R&R cycles too, no reply from them either...
Why do people have contact forms and mailto: links on their sites if they are't going to answer their emails?

[route66paul]

The great thing here is that speed parts and extra strong cases for EVOs can be had much cheaper. This was my point in my first post. If you want to design your own engine, this is a great way to do so, and you will have a backup just in case something bad happens.

[friscofrankie]

You know? I could use the patience that my age is supposed to have bestowed on me. Give it a clean up bore, install the heads, a decent cam, the air cleaner, Kit the carb, give me enough poop to keep from getting bored, then start buying pieces. Cases, that 103" Axtell/Truet & Osborne combo I like so much, Send my heads to O'Keefe Branch or whatever it's called now. take my time, find exactly what I want, ya know?

Nah, ain't built that way. Now, what I could do, is dump the RK, dump the '97, pick up this '95 fat boy I know about, dirt cheap. Give me a couple more thousand to play with. pull the stock motor, build from the ground up. It's a thought.

Still;
Dished pistons, 9.5:1. Huh?

[blackjackcustms]

S&S stock replacement heads hve bigger chambers and will give youn a way better shot at your 9.5-1 goal. Also, you know that your static comp ratio is only half the story. When you choose your cam, you get to mitigate the actual compression. I once ran 11.5-1 in my 80" with an S&S 600 cam on pump gas for about 8k miles. It was less punchy than my 10.5-1 with an Edelbrock 600, and probably less fun to ride day-in and day-out, but it was'nt gasoline sensitive at all. I would say that if you scale back to the range your in and run 10-1 and a bit more duration and later closing intake you will be fine on far eastern swill. Of course I don't know exactly how bad your gas is......