Which big twin for modifying?

[garethr]

If I wanted to buy a big twin, with the intention of modifying the engine, what should I be searching for?

Evo? Twin cam? M8?
Carburettor? Fuel injection?

I suppose I'd be looking at capacity increase, compression(?), cam(s), head work plus the usual intake and exhaust.

Ideally, the dyno curves would look like those of a stock engine, but with bigger numbers. With that in mind, is there an established best compromise between cost and performance? Is it advisable to go through the bottom end, and what ancillary upgrades would likely be required?

Thanks in advance.

 

[Army]

Re: Which big twin for modifying?

Speak to Alex mate he will inform you of the correct engine and he also offers a superb engine build to your spec

 

[Oddjob]

Re: Which big twin for modifying?

+1 on Alex from Fastlane, he's the man in the know (and a Club Member).

 

[Paul P.]

Re: Which big twin for modifying?

The Evo must be a contender if only for its strong bottom end - many wise people recommend fitting them to shovels. Should be a cheaper project I would think?

 

[chopper]

Re: Which big twin for modifying?

If I wanted to buy a big twin, with the intention of modifying the engine, what should I be searching for?

Evo? Twin cam? M8?
Carburettor? Fuel injection?

I suppose I'd be looking at capacity increase, compression(?), cam(s), head work plus the usual intake and exhaust.

Ideally, the dyno curves would look like those of a stock engine, but with bigger numbers. With that in mind, is there an established best compromise between cost and performance? Is it advisable to go through the bottom end, and what ancillary upgrades would likely be required?

Thanks in advance.

I think the first question is why do you want to do it and what do you want out of it at the other end?
A fast street bike is a very different build to a straight line bike, also things have moved on and a big engine Evo 100", 110" etc is now a stock size M8.
How much of it do you want to do yourself, build and tune or just tune or just pay someone else to build it?
if your gonna ride it you cant just chuck a high power motor into a stock chassis unless you want to watch it slide down the road at the first corner or obstacle you hit, you will need to start with something that can handle the power or factor in a brake and suspension make over into your build

 

[Dazzlin]

Re: Which big twin for modifying?

Final question perhaps is........what's your Budget as this will be the limiting factor as to what is the best bang option for your buck

 

[Fast Lane]

Re: Which big twin for modifying?

If I wanted to buy a big twin, with the intention of modifying the engine, what should I be searching for?

The questions to be answered first are what do you want exactly and how much do you want to spend?

Evo? Twin cam? M8?

Compression is the base of any performance build and that means displacement. Evo's are severely handicapped when it comes to compression. The liners can only be bored to + 0.030" which will net nothing in compression terms. You can get there of course but you have to look at a stroker crank just to get you to the same displacement as the first Twin Cams came with from the factory. It's fairly straight forward to get into the eighties in torque from an 80" Evo engine. The next 10 ft/lbs will cost thousands. Unless you're a die hard Evo lover with tons of spare cash I wouldn't consider one as a base for a high performance build. There are higher displacement crate Evo style engines available from S & S, Ultima, Tom Perone etc but again they're spendy.

The Twin Cam engine is a great base upon which to build. The crankcases are very strong and a stock 88" case can handle being bored to support 124" displacement no problem. Crankshafts are an issue throughout all of the TC production years, all of my higher output builds have the cranks trued, plugged and welded. The early 99-06 models had serious cam chain tensioner issues which are easily fixed. Early heads have issues which again are an easy fix. You can get over 100 ft/lbs of torque out of a 95" engine, over 115 out of a 103, over 120 out of a 110, 140 ish out of a 117 and I would say over 150 out of a 124". There's plenty of cam profiles available to fit every riding style. No major transmission issues, no clutch issues. The Softail range of TC engines have an internal balancer system which works very well. In my opinion the Twin Cam is the best engine to use for a performance build.

The Milwaukee 8 comes in a 107" and a 114" displacement and is proving to be a very popular candidate for huge displacement increases. Bolt on cylinders are available to bump the 107" engine up to 124" and the 114" up to 128". Screamin Eagle have recently released a 131" bolt on kit and a 131" crate engine - both very poor in terms of performance gained for the money spent. New cam profiles are being designed all the time which when combined with these bigger cylinders are producing torque figures well over 130 with stock cylinder heads. With head work many of thse are over 150 ft/lbs. They're not without problems though. The stock transmissions are not designed to handle these huge forces and there are many reports of failures which in fairness is to be expected. There also appears to be ongoing problems with air displacement and associated fluid transfer. The cylinder displacement is massive, the crankcase volume is small - expect problems. The M8 offers huge potential for serious performance but the final cost will be high due to all of the supporting components that take a beating.

Carburettor? Fuel injection?

Fuel injection. A carb cannot be tuned to anywhere near the accuracy of a fuel injection system. Some early TC's came with the Magnetti Marelli fuel injection system - avoid these.

I suppose I'd be looking at capacity increase, compression(?), cam(s), head work plus the usual intake and exhaust.

Yes but with the addition of a good dyno tune with a Power Vision. The heads control how much torque and HP an engine can develop. The exhaust system has a great influence on the shape of the curves - more so with M8 heads. Intake charge velocity determines how much torque can be developed and gas flow through the entire system coupled with the cam timing events and exhaust characteristics control horsepower. All of the components have to be compatible. Get one wrong and you're riding an expensive turd.

is there an established best compromise between cost and performance? Is it advisable to go through the bottom end, and what ancillary upgrades would likely be required?

It's always advisable to start with the bottom end. TC's are known for scissoring cranks, M8's have had a few that I've seen photos of but they seem to be better than TC's. Only a fool would build a high torque, high HP motor on a stock crank. No real compromise between cost and performance apart from expensive parts that just don't work such as the Screamin Eagle range which are designed to be EPA compliant. Most aftermarket manufacturers are not - they sometimes have a sticker saying 'not for street use' which of course gets ignored. Generally the more you spend, the better the outcome will be. Cheap, fast, reliable - choose two.

 

[garethr]

Re: Which big twin for modifying?

Thanks for the replies. Sounds like a TC is capable of far more than I'd ever want.

I'm sure I remember one of the American magazines building a 100bhp Evo engine many years ago, perhaps when it was first introduced. Is that an over-optimistic target?

 

[El Hombre]

Re: Which big twin for modifying?

Thanks for the replies. Sounds like a TC is capable of far more than I'd ever want.

I'm sure I remember one of the American magazines building a 100bhp Evo engine many years ago, perhaps when it was first introduced. Is that an over-optimistic target?

Alex is an expert and the advice given above is not easy to come by. I would go by what he says;-

"It's fairly straight forward to get into the eighties in torque from an 80" Evo engine. The next 10 ft/lbs will cost thousands. Unless you're a die hard Evo lover with tons of spare cash I wouldn't consider one as a base for a high performance build."

 

[watchman]

Re: Which big twin for modifying?

recon we have seen it before very vague ideas lead to vague results and with any project there needs to an accurate goal to work to with clearly defined parameters and aims to give what?s required otherwise the outcome may be less than desirable on many fronts with blame apportioning a big game after the event just like government

 

[garethr]

Re: Which big twin for modifying?

recon we have seen it before very vague ideas lead to vague results and with any project there needs to an accurate goal to work to with clearly defined parameters and aims to give what?s required otherwise the outcome may be less than desirable on many fronts with blame apportioning a big game after the event just like government

It's not a project yet. If it ever is, I'll know exactly where it's going before I spend any money, believe me, and if I decide to do something I take responsibility for the results.

This is just gathering information.

 

[garethr]

Re: Which big twin for modifying?

Alex is an expert and the advice given above is not easy to come by. I would go by what he says;-

"It's fairly straight forward to get into the eighties in torque from an 80" Evo engine. The next 10 ft/lbs will cost thousands. Unless you're a die hard Evo lover with tons of spare cash I wouldn't consider one as a base for a high performance build."

I have a soft spot for the FXR. Just trying to define the limit of affordable Evo performance.

 

[watchman]

Re: Which big twin for modifying?

the fxr is prob one of the best handling frames rigidity wise my one had a john Williams ex rmd 104? sputhe engine in went like stink and could take the frame to the limit he did a frame called an interceptor based on the fxr but far stiffer but could cope with the s+s 124 which back then was the about the biggest evo you could get mad performance coupled to 80s suspension and brakes a scream at the time but technology evolves and some of Alex?s work on twin cams will put one to shame these days and we can stop em too

never did get my interceptor though but they pop up from time to time not many made but all the main insurers know em :angel:

 

[Fast Lane]

Re: Which big twin for modifying?

one of the American magazines building a 100bhp Evo engine many years ago, perhaps when it was first introduced. Is that an over-optimistic target?

No it's not over optimistic - it's pretty mild. 100 BHP is about 85HP. If that's all you're after then use a pair of 12.9cc domed pistons, an Andrews EV46 or later intake closing cam, adjustable ignition, appropriate headwork, Mikuni HSR42 and a decent 2 into 1 exhaust and you're there.

Alternatively use a 103" TC engine. Use any cam with an intake close later than about 40-45 degrees, appropriate headwork and Power Vision dyno tune. Done.

 

[garethr]

Re: Which big twin for modifying?

Thank you again. The replies are much appreciated.

 

[chopper]

Re: Which big twin for modifying?

as Alex said 100bhp is easily done, i had 95bhp on my old evo RK after head work, cam, raised compression and a tuned CV with single fire ignition

as a owner of an FXR id say its a good starting point. you can also drop a Twin Cam into a FXR chassis relatively easily should you go that way