Topic: $500 engine upgrade question-78' cb750k

[Kev Nemo]

So this is hypothetical right now, but here we go.

You have a tuned and running bike with all the basics sorted out for safety and reliablity. Upgrades include bolt-on stuff-pods and 4-1.
You come across $500 that you can spend in anyway on the MOTOR (let's keep it on topic-no brakes, suspension,body,rearsets,whatever)

what do you buy?

[eldar]

Depends on the time you have.
I would say some head work from mike reich and a good cam.

[UnCrash]

Eldar's opinion is mine as well.

Mild port, F2 cam, ape studs, headgasket.

[Kev Nemo]

so how much of a gain hp-wise would that net?

[UnCrash]

That totally depends on the state of your carbureator, how in tune your bike is etc,etc,etc...

But you would find a noticeable difference. MikeR would have a good guestimate.

[Jerry Rxman Griffin aka MuthaF'er]

$500 might get you a 836 kit and the boring plus some heavy duty studs if you're lucky. You still need gaskets, etc. You will notice improved low end with this.

OR - cam, springs, titanium retainers. You will notice improved mid to top end with this.

Double your money and do both. New bike then.

OR - use that doubled money just on the head alone.

NOW - if you have $3000 you can start getting REAL serious.

[hymodyne]

get your head Rieck'd, its well worth it.

hym

[rbmgf7]

what about the ignition system? i hear hondaman's ignition module does wonders.

[MJL]

I hate carbs, so I would start researching and stocking parts for a fuel injection conversion.

[Kev Nemo]

I hate carbs, so I would start researching and stocking parts for a fuel injection conversion.

lol-no kidding Thanks for the advice. I'm new to modded motorcycle field; my previous experience is with my '62 Impala. I started with a tired 235/3 on the tree and ended with a 350/mild cam, Edelbrock intake, Speedway headers and Turbo350 tranny-that's an hp gain you can feel!

[goon 1492]

I hate carbs, so I would start researching and stocking parts for a fuel injection conversion.

lol-no kidding Thanks for the advice. I'm new to modded motorcycle field; my previous experience is with my '62 Impala. I started with a tired 235/3 on the tree and ended with a 350/mild cam, Edelbrock intake, Speedway headers and Turbo350 tranny-that's an hp gain you can feel!

Yeah but do you still have three on the tree or did you give it a four on the floor? and maybe some posi out back?

[doobiebro]

I too would invest in the upper end.  These 750s were so restricted due to emissions standards.  Getting more air through the head will add horsepower with a reasonable cost.  If we open up the head on our bikes for better air flow, you can see a nice increase in gitty up and go.

My reasoning comes through watching NASCAR races.  When they race at the 2.5 mile tracks, they use a restrictor plate between the carberator and the intake manifold.  The reduced air flow through the engine with this plate cuts horsepower by almost 100.  Our motorcycles are so restricted, although not with a plate but with a smaller intake, valves, cam lobes, etc.

[crashedupderby]

turbo

[ieism]

How many miles has this engine run ? Did you do a compression check already? If it's a low mileage bike but you plan to ride it a lot, I wouldn't do an overbore yet..

I would get it ported, and get a streetcam too.

It's the easiest upgrade, and you won't sacrifice much reliability. 

Perhaps it's best to ask MikeR if porting on a 750 without changing the carbs will bring big benefits. I always thought the 750 carbs were also somewhat restrictive.

I couldn't afford to buy a cam from abroad right now, so I went with a ported head, electronic ignition and Iridium plugs on my 550. I might get a hot cam next Christmas if budget allows.

[Jerry Rxman Griffin aka MuthaF'er]

Not likely you'll get much head work for $500. Standard job perhaps without retainers, springs, guides or valves.

[ekim98]

I went with pods,4 into 1 and weight reduction(approx. 60 lbs removed) then go with a mild cam and get the head reworked. Mike has several different porting stages that he can do to fit your engine build. Nothing is free but weight removal cost very little if you are willing to do the work yourself. They say about 1HP for every 10 lbs. or there about. The pods and exhaust are good for about 25 to 35 lbs.?? alone. Helps performance and handling at the same time. And if done right helps the looks some IMO.

[eldar]

Well if he goes with mild port and cam, then the stock valves will do just fine. But then if he wants something hot, well that is hard to do piece meal.

[mlinder]

500 would buy you a stage 2 job from MRieck. It might also get you new guides and guide honing.

Would you net much just from this? Not terribly much, probably. It would be noticeable at the top of your rev range, likely.

However, it WOULD set you up to be ready to use a hotter cam later, for sure. You'd get a whole lot more out of a 200 dollar cam (or hell, even an f cam) with MReicks work already in place. You could bump compression slightly with a custom cometic gasket too.

My opinion, is that if you are ever thinking about hotting up your CB now, or anytime in the future, you'd need to have the headwork done first, or else all the other mods you do down the line will be severely lessened in their effects.