GS1000 engine build

[1980c10]

So I've found a '79 GS1000 engine for sale locally, I'm going to pick it up Sunday. The plan is to build it N/A. I'm thinking full dyna ignition, Mikuni rs38 flat slides, 73.5mm 12to1 pistons, and a web cam part# wgs425(109) (70-071)

All the other supporting mods of course, that's just a rough outline.
But I have 3 questions.

1. Will 12:1 run on pump gas without sacrificing timing to avoid detonation?
2. Do I need sleeves to run 73.5mm pistons, or can they be ran with stock sleeves.
3. What kind of power at the wheel should I expect? Goal is around 125hp

[Nessism]

1) NO. 12:1 is too high. 10.5:1 is pushing it but possible (I think)

2) Wiseco makes a 73.5mm kit but the liners are getting really thin. Depends on how much reliability you expect.

3) Not sure

Not what you asked but I think you would be much better off with a 16v 1100 engine. Much easier to get power out of it. Talk to Rapidray. He's our forum engine expert. I think 125 RWHP would be a walk in the park.

[salty_monk]

Try looking at 80GS1000's GSXR suspension equipped build... His 1085 engine sounds similar to what you are trying to achieve & is 8v.

1100 engine (or 1150) is a better base for big power though as Nessism says....

[7981GS]

As Ed said, 10.5:1 is about the limit these days on pump gas.
I have two that are 10.7:1 and the 91 octane available here, even at high altitude, is really pushing it on hot (85-105 degree) days.
I have to add a touch of 100 octane to make/keep them happy.
I think that the cams that you posted are .425 lift? If so, they require shim-under buckets and shims for valve adjustments.
73.5 mm bore is the limit on the 997 (stock 1000) cylinders. I have one that has a little over 70,000 miles on it so far.
A better option would be to use the 1074 cc cylinders (stock 1100 2-valve) and mill accordingly.
And those carbs would be a total waste even if you used the much larger port '80-up head.
Other members may have other experiences to share.

Eric

[Big T]

All good advice so far

But , getting 125 RWHP from an 8V is getting to the edge of reliability. At that goal, you're looking at putting about $2k into the motor alone, and drivability could be an issue

[1980c10]

Well I'm not dead set on the horsepower numbers, they mean nothing. Its going in a hardtail bobber frame. Think muscle bobber lol.

I suppose the real goal would be low to mid 11sec 1/4 mile times, N/A on pump gas.

So any big bore kits people recommend, I've been reading about the big block kits, but I don't think they are made for the 8v 1000 any more.

What kinda combo to take me 11:00-11:50 on pump gas, around 800lbs with me on it? Is it possible with the 8v? I'm open to anything, teach me 8v gurus lol.

[7981GS]

HARD-TAIL, BOBBER?
Just shoot it out of a cannon or push it over a cliff.

Eric

[1980c10]

Am I doing it wrong? My 550 has suspension and my 1000 won't lol.

[1980c10]

Never mind the deal fell through. The hunt continues.

[rapidray]

A 16 valve engine is a bolt in, & will make WAAAAYYYY more power cc for cc. Plus, hot rod parts for the 16 valve 1100 & 1150 motors are everywhere! Ray.

[CocoTiTs]

My 02 gsxr had 12:1. And they still do. I always used pump gas nothin special. Usually 91 but I have pushed 87 through. I like 91 tho haha. Anyways. Also my chevy 350 has 11-1 also run 91. And with cool plugs had no issues with dieselin on me. you can push pump gas to 12:1 no worries.

[Nessism]

My 02 gsxr had 12:1. And they still do. I always used pump gas nothin special. Usually 91 but I have pushed 87 through. I like 91 tho haha. Anyways. Also my chevy 350 has 11-1 also run 91. And with cool plugs had no issues with dieselin on me. you can push pump gas to 12:1 no worries.

It's not so simple. The newer engines have a more modern combustion chamber shape so they tolerate high compression better. 11:1 on an old 2V engine is a BAD idea, as you will have detonation using pump gas, even if the ignition is retarded. And speaking of detonation, most modern cars (not sure about motorcycles) have a knock sensor and when detonation is detected, the engine control module retards the ignition timing. That's one of the main reasons you see such high compression in engines these days.

Of the 2V GS engines, the 650 has the best combustion chamber shape (commonly called "bath tub" shaped. This engine was developed a few years after the early 2V engines and Suzuki must have learned along the way. The 650 uses 9.4:1 compression compared to 9.2 on the 1000 and 8.7 on the 850. Personally, I wouldn't go higher than 10.5 on one of these old engines.

[OLDENUFF]

Liquid cooled engines also run about 100 degrees cooler so they can run a higher compression than an air cooled engine.

[CocoTiTs]

Yeas! U no I forgot about my examplea being water cooled.

But Ed I would like to know more about what your sayin because I don't quite understand the details of why your sayin they work that way.