tuned gs 750 for racing harris f1

[gizzmo]

Hi I thought I'd introduce my self and ask for your help, looking to build a gs 750 engine for classic racing in the uk what would be the best mods in order to achieve around 750 cc that gives performance and reliability any imput would be greatly appreciated.the engine is, t going to be in a gs chassis but in an ex tt race bike from 1984, for those who Don, t know that was the year that the cc class was dropped from 1000cc to 750 for the world tt f1. The bike was fitted with a gsx750 engine but due to classic racing rules in the uk no 16v engines, which is quite a joke, gpz 750 you pull out of your shed yes ex alan jackson isle of man tt 8th placed finish not a chance, alan jackson was a triple f2 world champion from the 1970s and is now alan jackson racing who currently support John mcguiness any help would really be appreciated and I will post some very interesting pictures of some of the bikes that we are running, thanks

 

[steve murdoch]

Welcome to the site.
Can't quite understand your post.
Are you limited to 750cc for your class?
I would have a look at some of the posts from Chuck78. He has some performance 750 knowledge.

 

[GregT]

Some questions come to mind...Are you obliged to stick with 750 or given it had previous history in the 1000 F1, could you go that way ?

The 8V 750 cases I think are longer than the 16V ones, and even if it's had a 1000 in it, it may be tight...

Years back there was a readers special in PB which was an alloy framed works Suzuki which had gone from 1000 8V to 750 16V and back to an ex works 1000 on the road...

 

[gizzmo]

Welcome to the site.
Can't quite understand your post.
Are you limited to 750cc for your class?
I would have a look at some of the posts from Chuck78. He has some
thanks due to the way the classes are set up we all ready are running a preckett and mcnab in Wat is called superbike 1 it's for pure as raced f1 bikes and grandprix machines unfortunately you are racing against tz 750 and alikes in order to take a second bike in another class the nearest one is a class called post classic 750 considering we already have a 750 built in around 83 to 84 that was fitted with a gsx 750 es engine were in but and this is a big but the race club allows for air cooled 8v lumps only itsI personally think because the likes of early formula one bikes just are not out their, manx nortons are far more common, iv been picking up ex street fighter conversations and barn finds for quite a few years and only ever seen 4 pure f1 bikes available got 3 off them and the fourth was far to much work no history in this class would be up against fz600 and gpz750 that's of course unless you can find yourself an ex 750 formula 1 like I said the 84 season was so interesting in many ways that is why the gsxr 750 was built and in 85 they were all on the grid gone were the likes of harris they had to move on straight to the dealership and off you go racing

 

[GregT]

OK Gizzmo, I thought Guy was hard to understand but I get the gist of what you're saying.
Yes, that period around '84,'85 was quick changes - and bikes from then don't always fit nicely into current Post Classic classes.
In some ways, you're in the wrong place. NZ and Aussie have a strong pre 89 class and there are several of those period specials running.
A friend of mine has an ex works Moriwaki CB750 16V in an alloy frame which with it's original works rider on board (Phyllis...) is hard to beat at the big meetings here
Another friend (currently in the IOM) has an Aussie special for which I'm supposed to do the 16Vbig bore 750 engine. It's a GSXR400 alloy frame with the big engine slotted in. Closest they could come to copying the works Suzukis and Moriwakis.
If you've got a spare P&M frame let me know, easy enough to slide it in with a sidecar coming back....

 

[gizzmo]

Sorry greg could help with a complete bike, could also speak to Richard preckett and have one made, it's quite frustrating in the uk a lot of it is very comercial now and the big superbike just Don, t exist other than the likes of gsxr slabside and fz 750 anything pre that is usally a copy with frame geometry of modern superbike and engine combinations that just didn't, t exist in the day last year's classic tt was a prime example 3 of the first 5 bikes were disqualified, and the year before quick shifters were banned so at least the classic club recognise this and have drawn a line under air cooled but no 16v engines which is not really fair for suzuki bikes as their bikes had 16v engines quite a few years before any one else. this is reason for my post I already have another harris 1 with a gpz engine, but would like to have as much information in order to build a 750 cc competitive engine to fit into the second bike for racing purposes, parts are quite ready available here for instance I can get my hands on a xn85 engine,would this work with a over bore? HELP

 

[GregT]

An XN85 would be a good base engine, yes. Plain bearing crank and oil cooling jets too...
AFAIK all the 650's use the same valve sizes so no one head is better than another
Don't know the relevant gudgeon pin sizes but 3mm over should be safe and is stock GS750 8V. Stays under 750 too.
Stock size 750 forged pistons would probably need some machining to adapt but could be a good starting point.
Bigger SS valves, shim under bucket, Ti retainers and good springs should let you use around 12 grand with the right cams.
I'd be looking for around .410 lift and plenty of duration....
Keihin CR's around 31mm bore...

Done proper, maybe 100 at the wheel. Possibly more.

 

[gizzmo]

Thanks greg you say standard forge pistons would the wiseco 740cc ones be sufficient and inlet valves up a size ? Was hoping for the engine take it up to 740cc throw in a set of cams and springs, I or ready have a set of keihin cr33s could develop the engine further but trying to get a base set up with out throwing thousands at it at this point cheers paul

 

[GregT]

If you can source Wiseco 740's, yes that'd work. Inlets up at least 2mm dia.
For the revs it will be capable of, I'd really go for shim under. I've used std Suzuki buckets ground flat on top with no problems, they appear to be hardened right through. I'm actually using modified Nissan aftermarket TI retainers with 10mm shims - because I could get them locally...

Carb size really depends on the size of circuit you run on. Here I'd only use 33's on one or two tracks as most are quite tight, especially the street circuits.

 

[gizzmo]

Thanks greg just making an enquiry on engine so think that would be sorted do you know we're to get hold of the inlet valves from

 

[GregT]

Last lot of replacement stainless valves we needed for the 1000 were made up from Manley blanks by a local head shop.
Price per valve was actually cheaper than buying made up off ebay.
Check with the car performance guys local to you.

 

[Rijko]

someone i know bought, afaik original Yoshimura GS "750" parts from mr. Superbike, Brian O'Shea.

Just for fun here are the 2 pics i have

 

[Rijko]

and nr 2 ..

 

[gizzmo]

Thanks guys for all the help suzuki performance in the uk I think can supply the valves and regrinding cams plus all the other parts I require, spoke to the eligibility officer this evening and all looking promising for the xn85 bored to 740cc I will post a build thread up once we start the build spec will be harris f1 1984 740cc marazzochi m1r forks dymag 17 rear 16in front 300mm brembo disks mid 80s brembo ball pinlock quick release callipers all other bits harris I was lucky enough to get the original harris fairings and mud guard with the bike that were reported unobtainable by Steve harris these have been reproduced, not xr69 repro once again thanks