M
mrbg19
Guest
Anybody bought one these"high performance" jobs they're selling now ? I'm wondering if the cheapo low-end can handle the stress, I only get a couple of years out stock one's.
Frankenstein
Deceased - Frankenstein 1991 - 2018
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You will need to clarify who is selling these motors you are talking about, some companies upgrades are substantial, others not.. A grubee upgraded motor would probably have very good quality parts and real upgrades. A gasbike version of an upgraded motor might be a copper head gasket and a cylinder that isn't damaged upon arrival.
Please clarify.
I'm talking about the reed valve, Keihin carb and high comp head. I've seen them on piston bikes, gasbike, and a couple of eBay vendor's...
Frankenstein
Deceased - Frankenstein 1991 - 2018
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You should know to avoid at least 2 people you mentioned.
The lower end might hold up, no telling how old it is or what parts ship with it.
You may be better off with a grubee for the next few years... Or go gasbike and expect problems..
Street Ryderz
Well-Known Member
If your a newbie to these kits then a grubee is a better way to go!But if you have some experience with them and are capable of deflashing crappy castings and making sure it's set up right and what to look for then you might be ok with the bargin engines but any savings will be negated by the cost of parts failing or being defective right from the get go!So not really ahead of the game in that sense also kits that come with so called performance parts and upgrades are just marketing tricks to help them sell more product!The reed block and carb you referred to are not matched to the engine very well,the reed blocks effective port volume is 15 mm the intake ports volume is around 17mm and the carb is 16mm also the reed block has a large case volume all these different volumes make the intake flow have a lag!Then the head is by no means a high compression upgrade it's actually 8cc and reduces compression in it's stock form It's only advantage is heat dissipation having more surface area!
gary55
Well-Known Member
I have built two of these gt80 engines, and have one I am keeping for myself. the first two came with the head on the right. It is a 8cc head. It will have 90psi.without removing material from the top of cyl.. .030" will get you to around 125psi. They both run good .Most stock engines with slant plug heads run around 135psi. as the slant head is a 6cc head.
There is a variable in this because the most recent gt80 I received came with the head on the left which is a true 6cc head.
I guess what I am trying to get at is these engines will be of no more abuse to the bottom ends than a stock slant plug head engine.
They will run better than a stock unmodified engine so a viable option for those who don't want to mess with modifications other than deck height pending on head received.. We have changed the keihin carb. out with a mikuni vm 16 and they run a little better.
Check to see which head you get with it. If it's the one on the left your comp. will be good, but the squish will be on the large end.
If it is the center or right you need to deck the jug to get your squish and comp.close to where you want them.
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Street Ryderz
Well-Known Member
Do they have round or rectangle shaped ports? I would prefer the round ones port to flange matching is much easier !The majority of gt 80's that ive seen have the rectangle ports.
Frankenstein
Deceased - Frankenstein 1991 - 2018
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Can I get a close up on your boost port work?I have built two of these gt80 engines, and have one I am keeping for myself. the first two came with the head on the right. It is a 8cc head. It will have 90psi.without removing material from the top of cyl.. .030" will get you to around 125psi. They both run good .Most stock engines with slant plug heads run around 135psi. as the slant head is a 6cc head.
There is a variable in this because the most recent gt80 I received came with the head on the left which is a true 6cc head.
I guess what I am trying to get at is these engines will be of no more abuse to the bottom ends than a stock slant plug head engine.
They will run better than a stock unmodified engine so a viable option for those who don't want to mess with modifications other than deck height pending on head received.. We have changed the keihin carb. out with a mikuni vm 16 and they run a little better.
Check to see which head you get with it. If it's the one on the left your comp. will be good, but the squish will be on the large end.
If it is the center or right you need to deck the jug to get your squish and comp.close to where you want them.
gary55
Well-Known Member
They do have rect, ports. The 40mm intake engines I just got have the round exh. port. Wish they had a third transfer. The gt 80's do seem to wind up a little slower. Probably due to the intake dynamics you spoke of.
