OBR Pro Stock Head

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Odr

Member
Messages
7
Hi guys. Im a newbie on this forum. Im from South Africa and i purchased a OBR Pro Stock ported 30.5cc upgrade kit with a stuffer crank. All fitted well. The compression felt high . After running in the motor i tuned it . Put it up against a 30.5 hi rev king motor car and got a thrashing of note. The cars are of similar weight and both are tuned by me.
What could possibly be the problem.
 
Hi guys. Im a newbie on this forum. Im from South Africa and i purchased a OBR Pro Stock ported 30.5cc upgrade kit with a stuffer crank. All fitted well. The compression felt high . After running in the motor i tuned it . Put it up against a 30.5 hi rev king motor car and got a thrashing of note. The cars are of similar weight and both are tuned by me.
What could possibly be the problem.
he bud welcome (y) id put it down to gearing :unsure:(y) what are the spur and pinion setups for both cars? and what pipe has each car got ? coz that will also play a big part(y)
 
he bud welcome (y) id put it down to gearing :unsure:(y) what are the spur and pinion setups for both cars? and what pipe has each car got ? coz that will also play a big part(y)

Both cars are running stock gearing 57/17 and the same pipes. Dominator shortys. The only differances are the heads. The OBR is 2 bolt while the King Motor is 4 bolt
 
Both cars are running stock gearing 57/17 and the same pipes. Dominator shortys. The only differances are the heads. The OBR is 2 bolt while the King Motor is 4 bolt

Sorry one other difference is the OBR set up is running the chokeless 813 and the 30.5 King Motor is the stock carb 668
 
The 990 carb is exactly the same as the 813 except the 813 has a pump jet which eliminates bogging . The 1107 has tje same bore size as the 813 except the venturi is about 1mm bigger
 
The 813 has an accelerator pump, not an additional jet, and most that have used them have found them to be problematic after a little run time. For performance sake the 813, 990, and 1107 are basically the same. I would personally not reccomend the 813. Depending on what cylinder design you started out with and how it was ported can make all the difference. Additionally a good cylinder design may not benefit from a stuffed crank. If the bottom end was designed correctly the stuffed crank could have been the difference. To compare both engines fairly, everything needs to be the same. I would even go down to the carb. The 668 is a huge limiting factor compared to any of the above mentioned carb. Heck even how the tires are hooking up can effect the outcome
 
From what I understand the 990 is slightly better than the 1107 for low end power? At the local on road track they often advise a bearing modified 990 but if you run a 1107, to delete the choke and fill the holes.
 
Bill, if you can honestly tell me you've ran both on the same motor and seen a difference I'll believe it. I've ran both. Couldn't tell the difference. Now if you know how to set the pop pressure and metering system and mess with the jet sizes. The choke less 1107 gets the win. It's just flows more then the 990. However since (I assume ) were talking stock replacement carbs. Theres really no difference.
 
I recently did buy a new 990 with the bearing to replace an old 990 that had worn substantially for one of my engines but I do intend to run it on a Scott Finlay 34cc that usually has a 1107 to see what it's like. It's a great engine but the low end was wanting a bit so was going to experiment to see how to sort that, including using a 990.
 
Going by your description you also are stating one is a HI REV style and one is a Pro stk ported. There is a difference there also with the hi rev version making more power if it is done right and is a true hi rev setup would mean more porting done than a Pro stock version if you go by the names only.
 
Going by your description you also are stating one is a HI REV style and one is a Pro stk ported. There is a difference there also with the hi rev version making more power if it is done right and is a true hi rev setup would mean more porting done than a Pro stock version if you go by the names only.
The king motor kit is off the shelf and is very similar to the obr set up except the head is not hand finished like obr. Was under the opinion that the obr set up was good for 5 to 5.5hp.
 
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