780 viper owners!!! What head are you running?

M

mountain_mod_viper

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Just wondering what heads people are using for the 780 vipers. I've currently got a peak head on my 700 cylinders. I've got some 780 cylinders to be put on, but don't know what to do about the head. I'm having a hard time getting peak to build some new domes (been waiting for a long time!) RKTek said they could machine my current domes, but he said he wouldn't be able to get the correct plug heights and all that, unless he started with some blank domes and machined them specifically for the 780. I'm considering buying another brand of head that will have 780 domes available without an "act of congress"

What do you guys think?

Thanks a bunch for any input!
 

780 Head Mod

What are you doing with this sled? Trail, drag, mountain riding? Who did the cylinders? Pipes what kind. Carbs stock? Airbox?
 
Mac said:
What are you doing with this sled? Trail, drag, mountain riding? Who did the cylinders? Pipes what kind. Carbs stock? Airbox?
Click to expand...

It's for mtn riding (I also do a lot of uphill drags at about 8000'). It's an 03 mtn viper with cpr pipes, Dave Lloyd cylinder and case porting, 38mm carbs w/stock airbox, plp front suspension, holz rear suspension, ekholm tunnel, rolled chaincase, 153 and 162 attack 20 track (I go back and forth).
 
780 Viper Heads

Sorry no experience at elevation like that. Sounds to me like your holding to the bar for looong pulls. I quess your going need to figure out the compression and the squish your gona run. Hope you have good fuel. You need the mountain guys to chime in here.
 
Allen, (srxspec) may be able to help you, Ulmer Racing on this site. I know they have done 780 BB kits for the Viper. Otherwise call Jeff at simonscpr. Mega power heads are probably a good set for what you want. Also Speedwerx have a one piece head that have several options for dome inserts. That's what I ran when I had the CPR pipes on my Viper, but I sold all of it. I do have a spare stock head if interested, but you would have to get new domes pressed in.
 
I have a peak head on my viper which I kept burning down. Turns out the squish angle is only 7 degrees on it compared to a stock 14 and a preferred 17 for tight squish applications. Anyway, after scrapping 2 sets of chambers my buddy decided to cut me a new set and they have turned out pretty good so far. We've got the lathe operation taken care of and today we are going to get the mill program done for the bolt holes and coolant slots. I don't think it would be that big of a deal to increase the diameter of the squish ring for the 780 diameter. The current chamber I have made for my 700 is a 21.5 cc size. What size are you looking for?
 
its easy to do this

Someone is feeding you a bunch of bologny about the plug height's, you dont cut the spot where the plug is? why would you??, simply use a radius cutter and open up the dome sides, machine your squish angle and set up the bore diameter, its not a space shuttle, its fairly simple. Its just that the radius cutter is a $100 tool bit for the lathe. I told you before I could do them for you, all I need is a bore of your bb kit and the squish your at now, and where you want to be, I can do the math from there.
 
mrviper700 said:
Someone is feeding you a bunch of bologny about the plug height's, you dont cut the spot where the plug is? why would you??, simply use a radius cutter and open up the dome sides, machine your squish angle and set up the bore diameter, its not a space shuttle, its fairly simple. Its just that the radius cutter is a $100 tool bit for the lathe. I told you before I could do them for you, all I need is a bore of your bb kit and the squish your at now, and where you want to be, I can do the math from there.
Click to expand...

Okay,
So right now I have 18cc domes and can't remember for sure what the squish is, probably around 56 to 59. With the 780, I'll want more cc's which would happen when my 18's were enlarged to the bigger bore. Now let me get this straight (sorry I don't know much about the necessitities of a good dome design), when the dished part of the dome is widened out, you're saying that the depth of the dished part does not need to be changed, therefore, the plug height remains the same. Is this correct? Sorry about all the questions, but I was under the assumption that there was alot of calculation involved that may require the depth of the dome to change also, which would change the plug height.
Another question: I know that the width of the squishband and the angle is very critical to a good dome design, but what about the dished portion? Is it the same radius from the squishband down to the center of the dome and back up to the other side? Also, is there a perfect plug height that would vary as the size of the bore varies?
Like I said, I know almost nothing about all this stuff and would like to have a better understanding of the whole thing. It was both Peak and RKTek that mentioned the plug height issue when I asked them about just re-machining the domes that I already have, so I assumed there must be a perfect plug height depending on some of the other variables.
Thanks again for any clarification.

Ryan
 
its like this

your putting a head that has a smaller diameter dome on a larger bore, so all that is needed is to figure the bore, subtract your squishabnd width(40-50%of bore width) and then open the radius out to the new squishband edge, then you can cut the squish height, then reangle it, thats all you have to do, you dont have to ever mess with the bottom of the spark plug height, and the radius stays the same just opened to a larger diameter which in turns opens up the volume, pretty simple
 
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