rotor housing water jacket mod
 

I read somewhere, I think maybe Zach's build that there is a mod you can do on the rotor housing water jacket to split one of the internal webs near one of the dowel lands in order to try and prevent the dowel lands on the plates cracking? can anyone shed some more light on this and if it si safe and really worth doing? interested to know how many are building their motors up with this mod done?

Cheers
Lee

never heard of it

You're thinking of this from silverfdturbo6port:
https://www.rx7club.com/20b-forum-95.../#post11930813

You beat me to it! Thanks.. Can anyone tell me the builder who uses this trick? Is it commonly done?

Search for MFR housings....

What do you want to know? You just cut the webbing..theory is it will relieve some combustion pressure on the dowel area....

Okay.. So it's pressure relief in that sense. Is it not torsional twist that cracks the lands then? I just want to know if it widely done.. has any potential negative risks or not? I also heard there is a mod to groove or remove some webbing around the leading spark plug holes for better cooling in that area? anyone heard of that?

Cheers
Lee

i have never seen it done, and so far it's just a theory that has yet to be proven. i have seen the fact that the whole engine twists to cause the iron breaks so this would really do nothing to prevent that. if the theory is that there is massive expansion in this area, well, it isn't located in the combustion pocket so, no, i'm not buying that either. detonation could cause expansion of that area, but it's going to cause damage no matter what, so, checkmate.

it may allow some slight flexing during engine torsion, but i doubt it will save you from much. either the rotors are going to hit the housings and jam the seals or the iron will still break from the bending force.

everyone has their own wierd theories but i'm not buying this one.



just get a set of studs and be done with it...


i did the cooling system porting mod around the spark plugs internally and it does help some, but it is a 'end of list' modification when you just have more time and/or money for the nearly impractical gains netted. a better alternative is to add coolant feeds to the rotor housings around the lead plugs instead, it's easier to do and more easily adaptable for future builds.


with how fragile the engines are eventually your work is going to be a bookshelf conversation piece anyways. if you are into competition, then sure go for it.

Do you have a picture of the spark plug porting mod for interest? It sounds like maybe for my weekend toy street car which will run no more than 1bar boost I need bot bother with these mods from what you are saying?

it is much more time consuming than it appears.

racing beat still sells the service IIRC. i believe they have it saved in an autocad file to CNC, which i never got around to doing because i'd never get my money's worth out of the procedure.

if they do it by hand it must be either very sloppy or very shallow because it took me almost a full day to do each rotor housing and only about 1/4 of the housing's jackets got modded. ie it's just not worth it as a shop to sell the service manually, and low sales wouldn't make it worthwhile to write files for a machine either.



then again due to current circumstances i shouldn't say i wouldn't....

I tried that one and saw some improvement but went to improved balanced flow for best results.
Barry

https://www.rx7club.com/3rd-generati...t=Barry+Bordes

i mentioned a similar method a few posts up, both offer improvements but ever so minor ones.

I dont know about the inside of the engine but my 20b is a race build and it got both oil and water feeds tapped into plates and housings...
No oil thermostat, no water thermostat, ewp150 waterpump, dual hp1 oilfilters, dual in series oilcoolers and a big v-mounted watercooler and so on.....this is my builders recipie and hopefully it will work out

That is much more involved than I expected around the plug holes! As I said maybe for my 1 bar max street car I don't need to worry? Nice set-up you have there RX7Jocke!

Thanks for input.. I have been reading up on stud kits and stuff too as that got mentioned. Seem to be arguments over those and dowels and whether you should run all studs or not! I suppose the point comes you make something too rigid and something will inevitably have to give somewhere.. So what breaks next!? I am in two minds. Studs seem better but seem pricey for what they are. The ones that fits stock holes seem like a good idea. Surely it is some plain bar with a thread tapped each end? easy enough to make I would think?


Cheers for all info and opinions though guys.

might pay to look into metallurgy...many different characteristics to metals with different make-ups.

Carlos lopez jr does this mod. Though hes not going to go on the net and argue with other builders. All i can say is he is a legend like jim from racingbeat and knows his shit. Hes never had a 20b dowel crack and like him I have been waiting for the proof of the motors twisting like people claim. The mod is allows relief of pressure that is transfered through that web to the dowels. Solid dowels dont do anything with that pressure but try to keep it contained.

If it was "twist" then the rear dowel would crack UPwards. They always crack DOWN, because the problem is the pressure spike of detonation balloons the rotor housing outwards and this pulls the dowel down.

The interesting thing is that some people have found that leaving the nearby transmission bolt out helps alleviate cracking. Iron is very springy, sometimes more give is better than less!

Spot on!!!

Thanks for posts.. That is good info. I am more inclined to do the mod now. As I can understand the reasoning behind it now. Can anyone post a better picture of the mod or let me know how to get a hold of Carlos ans see of he will share?! I am in the UK so although I have seen his name on here I don't know where he is from or anything?

Anyone able to post better picture of the mod in this post or know how to contact the man that does?

Thank you
Lee

*shrugs*

i have seen them crack in every single direction except inward....

most of them have 3 cracks, one on top, one towards the oil filter and one on the bottom.