731 head w/ 885 valves

[acolella76]

Whats the compression ratio going to be if i put 885 valves in a 731 head and then put that on an eta block? Due to the larger valves, the chamber has to be reshaped. Do you guys think this is going to be a big noticeable difference? What kind of power would i be seeing if i did this set up?

Also, if i did the 731 head with 885 valves on an eta block, would the 272 cam be alright if i used stock valve springs?

Here's a pic of a 731 head with 885 valves so you can see what I'm talking about, i found it while researching the 731 stroker.

[nando]

the size of the valves won't appreciably change the CR

you should be able to use a 272 just fine. be mindful of valve clearance at TDC. the minimum value is 1.5mm.

[RainierHooker]

I'm not sure how much you will gain from the larger valves in the -731 head. The main impediment to the -731 and the -200 would be the smaller intake port sizes. if you wanted to breathe better you would probably be better suited to using an 885 head. That and the valve/piston clearence issues as stated by nando may be a problem.
If you were going to go to all that hassle (and money) to modify a -731 head, it might be better utilized in putting S-eta pistons in your block and placing an "i" -885 head up top...

[acolella76]

the size of the valves won't appreciably change the CR

you should be able to use a 272 just fine. be mindful of valve clearance at TDC. the minimum value is 1.5mm.

I'm not so concerned about the valves, but how the chamber has to be reshaped to accommodate them, making it almost the size of an 885 chamber.

I'll check into the valve clearance, thank you!

I'm not sure how much you will gain from the larger valves in the -731 head. The main impediment to the -731 and the -200 would be the smaller intake port sizes. if you wanted to breathe better you would probably be better suited to using an 885 head. That and the valve/piston clearence issues as stated by nando may be a problem.
If you were going to go to all that hassle (and money) to modify a -731 head, it might be better utilized in putting S-eta pistons in your block and placing an "i" -885 head up top...

I would be using 885 inlet sizes. Basically turning it into an 885 matched for flat top pistons. I would honestly rather spend a few more bucks and only have to take the head off, than to completely dismantle my engine.. especially since I've never done it before.

[nando]

you are talking about deshrouding the valves, correct?

[acolella76]

yes i am

[digger]

why not use an 885 then?

[der affe]

i can't remember, but doesn't the ETA piston have valve notches also (i know my 11.2 euros do, but that is a different deal) with bigger valves you may need bigger valve pockets too.

have you priced out installing larger seats? it can be expensive to have them installed. you are missing the point too. even if you install larger valves without inlarging the intake and exhaust ports/runners you are going to gain almost nothing for your efforts and just spent $.

you will gain more from the 885 head stock than spending all that $ on reworking a 731 head and invest that money you would have spent on a set of SETA pistons.

[Rau]

sounds like it would be cheaper to just swap heads, but what do I know......

[hotballs]

The chamber isn't going to be reshaped really. There is enough room in the 731 head to run the 885 valves on the stock seat on the exhaust side but only enough room for +1mm on the intake side. I ran 885 exhaust valves and had the intakes ground down -1mm to fit the seat in a 731 head. No clearance problems.

If you wanna run the full +2mm 885 valve on the intake side you will have to have the seat removed and have a larger seat machined in that will accept the valve on the intake side. Is it worth it? IMO no, that's why I just ground it down 1mm to use the stock seats.

Have the head ported if you want more flow....and not dremel intake porting, like really ported.

It might be the angle, but that picture looks like an 885 intake valve and a 731/200 exhaust valve. Looks almost like 4mm difference between the two instead of 2mm. Could be the angle.

[der affe]

i am not sure what the formula is, but you also need to increase the valve sizes on BOTH the intake and exhaust.

an example i ran into was in the VW world, there were heads that came only on 1 specific model the Brazila . they had 39mm intake valve and a stock exhaust valve (the "041" head). they ALL cracked inbetween the valve seats because you could not get out the extra you were putting in. once you put in a 35.5 eahaust valve and seat. the problem was gone because you could now get everything out of the chamber.

just like i said before, stock 885 head and either SETA or EARLY EURO ETA pistons, cam if you want, you'l be better off.

[Gruelius]

yeah 855 heads flow better, even with the lower comp its still superior

[acolella76]

thanks guys, this seems to be too much work and money for minimal gains. I'll just spend my money on some pistons! :)