high compression 8/16v question

so just as a present warning if there's a thread about this already just point me in the right place and I'll get rid of this, but the search button isn't working on my phone so this is the next best thing right


so I'm looking at building a high comp N/A motor for my 89 245 wagon, and I'm planning on getting the yoshifab hi pro pistons, and I was planning on trying to figure out what compression would work in both the stock block with the 8v head for the time being as well as a 16v head when I manage to find one near me. I know plus T is the easiest way to go for more power but having a fun na is more my style and I figure that 200is whp is mostly doable with the 16v head, a ghetto tune, new internals and better intake and exaust

thanks everyone

I'd be interested in hearing what people have to say about this. I don't have an answer for you, but if you were going to build an NA motor and replace internals, I don't know that I'd focus on high compression (I don't know that I wouldn't focus on it either).

I know a lot of people have used stock pistons for their 16v projects and just used the valve relief milling tool that someone rents out around here to cut the reliefs into the pistons while they are in the block. Might be an option for our 16V phase two.

if you're going for a one-size fits all approach, you might have some issues with high compression and the shapes of the two combustion chambers, but perhaps it could work fine -I haven't checked, so I don't know specifically if a pent dome piston for a 16v head would clear an 8v chamber. then there's the possible issue of valve to head collision since the 8v valves drop down and the 16v valves come in from at an angle.

Most people that try this approach are going for a turbo build, so you have a dished piston and it's not that big of a deal unless you've got some kind of silly big cam.

Honestly, I'd pick a direction be it 8v or 16v, and go in that direction and do it up right from the get go. You'll get a better result and probably spend less money in the end.
the car cams will likely get you to 200whp with a decent header, good springs (be they good stockers, or the ford drop in springs), and maybe an intake manifold better suited to turn up a bit. That's without going higher compression. My gold car prior to putting the turbo on it (for.. reasons) with around 9:1, cams/springs, plenum style intake and the bone stock exhaust manifold and downpipe (and NA exhaust) made 170whp thru an automatic. A decidedly unfavorable NA setup.

I hear what all of ya are saying, especially with regards to the different valve movement paths, though with regards to that when I had a quick chat from Josh from yoshi he said that for at least the Pistons he makes they work in both the 16v and 8v head, as they are flat topped, a concern of course was how much squish you could ad before you get a smush, a smushed valve that is, and I'm just powering the idea as if I invest in a good piston set, bump up compression make everything else flow better , gain even a tiny tiny bit on the stock head, just to make hills and stuff on the highway a bit easier and to have a bit more fun, and then when I find a 16v head that I can More or less just swap heads, add all the 16v bits and bobs and then have a pretty happy little motor

and to Linuxman51 I'm assuming you had a 16v head in that right haha

and as a last thought, would bigger injectors / different spark plugs make much if any of a difference?

thanks again all

bigger injectors don't add power unless you're out of capacity with the current injectors. Plugs... wouldn't mess with them til they're a problem.

and yes, the gold car is a 16v car lol.

Even with flat topped pistons in an 8v, you wouldn't have issues with the valves hitting the pistons under normal conditions.. basically no need for valve reliefs. Break a timing belt though, and you'll be rebuilding everything.
Flat top 16v pistons will work just fine in a higher comp 8v. The only downside is that the CR will be slightly lower with that setup, due to the CCs added to the closed chamber volume from the valve pockets.
Depending on cam, you may need to enlarge the pockets in the 16v pistons. I had to sink them about .060in to get a "safe" running clearance, aftermarket cams though.

The only way to know for sure on internal clearances is to assemble the engine and measure it with clay or a dial indicator.

OP where are you?

so in theory there won't be an issue unless I've got some crazy cam and even then still may not be an issue , but again just take a little bit of meet outta the pockets , and of course a lower cr in the 8v makes sense, kinda what I was planning on because it would mean and even bigger (in theory ) hp boost once I swap heads, and if I do run the flat top pistons in the 8v just be vigilant of the timing belt because it would basically have such little clearance it would become and interference head correct?

on that topic does it make more sense to go with higher CR pistons or just to plane the block a bit and throw in a super thin HG ??

EivlEvo said:

OP where are you?

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I'm in Vancouver cananada

reasonably close to the boarder

linuxman51 said:

Honestly, I'd pick a direction be it 8v or 16v, and go in that direction and do it up right from the get go. You'll get a better result and probably spend less money in the end.

Click to expand...

Agreed. I've got a 10.5:1 8v in my daily 245 and I wasted a lot of time and money because I didn't spend enough time researching all the parts going into it. I should have looked at the whole lot - cam, pistons, rods, HG, compression, fuel quality, carbs or ems etc. before going to the engine builder. We got there in the end but I reckon the result could have been better and cheaper if I'd had a clear goal.

A local 242 owner built a 11:5.1 8v with a KG9 cam, carbs and race fuel and it made 170kw / 230hp at the wheels. I should have done something similar but with a traffic friendly cam and compression for pump fuel.

Ginger Ninja said:

Agreed. I've got a 10.5:1 8v in my daily 245 and I wasted a lot of time and money because I didn't spend enough time researching all the parts going into it. I should have looked at the whole lot - cam, pistons, rods, HG, compression, fuel quality, carbs or ems etc. before going to the engine builder. We got there in the end but I reckon the result could have been better and cheaper if I'd had a clear goal.

A local 242 owner built a 11:5.1 8v with a KG9 cam, carbs and race fuel and it made 170kw / 230hp at the wheels. I should have done something similar but with a traffic friendly cam and compression for pump fuel.

Click to expand...

Totally hear you on that front, and then if it help here's the end goal

200+whp
Not terrible mpg
Decently high redline not crazy High Maybe around 7 or 7.5k
Going to go with an decently agressive cam
Going to go with Ann aftermarket EMS eventually but I know someone locally who's can tune lh2.4
Plenum intake eventually
Better flowing exhaust headers
11.5 or higher cr
16v head Ported

Now if step one is a higher Sqish piston and thinner hg
Would it work with both heads just as I find a head and more funds
OR do I accumulate everything,and run stock till I can do the 16v swap with then pistons rods cam ect

John V knows a lot about NA Volvo motors.