Exhaust Port Size Differences

[Taz_Rx]

Hey all,

 

This is something I mentioned in a for sale thread last week, thought I'd take a couple of pics for those that want to see.

 

Basically, all K motors have the same size exhaust ports except for a 7ke. 7kc still is still the same size as 3/4/5k's.

 

Below is a couple of pics of a 7ke manifold gasket up against a 3k big port head.

And for anybody who didn't know 7ke's also have bigger oval shaped inlet ports. If you round out the holes they're then the size of a 3kbp.

 

 

size for the average pics, they're off my phone.

 

Cheers,

Si.

[SeptemberSquall]

for the average pics, they're off my phone.

 

[Boost+k]

whats the actual size in mm?

[Taz_Rx]

Of the exhaust ports?

 

Couldn't tell you sorry Todd, and I've already taken that gasket back.

However those bolt holes are 12mm, not 10mm like the rest, and they're nearly twice as wide as that so roughly 24-25mm squared.

 

Makes you wanna do some more research in head inter-changability hey!?

Yes a 7k has a wider block....but are 5k/7k heads still swappable!!!??? :)

I'm gunna get the tape measure out when I get home!!

 

7k's still have dished pistons IIRC so you might be able to keep the stock 5k CR. 7ke head would go off its tits on a 5k with those ports if it all worked! :)

[TRD ke70]

go on, open up the exhaust ports and see what happens, you'll be disappointed!!!

[opodden]

So, are 7KE ports bigger than 3K big ports or not? Would it be possible to bolt a 3K head to a 7K block, just leaving out the extra 3 bolts that the 7K head has?

[Taz_Rx]

Below is a couple of pics of a 7ke manifold gasket up against a 3k big port head.

And for anybody who didn't know 7ke's also have bigger oval shaped inlet ports. If you round out the holes they're then the size of a 3kbp.

 

This isn't a porn mag, you are aloowd to read the posts as well as just look at the pictures!!! :)

 

....and what would be the advantage of bolting a 3kbp head on a 7k????

[opodden]

go on, open up the exhaust ports and see what happens, you'll be disappointed!!!

 

I was just wondering what TRD ke70 meant by this. Are the 7K-E ports only bigger against the manifold? Or will the performance detoriate if the exhaust ports in the 3K big port are opened up? I'm not a native English speaker, and I certainly not an expert on K engines, so my question could certainly be better formulated.

 

I was thinking of a big bore 7K-E engine when I wrote the question. In that context there are some reasons for going for a 3K head: You can use flat top pistons, which are easier to find than dished pistons. Flat top or domed pistons can allow for shorter compression height and lower weight of the piston, which will allow for a slightly longer con rod and a more rev happy engine. You will get adjustable valve train, which is good for installing a reground cam....I believe the valves are already bigger in the big port, which is crucial in order to get the 7K revving better as well.

 

I have already confessed that I'm not an expert, so I won't be upset if someone sets me straight in these matters...

[Taz_Rx]

Noticed you put a thread on club-k as well. No. 1 rule there is what Blown5k says goes!!!! :)

 

Apparently all K motors have the same sized valves, 7k (C or E) included. 3kbp heads do have bigger ports, but the valves are just the same size as any normal 3k, 4k etc. Hence I think it would just be a better idea to do some work to your 7k head to take advantage of the fact its only 10 odd years old, compared to any 3kbp head thats now like 40 years old!!!

 

IIHO, 7k's are a torque motor. Use it for the torque and don't expect it to rev too hard.

If you want a revier K motor (but still with some torque) maybe look at a 5k as it has a better rod ratio. Or build a 3k screamer if you want 9000+rpm.

[opodden]

Thanks again for good input. I don't know where I got the idea that the big ports had bigger valves; I've been looking at so many web sites now that I've lost track.

I'm getting more and more sure that I will take the advice and go for a modified 7K-E at moderate revs, although a little more than the standard engine. Cleaning up the ports, free flowing air filter and exhaust and a new cam should be fairly easy to do.

 

With the risk of sounding stupid again...is it possible to regrind the original hydraulic cam with a moderate increase in lift without converting to solid lifters? The original lifters can take up some slack, but how much? As long as max revs are kept to around 6500, that would be the absoulutely easiest way of doing it, right? Even finding lifters with the same bore but slightly longer would be easier than converting to solid lifters and adjustable valve train?

[Boost+k]

yep you can get your hydro cam reground, but only mildly

 

adjustable valve trainis in almost every other k series so that a easy bit... theres a few different ways to get solid lifters,

1. 5k factory lifters = big bucks

2. chev lifters with datsun a12 pushrods + cheap but i hear the chev lifter is quite heavy? but it can't be that bad...

3. hollow out hydro lifters and find a pushrod to suit, (heard rumors of 3k rods)

 

there is some smaller valve out there in the 2k engine if i remember right

 

i don't know what the eariler post about opening up the eports is all about, but assume it means on a standard motor it an't gonna help you???

 

7k with the right diff would make for a really nice car IMO

[TRD ke70]

you were talking about opening up the exhaust ports in an earlier post, don't!!!

the exhaust shouldn't flow any more than 80% of the inlet.

If you don't believe me try it!!

 

 

solid lifters in a 7K is not as easy as changing lifters, push rods and adjustable rocker gear.

7k blocks are taller and there isn't any K series push rods longer enough, and i wouldn't think Datsun ones will be any better.

saying that it has been done, recently too.

 

if you are that keen to put solids in talk to Teddy.

 

I have said too much!!!

[Taz_Rx]

Myself and others have had power increases (though reducing the restriction of the exhaust ports) on 5k's............ which are turbo'd. :D

[TRD ke70]

yip, on turbo's that would be the way to go.

On an NA K engine if you open the ports up it can kill power, that doesn't mean don't clean them up, but don't get carried away.

 

Have seen one head where the guy changed them from square to round and killed the engine power. :P

[anastasios]

whats the reason for this?