186 heads - 1.94 vs. 2.02 valves

[Lenny D]

Hello All,

I have a question for anyone who has experience with '69/'70 186 heads... 

Are the castings and port sizes/runners identical for 1.94 vs 2.02 186 castings??  In other words, would 1.94 heads upgraded to 2.02 valves flow the same as factory 2.02's without additional port work?? 

Ultimately I want the correct casting number and spec heads on my '69 302 so that it performs exactly as new once it's rebuilt - I'm not worried about date codes.  It has a CE engine dated 1971 - warranty replacement, and has been running a set of 492's since the original heads gave it up in the 80's... 

So I located a set of 186 castings and had them completely rebuilt.  These 186 heads were supposed to have come off a '70 LT1, and are date coded for May 1970.  They did have the screw-in studs and guide plates when I got them, but of course these could have been added if they had been upgraded to 2.02 valves in the past.

However...  when I picked them up from the machine shop, they said they thought these heads had started life as 1.94's...  they were unclear on why they suspected this.  I have to decide whether to use these heads, or maybe do more work to them; so I popped an intake valve out of both the 186 head and a 492 head (2.02's) to compare the bowls and runners. 

 - I couldn't find any dimensions that were smaller in the 186's, and although the "uneven" machined shoulder below the valve seating face makes it look narrower; in fact if anything all the 186 bowl dimensions were marginally wider than the 492.  I think either these 186's actually are factory 2.02's, or there's virtually no difference between the 1.94's and 2.02's other than the larger valves.

I've posted some photos below compare the 186 and 492.  Appreciate if anyone can point out something I'm missing...
If it looks like these are legit 2.02 186's, (or nearly identical), then I'll bolt them on and be happy.

What do you guys think???

Thanks! Len 

[Stingr69]

When the small valve heads are converted to large valve heads in the field, the usual procedure is to use a "bowl hog" to open up the throats below the seats.  It does not look like the throats were opened as far or deep as what I have seen done in the past.  Not sure this makes any real measurable difference on a street car.  You could do some port work and even spend money to have them flow tested but that is a lot of effort.  Not worth the effort in my opinion.

The chamber walls on your heads were cut to un-shroud the intake valves so you did get the (more important) modification done there.  That needs to be done or the heads will flow less than the original 1.94" setup did.  The exhaust could be un-shrouded as well but the Vette heads did not get that factory mod.  I think the '69 Z/28 Camaro heads did, but those would be rarer than hens teeth today.  They also got special swirl polished and coated valves.

You could do a pocket porting job on them if you have a steady hand and a die grinder.  Might be worth 20 HP.  You would work to smooth any transitions where the cutters left any sharp edges in the casting.  Don't get too aggressive or you could end up trashing the head if you hit water.  The short side radius is pretty thin in there.

[Lenny D]

Thanks very much for the reply Stingr.

You're right, it doesn't look like there was any machine work done at all below the shroud area.  The throats look to be original - which is where my question stems from.

My understanding is the 492 head was a direct over the counter replacement for the 186 2.02; so therefore should have the same throat size as a factory 2.02 186, correct?
 - If the 1.94 version of the 186 head had the same throat size as a 2.02, then this is a moot point.

I was lucky to have a 492 head handy that I could compare those throat sizes, and they are nearly identical - if anything the throats are a touch bigger in this 186, which makes me think these are indeed factory 2.02 186's.  The way they machined the area below the valve seats (unshrouded) gives the optical illusion in the photo that the throat is narrower below that shroud than the 492, but it isn't.

To your point that 1.94 conversions typically have the throats opened up...  if the throat is already the correct 2.02 size and I'm going for "stock"; I'm not sure I should touch them further?

To be clear, at the end of the day, I'm simply trying to determine if these 186 heads were originally 2.02's or 1.94's.  Is there any way to tell for sure?

Thanks!  Len

[Lenny D]

I may have found my answer in a previous post...

http://www.camaros.org/forum/index.php?topic=18666.0

The photo below posted by jdv69z shows the face of the head is different between the 1.94 and 2.02 versions.
If this is in fact correct, then it would appear that I have a set of original 1970 2.02's.

I'd appreciate if anyone can chime in to agree or disagree with this dimension being a correct way to identify original 2.02's.

Thanks again - Len.

[Stingr69]

No. 

The chamber walls were cut around the periphery of the intake valve at the factory when they were manufacturing 2.02" heads.  This can also be done in the field later.  The cuts in the chamber make the distance between the adjacent chambers "thinner".  That is all you see in those pictures.

[CantRepeat]

It's pretty easy to tell when factory 1.94s have been cut to add 2.02s and they don't unshroud the intake valve.

[Lenny D]

Yes, I suspect it should be easy to tell, but I can't tell!!  It might be easier if I had a stock 1.94 186 head to compare.

It definitely looks like there was an extra cut made to unshroud the valve, however it looks like this was done over the original unshrouding cut from the factory and removed a little more material at the top.  (Again, comparing to the stock 2.02 492 head).  You can see this cut blend with the original factory cut line towards the bottom, as the new cut is not concentric with the valve seat surface.  The throat sizes are the same as the stock 2.02 492 head, so is it possible they did that cut to blend it more to the throat with emphasis to the top? (like perhaps someone might do to fine-tune a factory 2.02 head?).

 - - What gets me is the throat size being the same with these 186's and 492's...  Were 1.94 throats the same as 2.02 throats or not?  If 186's which were 1.94's to begin with have the same throat sizes as the 2.02's, then why would they require extra machining with a bowl hog to open up the throats (as Stingr69 mentioned earlier) when modified?  As mentioned, the throat has not been opened up in this 186, so I'm still leaning towards this being an original 2.02.

Again - just looking for something definitive one way or the other whether these 186's started life as 1.94's or 2.02's...

Pls see pic below...

[Stingr69]

Original big valve bowl.  Note the sharp edge at 9:00 left by factory cutter.


You should see this sharp edge on an unmodified big valve bowl.

[Stingr69]

This is a small valve 186 head modified to 2.02" valves. The bowls were hogged out and the chamber wall was cut around the periphery of the intake valve.

[Lenny D]

Thanks again Stingr69...  I really appreciate the info.

So from those pics and info it looks to be pretty clear that these are original big bowl heads then, as you can see that sharp edge; and also the cut area in the chamber (and throat) looks quite different on that example you showed of a modified 1.94.  My 186's look much more like a factory cut, for lack of a better term.

I'm going to say these are real 2.02's, unless anyone has something else to add.