Ultimate 2.2-.7 heads
 

Ok folks... I need some serious help/advise:

I am most of the way to a 2.8. Aluminum case, crower Ti rods, Mahle pistons, LN Engineering cylinders, and a GT3 oil pump. Did I mention C6 cams?

My question is what to do about heads. I have a set of 2.2T heads which I have twin plugged as well as bored and blended to 38/38 mm. From what I have pieced together, these really won't be enough over about 7k. As was put by one person: Porsche used 43 mm ports and 49/41.5 mm valves on the 2.8RSR for a reason.

So short of selling all my early 80mm stud spacing stuff and downsizing a 3.0 to get the big valve/port SC heads is there anything to be done?

The C6 cam has pretty low exhaust lift, could I use an SC intake valve in the narrow angle 2.2 head?

I looked at using SC heads on the early case by using offset case inserts to open up the stud spacing, but there doesn't seem to be anyway to make up for the larger 90 cc chamber volume. It can be reduced by flycutting the heads to around 84 cc, but that isn't enough (ends up around 9:1) for a non turbo. I guess I could use JEs with the SC heads, but then I 'miss out' on the Mahles I already have. I also am not interested in wacking the tops off the pistons to get the CR right.

Short of building a high reving 2.4L out of the 92s by using a 60 mm stroke crank (as is being discussed in the Carillo rod thread), I am SO out of ideas. I just hate getting nice compoents to spin the sucker and then throwing away top end by choking it off.

Any thoughts or help are most appreciated! I leaped before I looked on this one. :eek:

tadd

Tadd

Here are the intake flow numbers for a set of 38/38 mm port twin plug 2.7 heads with stock valves. I use them on my nominal Mahle 10.3/1 2.7 race motor w/46s. With an Elgin 915 cam it made 220 RWHP at 7100 rpm, so I shift at 7600 even though it feels like it is pulling well beyond that in 2d or 3d. RWT was 181 @ 5900, pretty flat from 3700 to 6900 rpm. These are Dynojet numbers, supposedly corrected to standard temperature and pressure.

At 10" of water, and lifts in 0.05" intervals from 0.05 through 0.55" in CFM rounded off:

17, 33, 52, 73, 92, 107, 116, 120, 126, 130, 132.

Don't ask me more, as that is all the info I have on these heads. The guy who did the head work kept telling me I had more air flow than I needed for my motor, especially when I would talk about 43mm ports and such. Somehow Porsche got 110 hp/liter from its race motors, and I don't suppose that most of the difference there lay in titanium rods.

I have never known how to translate flow bench numbers into engine needs, because the cam lobe design seems to play a role, and it looks like maybe you need to use calculus once you had an equation describing the cam's shape. Plus I suppose the pressure differentials between the cylinder and atmosphere vary with the crank cycle, etc. Easy to determine how much air you'd need to pump at any given displacement and RPM, but not so easy to figure out what kind of flow numbers are needed beyond trivial cases where they are way way too small.

What the hell - build the motor, you've got the parts. See what it does. It won't be a dog even if you can't match the factory numbers. You should be able to get a 1mm increase in intake valve size to work, I'd guess, for a little edge.

Walt Fricke

Tadd, What Walt says makes a lot of sense. You should just build it. I doubt you'll be disappointed.

The only alternative I see is buying either 2.8 RSR heads or starting over and buying a 76'/77' Euro Carrera 3.0/3.0 Turbo motor and de-stroking it to 2.8 using a 66mm crank.

But where can one find 2.8 RSR heads? Do you know anybody who has a set for sale?

Blue72s:
I've seen your trail of searching... :D I've always been one step behind! :(

There are a few sets out there, but I really don't think anyone will sell them as they will be building that motor "any day now". Experts have told me that they would most likely trade for between 6-8k. Not cheap, but not much of an alternative. I guess doing the shrink on a 3.0 is too easy as I would think that given the number of small chamber 2.8/2.9s out there SOMEONE would be reworking either SC heads or 2.7 heads and making some money.

That editoral in Octane? this month advocating hording early 911 parts as a retirement plan. This will only get worse.

There was a great article a month or so ago about a company (phase 9?) that CNCs heads for the 993. They did a bunch of computer flow stuff and then used a multi-axis machine to whip them out. If I could ever get my hands on one, damaged or whatever, I would absolutely work up a cad model. It might take a while, but whatever - the end result would be worth it. It would also be awesome on my desk :eek:

Walt:
Thanks for the sanity check. I am sure you are right and it will not be disappointing regardless.

tadd

Walt, if you give me the cam dimensions, I can give you some #'s as to what the heads flow. Of course, this would be a rough estimate b/c we only have some certain points to plot for the flow #'s, and it would be assuming 100% volumetric efficiency, so one would have to reduce the final #'s by a certain % depending on the VE at a certain RPM.

Well, you hit a couple of nails on the head.

All I know about my cams is what Elgin had to say in various catalogs, which I think is lift, duration, and lobe spacing. And I don't even know for sure if duration was at 0.005 or whatever the usual convention is or not. The 315s were speced for valve clearances of 0.008, which is certainly unusual (seems to work fine). But none of this says much about the ramps and how wide the top of the lobe is.

But maybe those other things don't matter that much for approximations? If lift, duration, and lobes are enough, I'll hunt them up.

I think I understand VE. But what I don't understand is how one measures it independently of dynoing an engine. A Spintron? Or can you deal with the effects of intake configuration and exhaust scavanging and so on on a flow bench?

Walt

Oh, this may get interesting fast! You go guys.

tadd

Ther is a set of 2.8 RSR heads on ebay from one of the members.

Mind tossing up a link? I've searched evil bay for every key word I can think of and can't find them.

tadd

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=006&sspagename=STRK%3AME WA%3AIT&viewitem=&item=160057664879&rd=1&rd=1

Better Hurry if interested

The link is to RSR 92mm pistons and cylanders, not heads. Did you mean to post anothe link?

no sorry for the confusion

Tadd;
I had a lot of similar questions about that series of motor and posted my findings on this thread, which I think will help you out. BTW, those flow numbers that Walt posted sound kind of low, but it may be the flow benches and the measurement process. Compared to the data in the earlier thread, I would expect ports which are bored out to 38 mm to flow similar to the 2.2S ports, but have greater flow from about .3 inches of lift on up, where the 2.2S heads tail off some.

Unless it's a full race motor, you might want to look at getting some larger intake valves, which will flow more at low lifts, and thus allow more flow with a shorter duration cam. This combination I would expect to give more HP in the mid-range (as a result of the shorter duration and less overlap) as opposed to hogging out the ports more which might contribute along with a longer duration cam to peak HP which only occurs at the very top of the rev range, at the expense of part throttle driveability.

John:
Actually I have been over that thread a number of times. It was quite instructive - thanks for putting it together. I've also been over your helpful postings to kenikh and I original postings about small bore motors (which was the plan until I fell into the 92 P&Cs at a price that was unavoidable :D).

I've been looking at valve suppliers for a 47 mm valve with a thinner stem. To try and make up some of the difference of that huge 49. I think ferra may have something usable.

Bottom line: I wanted a motor that had a lot of revs and was 'cammy' to replace my two stroke motorcycle habit.

The thought of a sprint cam 2.8 on a short box in a 67 makes my licence tingle, so I may still 'drop back' to a 2.1LS. The other kewel combo is a reground 66mm crank to a 60 mm stroke with a gt3 ti rod. That gives a 2.4L with the 92s or a 1.8L with 81s. the 1.8 would be something you could wring it's neck and not be going stupid fast. A turbo could be added for additional driving pleasure :D, but I am a NA kinda guy.

As I have machined both a set of 2.0 and 2.2 heads to 38/37 and 38/38 ports (and twin pluged both) I have a lot of options. The problem was that since my 67 is a 912, I have been pieces-parts on this and ended up with too many choices. If I had just had a motor to rebuild life would have been simpler.

tadd

Alternate valves
 

Well after checking out the Ferrea cataloge, the toyota 22R intake comes in a 47.1 head size (46mm stock). It also happens to be 113.4 mm in length (114.0mm) and 1mm narrower at 8mm in stem diameter (vs 9mm stock).

So between the extra mm in head diameter and the extra mm lost on the stem, that shouldn't that be equal to a 9mm stemmed 48? Not quite a 49 but getting awful close. I would guess it might be a bit closer in flow as the area over the whole length of the stem (roof to valve face) facing the incoming air-fuel mix is less.

A 'tip length' is listed as 4.6mm. Is that the distance from the tip to the first keeper groove? Anyone know what this value is for the stock 46 mm?

Hopefully, I will get time to call someone tomorrow about price.

BTW, there is a 45mm head, 8mm stem, 115.4mm length valve. It is 2mm longer than the super expensive 69S valves.

Cheers,
tadd

The first nominal 46mm valve I grabbed from my collection of bent or otherwise not useable ones measured 8.64mm from tip to top of first keeper groove.

The head measured 45.80mm, and the unworn portion of the stem came at 8.97. I got 114.45 for LOA, but the caliper wasn't up to measuring this quite right, so I think it is a little shorter (had to miss the valve's center dimple).

Walt

Thanks Walt!

So that means a bit longer spring (I think that is good), thick lower shim or thicker retainer.

I guess I will need to get one and do some experimenting!

tadd

OK, I am skippping to the end, so slap me if someone suggested this already:

Why not build up the material in the domes of your 2.7 heads with a welder and then have them CNCed to get the right CR for your pistons? I bet it's still cheaper than RSR heads. This is regularly done on the Honda CB450 race circuit to recontour the heads to a modern shape.

Tadd

While on the subject of flow, why stop at 8mm valve stems? How about 7? 6, even? You are going to have custom valve guides made anyway, right?

Ken - welcome aboard.

I have wondered about this welding and reshaping also, but on reflection it may not be the answer for our engines (leaving aside issues like what, if anything, might somewhat extensive welding do to the properties of the original aluminum - maybe re-heat treating would take care of any of that?):

1) RSR heads have more volume than 2.7 heads to start with (see Anderson's discussion of this where he warns that you will get too much compression using 2.7 heads with 92mm jugs). This suggests that reducing head volume may not be the issue. With high dome pistons you can probably get about as high a CR as you might want.

2) Porsche heads are basically hemispherical. Just where would you add, and what would be the change when you were done finishing it? How would this affect the existing valve seats?

3) The trick with RSR heads (other than that they came twin plugged) is that they had larger intake valves. To make these fit the valve angle was changed. I'd think that if any welding were to be done, it would be to move the valve seats and realign the valve guide hole in the head and all that goes with that. In short, to replicate a 2.8 head (not many of those made, even fewer floating around used and available, and most guys who could afford what is out there would just buy a cup car instead of beating their brains up). Might that be trickier than just adding some metal on the surface and machining it?

But what do the Honda guys do? I have no idea what a Honda head or piston top looks like.

Walt