fly cut 2.7 heads to reduce chamfer?

gestalt1 · 06-23-2010, 03:06 PM

hi, i have a set of 2.7 heads and i'm thinking of using either 81mm or 84mm cylinders on my early case. can the heads be flycut to reduce the chamfer enough for 81mm cylinders? i would add base shims to compensate some. i don't want to invest in welding up the chamfer and re-machining.

cgarr · cgarr's Garage

no, you would have to take off way too much. The most is usually about .010 but I have seen them up to .018 but they will not get you anywhere close to fitting a 84mm cylinder. The chamfer starts at about 83.5mm

kenikh · 06-23-2010, 05:04 PM

Supertec makes a spacer kit that sets the 2.7 heads for use on smaller pistons. Relatively cheap, too. Search on this forum and its there somewhere.

gestalt1 · 06-23-2010, 06:22 PM

hmm, i do remember the supertec spacers, i think henry sells his 81mm cylinders machined for the spacer to this also. i'm just thinking the 2.7 heads have 36mm ports which would be nice on a 2.0 mild race engine. kind of a free port job.

kenikh · 06-23-2010, 09:09 PM

Yep, the Supertec adapters and under 200 bucks are a pretty sweet solution to free ports.

304065 · 06-24-2010, 05:28 AM

What sanctioning body will allow you to use later than 2,0 heads on a 2,0 liter race motor? Not saying there isn't one, but the reason the 69S heads are in such high demand is because they are the cutoff, so I've heard.

If it's a street motor. . . why not let it all hang out and go at least 84mm? There's no replacement for displacement.

gestalt1 · 06-24-2010, 09:58 AM

good point, i'm not building to a sanctioning body. i do track days and solo1. the midwest council just classifies cars for race class solo1 by displacement, ie under 2L, 2-3L, 3-5L, over 5L. I do agree, i think i will increase the spigots and put the 90mm cylinders in for a 2.5ss. seems to be the cheapest hp. additionally if i use 81mm cylinders i would be in the 2L and under class which means i'm competing with formula fords.

304065 · 06-24-2010, 03:23 PM

Quote:

Originally Posted by gestalt1

good point, i'm not building to a sanctioning body. i do track days and solo1. the midwest council just classifies cars for race class solo1 by displacement, ie under 2L, 2-3L, 3-5L, over 5L. I do agree, i think i will increase the spigots and put the 90mm cylinders in for a 2.5ss. seems to be the cheapest hp. additionally if i use 81mm cylinders i would be in the 2L and under class which means i'm competing with formula fords.

Given those facts, I'd bring the car in at just under three liters. why not bring the thing in 2994cc, the Old 911SC 95x70.4? Or with a custom crank, 98x66, 2987cc?

gestalt1 · 06-24-2010, 05:32 PM

i'm using an early sandcast case, aren't the studs too close to the spigot opening to allow 98mm cylinders? i guess the stud bores could be plugged and re-machined to the sc positions but that seem like a lot of work and cost. i thought the max cylinder size that could be used is 93mm?

Walt Fricke · 06-24-2010, 10:15 PM

Yes, and 93 (a 2.9) is stretching it.

He's been working too hard.

Flieger · Flieger's Garage

Stick with 90mm. Street motors will use longevity more than the nth degree of power.

The 98x66 short stroke is based on a 3.0 liter 930 Turbo case or a 3.0 RS/RSR case with a 66mm stroke early crank. Or you can use a normal SC case with a 956 crank which has the journal spacing for the late case but a 66mm stroke.

Walt Fricke · 06-25-2010, 11:52 AM

Getting a 956 crank is going to be a bit of a challenge on several fronts, isn't it?

Henry Schmidt sells a 9 bolt 66mm crank, so the later 3.0 etc cases can be used.

A piece of art from the photos, with all the bells and whistles a guy might want (knife edge, lightened, all mains grooved for extra rod oiling, and probably lots of other, less obvious, stuff).

Haven't seen a price, though.

304065 · 06-25-2010, 01:18 PM

Quote:

Originally Posted by Walt Fricke

Getting a 956 crank is going to be a bit of a challenge on several fronts, isn't it?

Henry Schmidt sells a 9 bolt 66mm crank, so the later 3.0 etc cases can be used.

A piece of art from the photos, with all the bells and whistles a guy might want (knife edge, lightened, all mains grooved for extra rod oiling, and probably lots of other, less obvious, stuff).

Haven't seen a price, though.

Working too hard. . . trying to keep the place clean of "cvv dumps"

The Marine Crankshaft custom job is what I was thinking of, what jogged my brain to think of it was the very short stroke that F1 engines use-- it is speculated that the bore is 98mm, which means the stroke is 39.7mm to get their V8s under the 2,4 liter limit. Now THAT is a short stroke!

I didn't pick up on "early case," sorry. I think the custom nine-bolt, short stroke cranks are a great idea-- anything that would allow you to use a later SC, 3,2, or even 3,6 liter case-- all the advantages of the modern case, bigger spigot spacing, bigger heads, allowing the early cases to find their way back into early cars! (It's the preservationist in me coming out, I swear.)

I guess what monkey-wrenches that thought bubble is the cylinder head volume. In order to make decent compression with a shorter stroke, you would need to decrease the head volume or increase the dome volume. And we know what a bear it is using a bigger bump on the piston, even with twin plugs.

With a 90cc head volume and the standard 964 dome of 34cc and a 1mm deck. . . you could do some wild combos: 100x66 for 3,1 at 9:1; 102x66 for 3,2 at 9:4 and how about 104x58.8 for exactly three liters, bump the dome to 45ccs for a nice 10,3 to 1!

Working too hard is right. Such an engine would only work if you could rev it unbelievably high - the 964 has 41.5mm ports, which means that you'd need REALLY high revs to keep the gas speed up.

All right, enough hijacking your thread about 2,7 heads