We took the heads of my friends nova.
What we know so far. 781 heads with 2.06 and 1.77 valves.
Piston looks to be domed,with .250 relief.
Block and heads are 1973 with a 30 over rebuild pistons. Cam unkown,could be a comp cam.
The head gasket was .040.
Question?
What compression is this motor set up for?
Clean pistons and place a new cam and heads on top of the bottom end?
Will a 2.19 and 1.88 head fit with this piston setup if so what type?
Included are some pix.
Thanks for any suggestions. Fritz
P.S.Nova ran best of 8.22 in the 1/8 with 4.10 gears.
10741

It's real easy to cc both the heads and the pistons down in the bore a schosh so that you will know for sure!!

pdq67

that is the next step,but kind of thinking about using a different head with
the pistons that are already in the short block.
Fritz

Looks like my 10.2 domes. Check sig.

They look like a l2339f piston, about a 13.8cc dome. I'm thiking less than 9.1:1 if the heads are around 119cc and the pistons are down in the hole. Clean the top of the piston and see is you can find a part #. I think they are these:

http://store.summitracing.com/partdetail.asp?part=TRW%2DL2399F&autoview=sku

What you could do is zero deck the block and get the heads milled, that will bring the compression up nicely. Maybe cheaper just to get new pistons if you ant alot more compression though.

I say run it!

See that is the question?
Higher compression really not the issue yet.
Looking to see if there would be a head that will work with this particular
short block once cleaned up.
Tear down start over and build it like a raped ape?
The motor had good power for what its worth,but if you rebuild the top end,
clean the head,place new springs on there and new cam,go with it!
Find some good heads aloy or steel and go with the larger valves 2.19,
with these pistons that is kind of the issue.
Or tear the whole thing down and start over and do a ground up rebuild?
Thanks,
Fritz

It tell's you at Summit's site.

"These pistons are not compatible with Gen V or Gen VI engines. Approximate compression ratios: 10.10:1 with 100.9cc, 9.60:1 with 106.9cc, 9.40:1 with 109.4cc, 8.87:1 with 116.9cc, and 8.73:1 with 119cc head."

Not much help otherwise.

pdq67

They do resemble the Speed PRo L2399F. I mid grade forged piston. A little heavy but they work ok. from what i remember, the work with open chamber heads only. The 781 castings I believe come in at around 110cc. With larger valves and a decent bowl blend, these heads can flow well. I would stick with what you have if you like the way it runs. Its amazing how much increasing the intake valve size on a BBC head improves performance. I usually put a 2.25/1.88 setup in them. Its unbelieveable what it can do for the flow but its a little tuff to get a 2.25 in a 781. BOWL BLEND is a must though if increasing this valve size. If not, you are just creatign a funnel. ALso work the short turn radius a little. Hope this helps.

They do resemble the Speed PRo L2399F. I mid grade forged piston. A little heavy but they work ok. from what i remember, the work with open chamber heads only. The 781 castings I believe come in at around 110cc.

2399's (.095 tall dome) and the Speed pro hypers with the .100 tall domes work with both closed chamber and open chamber heads. I know this for a fact.
The minimum a 781 will come in at will be 119 cc's

Do all of the cylinders look as good as the one's in the pic's?? Have you taken off a main and rod cap?? Were you gonna take the short block apart?? My 781's cc'd 117.

Underwear for rags is kinda gross.:D

I was just gonna say that large ovals can vary ALL the way from 112/113 for almost completely quench flat-less smog heads to above 120 CC's for some -781's and -049's!

So CC them so you know for sure!

It's funny that the almost completely open smog heads cc less than the good ones.

pdq67

Well Scott feel free to chime in anytime?
He did cc the chamber looks close to 116 I believe.
The pistons all look about the same. All had about 180 psi compression,except no.2,
It was around 150.

See that is the question?
Higher compression really not the issue yet.
Looking to see if there would be a head that will work with this particular
short block once cleaned up.
Tear down start over and build it like a raped ape?
The motor had good power for what its worth,but if you rebuild the top end,
clean the head,place new springs on there and new cam,go with it!
Find some good heads aloy or steel and go with the larger valves 2.19,
with these pistons that is kind of the issue.
Or tear the whole thing down and start over and do a ground up rebuild?
Thanks,
Fritz


Only YOU can answer the above. If your on a budget, clean it up, re-ring, and go. With 116cc chambers your around 9:1, you can still get good performance with that. You need to decide if new pistons, bore job, R&R'ing pistons on rods, etc is worth more compression.

Or, hone/rings, bearings and gaskets. Shove a hot cam in there go to town! Remember, zero decking block should get you close to 9.3:1, and take another .020 off the heads will get you around 9.68.

FWIW, I have those pistons with the Eddy rovals 110cc heads, work mint.

In my experience most of the 781/049 heads I cc'd were on the smaller side closer to 110 to 112. Of course we alwasys resurfaced them about .015 which usually knocks off about 3 cc give or take so thats where I was coming from. Throw in new seats and a high valve job and you may gain another cc or so. The best thing to do is get the machine work done and then cc them. You may find that you can mill them a little more to custom tune your C.R.

Thanks for the advice on the pictures. I just got caught up on the posts. I am going ahead and pulling the block to ID all the componets. I am leaning towards refreshing what I got and run with it.
I just ran out of underwear and found some extra in the pictures as pointed out.

I'll put my money on sealed power L2465F

have a set sitting on the shelf in the garage

In my experience most of the 781/049 heads I cc'd were on the smaller side closer to 110 to 112. Of course we alwasys resurfaced them about .015 which usually knocks off about 3 cc give or take so thats where I was coming from. Throw in new seats and a high valve job and you may gain another cc or so. The best thing to do is get the machine work done and then cc them. You may find that you can mill them a little more to custom tune your C.R.

I have a set of 78 781's that I just installed 2.19's and 1.88's in and have not yet surfaced them and they measure 107cc. I am pretty sure they have not been cut before as the engine still had stock head gaskets on it when I tore it down. I did do exhaust seats and the valve job is high. The valves I used also do not have any recess in them. They are flat.

Those pistons look a little bigger than a L2399, probably a L2465F. You need to cc those heads.