Hi guys,

I've got a set of 081 casting heads that where ported by a friend of mine. We had them flowed a few time during the processes and they turned out "fine". (He ports heads as a hobby/ side bisness)

My problem is that the 58cc chambers grew to 63cc's. (this was intentional to get the right combustion chamber shape)

Now the heads are going on a 305 will a good almost stock bottom end. I lost compression on the engine for 9.3:1 to about 8.98:1. The goal is to get around 10:1 compression. More if possible. stock pistons.

Question:
Can somebody tell me how much the chamber volume changes during angle milling?? the chamber has been matched to the 3.75" bore to unshroud the valves.

btw. heres the flow chart for the heads for those who are intrested
Lift " 32"% 28" cmf Teor HP
0.1 12.5 65.3 134.2
0.2 24.5 127.6 262.4
0.3 31.2 162.2 333.6
0.4 37.3 194.4 399.7
0.5 41.1 214.2 440.3
0.6 42.6 221.6 455.6
0.674 43.2 225.1 462.7


the rest of the combo is:
a stealth ram
long tube hedman headers, ture dual exhaust
(haven't chosen a cam) I do have a crane HR-276 on the shelf

comments?

 

The HR-276-2S-12IG is what I had in my 305 in the G20. With the ported 081s, 1 7/8" primary headers, projection intake, 454 TBI, 2,800 stall speed converter in a 700r4, 3.73 gears, and lots of PROM tuning, it ran awesome for a 305 (312 but whos counting). Recorded a 15.24 @ 96 in a 5,500 lbs brick.

 

still need advice on how much the heads can be angle milled. Even a general guideline would help. I know I have to measure the exact max lift etc. with heads on the engine.

Could somebody help with the math part. So I know how much I need to mill the heads..

 

cheaper to change the pistons than $$angle mill$$ the heads and $$correct all the geometry.$$$ ( headbolts , intake, etc )

flat mill the heads back to 57/58cc (about .060") and install flat top pistons and a .015" shim gasket (350ci) You probabily deshrouded the heads a lot more than you needed to.
The flat milling limit on the 081 heads is the intake seat and spark plug boss.

bore 3.766" ( .030" over)

stroke 3.48"

deck clearance .025"

combustion chamber volume 58cc

piston valve relief volume -5cc

350 shim head gasket volume 3.5cc

quench clearance .040"

compression ratio = 9.93:1

use this Speed pro hyper piston Summit racing # STL-H534CP30

What size valves?

 

The valves are 1.94"/1.5"

Angle millin in Finland will be alot cheaper that than going through the whole engine. milling costs about 110€ (around 150$) for both heads.
The reason i'm askin is i need to know that how much can be milled this way, and will i get the compression I'm lookin for. Taking about 0,5mm off the head won't dramasticly change the heads angle, this shouldn't give me trouble with the head bolts.
I'm using a 305 gasket, so that won't hurt compression. Gasket thikness is around 0.04"
----------
The valves were de-shrouded using the head gasket as a guide and a flow bench to measure the affects. gains were noticeble.. The head flow won't suffer even at 0.67" lift (which shows a very agressive intake shape).
I'm only using 0,52" / 0,55" lift, the cams that have enough lift have too much durration. I don't wan to go over 212/222 " 0.05"

 

usually you want to use the motor bore as a guide for deshrouding, as the gasket is usually much larger, and you can end up cutting the heads to be larger than the bore (waste). I opened up my 416 heads to 64cc's though, so it's not unheard of.

Good flow results on your 081's!

was that the price for angle milling? sometimes that's more than flat, depending on who's doing it. Plus if you mill to drop 10cc's, that's a lot, and you'd want to redo you intake as well (more milling!). I know somebody has posted guidelines, ie, .005"=1cc for 305 heads, or something like that, but I'm not sure how accurate that would be. I would think you'd want to mill it, cc it (should be able to do it while it's chucked up to be milled), remill, etc.

How much is that set of pistons to you? $200USD grand total? (with shipping etc?)

 

I really don't want to change pistons. The price of only the pistons isn't the main issue for not changing them, the cost of re-doing the whole bottom end is (including machining the block). That whould cost over 1000$ total. If i change pistons i might as well do the connecting rods, have the crank balanced again etc. You get the idea.

we de-shouded the heads using the gasket as a guide, but we did measure gasket to bore difference and took this into account whine de-shouding. The chambers should be very closely matched to the bore.

My next project (next winter or summer, depending on money) well be a ls1 engine. I really don't want this 305 to eat a lot of budget since it's only a "temporary" engine put to gether with parts i've already had.

the head bolt alingment won''t be a problem i've got that sorted out. Piston to valve clearence worries me a little with the intake valve opening at 5* btdc.

Sealing the intake will not be a problem, it should be only 0.5-0.7mm (sorry for the metric units. I haven't gotten used to you're inches yet. LOL) off if i go with 1.5mm angle mill (this will put me at about a 55-56cc chamber. Correct???) Should I have the mill a litle bit, around 0.3mm from the intake side to keep the head angle bit more streight??

 

Ok. I got the heads back from the machine shop. Angle milling cost 105.08€ (exact price to the cent). Thats about 130$
Chamber sizes were from 58cc to about 56cc's. The friend who's porting the heads will size all of the chambers to 58cc (matching the to the bigest one).
The heads were milled down 1.3mm on the exhaust side and 0.1mm on the intake side.

How much compression will I gain using a copper head gasket (ultra thin)??
Compression with a stock head gasket is at aprox 9.3:1. (stock)
I'm just wondering will the larger bore size of the copper gaskets cause a problem.

Valve clearence isn't an issue, that i've sorted out.

Thanks guys for your intrest and answers!