i want to put a set of vortecs on my l03 305

i also want to be able to swap those heads over to a 383/400 at a later date after the 305 expires.

obviously, i'm going to have to deck the heads, as the l03 has 58cc chambers and the vortecs have 64cc chambers.

the challenge for me is that if i cut the heads enough to maintain stock compression on the 305, the chambers'll be too small to make my goal of 9.5-1 compression on the 383/400

i'm wondering if there's a compromise i could live with. maybe cut the heads to 60cc, for example, and run the absolute thinnest head gasket available, then run the thickest gasket available on the 383/400.

if such a compromise is possible:

1. how do i calculate how many ccs to deck the head to to reach that compromise.

2. how much will i have to mill the heads to get there.

3. what are the thicknesses/manufacturere/part numbers of the thinnest/thickest head gaskets needed to make it happen?

 

Don't shave them. Use a thin gasket on the 305, you'll see a performance increase bases solely on the improved flow. What gasket you use on the 383/400 depends upon the pistons and desired CR.

 

58 to 64cc would be a pretty serious compression drop. how much of that can you make back up with a thinner head gasket?

how thick is the stock 305 head gasket? what is the thinnest 350 gasket available (you have to use a 350 head gasket when you put vortecs on a 305)? how much compression will the thinner gasket make back up?

 

help

 

I'm honestly not sure what the stock gasket thickness was. The only later engines I've had apart had been rebuilt with composition gaskets. My LG4, though, had steel shims from the factory.

From those who have done it, the reports are that the increase in flow and improved combustion efficency of the Vortecs more than make up for the decrease in compression on a 305 - even on a really-low compression LG4. Good news is at least the LO3 has flat top pistons. Since you plan on putting the heads on a 383/400 some day, don't burn your bridges on the 305. You'll maintain the most compression possible by using steel shim head gaskets when you put the Vortecs on the 305.

 

I thought that the small chamber and dished piston was the way to go. If you get them to 58 cc now you could just buy the right dished pistons for the bigger engine.

 

That's a legit approach. With the larger dsplacements, though, the CR gets higher with the same chamber size. But, as you say, buy pistons with dishes to match.

Chevy High Performance mag, in a recent 406 article, used 68cc chamber AFR's to replace 64cc Vortec heads - still used 22cc dished pistons to keep compression down (was 9.5:1 with the Vortecs). With the same cam and intake type, they made more power & torque on 87 octane than they did with the Vortecs. Point is, though, if you need 22cc dish with 68cc chambers to get below 9.5:1, imagine the dish required with 58cc chambers.

 

Yeah that is true, the pistons would start looking kinda funny.

 

you've got it backwards. the gasket thickness is dependant on the distance of the piston down the cylinder. these two measurements should equal .035-.040" no more, no less. then the piston should be used to accomplish the desired compression ratio. goung to a thinner gasket in attempt to create more clearance or lower compression will actually make the engine more prone to detonation.

 

OK. If you go here..... http://members.uia.net/pkelley2/crc.htm you can enter the figures as follows.....

Number Of Cylinders 8
Bore Diameter [in] 3.735
Stroke Length [in] 3.48
Combustion Chamber Volume [cc] 58
Head Gasket Compressed Thickness [in] .039
Head Gasket Bore Diameter [in] 4.06
Piston To Deck Clearance [in] .025
What type of pistons do you have? Select "Dished or Flat Top"

Dish/ValveRelief/Dome Volume [positive cc] Enter "4.5"

You'll get...

Results:
Displacement, [cubic inches] 305.028
Displacement, [liters] 4.998
Static compression ratio 9.3018

If you change the "Combustion Chamber Volume" to 64cc, you'll end up with 8.689 : 1 "Static compression ratio".

That's kind of low, but not horrible.
If you go to a .026" thick GM gasket, you'll get it back up to 8.958 : 1.
A little better, and reasonable enough to get you by.

If you put the gasket thickness back to .039", then change the "Bore Diameter" to 4.030" (typical rebuilt 350), with 64 cc chambers, you'll get 9.87 : 1 comp ratio. Not too high for a street motor, but I wouldn't go any higher.

If you get the heads milled to 58cc's, then put them on a 4.030" bore with .039" gasket, and use 12 cc dished pistons, you get 9.71 : 1 comp ratio.

That's not too high at all for the street, nor 87 octane. The Vortec heads don't require a lot of total timing (~34* BTDC), and the chamber design allows you to kind of push the limits on 87 octane.

This is all based on .025" deck height. Add that to the .039" gasket, and you're at .064" quench area. That's ~.020" over the recommended quench on Vortec heads (.035"-.045") which will make it more prone to detonate.

What I would do is run the 305 with the Vortecs as is. Then you have more to work with later on when it's time to put them on the 350.

 

sounds like a great idea... lets take a detonation prone piece of crap, and make it even more detonation prone by not setting the quench distance like we're supposed to. i'd skip the Vortecs on the 305. you'd be wasting your money, save it for the 350 you're planning on putting in already.

 

It's temporary.

If you don't have any realistic points of view, or recommendations that are helpful, then lay low for a while.

While 35-45 thousandths is optimum, it doesn't mean that anything over that is disastrous.

 

regardless of if its temporary or not, its pointless, because its still going to shroud the hell out of the valves like a 305 is doomed to do. you cannot bore it out enough to unshroud them. that kills flow. i've got plenty of realistic points of view, and helpful information. i just did the research about 2 weeks ago... i have a set of 906 Vortecs on the shelf, and a 305 that was a bare shortblock 2 weeks ago. in short, the 64cc Vortecs werent worth the extra cost over the stock 58cc heads. power gain was too minimal to warrant spending the extra money on an intake that i really didnt need. the small bore is what would've killed it.

 

aj,

thanks for the info ... it really helps. i read in a magazine tech section this weekend that you'll see about 1 cc loss in chamber volume for every .006 milled off the heads. if that's correct, taking .020 off and using a thin gasket should be good for about 60ccs and stay close to tolerances on the quench area as well. i need to do more checking before i settle on that, though.

backinblack .... i agree with you that it's not worth it to spend the money on heads for the 305 alone. that's why i'm trying to do this in such a way that the heads will swap over to a 383 or 400 later, where i'll see their full benefit.

i disagree, however when you say there'll be NO benefit of putting better heads on the 305. there are too many people on this board who've done that swap and seen big performance gains.