I could spend money and mill the heads down but then I’ll probably run into intake manifold fitment issues. My attitude in all this would change if there were flat top pistons there. Trucks going to be a dog with those compression numbers
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Bad Valve Guides?
- Thread starter Operator238
- Start date
yes change the head cc to 56cc and see 9 to 1 will run. https://www.summitracing.com/parts/tfs-30310002/make/chevrolet
Nine to one is still kind of low they make a 2 inch valve intake and a roller cam style head?
Did I do this right?
no the spec I came up with on those pistons is 1.54. not sure where you got .185, that would very small, like maybe 2 valve eye brow relief in flat pistons
9 to 1 with today's gas is a safe compression, with cast iron heads. Aluminum can go a little higher. Unless you have computer controlled timing.
https://www.summitracing.com/parts/slp-h580cp60/make/chevrolet my lap top is to small to screen shot enough of this page.
look at compression height
look at compression height
That’s just the distance form wristpin centerline to the crown.
That is the spec that the compression calculator wants. How it is measured I am unsure. Personally I like cc which I believe is the displacement of the piston crown to the top compression ring.
Trick Flow Fast As Cast Heads
175cc heads 56cc chambers 1.94 /1.5 valves
1.460 springs (Max 600 lift)
Cosmetic MLS Head Gaskets C5245-023 (.023)
Howards CL183215-10 Cam and Lifters
217/225 .495/.500 110 LSA (@.050)
SCR should be 9:1
DCR should be 8.04:1
How does that look to yall? Should be a fun street motor?
I’m using
4.06” bore
3.48” stroke
5.7” rod length
56cc combustion chambers
.023 compressed head gasket 4.06 bore
+26 cc dish piston
.20 piston in the hole (deck clearance)
Calculated the IVC to be 34.5*
175cc heads 56cc chambers 1.94 /1.5 valves
1.460 springs (Max 600 lift)
Cosmetic MLS Head Gaskets C5245-023 (.023)
Howards CL183215-10 Cam and Lifters
217/225 .495/.500 110 LSA (@.050)
SCR should be 9:1
DCR should be 8.04:1
How does that look to yall? Should be a fun street motor?
I’m using
4.06” bore
3.48” stroke
5.7” rod length
56cc combustion chambers
.023 compressed head gasket 4.06 bore
+26 cc dish piston
.20 piston in the hole (deck clearance)
Calculated the IVC to be 34.5*
That looks like a good plan, I have a few concerns I will mention though.
I ran the numbers through my app...I like to use the advertised duration when it comes to dynamic compression calculation because it can't actually start making compression until the valve is closed. Theoretically if the piston speed is high enough it could but it will be leaking pressure until the valve is closed.
Second, although I like your planning to reduce quench and increase compression, I don't think I would recommend that gasket for this application. Due to gasket compression, tolerance stackup, bore chamfer, etc, you shouldn't use a 4.06 bore gasket with a 4.06 bore. You should use at least a 4.08-4.09 bore gasket.
The other issue is that MLS gaskets require a very fine finish on the deck surfaces to seal, so I don't usually recommend them on older style blocks unless they have been decked and have the proper surface finish for a MLS gasket. MLS gaskets are very good, and I recommend them over a traditional composite surface head gasket, but they need a finer finish.
Also, I noticed you mentioned the piston is .020 in the hole, however, did you measure it? Because the compression height is .020 low, and typically the blocks can be .020 high unless they were decked. So it's possible the piston is .040 in the hole or more...
This is what I get if you run it with a regular gasket...if you can find a thinner gasket you trust, or you find the deck finish is fine enough, then you can use the 4.8 cc thinner gasket which will help.
I ran the numbers through my app...I like to use the advertised duration when it comes to dynamic compression calculation because it can't actually start making compression until the valve is closed. Theoretically if the piston speed is high enough it could but it will be leaking pressure until the valve is closed.
Second, although I like your planning to reduce quench and increase compression, I don't think I would recommend that gasket for this application. Due to gasket compression, tolerance stackup, bore chamfer, etc, you shouldn't use a 4.06 bore gasket with a 4.06 bore. You should use at least a 4.08-4.09 bore gasket.
The other issue is that MLS gaskets require a very fine finish on the deck surfaces to seal, so I don't usually recommend them on older style blocks unless they have been decked and have the proper surface finish for a MLS gasket. MLS gaskets are very good, and I recommend them over a traditional composite surface head gasket, but they need a finer finish.
Also, I noticed you mentioned the piston is .020 in the hole, however, did you measure it? Because the compression height is .020 low, and typically the blocks can be .020 high unless they were decked. So it's possible the piston is .040 in the hole or more...
This is what I get if you run it with a regular gasket...if you can find a thinner gasket you trust, or you find the deck finish is fine enough, then you can use the 4.8 cc thinner gasket which will help.
Last edited:
I use CC, most piston manufacturers will show the dish or dome in cc. I often measure the combustion chamber with a large syringe or a buret and a flat piece of lexan with a tiny hole in it to fill it.
6.79 DCR? Ouch. I’m pulling the motor. Haha
this is why I recommended 56 cc combustion chambers. Also why you found 305 head on your 350, they have 56-58cc combustion chambers.
need to measure the piston from deck so we can get a very accurate picture.
need to measure the piston from deck so we can get a very accurate picture.
that is just what came on the truck. Driver side is a 601 head and passenger side is an 801 head
Yes both 305, and very very similar casting. That engine might have been overhauled for a parts store . The 400 on my burb had 2 different casting numbers on it. Paper work said was done in Glendale ca shop. Still under warranty to original purchaser. Very crappie work.
I pulled my build, out of beat base trim square , and stuck in the Silverado I have now. That 21 years ago.
I pulled my build, out of beat base trim square , and stuck in the Silverado I have now. That 21 years ago.
- Joined
- Feb 17, 2000
- Posts
- 1,009
- Reaction score
- 185
Fyi summits listing says 23cc dish on those pistons. Not much help but every little bit helps I assume.
Although we are overlooking the most logical solution. 72cc heads and an 6-71 blower.
Although we are overlooking the most logical solution. 72cc heads and an 6-71 blower.
Last edited:
You are correct, I had the 56 cc heads in there but I must have done the screen shot before I did that.
The thin MLS gaskets would help, but I worry they won't seal reliably if the deck isn't perfect.
Figuring dynamic compression, is not something I have a lot experience with. What would be an acceptable dcr for reg pump gas and street performance
