PLEASE NO -305 sucks, 350 is best, swap that in- posts! Thanks!

Howdie folks,

today my brain start to melt itself. My enginebuilder is in process of doing my 305. I ordered the Speed Pro H534 pistons with .030 oversize and 5cc valve reliefs flat top pistons: https://www.summitracing.com/parts/slp-h534cp30

My builder is not amazed by the bump in compression with them over the OEM dished pistons, he told me to watch the DCR with the camshaft. My fault was, I never dealt with the DCR before. The engine get new trickflow heads: 175cc runner volume, 56cc combustion chamber, 1.94,1.5 valves. So part of that, I got myself more into it and already knowing my SCR (~) with aimed values when the engine is finished.




As you can see, I´m going pretty high in DCR, as far I typed everything right in.
I wanted those pistons cause of the 1.56" compressions height that I wont sit deeper in the bore with the 1.54".
But then I had to choose the flat top pistons, no other were available. So I have this bump up in compression, which is a good thing I thought.
But with the valve timing of the SLP51002 cam I have with 31 intake valve closing ABDC @.050" it will have high DCR numbers.

All maths were taken with the Mr. Gasket 5870G head gasket, which is a 3.87" bore gasket size and a 0.028" gasket thickness.
Till yet I dont know if the 3.87" gasket bore size will clear the trickflow heads, as the manufacturer says something with 4.166" gasket bore size.
Question is sent but no answer yet. Maybe my enginebuilder could measure that, the heads are at the shop right now.
Aimed quench is .040" - .045" but that can be clarified after their engine block work, they will measure the pistons depth for me. The block will be decked somewhat, but not zero decked.

What do you guys think about those numbers and the camshaft with that SCR + DCR?
Im a little lost, I want this camshaft so bad in my engine.... But dont want to run premium gas all the time.
What can I do? Some advise would be greatly appreciated!

 

You're within reason having alumium heads and I'm assuming fuel injection. 9.0 isn't unheard of.

As for right now those numbers are all ballpark guesses and no actual measurements. Bigger head gasket bore and that'll bring it down. You're also guessing on the piston to deck clearance which will likely change everything about head gasket choice. Measurements mean something. Guesses don't. You'll be fine. I know how easy it is to get entangled up in the details of your build

 

Thanks for helping me calm down.
Yes, its fuel injected.

Of course, I´m just waiting for measurements. But if its already guessed to high, I would have bought another camshaft with the next summit order.
I will keep you updated as soon as I have measurements and answers.

 

Hey guys,

finally, I can pick up my rebuilt engine coming monday from the builder.
They gave me the infos I needed to make a correct calculation on my CR.
So the deck surface has been worked over, 0.004" of material came off. The deck clearance (how far the piston is in the hole) is 0.022" - 0.024". (rounded up to last full decimal)
Thanks to the info with the compressions height of the pistons that 1.56 being right.

The head gaskets im inclined to work with are Mr.Gasket 5780G with 3.870" bore size and .028 compressed thickness. They fit well to my 305 bore size beeing a small bore engine. All other gaskets I can find are 4" or over and that is a eyesore for me. Maybe you can come over with arguments to convince me to take 4" gaskets but I think the smaller gasket are better. Only downside: I would have a quench of .050 -0.52" then not being ideal. And I like having it ideal.

So please throw me out your two cents here guys!

The SLP 51002 camshaft was successfully degreed in according to camshaft manufacturer specs with intake valve closing 31° ABDC.



So according to this calculator my static CR is 10:1. But the dynamic again shows pretty high. But I dont know what to type in "adjusted stroke" beeing calculated automatically? Please clear my mind!
If you need any more specs, just ask.


Another calculator show me this, quite a difference for DCR but with the same values.

Greetings,

Chris

 

My 11:1 383 is at about 9.6:1 dynamic and 225 psi cranking compression yet runs great on 91+. Just run the premium, you will likely get enough MPG gain to equal out the higher cost for the premium running a more aggressive advance curve than trying to skimp by on less timing. More power and nearly the same running cost is what I have found everytime I tune for premium. As a side benifit premium gas has added detergents and your engine will stay cleaner.

 

Don't give the DCR another thought. Back in the day. I used a similar grind in a number of L69 305s with cast iron heads - you WILL NOT have an issue. That's going to be a really good cam for you in a 305 with those heads. (EDIT - adding after seeing FAST355's post. All those used premium fuel and suggest you do as well.)

A friend recently built up a L69 305 (carbed), used the Comp equivalent cam, and the TFS175 heads. His is running extremely well. He did run into some issues with the heads though. I got him to breakdown the heads to check the valve and seats. Good news the valves and seats were good. Bad news is he noticed what appeared to be a hairline crack in a keeper. Was able to snap it into with his fingers.

crower chromoly machined valve stem locks
That could have been a really bad deal if he hadn't caught it. He lost faith in the rest of the pot metal keepers and ordered a set of Crower chromoly machined valve stem locks.

Next, he did a mock build with the guide plates off and found the 1.6:1 roller rockers were causing the pushrods to kiss the heads - the pushrods would have probably cleared with 1.5:1 rockers.


THEN, he noticed where the pushrod slots had not been fully machined causing additional clearance issues on a few pushrods.




Only took a little grinding to "fix" the pushrod clearance issues, but make sure you have your builder THOROUGHLY check the heads and do a mock-up before bolting them down!

 

I agree, too much attention is played on dynamic comp calcs. Run premium fuel and being efi, tune it to run right. You have excellent control over fuel and timing that most carb guys dont have. You should not have any issues

could go up in cam tho

 

You MUST know how the DCR calculator that you are using handles the volume of the piston - whether a dished piston is a positive or negative number.
Re run the DCR calculator with -5 for piston volume and see if that agrees with the results from the other calculator.

Adjusted stroke means what the stroke actually looks like to the engine. In other words, compression does not happen until both valves are closed. So in your case, the intake valve closes 31 degrees ABDC. The exhaust valve is already closed. Theoretically, if your intake valve closed right at BDC, then the full stroke of 3.480" would be available to build compression. Since your intake valve closes 31 degrees later, then the actual compression building part of your stroke is reduced to 3.3024". Get it?
You should be targeting a DCR of no more than 8.3. A bigger cam with more duration will help bring that number down some.
Assuming that all of your measurements are correct, then a camshaft with an IVC of 59 degrees gets you down to 8.32:1 DCR.
Keep your quench tight to avoid detonation (.040 target).

Your head gasket needs to match the heads, not the bore. Your Trick Flow heads will not have a round chamber, especially with the larger valves.
Here are pics from my engine. I had to notch the tops of the cylinder bores.

 

I know how the calculators handle the dished/domed values. That has been done right. Maybe I tiped in something wrong with the adjusted stroke.
Yes, that makes the adjusted stroke clear to me, thanks!

Trickflow recommends a 4" bore gasket (I think for the 350s?) while a gasket with 3.750" beeing the smallest size I could use.
My gasket has 3.870" and suit better to my bore size thats why im attempting to use those ones.
What would you say? Bore notched would be nice, yes, but thats too late now.^^

So thats funny. 3 guys here say run that engine with the (D)CR and 1 say lower it with more camshaft duration (dont want too much overlap since powerband is 1000-5000) and it still be kind of a daily driver. And lass radical camshafts get tuned better. And as far the builder is done with degreeing and so on and sealed it for warranty the part with the camshaft is done for me.

Now just the head gasket matters. I will come to .050"-0.52" quench so that would allow to get another gasket (then with 4", is it bad for such a small bore?) and bring it down to proper quench...?

 

Chamber diamaeter is what matters for the head gasket. The head gasket needs to be large enough not to overhang into the combustion chamber. How far down the bore are the pistons at TDC?

 

Without wanting to get into an in-depth discussion about Compressions Ratios...

I just want to say that there are many, many variables in regard to both Static and Dynamic Volumes...
as to the behavior or outcome of each.

Strictly discussing Iron Block and Head Gen-! SBCs...
Quench area and Valve Events are going to be the Hot Topics, pertaining to Dynamic Compression Ratio.

 

The pistons are .020 - .022" down the hole at TDC.
I really cant find another good gasket that is in stock and fits my needs perfect. Either 4" with round holes would work or under 4" with not rounded bore holes.
And the gasket thickness should be less than .028" cause thats what im having here with the Mr.Gasket 5780G.

https://www.summitracing.com/parts/c...make/chevrolet

Maybe that one? Bumbs up my CR a liiiiittle bit but brings my quench to .045 - .047" at least. I will check tomorrow if the mr gasket fits the head size.

 

I've used these before with good results on some budget builds - the guy used them on his 305 with the TFS175 heads. 4.100", .026" compressed (5.4cc total). $19 each and currently showing 3 in stock at Summit.
https://www.summitracing.com/parts/mah-5746

 

Measure your cylinder head chambers and confirm they are smaller in diameter than your 3.766 engine bore, then give Cometic a call and order a set of custom ones tailored to your engine. They are worth the wait, and the cost. This is the center layer of my MLS gasket from my old turbo 305, compressed thickness of 0.030", was used with ported 416 cylinder heads in which were slightly smaller in diameter. Held 20-psi like a champ, sealing was excellent. The piston rings on the other hand, weren't...

- Rob

 

Hey folks,

my engine is finished with building and in the car and runs. I wanted to say thanks to all who helped me.
And of course I leave some pictures and infos for you that other guys can benefit from this story.
It has some power, didnt go so far cause it has only 700 miles on it and my ECU makes problems, switching to holley HP EFI soon.
Sorry that the order of the pictures are backwards.

The are some pre ignition when I use normal unleaded fuel (here its 95 octane, I think its comparable with your 91 in USA) at 3000 rpms (torque peak?) with 30° - 31° BTDC totally, if I put better fuel on it, theres nothing. And with the normal fuel, its also very knock resistant. I run 195° thermostat and no EGR, so combustion temps will be on the higher side. Its ok for me, tempting to go with headers now and soon after put the Holley EFI in it im ready for some dyno pulls.



Finally done.

Nearly complete assembled, the frostbite radiator fits nice in it!

Before putting it in the car.

So back in the car

Measured the pushord length and installed roller rocker arms from comp cams. Theyre quite loud, need to figure out that.

The pistons have enough clearance during rotating, thanks to the mild cam. Maybe I should have gone up a notch in duration on that cam but however, nothing is impossible later on.

Put the heads on and begin to make the "check-work"

Layed the head gasket on top and marked where the blank surface shines through to ensure nothing is rusting after building.

Assembled the engine from the bottom to top and began to put some paint on it.

So back to work B-)

That how I picked up the block from my engine builder. They did a great job and correctly adjusted my camshaft SLP 51002

 

Need to back the timing off 4-8° in the 2,400-4,000 rpm range where the TPI is really boosting the VE.