462 build, help with static and dynamic compression

I'm having a hell of a time figuring out the dynamic comp. ratio, and could use some help to verify the static comp ratio.

I have a .030 over 455(462 cid) with stock rods and TA forged stock type pistons with valve notches(TA2353's) and a 10/10 crank. I will be useing TA Stage 2 SE heads. I believe those heads are 58cc and the pistons are 25cc. The pistons are .050 in the hole(yes thats right, I checked it twice), and lets figure on a .040 head gasket w/ a 4.40 head gasket bore(I'm guessing). I come up with an even 10:1 static comp. ratio.....

I've included the cam card for the TA288-92H cam I have...I want to make sure I have a correct dynamic comp. rato, so if someone could please help me with that I would be most greatful. I need to know what it is and if its OK, and if its not OK, please advise what I should do to correct it.
Thanks!

 

Collin

You are right on for the Static compression ratio.
The cam card shows the cam installed without any advance which means the intake closing .006" lobe lift is 74 degrees ABDC as shown on the left hand side of the card.

Plugging the 74 degree value into the DCR calculator will give you a 7.4 Dynamic compression ratio.

Paul

 

Thanks Paul...



and 7.4 DCR is acceptable correct? I believe 8.0 is the goal from what I've read on here...but I'm still good I assume?

 

Yes you are good to go!

I do have a question. Do you know for sure that the heads have a 58 cc chamber?
The Stage 2 head can have as high as a 64 cc chamber but usually come in a little less.

Paul

 

No, I'm guessing I was wrong. Looks like you and Larry are correct.

Yes those are the pistons I have, sorry for my errors. You and Paul must be right. I thought I had read that the Stage 2 SE heads were 58cc. I need to bring those numbers up...Buy going with a .027 gasket and shaving .030 off the deck to put the pistons .020 in the hole(I'm at .050 now) would bring it up to 9.71:1 SCR. Where does that put my with the DCR?

Any other suggestions to bring it up? Should I just zero deck the block instead? Please advise...

 

The best way is to zero deck the block to maximize quench providing you can still have a workable DCR.
In your case IF
chamber is 64cc
piston volume is 28 cc
.040 head gasket
Zero deck

You have a 10.3 static compression ratio
If the cam is advanced 4 degrees the Dynamic compression ratio will be 7.87 which is still good.

But, you must measure the chamber volume and piston head volume before you deck the block. No guessing allowed!
Then you can know how far the block can be decked.

Will the heads be ported?

Paul

 

Paul,
I dont have the heads yet. I havent made that BIG purchase yet, so I can't cc the heads. I have the pistons and can cc those.

If I understand correctly, when zero decking the block, the top of the piston is even with the top of the deck which yields the "zero deck". If I do this then the only clearance I have from the piston hitting the head is the head gasket thickness, correct? I'll assume this will suffice. I'm learning...just slowly at times


To answer your question about porting the heads, I hadnt planned on porting them. Just use em right outta the box.

 

If the piston is at the top of the deck then the quench distance is the head gasket thickness. .038" to .040" is good.

The reason why I asked about head porting is the chambers can be adjusted to a specific volume as part of the job (Within limits)
You should wait until you get the heads before decking the block.

The Stage 2 head is a good choice.

Are you doing the engine assembling?

Paul

 

With help from an experianced engine builder yes...I wouldnt tackle this on my own. I'll wait till I get the heads

and scream is what I'm hoping for:grin: I've heard from others that this combo should rock. I just need to get the numbers right.

Speaking of combo, I had planned on useing a TA SP1...should I be considering a B4B instead? This is a street car....

 

Collin

Have you already installed ARP bolts and resized the factory rods?

Paul

 

Paul...yes I have.

---------- Post added at 02:44 PM ---------- Previous post was at 02:39 PM ----------

Larry...
Thank you for the input. I will stick with the SP1 and go with the Q-Jet base.

 

Collin
I was hoping you hadn't invested anything into the stock rods yet. IMO you will be pushing the limits of the stock rod but I will let you decide.

When the piston approaches TDC at the end of the exhaust stroke the rod is stretched and the hole in the big end goes oval.
The diameter at the parting line decreases while the diameter along the line of the beam increases.
That why a rod bearing has more clearance at the parting line than at the vertical.

If you look at the factory rod beam you will notice a 90 degree notch removed from the beam to clear the head of the rod bolt.
That notch becomes a pivot point as the big end flexes between oval and round and even if the rod never breaks at that point it allows too much distortion at high rpm levels affecting bearing clearance.
The worst offender is the rod cap. Notice on this cap (lower picture) how there is very little rib left where the arrow is.
If you look at area behind the black dot there is very little material left at that point also.

Our shop is just starting a BBB build and we did our best to talk the customer out of using stock rods for a performance build and he listened.
You decide.
Paul

 

Not disagreeing with anything you are saying Paul, but do you think he'll be making enough horsepower to be worrying about a stock rod? The 288-92H cam isn't that radical and will probably top out at 6,000rpm or less o No: I would think something else would give before the rods would, like main webbing, or oiling system not keeping up, etc.

 

I'm not disagreeing with you guys either and I value your input greatly. That said, do I need to worry about the stock rods on this build even though its a street car? I will not be on the track at all, nor on the high side of the RPM range. Maybe this is to much for a street car? :Brow::laugh:

 

I see RPM more than horsepower being a factor in what Paul is talking about, namely on the exhaust stroke. If he were worried about bending the rod like a preztel from HP on the compression stroke, ok that's one thing, but citing an exhaust stroke failure from what I can tell is purely an RPM thing. Granted the pistons are heavy, but they shouldn't be inevitably to rip the rod apart heavy below 6,000 rpm. I think the oiling system at 6,000rpm would be a bigger concern and knowing if the mains are straight and round and evenly torqued, etc.

And in compression, you should be able to cram a ton of HP through a stock forged rod if the crank is past 10* or or so of it's 360* rotation (aka, don't hit it with too much advance on the ignition).


Skidmark, I'm running stock rods with ARP bolts in my engine, though I am running the lighter .038" pistons (I did run the 10:1 .030" cast ones for ~35,000+ miles until detonation took them out on iron heads and 118 cam), but 232* duration and almost as much lift at .515" on a 110* LSA. I've got probably 12,000 miles on this combo and winging it to around 6,000rpm on the track and from time to time on the road. I could be on borrowed time, but I don't think it'll be my stock rods that'll be the weak link.

---------- Post added at 02:08 PM ---------- Previous post was at 02:01 PM ----------

Okay, I shouldn't of said HP, I meant RPM. I still don't think HP is a factor yet.