comp ratio with solid roller cam

[danta]

I would like to know if(355 sbc) 9.4 cr is too low for 255°@0.050" solid roller .612" lift 110°ls 106°icl. Its a street build with spare parts, the heads flow 295cfm at 0.600" ,victor jr and 1 3/4" headers .thank you

[F-BIRD'88]

It's on the low side of what is going to work well on the street. You can advance the cam more, you can set the valve lash a bit bigger. You can do BOTH. You can sell the cam and get another. You could change or mod. things to kick the cr up some... 10.5:1 is. You can put some more gear in the car to help. Gear multiplies torque.

Consider moving the cam to 102 and hry it there.
You can upen the lash within reasonable limits.

[F-BIRD'88]

Re moving the cam.,
With it being a throw together do this FIRST before moving the csm to 102 in c/l.
First move the cam to 98 deg in C/l.
Now set the valve lash on cyl 1 and 6 to 0 valve lash.
Now BY HAND rotate the crank BYHAND thru 2 complete revolutions. If there is no intake valve- piston contact
Then you are good to go to now move the cam to 102 deg in c/l. You have enough VTP clearance.
102 is a good place to put the cam to start, for this one.
It will want converter and gear....

[ClassAct]

Either get the CR up to 11.5:1 or buy a different cam. I'd up the compression.

[danta]

thank you F-bird 88 i will do that and install ss coated shims 0.015" (felpro 1094) it will raise it to 9.7cr ,its for a friend and he gave me 1.560 comp height that he already bought, this is the problem the piston is 0.050 in the hole .

[travis]

thank you F-bird 88 i will do that and install ss coated shims 0.015" (felpro 1094) it will raise it to 9.7cr ,its for a friend and he gave me 1.560 comp height that he already bought, this is the problem the piston is 0.050 in the hole .

Are you sure they are 1.560”? Even on an undecked block that should put you in the .020-.030” DITH range. I’ve never seen deck clearances like that unless it is a reduced deck height rebuilder type piston which are usually around 1.540”...and you don’t want cast rebuilder pistons in anything that has the potential to rev as high as this thing will.

[CGT]

Op. Whats the application, heads, how many rpm's?

[danta]

thank you F-bird 88 i will do that and install ss coated shims 0.015" (felpro 1094) it will raise it to 9.7cr ,its for a friend and he gave me 1.560 comp height that he already bought, this is the problem the piston is 0.050 in the hole .

Are you sure they are 1.560”? Even on an undecked block that should put you in the .020-.030” DITH range. I’ve never seen deck clearances like that unless it is a reduced deck height rebuilder type piston which are usually around 1.540”...and you don’t want cast rebuilder pistons in anything that has the potential to rev as high as this thing will.

sorry the ch is 1.549 and the piston is .043 in the hole

[danta]

Op. Whats the application, heads, how many rpm's?

Its a street engine with left-over parts 355, 1142 crank, Eagle SIR rods , Speed -pro hyper pistons ,Dart iron eagle 215 flow 295 cfm@0.600,max 6500, 9 in converter, th 350, 4.10 gears in an AMC Spirit

[In-Tech]

thank you F-bird 88 i will do that and install ss coated shims 0.015" (felpro 1094) it will raise it to 9.7cr ,its for a friend and he gave me 1.560 comp height that he already bought, this is the problem the piston is 0.050 in the hole .

Are you sure they are 1.560”? Even on an undecked block that should put you in the .020-.030” DITH range. I’ve never seen deck clearances like that unless it is a reduced deck height rebuilder type piston which are usually around 1.540”...and you don’t want cast rebuilder pistons in anything that has the potential to rev as high as this thing will.

sorry the ch is 1.549 and the piston is .043 in the hole

Yes, more info please, cast piston? Is the block already decked to 9"? Don't get too bummed, plenty of 9:1 circle track engines making power.

[KnightEngines]

Deck the block to .015" deck height & use .027" gaskets, mill heads to 58cc & you'll have 11:1 - assuming 5cc valve reliefs in flat top pistons.

[F-BIRD'88]

Your money is better spent replacing the pistons. The hyper pistions from Summit racing are T5 hyper and plenty good for this. Swap them in and use the .015" gaskets too... Retorque..
Install cam in 102 to 104. Check vtp clearance as discribed. These summit pistons are cheap and fine.
Get the cr up.

[randy331]

I would like to know if(355 sbc) 9.4 cr is too low for 255°@0.050" solid roller .612" lift 110°ls 106°icl. Its a street build with spare parts, the heads flow 295cfm at 0.600" ,victor jr and 1 3/4" headers .thank you

I did a 383 for a guy with a street 66 chevy 2. He got tired of buying race gas with his 14-1 comp, and he still wanted some sound.
I put it spot on 10-1 comp, and used a 256-270-108 LSA cam in at 106 ICL with a little more lift than you have. Ported his heads etc.
It made 530 Lbs tq and just over 600 hp.

It runs fine without having ideal compression for the cam.

Do what Knight said. Thinnest gasket you can safely use to get what compression you can, advance the cam to 104 ish ICL and run it.
Unless the budget is there to buy a new cam.

Randy

[F-BIRD'88]

With the new pistons .025 in the hole and .015 gaskets
And 64 cc heads the cr will be 10.3:1...
A good place to be.
Be sure to re torque alum heads when using shim gaskets.
Put cam in at 102 to 104.
Email cam co for allowed lash range and use it.
Those 1.54" ch pistons are junk any way.
The summit house brand piston are much better.
1.56" ch. T5 hyper made by Uem KB.
Pay attention to the ring gap instructions
They are like KB.
That whole summit 350 sbc rebuild kit with these
Pistons inc is very good.
The lil Spirit may want 4.56 4.88 gears if your serious.

A machine shop will charge you so much to deck the block that much its cheaper and better to judt swap in the Summit 1.56" ch pistons. Now its done right.
I'd start with the cam on 102 and try it there.
Car needs gears

[plovett]

No, not high enough compression. But what is "enough"? It is not enough to be optimal, but like others have said, add lots of gear and advance the cam as far as is practical and it could be okay.

JMO,

paulie