Discussion Forum - Northstar Chevelle Club

Do those air tires have a load rating on them? Might help you determine if they're going to "squish" if you're close to or over their weight limit. ???

Today, John and I pulled apart the engine that will go back in the '66 after the chassis restoration. It was rebuilt in the late 70's with flat top pistons to lower the compression and a cam that was way too much for the pistons. It will get new pistons to get the compression to around 9-9.5 and a street friendly torque cam.

67ss wrote:

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Didn't you say this was a LS5 454 motor or something like that?

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 Last pic...CRT...

How do I figure the comp ratio with 97.2 cc head and the flat top piston ? Bore is +.030

-- Edited by Lost in the 60s on Wednesday 18th of November 2015 08:23:49 AM

67ss wrote:

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https://www.uempistons.com/index.php?main_page=calculators&type=comp&zenid=3ae66e375eb987304caacc59ee0a75d5 

 

I use the calculator above though it needs a few more inputs to be accurate. Any part numbers on the pistons to try and figure out the valve relief volume? That has closed chambered head on it?

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 Getting way technical for me. I didn't see any part number on pistons and as they are already out, no way to measure deck height/volume. They were pretty much even with the deck. The block is original, uncut. I'll clean up a piston better today and look for more numbers. Valve relief is minimal. If necessary, I'll pop a piston back in.

Heads are closed but not original 290's. These are '65 206 heads.

With a closed chamber head and flat top pistons you might be close to where you want to be. Just having the block zero decked could be enough to get what you want without buying new pistons.

Perfect is a silvolite 1448

https://www.uempistons.com/index.php?main_page=product_silvolite_info&cPath=6_25_27&products_id=1676

Let me run some numbers and see what I come up with. The machinist I use says he can deck the block without taking off the stamping. I asked him about it as the 327 for my chevelle is the correct 275 horse block and he said he can do it?

So it comes in at 9.2. This is using a felpro 1037 gasket. Yes you could use a thinner gasket and maybe get it up a bit. If you did deck the block changing nothing else it comes out at 9.6. But I understand not wanting to to that but just wanted to give you a comparison.

 

ENTER YOUR DATA		CALCULATED DATA		Cylinder Head Volume (cc)		Cylinder Head Vol (cubic in.)	5.929	Piston Head Volume (cc)		Piston Head Vol (cubic in.)	0.122	Gasket Thickness (in.)		Swept Volume (cubic in.)	57.549	Gasket Bore (in.)		T.D.C. Volume (cubic in.)	6.996	Cylinder Bore Diameter (in.)		Gasket Volume (cubic in.)	0.585	Deck Clearance (in.) Note: Neg. number above deck, Pos. number below deck		Deck Volume (cubic in.)	0.360	Stroke (in.)		STATIC COMPRESSION RATIO	9.226

-- Edited by 67ss on Wednesday 18th of November 2015 02:05:17 PM

Are you trying for a good quench? Around.035" clearance?

Hmm..are you sure about that measurement because I just realized the pin height on those pistons is different. It shows 1.627 and when I look up other 454 pistons is shows pin height of 1.645. I have seen this before on cheap rebuilder pistons they do that to lower compression even more. So I would expect your pistons to be about .043 or more in the hole which would bring the compression way down. Did you lay a flat edge across the opening and use a feeler gauge to check to the top of the piston?

There is one other thing we can do to be totally sure and that is to cc the whole volumn with the piston at TDC in the engine. I have a cc setup I can bring over and help you with it one night after work.

Guessing those Pistons being older they have a normal pin height. To answer your question is 9.2 to 9.6 going to make a big difference, no. But here are the two thoughts of why I would try and run the higher compression and why I would deck the block and not mill the heads. First decking the block is going to tighten the quench as John mentioned, this in turn makes the engine less prone to detonation to run higher compression. Second running most any aftermarket cam is going to give you some valve overlap, this is going to cause loss of cylinder pressure and or dynamic compression. So with the higher compression what you do lose won't be as bad which will give you better low end. Hoping this makes sense and is helping.

 I know you are on a budget but it would also be a good idea to line hone the mains on a 40 year old block. Then everything will be nice and true.

Do you have the specs on that roller cam?

67ss wrote:

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Guessing those Pistons being older they have a normal pin height. To answer your question is 9.2 to 9.6 going to make a big difference, no. But here are the two thoughts of why I would try and run the higher compression and why I would deck the block and not mill the heads. First decking the block is going to tighten the quench as John mentioned, this in turn makes the engine less prone to detonation to run higher compression. Second running most any aftermarket cam is going to give you some valve overlap, this is going to cause loss of cylinder pressure and or dynamic compression. So with the higher compression what you do lose won't be as bad which will give you better low end. Hoping this makes sense and is helping.

 I know you are on a budget but it would also be a good idea to line hone the mains on a 40 year old block. Then everything will be nice and true.

Do you have the specs on that roller cam?

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 If John is suggesting a .035 clearance is a good quench then wouldn't the .032 I have be good ??

The block was checked in '78-79, when it was rebuilt with these pistons. The crank was polished and I believe the block was checked for main cap alignment or honed then. The only other thing they did was bore it the 30 thousands. There was very little use on it when it was removed from service in the mid 80's. It had sat in my former B-I-L's garage since then until I got it back about 8 years ago. This is the original engine from the '70 SS 454 Chevelle I bought in 1973. I know where the engine has been for 42 years... Not that it makes any difference to what we are doing right now, but I would sooner buy custom machined pistons than deck the block.

I didn't get a part number on the cam to look up the specs. You're saying less overlap will retain more of the compression. What is a good number for that...108, 110, 112. I get confused remembering if the lower number is the better.

What Chris said. A good quench distance can maximize the potential of the engine and provide more resistance to detonation even though you may increase the compression to get it.

What do you know about the 454 that is in the car right now? It is a newer 1 piece block I think you said, is it also a factory roller cam block, and a 4 bolt main? 

67ss wrote:

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What do you know about the 454 that is in the car right now? It is a newer 1 piece block I think you said, is it also a factory roller cam block, and a 4 bolt main? 

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 It's a Gen V, so still flat tappet. It is a 1 piece seal and 4 bolt mains.

Lost in the 60s wrote:

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67ss wrote:

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Guessing those Pistons being older they have a normal pin height. To answer your question is 9.2 to 9.6 going to make a big difference, no. But here are the two thoughts of why I would try and run the higher compression and why I would deck the block and not mill the heads. First decking the block is going to tighten the quench as John mentioned, this in turn makes the engine less prone to detonation to run higher compression. Second running most any aftermarket cam is going to give you some valve overlap, this is going to cause loss of cylinder pressure and or dynamic compression. So with the higher compression what you do lose won't be as bad which will give you better low end. Hoping this makes sense and is helping.

 I know you are on a budget but it would also be a good idea to line hone the mains on a 40 year old block. Then everything will be nice and true.

Do you have the specs on that roller cam?

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 If John is suggesting a .035 clearance is a good quench then wouldn't the .032 I have be good ??

The block was checked in '78-79, when it was rebuilt with these pistons. The crank was polished and I believe the block was checked for main cap alignment or honed then. The only other thing they did was bore it the 30 thousands. There was very little use on it when it was removed from service in the mid 80's. It had sat in my former B-I-L's garage since then until I got it back about 8 years ago. This is the original engine from the '70 SS 454 Chevelle I bought in 1973. I know where the engine has been for 42 years... Not that it makes any difference to what we are doing right now, but I would sooner buy custom machined pistons than deck the block.

I didn't get a part number on the cam to look up the specs. You're saying less overlap will retain more of the compression. What is a good number for that...108, 110, 112. I get confused remembering if the lower number is the better.

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The tighter you go in LSA  (lower number) the more overlap youll have... Overlap is also a function of duration as well..

Lost in the 60s wrote:

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I have a flat tappet cam I bought many years ago for this engine, but it may be too much overlap for the compression too. It's a Comp 280H. LSA is 110 with 280 degrees of duration. valve lift is .52. Their description is rough idle and 2-6k power range. Not really what I'm looking for anymore. I bought this along with an old Torker manifold that mounts the carb at an angle. Was looking for a "day 2" set up at that time.

Would that work with the pistons and deck clearance Chris ?

Not really in a position to funnel much for funds to the engine right now. I'm more concerned with the chassis and body restoration.

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Mitch, I had that 280H in the white w/black stripes '71 Chevelle a few years ago with a 396 and a Saginaw 4 speed.  That was a great cam, and I really liked it.  It had a nice lopey idle, but still had a lot of torque on the low end.  At first the Chevelle had a TH350 with a 3K rpm stall in it, and it would squawk the tires leaving the light if the rpm got too high...  then when I put in the Saginaw, I could overtorque the clutch pretty easy if I wanted to while it was in gear.  It was a good cam for that motor. 

Sounds like Stan had good luck with that cam. My opinion is that cam is borderline for your combination and what you want out of the engine, but I think you can get away with it because your larger displacement engine will give you more low end torque. Another thing you could do is advance it 4 degrees to move the power band lower in the RPM range.

OK, how about the XE268H ?? Seems to be more low compression friendly.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=395&sb=2

I like this one. I still think we should cc everything  on your engine to be more accurate on the compression. I think it is less then what I calculated.

 https://www.lunatipower.com/Product.aspx?id=2150&gid=287 

67ss wrote:

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I like this one. I still think we should cc everything  on your engine to be more accurate on the compression. I think it is less then what I calculated.

 https://www.lunatipower.com/Product.aspx?id=2150&gid=287 

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 There's this one too https://www.lunatipower.com/Product.aspx?id=2149

It still has plenty of lift but even less duration and overlap to prevent bleed off.

If you want to take the time to cc it first, that's OK with me.

Interested in learning more about Static CR and Dynamic CR and how little changes make changes.  I plugged in the numbers for my current engine, cam, and Fel-Pro gasket thickness of 0.39 and bore of 4.370,  I came up with a Static of 9.289 and a Dynamic of 7.907.  When I used a steel shim with thickness of 0.18 and bore of 4.370, the numbers were 9.736 and 8.279 respectively. With a copper gasket with  thickness of .021 and diameter of 4.250 I got 9.694 and 8.244.

I read a couple of articles on Static vs Dynamic compression ration, which I don't quite understand; but it seemed to say that Dynamic is important when you are using 91 octane gas.  Seems to say you would have a dynamic of 7.5-8.5.

This is the article I read.  http://www.enginebasics.com/Advanced%20Engine%20Tuning/Static%20vs%20Dynamic.html

-- Edited by jim larson on Thursday 31st of December 2015 08:46:48 AM

Stopped by Mitch's house last night to CC his heads and top of piston to deck height volumn. Heads were supposed to be 97 CC chambers and they came out to about 120CC so not sure what is going on there. But case in point had we assumed they were 97 and put it together it would probably not have performed as expected.

 

Mitch here is a picture of the chamber on the 215 heads for the 396 I have. I think the chambers on your 206's looked a bit different, see what you think. I will CC one of them when I get a chance to see if it comes up as 101 CC that is stated on the internet.

This is a photo from a pair of 206 heads I have that I am not going to use.  Do yours look much different?  I don't think these have been machined or worked on.

-- Edited by jim larson on Monday 18th of January 2016 03:43:13 PM

A difference of 23 cc from standard to what you got at 120 on Mitch's head seem a lot.  That a little more then a 1" cube of ice.  When I cc'd my 207 heads they came out just a little over 98cc's according to the book they are suppose to 98.427 cc's.  Something drastic must have been done to Mitch's heads. Could some of the liquid leaked down through a crack?  His should look just about identical to the photo of my 206 head.  Thats why I posted the photo.  Unless something was wrong with the container you used to volume.   I just used  25 and 10 cc syringes.  Those kits designed for this task look to be the clear deal.  I must have been off in space when you cc'd Mitch's head.  I didn't realize what that head sitting on Mitch's frame was for.

-- Edited by jim larson on Monday 18th of January 2016 04:47:15 PM