need advice from engine builders quench vs compression on 355 build
 

OK so I touched on this a while back but after double checking some measurements and realizing that speed pro rates their compression ratios with their pistons with a .066 quench! I'm in a pickle on which way the go....
I also found counterdicting specs.... this site rates them at 9.47 http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=200654304491

And this site rates them at 9.35:1 with same 64cc heads? http://www.northernautoparts.com/ProductModelDetail.cfm?ProductModelId=10 712

I have flat tops (H345ACP30) with 64cc iron eagle heads...I just double checked the CC volume of the heads and it is indeed only 64cc despite my previous measurements being 66 CC

The H345ACP30 pistons are rated at 9.47 car with .025 deck and .041 gaskets. (Bad .066 quench) and 64 CC heads this comes out to a +7.5 CC relief piston even though its advertised at 5cc?

I have confirmed I have a whopping .034 deck height with the rebuilder pistons.

I know the quench will be terrible at .066 but if I use the felpro 1094 gaskets (.015) I will have a .049-.050 quench but my compression will climb to 10.1 screen and 8.5 DDR with 5cc spec or 9.9:1 screen and 8.4:1 dcr with 7cc (this is what I measured with syringe for the reliefs).
This is with my 268h cam (not xe) with 110Lsa and 6 degrees advance...
Now if I use the .026 gaskets I have my quench will be at .060 but my compression will be 9.69scr and 8.13:1 dcr with 7cc reliefs and 9.9:1 dcr with 8.31:1 dcr if I use the 5cc relief specs....

What do you recommend I do? I would like to be able to run 93 octane as this is going to be a street car? I'm losing sleep on this...

My 70 350/350 was rebuilt with a 10.4/1 compression and runs fine on 93 oct., 10 degrees initial timing, all in (36) at 2800.

Revi do you have iron heads? Also what cam are you using? I've read that effects the dynamic compression quite a bit.. also if you have GM heads your compression is not really what it was advertised as.... they speced their heads a few CC's smaller than they made them for the race crowd to have wiggle room to improve and stay legal so I've been told. Example l48 rated at 8.5:1 is actually 7.6:1 so I've read here before... that's why I pulled everything apart to double check before running.

I'm running a 355 with 10.7 scr and 8.3 dcr, 280* retro HR cam, AFR 195 65cc heads, quench is .049", advanced 34* at 3000 rpm, 46* with vacuum. No pinging on 91 octane.

First of all with all the online calculators for compression ratio. Just do it your self.

From experience - Your cam is to small to use flat tops (-5 cc) and 64 cc heads.

DCR calculators are at best a rough guide. Because different ones come up with different numbers. They don't account for higher flowing ports, swirl polished or multi-faced intake valves....................blah, blah, blah.

So small cams with a 64 cc head and -5 pistons are a no-go iron or aluminum heads.

I just put some new heads on my motor. I used the new Fel-Pro MLS .021 inch

Are the pistons already a done deal or can they be changed? I found the same problem when considering pistons. The speed pros have the wrong compression height for a block that has not been decked. I ended up gong with Keith black pistons because they have the correct compression height for a non-decked block. 1.56" is for stock non-decked block.
Here is a link to figure correct comp height.

http://www.lunatipower.com/Tech/Pist...ionHeight.aspx
using this page you come out with a CH of 1.585. That's total, to the top of the block. Subtract your .025" on a stock deck and you get 1.56". That's where you need the piston pin to be.

If getting a different cam is an option then get a longer duration cam or one with a wider LSA to reduce DCR. A 280 on a 110 would work or a 268 on a 114 LSA. Both would bring the DCR below 8.0:1.

If everything is together now and you have just discovered this problem and need to reduce compression I see three options without tearing everything apart.
1.) Gasket match the heads. This would require you grinding away material to match the heads to the gasket and this would remove material from each combustion chamber reducing your compression without increasing your quench distance.
2.) Retard the cam to reduce DCR. If you reduce the cam timing to only 2* advance or 0* advance you can get the DCR down to something around 8.0 DCR. This will affect the performance of the engine to some degree making it a bit lazier off the bottom but extending the top end a bit, if memory serves.
3.) Restrict the intake air prior to the carburetor . In other words make the VE% less efficient by choking the engine for air. This would reduce the amount of air and fuel in the combustion chamber and reduce your DCR. Sort like a restrictor plate in Nascar.

Thanks for the replys..nothing like learning the hard way.. I can't believe they rate the pistons with such a huge quench!

Engine already has everything assembled minus one head.... I am looking at replacing the cam with something like you suggested... anyone have a suggestion that meets the criteria and will be good for 3.08 gears and a 2000rpm converter in a street driven 74? I know the rear gears are not helping my situation.
I plan on keeping the .015 felpro gaskets and the .049 quench since without ripping it apart and more machine work that's the best I can do...

I put all your particulars into this calculator
http://www.jeepstrokers.com/calculator/
I come up with a CR of 9.71:1 and a DCR of 8.12:1.
This is with a 4.00" bore .034 deck to piston .015 gasket 5.7" rods 7cc piston, a 268 cam on a 110 LSA with 6* of advance all at your town altitude of 575 feet (elevation above sea level reduces effective CR)
Are these specs right?
If they are, you are very close to being all right on your DCR. 8.0 is commonly used for iron heads.
If it was me I would get an adjustable cam timing set with a split timing chain cover and just retard the cam to 2* advance to start with. That wold give you a DCR of 7.90. If it were timed straight up ( 0* advance) it would drop it to 7.78. With the adjustable cam and split cover you could adjust timing without tearing everything off to get to it.

http://www.summitracing.com/parts/cca-8110
http://www.summitracing.com/parts/clo-9-221/overview/

Both are expensive but if you don't want to gasket match the heads then it seems the next best option. Two cc's of metal removal from each combustion chamber would give you a DCR of 7.95:1

Or like you mentioned you could change the cam. Is a higher stall torque converter in the budget? If so then change the cam and increase the stall of the converter. It would at least help with 1st gear.
Once it's up and running reducing timing is also an option to stave off detonation. You could run colder plugs also. Get Ethanol free fuel if you can, if you can't then you'll need to jet the carb richer to compensate.
Also keep in mind that as the temperature goes up your effective altitude increases which will help lower your effective CR. Of course as the temperature goes up so does the temp of your intake charge and this is worse for detonation so those two may just cancel each other out.

Ithank you very much!

I used the same calculator but didn't take the sea level into account...

I had also found this cam which almost looks to be a better fit for me anyway.... http://www.lunatipower.com/Product.aspx?id=1955&gid=278
Question,
The cam I have now has 10,000 miles on it and the lifters.... should it be a bad idea to use these slightly used lifters with a new cam? They still look flat and new on the surface?
Also its a 4.030 bore

Don't. New flat tappet cams need new lifters.

I don't know what am doing wrong but I'm still getting 9.83 and 8.22 ? Gasket bore is only 4.1 not sure what you used?

OK thanks thought they spun so it wouldn't be criticle

They do but I've always heard from guys that were smarter than me NEVER reuse a flat tappet. I've personally reused roller lifters with no problems but I won't chance a used flat tappet.

:iagree:

To the OP -

Lifters take on the pattern of the lobes.
If you don't keep track of the original lifter for each lobe (if you are using the original cam), you need to chuck them in the metal recycle bin.
And if the cam is used and no matching lifters came with it, then new lifters are your only choice.
$50 is a lot cheaper than tearing down an engine when you wipe a cam lobe 6 months later.

Good luck with your project.

Bman :thumbs:

I have a similar engine build in my 64 Impala SS that the compression and quench are close to yours with iron heads. I didn't build this one, it came in the car, and I would not have built it like this. It is backed with a 350 Turbo with a stock converter and 3.36 gears.

The cam specs are hydraulic flat tappet 214 in, 224 ex @ .050" with a 114 LSA installed at 108 on the intake. There is no cold air intake, the air cleaner is under the hood. I have the timing set up at 10 degrees initial with a stock replacement vacuum advance on manifold vacuum with timing all in at 3000 @ 35 degrees. The engine runs really sweet and is strong for what it is. It is however temperature sensitive. I have the stock radiator in excellent shape with dual electric fans on it. The car will not ping on 93 unless it is above 85 to 90 degrees outside. Under 80 degrees ambient, the engine temp never exceeds 185 to 190. The engine temp will start to rise with the ambient temp. Once past 85/90 ambient and 200/210 engine temp, the engine will ping if you put it under much load. Normal driving it does not ping and never goes above 210 for temp. I think this will be similar to what you will experience.

Oh, I should say I have an electronic ignition conversion with an MSD 6AL, one step colder plugs and a wide gap at .045". This helped some over when I got the car with points and hot plugs.

I could probably cure the car by going to a larger aluminum radiator, but I may also put my spare full roller 406 in the car some time, and it doesn't have the same problem. It would need the larger radiator though.

Or 6 miles later!:ack:

Yes I read this before but since the lifters only had 10k on them and no visible wear I thought I'd ask....

Thanks I think I will go with the 301a7 cam which should bring my dcr down into the 7.7-7.8 range.... there goes $300 bucks I wasn't planning on spending...serves me right I guess for bragging how cheap my build was going...

Ouch............................:(

Not sure. I used a 4.1 gasket bore also.

That 301A7 cam drops it down quite a bit into a usable range with some cushion for higher engine temps. Looks almost like an L-82 cam. Should get the job done with a 9.82 CR.