[John Milner]

Originally Posted by pastry_chef

What cam in the 10:1 400 John?

On my 96,000 mile 10:1 YS 400, I am running the stock 067 Pontiac cam. On the other 10:1 400, I am running a ram air 4 cam. Both run fine on 91 octane. One engine has never been into other than a timing chain and I have owned and driven it regularly since 2004. The one with the ram air 4 cam, I have been running it since about the same time period, 2003 or 2004. It runs on the same 91 octane fuel. It doesn't overheat and it doesn't ping any.

[TAQuest]

Originally Posted by John Milner

On my 96,000 mile 10:1 YS 400, I am running the stock 067 Pontiac cam. On the other 10:1 400, I am running a ram air 4 cam. Both run fine on 91 octane. One engine has never been into other than a timing chain and I have owned and driven it regularly since 2004. The one with the ram air 4 cam, I have been running it since about the same time period, 2003 or 2004. It runs on the same 91 octane fuel. It doesn't overheat and it doesn't ping any.

How did you determine what the compression was on those engines?

[John Milner]

I built the engine with the ram air 4 cam. It has flat top pistons with 4 valve reliefs (6cc), deck height is about .015, .041 gasket thickness, 4.12 bore, 3.75 stroke, 72cc heads. It all works out to be right at 10:1 compression when you calculate the numbers.

My stock YS 400 will be the same since it has the exact combination (heads, piston style, etc). I know it is advertised as 10.75:1 stock but that is not correct. When you run all of the numbers, it comes out right at 10:1 compression too.

[chiphead]

John- What timing curve on these 10:1 engines? I assume the timing is coming all-in at 3000 RPM or higher?

[John Milner]

Originally Posted by chiphead

John- What timing curve on these 10:1 engines? I assume the timing is coming all-in at 3000 RPM or higher?

To be honest, I do not remember. I haven't had a timing light hooked on either of these in 10 or 12 years. I just haven't had a reason to check the timing on them since they both run good, start good and have no signs of detonation. I don't race either of these cars. Both engines run a stock HEI ignition. It seems like I used one of the medium springs you get in those cheap weight/spring kits that used to be sold at the auto parts stores. I converted the '69 over to electronic ignition probably 15 years ago.

[Jay S]

John is the YS engine a 69? Looked at your profile, guessing that it 350 hp with 62 heads? (Nice car collection btw). I have calculated around 9.6 when trying to use ours 62s. The 62 heads we have measure 75 cc untouched. Seen some folks say they run 77-78 sometimes. I had a set of 13s years ago off a 70 gto 350 hp, seemed like they ran closer to 77cc. Thought they were all 72cc for years, until some others said some castings ran more cc’s and I checked what I had. Two sets of 16s have run 72. Have single nice 48 laying around I will never use to if some needs one. I think it was 72cc.

I think I posted a few weeks ago my 70 455 Olds has 10:1 with factory pistons with a 214/224 cam. Got to looking the other day at some engine specs I had down, it is 9.6. Pontiac was not the only one over rating stuff.

FWIW, My 452 with the roller cam is a pump gas F.A.S.T. type build. So I have different reason for going on the high side of compression. If I was running a big intake, carb and headers it would been fine some place in the 9s. Factory appearing is a little different deal for big hp.

[John Milner]

Originally Posted by Jay S

John is the YS engine a 69? Looked at your profile, guessing that it 350 hp with 62 heads? (Nice car collection btw). I have calculated around 9.6 when trying to use ours 62s. The 62 heads we have measure 75 cc untouched. Seen some folks say they run 77-78 sometimes. I had a set of 13s years ago off a 70 gto 350 hp, seemed like they ran closer to 77cc. Thought they were all 72cc for years, until some others said some castings ran more cc’s and I checked what I had. Two sets of 16s have run 72. Have single nice 48 laying around I will never use to if some needs one. I think it was 72cc.

I think I posted a few weeks ago my 70 455 Olds has 10:1 with factory pistons with a 214/224 cam. Got to looking the other day at some engine specs I had down, it is 9.6. Pontiac was not the only one over rating stuff.

FWIW, My 452 with the roller cam is a pump gas F.A.S.T. type build. So I have different reason for going on the high side of compression. If I was running a big intake, carb and headers it would been fine some place in the 9s. Factory appearing is a little different deal for big hp.

Thank you, I have a car addiction I guess you could say. Yes, it is a '69 model. You are probably right in that it is closer to 9.5:1. It does still have the stock un touched 62 heads. I am running 216 heads on the ram air 4 cammed 400. They might have deeper chambers than advertised too.

[HWYSTR455]

My last iron head engine was a .030 over 400, scr was 9.98. I swapped multiple cams thru it, and it just wasn't worth the effort of tuning to keep it out of det. Bad tank of gas, dial the timing back. Weather gets above 90 degrees, dial the timing back. 3-4 people in the car, dial the timing back. It was insane, would literally carry a timing light with me and dial it back on the side of the road. I had marks on the dizzy base and a mark on the block, could do it that way, but preferred to use the light, was more accurate.

I'm at about 300' elevation though.

455s, different story, they needed a half a point less everywhere to keep it out of det than the 400s.

So along the same lines, you can see why folks with 289s, 302s, 350s, and 351s can get it to live at 10:1. You might be able to do it with a 400P, but still think it's not worth it, the minor power you might gain will be lost having to dial the timing back, so, again, pointless.

.

[unruhjonny]

FWIW: 1969 #62 & 1970 #13 heads do have larger combustion chambers than 12/48 heads;

here is info on 1970 engines:

note the chamber volume for #13 heads is clearly listed as being 75.7cc's, while the #12 head is listed as being 66.27cc's


Also, it looks like my posted recollection from the other thread was wrong, as originally built, the slugs are supposed to have been 0.023" down the hole:


If I punch in the following criteria into the Wallace Racing compression calculator, I yield 10.35:1 compression on a standard bore block with virgin #12 heads:
bore (std): 4.12
stroke: 3.75
head chamber: 66.27
valve relief: 6.6
gasket thickness: 0.041"
gasket bore diameter: 4.30"
deck height: 0.023"

So the advertised numbers are a little high - but as I recall, that's where Royal would "fix" things with the thinner head gaskets...

[HWYSTR455]

Yeah, you can't go by listed numbers, for one, it doesn't take production tolerances into account.

steve25 has more accurate head CC info from years of collecting data, they are not what is listed, the listings are only a 'general' number.

.

[unruhjonny]

Originally Posted by HWYSTR455

Yeah, you can't go by listed numbers, for one, it doesn't take production tolerances into account.

.

Except the issue at hand is a rebuilding of a 1970 YZ engine with it's original #12 heads, so they should be used as a basis, until real numbers can be had/seen.

I was concerned when in the last thread the mention of zero decking the block was made, and it has been repeated here;
In light of your prior comment I would have thought that rather than poo-poo what I am trying to point out, you might say something more like, "yeah, I'd check your numbers before you mill the deck so that you don't have too much compression like my last 400 build."

if this was his engine, I'd be less incline to repeat myself, but this is a customer's engine.



I have info from one member here who runs a '70 400 w/#12 heads which has the block zero decked, and iirc he said something along the lines of "needing to run race gas all the time gets old fast".
I'm trying to recommend a build that doesn't potentially render the block unusable without custom slugs.

[HWYSTR455]

Ah, ok, I understand better now, and I hear ya. Not trying to throw stones or anything, and agree it's at least a good basis for making initial calculations.


.

[Stan Weiss]

JMO. But I would go with 0.005" down to zero deck and if needed a dish in the piston. If the piston is to far down the hole you have to to much piston to head clearance than I like.

Stan

[chiphead]

Originally Posted by HWYSTR455

My last iron head engine was a .030 over 400, scr was 9.98. I swapped multiple cams thru it, and it just wasn't worth the effort of tuning to keep it out of det. Bad tank of gas, dial the timing back. Weather gets above 90 degrees, dial the timing back. 3-4 people in the car, dial the timing back. It was insane, would literally carry a timing light with me and dial it back on the side of the road. I had marks on the dizzy base and a mark on the block, could do it that way, but preferred to use the light, was more accurate.

I'm at about 300' elevation though.



.

Do you know the deck height on that combo? Just trying to account for all the variables.

[Skip Fix]

Originally Posted by ponjohn

Question is why?

The power gained from a 1/2 point won't be that much.

Yep-you can pick up the HP somewhere else and not have to worry about gas quality. What is 4% per 1 point compression. So on a 500 HP motor 20HP you can't get with cam choice, timing and carb tuning??

[Cliff R]

The "4% per one full point of compression" is old/outdated information taken from one of the HO books.

In static terms it's probably pretty close, but in the real World the difference between 9 and 10 to 1 would be considerably more.

Here's why. Build a 400 engine with 8 to 1 compression, it will like a stock 066 cam or even a 204/214/112 cam or something close to it. Idle nice, good street manners, about 300hp or so.

Take the same 400, 9 to 1 compression, move up to the 068 cam, or a 214/224/112 cam and it will idle equally as well, good street manners, and at least another 40 hp or so.

Bump the compression up to 10 to 1, 224/234/112 or even move up to a Crower 60243 (228/235/112) cam, add high ratio rockers, Rhoads lifters and guess what. It will idle with plenty of vacuum for power brakes, great street manners, but closer to 400-430hp. Ours actually made 424hp on the dyno and 465 ft lbs torque with umported heads. Vacuum at idle speed 12" at 750-800rpms.

So a 1 point bump in compression opens the door for a larger cam with less negatives and considerably more than a 4 percent power increase.......Cliff

[ponjohn]

Originally Posted by Jay S

With the same cam that this absolutely true. With a well matched cam we have seen very little improvement in performance from the increase from 9.5 to 10. Where we find the gains is when you increase the cam size to match the compression. Then add extra head flow in combination with the bigger cam and head flow and it makes the hp gains much different. Stock heads you can easily run out of cam and head and the compression just makes it miserable to tune.

Cams have compression ceilings where the hp more or less levels out to. We have done many of the 2801 summits type grinds (214/224) profiles, after 9:0 on a 400+ Cid engine size the performance gains we have seen where small. I have had the 204/214 cam in a couple 440 mopars at 8.2 and 9:1. The 8.2 ran every bit as good as the 9. In fact with headers the 8.2 would take the 9:1 engine with manifolds. Lost track of the over 10:1 engines we have done. We keep pushing higher on cam size and head flow to see were the limits are for compression I honestly do not know where it is. My 452 cid fully ported 6x head combo sitting at 10.5 scr with a bullet 300/308, 245/253 @.050 with a 114 lsa, .630/.630. It is a solid roller on a hyd profile. Tim at bullet helped set it up so we can move the lash around to see what the engine is wanting. My biggest effort on a pump gas cast iron headed Pontiac so far in a roller. Biggest solid so far is a 256/264 at .050 w/112LSA solid flat tappet, it would go well into to 10s scr.

Putting these bigger cams with good heads, drag radials and the super eff tight 9.5 converters and you go from keeping up with a Toyota Camry to giveing a Hellcat a run for the money. More fun to beat the Hellcat.

And...how well did they dyno OR run at the track?

I'd rather exchange compression for head flow.

[pastry_chef]

Originally Posted by ponjohn

I'd rather exchange compression for head flow.

I'll take MAF (heads and cam) over compression.

8.2 compression - 567 HP

https://www.hotrod.com/articles/bolt...ome-big-block/

[TransAm 474]

Thanks for the feedback and help guys. I think since this is for a customer, we would rather error on the safer side, and Cam it accordingly. Just for the heck of it, I figured compression with a 69cc chamber(which some have said the 12 heads measure at times)along with the L2262F30 Speed Pro Flat Tops, block Zero Decked, and a 1016 .039" gasket, and it comes out at 10.66-1.

While we would like to push the envelope with a high compression build if it were our own, we probably shouldnt since this build is for a customer, we better stay a little safer with compression and Cam it for the correct compression so that it has good strong power, but yet pump gas friendly. I did some more figuring with compression, and with the 14cc dished Icon IC891 piston, and deck the block for .005" in the hole and the .039" gasket would put it at 9.90-1, or 10.0-1 at Zero Deck. Now, this is just an example, we haven't cc'd the heads yet, still waiting to get them rebuilt with hardened seats, guides, and valve job, so after they are done, I will cc them to see exactly what we are working with. I assume the chamber volume may increase a little after the head work, but we will have to wait and see what the final number is. I like the look of that Icon piston, and I bet it is quite a bit lighter than the Speed Pro, and also has a better 1.720" pin height.

If after the head work, they happen to come out at a true 72cc, the compression would come out around 9.6-1 with the piston .005" in the hole, or 9.7-1 compression Zero Decked, with the 14cc Icon piston and .039" 1016 gasket.

Just to clarify since it was mentioned earlier, those 4340 Eagle H-beams we bought are Pressed Pin.

[shoebox1.1]

“Bump the compression up to 10 to 1,
224/234/112
or even move up to a Crower 60243 (
228/235/112
) cam, add high ratio rockers, Rhoads lifters and guess what. It will idle with plenty of vacuum for power brakes, great street manners, but closer to 400-430hp. Ours actually made 424hp on the dyno and 465 ft lbs torque with umported heads. Vacuum at idle speed 12" at 750-800rpms.

So a 1 point bump in compression opens the door for a larger cam with less negatives and considerably more than a 4 percent power increase.......Cliff“

I’ll take door number three for 300 bob!....