How many people are successfully running 10-1+ compression Iron Head 400's on Pump
 

I don't intend to open a can of worms here, but just like the title says, how many people are succesfully running 10-1+ compression 400's with factory Iron Heads on 91 octane Pump Gas without any issue of pinging/detonation? I know Cliff and others have, where as others have not had success. I know this question will get conflicting answers from people's different experience, Im just curious as too how many are doing it without problem. Obviously a tight quench by Zero Decking, along with a well chosen camshaft with a later Intake Valve Closing point plays a big roll in making these work. I would also be interested in hearing from the people that DID NOT have success making it work, and details about the combination that didn't work, as far as Quench distance, Camshaft specs and so on.

I'm no expert so take this for what it's worth. If I'm building this for a customer, the only way I go up in the 10+ compression range is if I Know the customer is a capable tuner. Otherwise I'm going with a custom piston with a dish....

A person in the mountains says he can run 10.5 with iron heads and pump gas. And, he might. He won't do it down here in Louisiana. Especially now, in the summer.

I'm one

https://youtu.be/er1z7PpqsnY

I also daily drive it. All on crappy 91 octane. My wife's driver is 11:1 with iron heads and the same pump gas ;)

However I do agree with 72 Luxury. It depends on the customer whether I do this sort of thing or not.

I just built an iron headed 455 for a customer and friend on the forum here. He's very familiar with tuning having run dirt modifieds competitively for many years. So we went with 10:1 with the iron heads and a custom cam designed around it. Made 507/571 on the dyno with 91 octane and idles with a very mild lope and makes 12 inches of vacuum up at 5,000 feet elevation. It was dyno'd however closer to sea level and showed no signs of detonation issues, even with a slightly lean AFR.

We do it at all elevations. We can't drive 20 miles in any direction without the elevation changing. The fact that we frequent Phoenix at near sea level with these cars on a regular basis, and incidentally drag race them down there as the only 1/4 mile track around, means I have to be sure it's built properly to deal with that. So I tend to build these things with sea level in mind, and if it spends time up on the mountain, all the better. They live fine in the 100+ summer temps we have. My bird has been flawless at 10:1 and iron heads, and my Z is flawless at 11:1 with iron heads.

Dad's 571 is 10.84:1 compression and lives on 91 octane. That engine was build in Ohio and lived there for 2-3 years on the streets at near sea level. Still together today in Arizona.

It's not for everyone though. If someone isn't willing to do their homework on cam timing events and then spend the time to make sure it's tuned properly then they'll likely have issues.

I'll agree with that. One better have his game on. But, most don't.

Hughe Engines.

What heads on your dad’s 571?

What is the cranking compression on these engines?

Stan

Iron or Alum heads?

Stan

We have been for almost 20yrs

A few 400 Engines that went through our shop and engines we built or tuned with various results.

70 RA 3 GTO Judge, 400 origal 12 heads, all stock carb to pan and RA manifolds 10.04 SCR, melling 041 spec-8 with the stock 1.5 rockers. No issues on pump gas. Had all the characteristics of a big cam. Doing it again I would pick something more aggressive, seemed lazy. Original q jet.

70 RA 3 GTO Judge, 12 heads, upper 9s on the scr, with a straight duration isky, had some issues. Pinged some in the midrange, needed 91, pulling the timing out some mid 30s total, IRC it did fine. Original q jet.

67 Firebird 400 small valve, logs manifolds, tuned it only, reportedly had a 067 cam with 10:0 + compression. Lots of issues on pump gas. Never made it run good. Tuned and tuned on that, had holley 600 and a performer intake.

FWIW, nothing wrong with dropping the compression with the dish and going with a cam that does better filling the cylinders. Like the last cam we did for a 70 455. It was a Ultradyne 280/288 232/240, 112LSA .550/.550 with 1.65 rockers, we dropped the SCR to 9.5. He wants to run on 87 octane if possible.

Seems like low compression stock engines have been just as likely to get hot and the well designed higher compression stuff that we worked over. My t/a w72 had the stock cam with 8.2 Scr and lost a rod bearing. Listening to the radio and not paying attention. Had an some type of issue with the heater core. Looked down saw the temp going up, turned the radio down, it was pinging like crazy. Too late, hammered a rod bearing out.

Question is why?

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

I am on several engines. My stock 96,000 mile ys 400 in my 69 gto, 10:1 455, 10:1 421, 10:1 428, 10:1 400. Just run the best fuel you can and have your timing dialed in and you’ll be fine.

Great question Stan.

Related thread and a comment from the legendary Joe Sherman, right in the same zone as David Vizard. Joe later adds cranking is less relevant with true race engines with very high static CR and very large cams.
http://speedtalk.com/forum/viewtopic...=4833&start=30

What cam in the 10:1 400 John?

Many times over have built a minimum 10:1 pump gas street/ strip engines.

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.

@ OP:

I tried to point out in the other thread without coming across too strong that zero decking that engine might get you into trouble - it can quickly put you in the realm of 11:1
I am repeating myself, just to be sure you don't miss it this time around.

Once you cc the heads, then you can see what you might need to do to get your compression to something which will be liveable on pump gas;
So get the heads done, then cc them - hopefully you won't have too much variation, or anything which might warrant looking further at the heads before proceeding to block work.

The only way that I see you getting that engine on the lower side of 10:1, is to back off the notion of doing a true zero deck on the block.

I pause admit to my bias, it comes from this angle;
1) Heads are what they are; #12 heads are known to have smaller combustion chambers
2) Once a block is decked, you'll never get it back; if dealing with small cc heads, decking too much necessitates expensive slugs, or custom head gaskets.
3) I'd rather go with an off the shelf slug with the piston further from the deck top, over having to get a custom dished piston to lower compression because too much was milled off the block
(yes, 2 & 3 overlap, but hopefully you understand why I said it anyway.)

:)

When I rebuilt the YZ RAIII in 1998 I never cc'd my heads, because I was twenty-one and didn't know any better.
I had my YZ running 0.040" over, never checked how far down the slugs were, because I was twenty-one and didn't know any better.
I replaced the 067 cam that was in it when it was 0.030" over with a '744 cam - this should have only served to have help me by lowering static compression.

I was in a bad spot several years ago, and sold it, then in a rare moment of luck last year, I had opportunity to buy it back!

https://forums.maxperformanceinc.com...1&d=1566792964

I'd listen closely to other members running #12 or #48 heads, to see what they have to say - there is probably more of them that you might think at first glance.

Good luck with the build!!

I am a iron head pump gas guy. Been for years. Back when Whittmore first speced out my 455 build (it was about 1986) he gave me his opinion on iron head pump gas Pontiacs.
455s, 9.3 CR. 400s, 9.6 CR. You can go higher but its not worth the extra risk. Little extra power to be had. All it takes is a bad batch of gas, real hot day, timing a little off ect and a blown head gasket. Or worse, beat out top rod bearings.
The 455 was done in the late 80s and ran about 1990. Still going strong as ever. 10.84, pump has 455 with TRWs in a 69 GTO. Never have hurt it. Blown a head gasket or hurt a rod bearing.
Its not worth it IMO. I have proved it.

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?

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.

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.

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.

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.

.

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
https://forums.maxperformanceinc.com...8&d=1530617522

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:
https://forums.maxperformanceinc.com...0&d=1530617546

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...

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.

.

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.

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.


.

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

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

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??

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

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

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/

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.

“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!....

“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!....

Hard to beat head flow.

Good running 454 for 8.2 scr. I have read that article before. Did good for what it was.

Just got the cam last week for that engine mentioned earlier Ponjon.. So I don’t know hp or e.t. yet. Shooting for around 530 hp with the ported stock intake, qjet and ra manifolds. 6x heads are 190cc. I don’t have final flow numbers yet though. Hoping it kind of keeps up with our 510 cid pump gas 69 Charger with 10.50 scr, ported cast iron heads and a big flat tappet mech cam. The Trans Am needs to come close to 11.50 to match my brothers et in the Charger. I think it has a shot. My brother and I have had the charger since 1988.

The dished icon with the 2802 or 60243 Crower looks like a good combo to me transam474. IMHO, no reason to do the flat tops unless the heads cc’s are larger than expected.

What is the max lift from the Summit 2802? How much of that head flow is above that max lift? After looking at the head flow numbers you might want a cam for more lift.

Stan

The 2802 has .465"/.488" lift with a 1.5 rocker. The heads that will be used are the numbers matching #12 heads, and will be completely bone stock except for hardened exhaust seats, valve job, Crower 68404 springs, and Ferrea F5143/5144 stainless valves. We are thinking if this engine comes out in the 9.6-9.8-1 area, we will probably use either the Summit 2802 or the Crower 60916.

All the stock D ports we have had on our flow bench seemed to go turbulent at very close to .5. I have never flowed a 12. Only a 48 for the ra 3. Stan I noticed you had a ram air 3 head listed on your compiled head flows that had a little left after .5. Not sure what it is though, just says ra 3.

Stan has the best head flow compilation across brands I know of.

http://users.erols.com/srweiss/tablehdc.htm#Pontiac


The 2802 does look better with 1.65s. It would be a good candidate for 1.7 rockers too. Not sure how bad it needs them with stock heads. I am pretty sure Summit has the rating wrong, suppose to have 298/308 for the SAE rating, not 298/303, someone got a 8 and a 3 confused somewhere.

Adding 12 degrees to the crower advertised ratings will get you close to the SAE numbers if you want to compare the crowers to the 2802. The advertised 2802 numbers summit lists are generally numbers someone in sales picked to sell more cams. IRC, subtract 14 degrees on the 2802 SAE numbers to get to Crowers rating at .006. Summit is a lazier cam.

Looks like you have the right idea. See where the compression lands and pick a cam from there.

Ok guys, I recieved my CC'ing kit today, and even though I haven't had the heads rebuilt with hardened exhaust seats and a valve job yet, I played with them this evening, and put our new Ferrea valves in them and checked them 3 different times. The first time came out at 70cc, the second time came out at 69.5cc, the third time it came out at 70.5cc, so I am gonna call them 70cc. Now like I mentioned earlier, this is before the heads are rebuilt, but I was just curious what they measured. Calculating Compression with the 14cc Icon piston, .039" gasket, Zero decked, it comes out 9.82-1. I feel that it will be much more managable for pump gas than the Flat Tops 10.6-1. If may come out even a hair less than than that if the heads gain a couple cc after being rebuilt?

What do you all think? Would you feel safe?

Good.

I have the original motor and tranny and rear end in my 67 GTO..670 heads ..matching intake and a 1969 Service carb...Q -Jet.....just put 93 octane in it....no problem.

Just as a side not, I used the Diamond Pistons Compression Calculator....