[TransAm 474]

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.

[72LuxuryLeMansLa.]

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....

[PunchT37]

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.

[Formulajones]

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.

[Formulajones]

Originally Posted by PunchT37

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.

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.

[PunchT37]

Originally Posted by Formulajones

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.

[pastry_chef]

Originally Posted by PunchT37

A person in the mountains says he can run 10.5 with iron heads and pump gas.

Hughe Engines.

Altitude. As it gets higher, the cylinder pressure drops. This starts to really affect cylinder pressure around 1200’ – 1500’ altitude, and we have some racers @ 6000’. And it really hurts them.

Now you know why no one wants to talk about cylinder pressure. It is not a subject that is easy or fun to discuss or understand. Getting your local engine builder or some mail order shop to discuss it with you is impossible. What frightens many customers is when we tell them they need 12:1 or 13:1 compression and want to use 92 octane with their combination. They never heard of such things. That is because the people they are talking to don’t understand about cylinder pressure. We have customers running over 14:1 on 91 octane. They are at 6000’ altitude, aluminum heads and a BIG cam.

[grivera]

Originally Posted by Formulajones

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.

.

What heads on your dad’s 571?

[Stan Weiss]

What is the cranking compression on these engines?

Stan

[Stan Weiss]

Originally Posted by Formulajones

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.

Iron or Alum heads?

Stan

[slowbird]

We have been for almost 20yrs

[Jay S]

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.

[ponjohn]

Question is why?

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

[John Milner]

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.

[pastry_chef]

Originally Posted by Stan Weiss

What is the cranking compression on these engines?

Stan

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

Sun Dec 24, 2006 10:51 pm
I dont build an engine to any certain cranking number, BUT, I always just take a reading anyhow. For street engines ( 91 pump gas) I find they run real good at 200 PSI. The Engine Masters contest showed almost everyone was up around 245 lbs on pump gas.BUT , this was like a hand gernade. NOT real wourld. THe cranking compression thing works good for street engines. I use it to see if I can run on pump gas or not. JOE SHERMAN RACING

[pastry_chef]

Originally Posted by John Milner

I am

What cam in the 10:1 400 John?

[shaker455]

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

[Jay S]

Originally Posted by ponjohn

Question is why?

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

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.

[unruhjonny]

@ OP:

...Obviously a tight quench by Zero Decking, along with...

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!



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!!

[Dragncar]

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.