[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]

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.

[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]

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

[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.

[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.

.

[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.

[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.

[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.