Vacuum Secondary Conversion

[AJ/FormS]

If your 340 has a true 12.5 Scr, it's gonna need a pretty late intake-closing event to get the pressure under 200psi. You cannot run that high with iron heads anywhere near sea-level, on pump gas. You're just fooling yourself talking about distributors and carbs.
>In your case;
Since the engine seems to be out and the heads not yet on;
The way I see it, is you got a choice, either; reduce the cylinder pressure now, or install a high-quality water-injection system later. I would have recommended alloy heads but I doubt you can get the pressure under 200 with any of them, without changing or modifying the pistons.
Some pistons have enough meat in the crowns that you can mill some off.
Sometimes you just gotta back up to go ahead; it happens.
>Finally
IMO-1
If you do have a really big cam, you MAY need a matching really big convertor and WILL NEED really big gears. If you don't match things up you're gonna be really unhappy. If your combo currently has a factory stall convertor and say 3.23gears, that's NOT gonna match up to a 292 cam, and so, it'll cost you MORE to change all that, than to get rid of those 12.5 pistons.
IMO-2
with iron heads and a tightQuench under 040, about the most pressure you can run on pumpgas and without water-injection, seems to be 165psi with; full timing, a typical stall, and typical street gears, at sealevel. You can try it at 170, but be prepared to make changes; so build the combo in such a way that you can drop pressure with a thicker gasket, but do not exceed 050 quench, cuz then you are likely to get back into detonation. .
IMO-3
Vacuum Secondary Holleys suck, lol; they're always too slow. When I floor it, I expect chit to happen, like instantly!
If I want slow, I just won't floor it.
>In my case;
I solved the whole too-high pressure issue by running closed chamber Alloy heads on a slightly higher than Zero-deck 367. With those, I have run the cylinder pressure up to [email protected], and she still burned 87E10 Canadian gas.
In my combo I can change the pressure about 7psi/4degrees of cam-timing.
I built mine with an 028 gasket/028 quench, and it ran up to a tic over 200psi with no detectable detonation, even on 87E10.
But the 028 gasket I used, couldn't take it. So I took the engine apart, decked it to pop the pistons out some, installed the 039 FelPros, and this increased the Q to 032. It's been that way now thru two more cams and 100,000 plus miles. Oh and BTW, still on the same plugs, lol

 

[340inabbody]

If your 340 has a true 12.5 Scr, it's gonna need a pretty late intake-closing event to get the pressure under 200psi. You cannot run that high with iron heads anywhere near sea-level, on pump gas. You're just fooling yourself talking about distributors and carbs.
>In your case;
Since the engine seems to be out and the heads not yet on;
The way I see it, is you got a choice, either; reduce the cylinder pressure now, or install a high-quality water-injection system later. I would have recommended alloy heads but I doubt you can get the pressure under 200 with any of them, without changing or modifying the pistons.
Some pistons have enough meat in the crowns that you can mill some off.
Sometimes you just gotta back up to go ahead; it happens.
>Finally
IMO-1
If you do have a really big cam, you MAY need a matching really big convertor and WILL NEED really big gears. If you don't match things up you're gonna be really unhappy. If your combo currently has a factory stall convertor and say 3.23gears, that's NOT gonna match up to a 292 cam, and so, it'll cost you MORE to change all that, than to get rid of those 12.5 pistons.
IMO-2
with iron heads and a tightQuench under 040, about the most pressure you can run on pumpgas and without water-injection, seems to be 165psi with; full timing, a typical stall, and typical street gears, at sealevel. You can try it at 170, but be prepared to make changes; so build the combo in such a way that you can drop pressure with a thicker gasket, but do not exceed 050 quench, cuz then you are likely to get back into detonation. .
IMO-3
Vacuum Secondary Holleys suck, lol; they're always too slow. When I floor it, I expect chit to happen, like instantly!
If I want slow, I just won't floor it.
>In my case;
I solved the whole too-high pressure issue by running closed chamber Alloy heads on a slightly higher than Zero-deck 367. With those, I have run the cylinder pressure up to [email protected], and she still burned 87E10 Canadian gas.
In my combo I can change the pressure about 7psi/4degrees of cam-timing.
I built mine with an 028 gasket/028 quench, and it ran up to a tic over 200psi with no detectable detonation, even on 87E10.
But the 028 gasket I used, couldn't take it. So I took the engine apart, decked it to pop the pistons out some, installed the 039 FelPros, and this increased the Q to 032. It's been that way now thru two more cams and 100,000 plus miles. Oh and BTW, still on the same plugs, lol

Great write up thank you for taking the time to explain all this. I think I understand most of it. BTW the engine is in the car. I did have it running for a short time. I putt 3:55 gears in the rear. I am trying to get some incremental improvements prior to a complete rebuild. I know at some point I will need to do this but it mostly a money issue. If I had lots of money I would rebuild it with aluminum heads and a stroker kit. I just want to try and drive it for just a little while I save up for a rebuild or get lucky and make it workable for a little while.

 

[Newbomb Turk]

Great write up thank you for taking the time to explain all this. I think I understand most of it. BTW the engine is in the car. I did have it running for a short time. I putt 3:55 gears in the rear. I am trying to get some incremental improvements prior to a complete rebuild. I know at some point I will need to do this but it mostly a money issue. If I had lots of money I would rebuild it with aluminum heads and a stroker kit. I just want to try and drive it for just a little while I save up for a rebuild or get lucky and make it workable for a little while.

I’ll say it again. An aluminum head has no more detonation resistance than an iron head.

You can use pump gas and 12:1 compression but you have to relearn how to tune and set up the engine.

Never let anyone tell you how to do unorthodox compression ratios and pump gas when they have never done one. That’s number ONE.

 

[4eighteener]

I’ll say it again. An aluminum head has no more detonation resistance than an iron head.

You can use pump gas and 12:1 compression but you have to relearn how to tune and set up the engine.

Never let anyone tell you how to do unorthodox compression ratios and pump gas when they have never done one. That’s number ONE.

Newcomb,
A lot of builders here, myself included, use tips off the hughes engine's website, which they gleaned from many decades of building engines. I am no engineer, but If you say that this information is no longer true or relevant, can you cite where you got the information, or is it your personal experience?

 

[Mattax]

I don't see any substantial contradiction between what is posted here and the snip you posted.
Don't get hung up with the casting material. While the change in material does effect rates of heat transfer, and the change in dimensions for a given change in temperature, they are also a different casting and machining. So any broad simplified sweeping statement once can say fairly absolutely is that aluminum heads ought to be lighter weight.

 

[4eighteener]

I don't see any substantial contradiction between what is posted here and the snip you posted.
Don't get hung up with the casting material. While the change in material does effect rates of heat transfer, and the change in dimensions for a given change in temperature, they are also a different casting and machining. So any broad simplified sweeping statement once can say fairly absolutely is that aluminum heads ought to be lighter weight.

Well, there's that!

 

[Newbomb Turk]

Newcomb,
A lot of builders here, myself included, use tips off the hughes engine's website, which they gleaned from many decades of building engines. I am no engineer, but If you say that this information is no longer true or relevant, can you cite where you got the information, or is it your personal experience?

View attachment 1716239084

Since I have been proving it wrong for decades I can say it’s wrong.

All they are doing is repeating the same nonsense that’s been getting repeated for decades.

I’m certainly not advocating for iron heads. I’m saying you can’t just say I have aluminum heads so I can run a full point of compression with them.

I went back and watched the Engine Masters test again last night. When you heat load a head like they did, you will get run on and such.

Making a long pull like they did and then shutting the engine down like they did should never ever happen in the real world.

When was the last time you pulled a long grade, didn’t downshift and one you got to the top you pulled over and shut it down?

I can name more things like that they did but why bother? I have been arguing this same thing since 1980.

Remember that long ago? I do. Every magazine, every speed shop counterman and virtually EVERY engine builder in my area was tapped out at 8.5:1 or maybe if you begged you might get 9:1 out of them.

Those engines were pigs. They ran huge exhaust temperatures. There wasn’t a damn thing good about them.

And yet the argument still goes on.

Even Dulcich said you can’t transfer heat fast enough that heat transfer wouldn’t matter. And he was correct, except when you brutally load an engine to death.

 

[273]

For the AVERAGE guy you only can go by what people are averagely getting away with, in the 80s/90s it seemed like 9:1 was the safe bet on the street, but in the last couple of decades 10:1 is a pretty common occurrence on iron and 10.5:1 with aluminum and a decent cam.

I see no evidence that aluminum is effecting cylinder pressure all that much as you don't generally see a drop in torque per cid in similar built iron vs aluminum headed engine as for less sensitive to detonation it's hard to tell, more iron headed guy's would have to bump up there cr and we'd see, till then for MOST it's just a guess, and the safe bet for most is to not venture far from the generally proven path.

 

[4eighteener]

Here is the snip from hughes that I wanted to post earlier, but couldn't find. It is more to do with cylinder pressure, but does bring cylinder head materia in it too.
Perhaps it is a guide that is no longer relevant, the 165 for cast vs the 195 recommendations for aluminum heads, but probably one I will continue to adhere to until I see better information.
Anyway, I don't want to take over the op's thread on vacuum secondaries/distributors.
I was just hoping for clarification for my own benefit on cylinder pressure.
Perhaps someone will start a thread on cylinder head material vs cylinder pressure and people can post what they are running on what.
Unfortunately, I do remember engine building back in the 70's/80's/90's.

 

[Newbomb Turk]

Here is the snip from hughes that I wanted to post earlier, but couldn't find. It is more to do with cylinder pressure, but does bring cylinder head materia in it too.
Perhaps it is a guide that is no longer relevant, the 165 for cast vs the 195 recommendations for aluminum heads, but probably one I will continue to adhere to until I see better information.
Anyway, I don't want to take over the op's thread on vacuum secondaries/distributors.
I was just hoping for clarification for my own benefit on cylinder pressure.
Perhaps someone will start a thread on cylinder head material vs cylinder pressure and people can post what they are running on what.
Unfortunately, I do remember engine building back in the 70's/80's/90's.

View attachment 1716239155

Can you post a link to that page? I can’t read it and if I blow it up it’s worse.

TIA

 

[Newbomb Turk]

Here is the snip from hughes that I wanted to post earlier, but couldn't find. It is more to do with cylinder pressure, but does bring cylinder head materia in it too.
Perhaps it is a guide that is no longer relevant, the 165 for cast vs the 195 recommendations for aluminum heads, but probably one I will continue to adhere to until I see better information.
Anyway, I don't want to take over the op's thread on vacuum secondaries/distributors.
I was just hoping for clarification for my own benefit on cylinder pressure.
Perhaps someone will start a thread on cylinder head material vs cylinder pressure and people can post what they are running on what.
Unfortunately, I do remember engine building back in the 70's/80's/90's.

View attachment 1716239155

Ok, I went to Hughes and found it.

That article should be called Horseshit because it's full of it.

I have never ever seen any correlation between cranking pressure and detonation. Ever.

I've seen 200 on the gauge and zero detonation and I've seen 150 rattle its bearings out.

My last engine was bumping 185 and zero detonation. And that was 11.75:1 on iron heads. When it goes back together it will be 12 or a skosh over that.

Again, you can build your stuff any way you want. The biggest killer of power is not enough compression. Compression is our friend.

There was a time when no one at the drag strip ever left below 180 degrees. Now no one does that. What did they learn? That hot oil and cold engines make more power, are far more detonation resistant and will live longer not running coolant temperatures that high.

We have guys on here who run 200 plus engine temps and they wonder why it will rattle its brains out at 10.5:1.

Head materiel means NOTHING when it comes to making power, reducing detonation or anything else along those lines.

You could learn this for yourself. Go build an 11.5:1 iron headed pump gas engine. See what you find.

 

[RustyRatRod]

I’ll say it again. An aluminum head has no more detonation resistance than an iron head.

You can use pump gas and 12:1 compression but you have to relearn how to tune and set up the engine.

Never let anyone tell you how to do unorthodox compression ratios and pump gas when they have never done one. That’s number ONE.

<raises hand> I've done it, I've done it! lol

 

[4eighteener]

Sorry, i will post a link next time. Whenever I try screen shots, they tend to come out blurry.
Unless some company starts producing modern cast iron sbm heads, I doubt I would ever build with iron now except for a basically stock rebuild.
I have no doubt people are building 11.5 cr iron headed street motors, but not sure if that is a function of cam events and SCR.
If you have a build that you have done that used iron heads and 195-200 psi on pump gas, I would love to see those specs and run it through wallace every which way.
Anyway, like I said, I don't want to hijack the op's thread

 

[Newbomb Turk]

Sorry, i will post a link next time. Whenever I try screen shots, they tend to come out blurry.
Unless some company starts producing modern cast iron sbm heads, I doubt I would ever build with iron now except for a basically stock rebuild.
I have no doubt people are building 11.5 cr iron headed street motors, but not sure if that is a function of cam events and SCR.
If you have a build that you have done that used iron heads and 195-200 psi on pump gas, I would love to see those specs and run it through wallace every which way.
Anyway, like I said, I don't want to hijack the op's thread

That’s ok. I went to Hughes and found it. Usually I can’t find anything on that site but I did find it.

I’ve already said when I put my junk back together I’ll make some videos to cover it.

It will be 12:1 or a bit more. Who knows? When I build the W2 headed engine I may try for 12.75:1 just for fun.

And really, cam timing doesn’t play into how much compression you can run. At least within reason. 11:1 is so easy to do (if you can find pistons any more) I can’t believe guys still struggle with it.

And you’re right. Not many iron heads left out there (THANK GOD for that!!) but the W2 is still the best inline valve, 18 degree, standard port head out there. There’s not a 23 degree Chevy head (in iron) that would touch it.

And even if you never build another iron headed engine, do you really think that if I switched to an aluminum head I could be at 13.1 plus on pump gas? No chance.

I’m thinking the limit of pump fuel is 12:1 or a bit more, regardless of cam timing or any thing else.

As to cam timing, it makes little difference in how much compression you can run, except we both know more compression allows you to run more cam timing IF you need it.

The two biggest factors in using higher than orthodox compression ratios are the cooling system and the timing curve.

 

[4eighteener]

That’s ok. I went to Hughes and found it. Usually I can’t find anything on that site but I did find it.

I’ve already said when I put my junk back together I’ll make some videos to cover it.

It will be 12:1 or a bit more. Who knows? When I build the W2 headed engine I may try for 12.75:1 just for fun.

And really, cam timing doesn’t play into how much compression you can run. At least within reason. 11:1 is so easy to do (if you can find pistons any more) I can’t believe guys still struggle with it.

And you’re right. Not many iron heads left out there (THANK GOD for that!!) but the W2 is still the best inline valve, 18 degree, standard port head out there. There’s not a 23 degree Chevy head (in iron) that would touch it.

And even if you never build another iron headed engine, do you really think that if I switched to an aluminum head I could be at 13.1 plus on pump gas? No chance.

I’m thinking the limit of pump fuel is 12:1 or a bit more, regardless of cam timing or any thing else.

As to cam timing, it makes little difference in how much compression you can run, except we both know more compression allows you to run more cam timing IF you need it.

The two biggest factors in using higher than orthodox compression ratios are the cooling system and the timing curve.

I should say never say never.
Funny thing, I am currently porting a set of cast iron 302 heads now, although more for the experience than any planned project. I was inspired by the postings and pictures of MoparOfficial herr, and watching all the Charlie S videos online, that I wanted to give it a try. Not sure if I will ever use them.

 

[340inabbody]

I was under the impression that a solid roller set can ramp faster than say a flat tappet set up and the faster you can control the cycle (I don’t recall if just the compression stroke) the higher the lift and compression you can effectively use with lower chance of detonation. I think I am hearing here that this isn’t true.

Is there anything to this? If so can someone please explain?

 

[Newbomb Turk]

I was under the impression that a solid roller set can ramp faster than say a flat tappet set up and the faster you can control the cycle (I don’t recall if just the compression stroke) the higher the lift and compression you can effectively use with lower chance of detonation. I think I am hearing here that this isn’t true.

Is there anything to this? If so can someone please explain?

Like I said, cam timing does little to reduce detonation.

I see it all the time. Way more cam than the compression will handle and they run like crap.

The fix is less cam or more compression.

I know everyone wants one answer for detonation and how to control it but that’s not how it works.

It is the aggregate of things done when you build the engine on paper that allows you to run more compression than others do. It’s ALL of it and if someone doesn’t want to do ALL of it then they should build a low compression engine and live with it.

 

[340inabbody]

Like I said, cam timing does little to reduce detonation.

I see it all the time. Way more cam than the compression will handle and they run like crap.

The fix is less cam or more compression.

I know everyone wants one answer for detonation and how to control it but that’s not how it works.

It is the aggregate of things done when you build the engine on paper that allows you to run more compression than others do. It’s ALL of it and if someone doesn’t want to do ALL of it then they should build a low compression engine and live with it.

How many items would entail “all of it”? Just curious if you could break it down at all? Or is there an engine building book you recommend that I could learn from that goes through the process of a decent design?

 

[Newbomb Turk]

How many items would entail “all of it”? Just curious if you could break it down at all? Or is there an engine building book you recommend that I could learn from that goes through the process of a decent design?

Cooling system, ignition timing and curve, carb selection/tuning, flywheel weigh (for those of us who can operate 3 pedal cars) and chassis/suspension.

All of that conspires to allow unorthodox compression ratios.

Notice I didn’t mention cam timing??

 

[340inabbody]

Cooling system, ignition timing and curve, carb selection/tuning, flywheel weigh (for those of us who can operate 3 pedal cars) and chassis/suspension.

All of that conspires to allow unorthodox compression ratios.

Notice I didn’t mention cam timing??

This sounds like a very iterative approach, and empirical Meaning, a lot of trial and error with some good basic foundation. This must be especially true for chassis, tuning and rear gear ratio and cam design. Meaning more experience than plugging everything into a computer program and getting an output.

 

[Newbomb Turk]

This sounds like a very iterative approach, and empirical Meaning, a lot of trial and error with some good basic foundation. This must be especially true for chassis, tuning and rear gear ratio and cam design. Meaning more experience than plugging everything into a computer program and getting an output.

Not really. It’s more about unlearning and relearning.

You have to change the way you think. And not you as in you personally but as in the general sense of you. I had to do it.

I heard all the same crap that you probably have. Like the fuel is garbage (lol it is but it’s no worse today than it was in 1980 except the reformulation for EFI and the lower grades of fuel have even looser standards than they did back then) and you’ll have to take timing out and that will kill your power, junk like that.

I put the cooling system first because that’s where you MUST start if you want to be successful with higher than orthodox compression ratios.

If you can’t keep your coolant at 160 degrees you have no business trying to get much over 11:1. I think that’s what will stop me from getting to 13:1 on pump gas. I can keep the engine at 140 degrees but I won’t have a defrost. So that’s no bueno.

And, keeping the engine cool like that brings in a whole different set of things you have to do differently.

 

[fishmens67]

Notice I didn’t mention

quench or chamber shape

 

[Newbomb Turk]

quench or chamber shape

Frack me. I forget to mention that.

THANKS

 

[340inabbody]

Not really. It’s more about unlearning and relearning.

You have to change the way you think. And not you as in you personally but as in the general sense of you. I had to do it.

I heard all the same crap that you probably have. Like the fuel is garbage (lol it is but it’s no worse today than it was in 1980 except the reformulation for EFI and the lower grades of fuel have even looser standards than they did back then) and you’ll have to take timing out and that will kill your power, junk like that.

I put the cooling system first because that’s where you MUST start if you want to be successful with higher than orthodox compression ratios.

If you can’t keep your coolant at 160 degrees you have no business trying to get much over 11:1. I think that’s what will stop me from getting to 13:1 on pump gas. I can keep the engine at 140 degrees but I won’t have a defrost. So that’s no bueno.

And, keeping the engine cool like that brings in a whole different set of things you have to do differently.

That’s where I started as well. I installed a duel fan aluminum radiator with shroud and no heater or defrost. I live in AZ which is my first up hill challenge. Also running a 160 degree thermostat. I successfully tuned my set up for no audible detonation however I am on the line with no margin. My bottom end is what it is for now. I could throw money into aluminum heads but am trying to buy margin. If my duel plane (which is at the machine shop STILL!) helps me add a degree or so of timing I believe I can add a very small amount of margin to staving off any detonation on the corner cases ie excessive heat days or under heavy loads. If a VS can help eek out a bit more timing then it would be worth trying that as thats not an expensive thing to try out.
gain this is more for improving on what I had done prior to my restoration work.
Heres a pic.

 

[273]

So basically the average dude should restrain from adding too much CR.