[Stan Weiss]

The way I read what the OP wants. The HO heads are not the way to go. Look at the slope of the torque curves @ 3000 RPM. The OP is looking better torque at a low RPM than 3000

Stan

[25stevem]

My question for the OP is this.

Have you every even driven a car with a good running stock 455 in it tocome the across the board conclusion that needs to have more power down low?

[SD455DJ]

That's what the comparison I made is to show...that there isn't much loss of torque from too small of intake ports, just where the torque is produced. The HO's intake ports are none too large to begin with and the small valve head intake ports are like sucking through straws, however, they do work to make torque 500 rpm below the HO head.

My '71 Bonneville with the original 455 YH 2-bbl engine (swapped to #66 large valve heads with the 114 cc chambers and 7.8 SCR and 4-bbl intake/Q-jet) and the original 066 cam is not that impressive of a torquer. It doesn't like 87 or 91 octane fuel, so needs a slow (factory) timing curve and 93 octane. I'm sure it has non-effective quench in the heads. I would love to rebuild it to be a torque monster with more compression (9.0), .040" quench, and at least a Summit 2801 cam. It would make more power down low to move the 4500 lb. beast than it does now. If the OP is going to tow with his '65 Tempest Custom, I still like the 6X-8 heads on a 9.0 SCR 455 with a 2801 cam with RA exhaust manifolds. It would be rough on that 200R4 trans!

If gas mileage is your concern, I agree with using a 400 block and getting a 4.25" stroker kit if you want callosal torque output. Like Formulajones said, it's hard to not make torque in a 455, there are just better ways to do it than others.

Dennis

[Jay S]

A couple more quick thoughts. I don’t recall the OP calling a 455’s tq inadequate, it was more directed at the question if smaller valves on a 455 offer anything combined with a 200R4. I can’t say that I have ever seen a great link between making colossal TQ on a dyno to better fuel efficiency at partial throttle. The small valve heads on a 455 likely would make less overall peak torque against a big valve head. But may be a little more efficient for better mpg with the 200R4. Might need some type of lock up converter to really see a difference. A normal 2000ish converter the gains are probably enough just have the AOD, then the small valves 1.96” might not offer much against the 2.11” .

One of our race engines made 567 lbs torque @ 4500, and the curve was pretty flat down to 3000, never dropped below 500. It made some decent tq numbers, but for driving on the street at partial throttle it is not efficient at all, in this case, it is still a race engine. I could pull it to it’s knees with a AOD tranny and it would do ok, but fuel milage would never be very good in it’s case. Depending on what you may be looking for out of the combo, more can mean less.

[Formulajones]

Here's another 455 I built. 72 455HO. This one had a 239/243 @ .050 cam, the 7K3 round port heads were ported to around 280-285 cfm, I have the flow sheets around here somewhere. It was 9.98:1 compression. Stock intake, stock Q-jet, and stock ram air manifolds in place.

After a couple tweaks it did a best of 507/571 but the most impressive part is the torque way down low. I think we pulled this to 3000 on another sheet I have where it was still making well over 500 ft lbs, and we meant to pull it down to 2000 but got busy and forgot. Safe to say this thing makes a very broad torque band with a spread of 1800 rpm between peaks, which is fantastic. Most engines usually show 1200 to maybe 1500 peak to peak on average. This thing also holds on to the power very well. This was a pump gas deal that went into a very stock appearing street car, and runs the power brakes and A/C just fine.

[hurryinhoosier62]

Originally Posted by Formulajones

Here's another 455 I built. 72 455HO. This one had a 239/243 @ .050 cam, the 7K3 round port heads were ported to around 280-285 cfm, I have the flow sheets around here somewhere. It was 9.98:1 compression. Stock intake, stock Q-jet, and stock ram air manifolds in place.

After a couple tweaks it did a best of 507/571 but the most impressive part is the torque way down low. I think we pulled this to 3000 on another sheet I have where it was still making well over 500 ft lbs, and we meant to pull it down to 2000 but got busy and forgot. Safe to say this thing makes a very broad torque band with a spread of 1800 rpm between peaks, which is fantastic. Most engines usually show 1200 to maybe 1500 peak to peak on average. This thing also holds on to the power very well. This was a pump gas deal that went into a very stock appearing street car, and runs the power brakes and A/C just fine.

Experience verses “computer simulations”; experience wins every time.

[Stan Weiss]

Originally Posted by Formulajones

Here's another 455 I built. 72 455HO. This one had a 239/243 @ .050 cam, the 7K3 round port heads were ported to around 280-285 cfm, I have the flow sheets around here somewhere. It was 9.98:1 compression. Stock intake, stock Q-jet, and stock ram air manifolds in place.

After a couple tweaks it did a best of 507/571 but the most impressive part is the torque way down low. I think we pulled this to 3000 on another sheet I have where it was still making well over 500 ft lbs, and we meant to pull it down to 2000 but got busy and forgot. Safe to say this thing makes a very broad torque band with a spread of 1800 rpm between peaks, which is fantastic. Most engines usually show 1200 to maybe 1500 peak to peak on average. This thing also holds on to the power very well. This was a pump gas deal that went into a very stock appearing street car, and runs the power brakes and A/C just fine.

Really would like to see the dyno pull down to 3000 RPM. Lets add your numbers to the 2 dyno pulls from Dennis. It is hard to say what your torque numbers would be where the OP is looking for best torque.

Stan

[Formulajones]

It would be very similar to the dyno I posted in post #75 where Paul pulled that one down to 1600 rpm.

That is basically a very similar engine that Paul built, using the exact same camshaft installed on the same ICL, same intake, carb, similar RA exhaust manifolds. The heads are D-ports that Dave ported to a very similar CFM that the round ports were ported to that I used. In fact, Paul did all the same machine work on the engine I built, and then Paul dyno'd it after I finished assembly. So they were both on the same dyno.

As you can see the numbers are very similar. That thing made 456 ft lbs. way down at 2000 rpm and already over 500 ft lbs by 2500. Who wouldn't like that? Since mine peaked a bit earlier it's pretty safe to say it may have done a little better down in the 2000 range.

That engine would have no issues at all lugging a 65 tempest around with an overdrive.

[Stan Weiss]

While they may have almost the same parts yours and Paul's curves do look different. Not only do you make more torque but your torque carries better than his.

Sorry my bad. I just double checked and this engine from Paul was 413 ci engine.

Stan

[Formulajones]

Originally Posted by Stan Weiss

While they may have almost the same parts yours and Paul's curves do look different. Not only do you make more torque but your torque carries better than his. Maybe some of that is the difference in where the ICL is?

Stan

Paul's came in at 107 ICL. Mine came out to 106.25 ICL so we just called it good there.
I personally would have also liked to see a richer AFR on mine, especially through certain parts of that pull where it was very lean but we didn't have the parts to change what we wanted. But that worked out good in the car where it richened up quite a bit with air cleaner and exhaust in place.

[promptcritical]

Originally Posted by Formulajones

Here's another 455 I built. 72 455HO. This one had a 239/243 @ .050 cam, the 7K3 round port heads were ported to around 280-285 cfm, I have the flow sheets around here somewhere. It was 9.98:1 compression. Stock intake, stock Q-jet, and stock ram air manifolds in place.

After a couple tweaks it did a best of 507/571 but the most impressive part is the torque way down low. I think we pulled this to 3000 on another sheet I have where it was still making well over 500 ft lbs, and we meant to pull it down to 2000 but got busy and forgot. Safe to say this thing makes a very broad torque band with a spread of 1800 rpm between peaks, which is fantastic. Most engines usually show 1200 to maybe 1500 peak to peak on average. This thing also holds on to the power very well. This was a pump gas deal that went into a very stock appearing street car, and runs the power brakes and A/C just fine.

Those are 7F6 heads on that motor. And does run splendidly Larry.

[Formulajones]

Originally Posted by promptcritical

Those are 7F6 heads on that motor. And does run splendidly Larry.

Aaaa not sure why I said that, had 72 D ports on the brain I guess. Thanks for the correction

[Dragncar]

Dump the idea of the small valve heads on a 455. It is not worth even making 15s or whatever small valve head screw in stud.
Get some 96s, 6X8s or even 4X heads and be done with it. All you will do with small valves is lower your peak tq and give up free horsepower.
455s have torque a plenty in whatever form.
I would not even think about early closed chamber heads either. You might make a ping monster.
Sometimes people give away 6x8s or 4X heads.

[Cliff R]

On a 455 build the compression ratio and camshaft used are going to be the big players in engine power as far as how much and where it is made. The valve size in the heads will have the smaller heads making less power (torque) at every RPM since they are slightly more restrictive under the valves which would promote less cylinder filling, all else being equal.

That statement is simply my opinion based on the fact that for all practical purposes "D" port heads post 1967 are very close from a flow standpoint, runner cross section and port volume. Keeping that in mind the smaller valves bring less to the table at every RPM.

The factory used them in the lower performance applications simply because most of those engines didn't need the added airflow as they used small camshafts, often 2bbl intakes, restrictive "log" exhaust manifolds, etc.

The big valve heads got screw in studs for improved reliability as most of those engines had longer duration camshafts, stronger springs and would see higher RPM's.

One also needs to realize here that the HUGE 455 engine is sucking pretty hard on the entire intake tract and Pontiac heads don't have much more runner volume or port flow than an average SBC head. This is why they respond very well to larger carburetors and bigger camshafts. The smallest cam I'd ever put in a 455 built here would be 230 @ .050" and 280 @ .006". Attached is a dyno chart from a 455 build I did here a while back using a 230/236/112 HR cam. It made 16" vacuum at 700rpm's, dead smooth idle and desptite having good flowing heads on it was running out of wind just past 5000rpm's..........Cliff

[SD455DJ]

I agree with Dragncar and Cliff! I attached another dyno sheet that exemplifies their points. This example is of the same YH code 455 I posted the dyno sheets earlier, however, this run we swapped on a 2GC 2-bbl intake and carb from a '71 455 engine just to see what type of power it would make compared to the 4-bbl set-up. You can see it lost hp and torque everywhere (down 67 hp and 40 lb-ft of torque from max values). The 455 needs bigger valves, bigger ports, bigger manifolds (intake and exhaust), bigger carbs, and bigger cams to take advantage of the piston speed the have and will make more power down low, in the middle, and up higher (not to mention higher compression...at least 9.0 to 1).

Dennis

[hurryinhoosier62]

Originally Posted by Cliff R

On a 455 build the compression ratio and camshaft used are going to be the big players in engine power as far as how much and where it is made. The valve size in the heads will have the smaller heads making less power (torque) at every RPM since they are slightly more restrictive under the valves which would promote less cylinder filling, all else being equal.

That statement is simply my opinion based on the fact that for all practical purposes "D" port heads post 1967 are very close from a flow standpoint, runner cross section and port volume. Keeping that in mind the smaller valves bring less to the table at every RPM.

The factory used them in the lower performance applications simply because most of those engines didn't need the added airflow as they used small camshafts, often 2bbl intakes, restrictive "log" exhaust manifolds, etc.

The big valve heads got screw in studs for improved reliability as most of those engines had longer duration camshafts, stronger springs and would see higher RPM's.

One also needs to realize here that the HUGE 455 engine is sucking pretty hard on the entire intake tract and Pontiac heads don't have much more runner volume or port flow than an average SBC head. This is why they respond very well to larger carburetors and bigger camshafts. The smallest cam I'd ever put in a 455 built here would be 230 @ .050" and 280 @ .006". Attached is a dyno chart from a 455 build I did here a while back using a 230/236/112 HR cam. It made 16" vacuum at 700rpm's, dead smooth idle and desptite having good flowing heads on it was running out of wind just past 5000rpm's..........Cliff

Cliff, in other words it IS an excellent street engine.

[Jay S]

For more power and torque I totally agree with everyone that is saying go with the bigger head, bigger valves, ect. The cam, heads compression also need to match up, again, absolutely agree.

The OP was talking about using a Lunati 700 flat tappet cam. Which is 207* intake and 213* on the exhaust at .050” lift, 112* LSA and 108* ICL. I don’t know if that cam is set in stone. But it is going to pump around 180 psi in a 9:1 455, which would be in the range of a 6X-8 heads, and still be very high well down into the lower 8s compression. I think the small valve head may allow the engine to pump a little more compression before it pings. Especially at the 2000 below or so rpm range, but also at peak tq. I don’t know how much, maybe 10 lbs. Still pretty high for pump gas.

The bigger cid really need more cam(and head) to work right, the compression needs to be down to accommodate that small cam for pump gas, and in the engines operating range, it actually looses power and efficiency basically everywhere doing that. Cam should be the 702 Lunati with the big valves head in the 455, not the 700. 700 is really way to small, even with small valve heads, I would never want less than the 702 no matter what head got used. IMHO dropping the compression to manage a tiny cam is generally a poor comprise. The Lunati 702 is even pretty tiny in a 455.

If the goal is to absolutely maximize things below 2000 rpm with a tiny cam then the small valve combo might be the way to go, the gains would likely just be fuel economy, I don’t think it would ever really show power increase. In fact a bigger 702 cam with the bigger heads and more compression would still make more power at those low speeds.

[Jay S]

Power and efficiency the best of the best is still probably Richard Guido’s 65 GTO with its 8 second quarter mile at 160 mph, even using a 500+ cid turbocharged Pontiac. It averages in the lower 20s mpg on those big road trips from Canada to drag week type events here in the US. Quite honestly goes against any idea of what smaller cid , small cams, small port volume provide. But small valve stuff still has it’s place, depends on what the combo is.

https://www.racepagesdigital.com/blo...road-trip/3020

[SD455DJ]

My stock 8.1 compression '71 455 HO Formula with M22 & 3.42 gears gets 15 mpg best, but my '70 Lemans with a 400 stroker (461) with M20 and 3.08 gears gets 18+ mpg easily. It has 9.5 compression, RAIV clone cam, SD Perf CNC 6X-8 heads (255-265 cfm intakes/200 cfm exhaust), RA manifolds. Higher compression and big cam works well in that car.

Dennis

[Sirrotica]

I own a 455 that I put together in the late 80s for a customer of mine. He ended up giving the car to me after it got so rusty it would no longer pass PA state inspection. I only have the subframe with the engine still sitting in it, I scrapped the rest of the car.

I ported the 5c heads (2.11 intake, 1.66 exhaust, 9 to 1 comp ratio), used a C/C 280 Hi Energy cam in it stock cast iron intake. re-jetted Q jet and Hooker headers, full dual system with crossflow muffler from a Buick GN turbo car. It had an extraordinary amount of low end torque, and with a 3.23 axle, stock convertor T400 in a 76 T/A it would probably knock down nearly 20 MPG, but you had to use 93 octane fuel, and it would still ping under the right circumstances. It undoubtedly would be better with a little bit larger cam in it. The efficiency is so good that it has a lot of cylinder pressure at low RPM, leading to the need for 93 octane gas, and as I said, it will still ping a little bit under the right load.

The guy i built it for called me up shortly after I gave the car back to him and told me "I have to complain about the T/A", I was dumbfounded of what he could have to complain about?. He then goes on tell me the other day he left work to run to the store and on a tar and chip road he actually spun the car around when he applied just a little too much throttle and was laughing about it as he told me.

I guess be careful what you ask for, that car was actually a little challenging to drive, and he had me take his 16 YO daughter out in it just to school her in how easily someone could lose control of it on a road that was less than maximum traction.

Just my own experience with a 455 and a rather small camshaft. I think I advanced it a couple of degrees if I remember correctly further adding to high cylinder pressures at low RPM.