large valves on a stock 400?

[dodgeme]

Hi Everyone, My first post here, but I've been readin like mad. I've got a choice to make on a fairly stock 400 I've got in a 66 charger. Car has 3.91s, a conservative cam ( crower .456 lift and 220 @ .50 duration ) a almost factory stall ( factory 10 3/4 converter ). 452 heads with a fresh valve job. Now my question. I've also got a sweet set of 906 heads with 220 / 181 valves, some porting, and I cc'ed the chambers at around 83cc. ( shaved .030 ).
They were going to be for the motor I was going to build but with $ being tight around here that could be quite some time. So I'm debating sticking them on my old 400 and seeing what I get. I'm wondering though, am I going to get anything out of them with such a low comp, mild bottom end? Or are those big valves and such wasted and I'd be about even with the factory 452s back on it? I've read about overheading these engines, about the velocity with the factory valve sizes being an advantage to a mild or stock 383-400.
Thanks everyone for any input you all have on this. And thanks for a great forum!

 

[Cranky]

For a street car that's driven a lot....think I'd stay with the 452's. They have hardened exhaust seats from the factory too. One thing that would help wake up the 452's would be a pocket port job. The factory valve pockets are pretty sorry. 2.20 intakes on the 906's? Usually it's 2.14's and 1.88's.

 

[PoppaSmurf]

Cranky is right .. with a little un-shrouding in the bowl areas and blending into the seats (BUT NOT the seats) and touch up or gasket match the ports, those heads will flow nicely....you alittle info for those 906's of yours they have been worked on before
the 2.20 intake is a hi-po intake valve built originally for Direct Connection by Manley p/n p4876396
do you have any history on the heads at all......they may already have a port and polish on them... and I'm not goin to pick this to death, but are you judging your CC's by the amount the head was cut (.030) or did you actually do a pipette test??

 

[Meep-Meep]

Big valves on stock heads are said to be a waste of time unless extensive porting is done - and this is old info that comes from Bob Mullen. Even if ported correctly to take advantage of the larger valves to improve high RPM breathing, how much of that do you need on a stock low compression engine? Your best gain for the buck is to raise compression. A steel shim gasket can add .4 points over a composition one and going to a closed chamber head can add another .4-.5 points. CC-ing should be done to determine exactly what you have. The .030" milled 906's and a thin gasket might pep your engine up but it would be more due to the increase in compression rather than the big valves. The small cam is a plus. I'll agree the 452's with the already hardened seats (assuming someone didn't break through the hard face by over grinding) are probably the best option to keep it on the cheap.

 

[IQ52]

I see that you say the 906 heads have been ported and that you have cc'd the heads, so therefore you already know what you have. Run the 906 heads, you will be pleasantly suprised. Velocity is controlled by the port volume and shape and not the valve size. The large 2.20 valve will give flow increases in the cam lift range that you have and will be a big improvement. The more air you can get in that 400 the more it will feel like you have raised the compression. The exhaust seats in the 906 heads will give good life as long as you don't use the heads on a truck engine and do a lot of towing.

Feel free to ignore this post, as it is opposite from almost everything else posted (I wonder why that is?), and do anything you want.

 

[dodgeme]

Thanks for the input everyone. A little more info on the 906s, I did cc them myself using the plexiglass and a burette. Not the most accurate I know, but I've got a fairly close idea now anyway.
They've got a fair bit of port and polish work done as well. I didn't have the work done personally I bought them complete and only cc'ed them myself to get a better idea of what I had. Meep-meep, what you are saying is kind of what had me scratching my head to begin with as to if I'd get any gains at all other than compression bump. I figured with no high RPMs in the current motors future, the big valves, porting etc, might be wasted and I may as well keep the 452's and leave the 906 on the shelf.
However... IQ52, what you're saying makes a lot of sense to me, I really hadn't thought about the possibility of the overall flow increases across the board, even down lower RPM-wise. More air in...
Oh and I've got the steel shim gaskets already, sitting there waiting for me to make up my mind
Thanks everyone !

 

[PoppaSmurf]

Heres a link to some VERY interesting reading, and my bible when it come to porting and polishing Big block heads also dealing with flow and port velocity....stay with the late model 452's ....in my opinion
http://www.moparmusclemagazine.com/techarticles/5115_cylinder_heads/index.html

 

[Cranky]

At low rpm, big ports and valves are not going to have the flow velocity as a smaller head so your low end performance will suffer some. A cam with a late intake opening event will usually help in that department and will help boost cylinder pressure at lower rpm. If you decide to use the 906's....I'd go with a good intake, headers, stall and a better gear to help take advantage of them. Keep in mind how heavy that early Charger is too. In the early 80's I ran a 68 Road Runner that was running ported 906's with 2.14's and 1.88's with a 2x4 tunnel ram, .660 lift cam, 11-1, 4500 stall, 4.88 gears and the thing was running 10.68. It was with a 440 tho with a longer stroke. I also had a pickup with a 400, 68 Road Runner intake (stock), RV cam, stock 452 heads, headers, stock converter, and 3.54 gears. This was on a 3/4 ton so the tires were probably around 29" tall and the truck was right at 5000 lbs. It was a tire fryer and I had to feather it off the line and yet it ran a 15.40 ET. That was right in the Mustang GT area back in the early 80's and yeah, I took on a few. If I could go at em on a roll, I'd stayed right with them. Running a mid 15 wasn't a ball of fire but it was rather respectable for a 3/4 ton truck. Yeah, the big heads will flow more air but it's flow velocity that makes things happen. I have to say that they will be lazy at low rpm and sounds to me that you won't be in the upper rpm ranges much. With lazy heads, fuel has a tendency to drop out of the charge. If you're unsure, start doing some research on flow and fuel suspension. Air will flow through just about anything but fuel won't.

 

[PoppaSmurf]

AMEN !!!!!!!!!!!!!!!!!! and thanks Cranky...alot of people including so called engine builders, don't understand "Flow Characteristics" I can't tell you the numbers of heads I have seen that have been wallerd out (southern slang term) all in the name of porting....sometimes smaller is better...you may be able to pack it in....BUT if it dont come out...you've (as they say down here) kilt the engine....there HAS to be a balance of what goes in and what comes out

 

[Meep-Meep]

I see that you say the 906 heads have been ported and that you have cc'd the heads, so therefore you already know what you have. Run the 906 heads, you will be pleasantly suprised. Velocity is controlled by the port volume and shape and not the valve size. The large 2.20 valve will give flow increases in the cam lift range that you have and will be a big improvement. The more air you can get in that 400 the more it will feel like you have raised the compression. The exhaust seats in the 906 heads will give good life as long as you don't use the heads on a truck engine and do a lot of towing.

Feel free to ignore this post, as it is opposite from almost everything else posted (I wonder why that is?), and do anything you want.

Hey, I thought you were gone?

 

[Cranky]

My Eddy RPM heads flow about the same as my old 906's did but due to port and combustion chamber design and plug location, they are a better head and will perform better. I've had plenty of arguments with people who only look at flow numbers and say the higher number will always outperform the lower flowing heads. This is simply not true.

 

[Meep-Meep]

At low rpm, big ports and valves are not going to have the flow velocity as a smaller head so your low end performance will suffer some. A cam with a late intake opening event will usually help in that department and will help boost cylinder pressure at lower rpm. If you decide to use the 906's....I'd go with a good intake, headers, stall and a better gear to help take advantage of them. Keep in mind how heavy that early Charger is too. In the early 80's I ran a 68 Road Runner that was running ported 906's with 2.14's and 1.88's with a 2x4 tunnel ram, .660 lift cam, 11-1, 4500 stall, 4.88 gears and the thing was running 10.68. It was with a 440 tho it a longer stroke. I also had a pickup with a 400, 68 Road Runner intake (stock), RV cam, stock 452 heads, headers, stock converter, and 3.54 gears. This was on a 3/4 ton so the tires were probably around 29" tall and the truck was right at 5000 lbs. It was a tire fryer and I had to feather it off the line and yet it ran a 15.40 ET. That was right in the Mustang GT area back in the early 80's and yeah, I took on a few. If I could go at em on a roll, I'd stayed right with them. Runner a mid 15 wasn't a ball of fire but it was rather respectable for a 3/4 ton truck. Yeah, the big heads will flow more air but it's flow velocity that makes things happen. I have to say that they will be lazy at low rpm and sounds to me that you won't be in the upper rpm ranges much. With lazy heads, fuel has a tendency to drop out of the charge. If you're unsure, start doing some research on flow and fuel suspension. Air will flow through just about anything but fuel won't.

Yep, it's called wet flow. Like you say big ports are not the end all be all but keeping the fuel (which has more mass than air) on the right track and headed for the cylinder is the name of the game.

 

[Meep-Meep]

I see that you say the 906 heads have been ported and that you have cc'd the heads, so therefore you already know what you have. Run the 906 heads, you will be pleasantly suprised. Velocity is controlled by the port volume and shape and not the valve size. The large 2.20 valve will give flow increases in the cam lift range that you have and will be a big improvement. The more air you can get in that 400 the more it will feel like you have raised the compression. The exhaust seats in the 906 heads will give good life as long as you don't use the heads on a truck engine and do a lot of towing.

Feel free to ignore this post, as it is opposite from almost everything else posted (I wonder why that is?), and do anything you want.

The laws of thermodynamics and engine builders for the last 100 yrs suggest a compression increase works http://chemcases.com/fuels/fuels-c.htm

 

[dodgeme]

Thanks for the link to the mopar muscle article, very helpful. The port flow vs. velocity section alone helped explain a lot of bits and pieces I'd picked up along the way, but hadn't really put together yet. Amazing to me to learn how easy it is to go backwards on these heads and end up with something maybe no better than stock or even worse.... holy smoke I haven't even started my search on "wet flow" yet... Thanks everyone, I've got more time than money, so I'm going back to reread that article and then learn more about "wet flow" and "fuel suspension".

 

[383man]

The bottom line is the 906 heads with the larger valves will not do any good on your 400.There is many reasons why as some here have said and not to mention with the small cam you have it could not take advantage of the flow even if it needed to which it dont. They would be overkill for sure on your 400. Just keep the 452's on it. Heck that has a larger intake valve then the Indy EZ head has on my 493 eng in my 63 as it only has a 2.19 intake valve. Ron

 

[dodgeme]

yeah after reading through everyones comments ( thanks everyone by the way ) and going over the suggested reading a couple times ( it's more of a science than I realized ) I'm leaning now towards maybe just selling them in their pristine state. The more I tally up the engine I wanted to do originally, it'll be a long while....

 

[Cranky]

Thanks for the link to the mopar muscle article, very helpful. The port flow vs. velocity section alone helped explain a lot of bits and pieces I'd picked up along the way, but hadn't really put together yet. Amazing to me to learn how easy it is to go backwards on these heads and end up with something maybe no better than stock or even worse.... holy smoke I haven't even started my search on "wet flow" yet... Thanks everyone, I've got more time than money, so I'm going back to reread that article and then learn more about "wet flow" and "fuel suspension".

And once you are done with that (but who is ever done!), read up on quench!
http://www.forbbodiesonly.com/moparforum/showthread.php?t=12581&highlight=quench
Then if you really want to go in deep, study up on cams....and don't forget about cylinder scavenging. Head spinning yet? :headbang:

yeah after reading through everyones comments ( thanks everyone by the way ) and going over the suggested reading a couple times ( it's more of a science than I realized ) I'm leaning now towards maybe just selling them in their pristine state. The more I tally up the engine I wanted to do originally, it'll be a long while....

Yup, it is a science and a lot of folks think you can just start throwing parts at them and it'll run better when in fact lots of times it does but if everything is well thought out, it can be a screamer instead of just a moaner