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Cylinder head questions

2K views 25 replies 5 participants last post by  92z28400sbc 
#1 ·
Hey guys I've got a set of aluminum edelbrock performer rpm cylinder heads 170cc int. runner and 60cc exh. and 70cc combustion chambers. These heads are holding my 400 back and I need more flow so how far can I hog these babys out. Can I get 230 int. and 85 exh.? And where should I send them? What kind of price would I be looking at?

Thanks.
 
#2 · (Edited)
Thanks a lot, was worried I might not be able to do anything with them.

The reason they're holding me back is that the car seems to be lacking on the higher rpms. I've got 10.8 to 1 compression, comp cams hydralic flat tappet 292 dur. 504 lift not a dual pattern cam, edelbrock performer rpm intake, a holley 750 carb, 1.6 rockers, the edelbrock heads 170 int. 60 exh. 70 cc chambers 2.02 1.60 valves and 3 inch exhaust the primary tubes are 1 7/8. And its bolted to a 700r4.

On the box that these heads came in it said these heads will make 420 hp on a 9.5 to 1 compression 350. So how much horsepower do you think I'm making?
 
#3 ·
General rule of thumb of cubes x 50% for a street engine, and 55% for a high performance engine.... says the 170 cc heads are quite small for a 400, but they should make torque up to 5300 rpm.

The Comps 292H cam duration @ .050 is 244* and the lift is .501. And on a 400 has a range of about 2100 to 6100 rpm.

Your headers seem to be overly large for the combination you are running, 1 5/8, or 1 3/4 at the largest.

From the information you gave I see this.
Heads too small, cam too big, headers too big, timing advance curve unknown, mufflers unknown.

I would suggest you rethinking your goals for this engine and adjusting components accordingly.

"The best cars and the best engines are all simply the best combination of compromises that can be assembled." Steve Henderson
 
#5 ·
thanx for the reply xntrk. Your criticism is helpful ,but you could have saved a few words and just said my heads were too small. Which is why I posted this thread. When we built this engine originaly we wanted an agressive loping sound and still have a car was managable on the street. We put 1and5/8th primary tube shorty headers on the car with 1.5:1 rockers and the car did exactly what we built it for. Now were trying to get more topend horsepower out of it for the strip. This car was a beast when we first got it running, the components were selected based on what we wanted to do, no wierd sounds from the motor and it beat just about everything we came up against, which aint saying much since we live in pensacola florida. I know the flow on the heads is 237 at .500 on the intake with 170 cc intake runners. Trying to find what can be achieved with the intake runners opened up. Can the intake runners be opened up to 220 ccs? can the exhaust runners be opened up to 85ccs can I get 250-260 cfm uot of these heads?
 
#7 ·
92z28400sbc said:
... I know the flow on the heads is 237 at .500 on the intake with
170 cc in intake runners. Trying to find what can be achieved with the intake
runners opened up. Can the intake runners be opened up to 220 ccs?
I have a set of RPM heads in the shop that have been radically ported. The
port can be raised substantially but care must be taken not to cut into the
rocker area. The normal push rod pinch is an issue but the divider wall can
be cut down to widen the pinch. I'll try to get pictures if you'd like.

220 cc is a bit much to ask for but these heads will run great without going
that large. besides if you do get the ports that big you will need bigger
valves and before you know it you spent more time and money than it's worth.
 
#9 ·
automotive breath said:
I have a set of RPM heads in the shop that have been radically ported. The
port can be raised substantially but care must be taken not to cut into the
rocker area. The normal push rod pinch is an issue but the divider wall can
be cut down to widen the pinch. I'll try to get pictures if you'd like.

220 cc is a bit much to ask for but these heads will run great without going
that large. besides if you do get the ports that big you will need bigger
valves and before you know it you spent more time and money than it's worth.
Yeah I want to keep it within reason. Could I get 550+hp out of these heads without going too extreme? Should I just get new heads?
 
#10 · (Edited)
With porting these heads respond very well. I have ported several sets, low
11s to high 10s 355 CI in 3200 lb cars with hogging them out.

Alternately, a set of AFR 210s will get you where you want to be easily.


Here's a picture of the RPM's I mentioned. Someone hogged them out and
cut through in a couple of places, I'm repairing the damage. I don't have
a flow bench, I wish I did, these heads will flow a bunch, my guess ~ 280
on the intake side.

A milder version of this port job would make a good set of heads for your SBC.
The parts F-BIRD'88 or something similar will be needed to wake up the beast.

 
#11 ·
automotive breath said:
With porting these heads respond very well. I have ported several sets, low
11s to high 10s 355 CI in 3200 lb cars with hogging them out.

Alternately, a set of AFR 210s will get you where you want to be easily.


Here's a picture of the RPM's I mentioned. Someone hogged them out and
cut through in a couple of places, I'm repairing the damage. I don't have
a flow bench, I wish I did, these heads will flow a bunch, my guess ~ 280
on the intake side.

A milder version of this port job would make a good set of heads for your SBC.
The parts F-BIRD'88 or something similar will be needed to wake up the beast.

Will getting my heads to flow 280cfm cost as much as a new set of afr210s?
 
#12 ·
92z28400sbc said:
Will getting my heads to flow 280cfm cost as much as a new set of afr210s?
A realistic goal for the performer RPMs would be in the 260-265 scfm range.
These heads have a very good port design, they will support a large amount
of power.

There is no set price for porting so I can't say what someone else would charge.
Do you have someone in your area? If so get pricing.

The AFR heads cost about $1,550; they are worth every penny.
 
#13 ·
F-BIRD'88 said:
if you really want 550hp from your 400 I would not use the RPM heads. They can be ported to support that power level but at that point they will have thin port walls.
Start with a much larger head that either flows enough air to start with or very near that only needing standard port cleanup, radiusing and profiling the guide boss.

Have you considered supercharging. A 550hp supercharged motor is very streetable and easy to live with. A 550 hp N/A motor will need all the racey supporting parts and be a radical beast.

My earlier post recomendation will get you to the 475-500hp level with more top end than you have now, but not 550hp.
Brodix makes a cool 18deg head that will take you to 550hp and far far beyond if you choose.. Sell the RPM"S or use them on something else. Don't try to make them into something they are not.
We thought about supercharging ang turbos but thats really axpensive and we'd have to replace the 6" conrods and pistons, more money
 
#14 ·
automotive breath said:
A realistic goal for the performer RPMs would be in the 260-265 scfm range.
These heads have a very good port design, they will support a large amount
of power.

There is no set price for porting so I can't say what someone else would charge.
Do you have someone in your area? If so get pricing.

The AFR heads cost about $1,550; they are worth every penny.
Thats probably the way to go. Only problemI see is the combustion chamber size. 64cc would put me over 11:1 comp ratio and 75cc would drop me down to 10:1. I'm at 10.79:1 right now with 70cc chambers and we have to retard the timing for street driving.
 
#16 ·
automotive breath said:
If you go with the AFR heads you can tell them what combustion chamber
size you need.

With the Edelbrocks the chambers can be opened slightly by un-shrouding
the valves.

Either way you need to get to where you can run the correct amount of
ignition advance for maximum power.
I didnt know you could get what chamber size you want. Thats cool. Yeah, we need a better way of timing, got the tab and tape for the balancer just spaced it out when we assembled the motor. Got in too big of a hurry
 
#17 ·
I tell you something I'm having a problem with is the horsepower numbers. These heads should make 420hp on a 9.5:1 350sbc with a 750 cfm carb. Weve got a 10.79:1 comp ratio and 408 cubic inches with a 750cfm carb. I know that the limited flow of these heads is going to keep this motor from reaching its full potential but we smoked a 2003 supercharged mustang that the guy claimed made over 500 hp on a dyno. Weve got to be in the 500 hp range right now.
 
#18 ·
F-BIRD'88 is right, comparing the performance of two cars is useless exception
being at the race track with accurate timers. More times than not, the ability
to use the available power to accelerate the car becomes the determining
factor as to which car can ET the best. Secondly comes the ability to leave
the starting line with out a red light.

A good 170 cc port on a well built 408 will make tons of power at low RPM. This is
great if you have a chassis that can handle it. With a set up like that you can
ET quicker than a car with much more horsepower if it is not set up to use it.
 
#20 ·
F-BIRD'88 said:
A lot of people clam to be making 500hp.
The only way to know how much power you are making is to dyno your motor. You can get a good idea of the power of your motor by going to the drages and testing it. You can easily calulate the horsepower from the ET slip and actual car weight with driver.
Saying you "smoked" another car that the owner claims makes X amount of power does not tell you anything.

You are making less than 500hp. Your motor is not that much different than the Edelbrock 350 performer RPM motor. I'd estimate you are within 30hp. 30 more or 30 less :D
Your crazy, 58 cubic inches doesnt make a difference, niether does the comp ratio, right. Are you an idiot or do you think I'm an idiot
 
#22 ·
F-BIRD'88 said:
You'd have to be errrrr....inexperienced to think that adding 58cid under the same cylinder head , intake manifold and a very simular hyd camshaft and 1 ratio more cr will get you 80hp more.

I'll let you go on your remark..... this time....we all start off somewhere...... :rolleyes:
You came down on me hard with the magic squirrel remark. I let that slide.Whats up? did I do something to you in a former life or something? I was trying to get a ballpark figure of the hp this motor produces. I've read a few posts where people were glad to estimate hp based on thier experience, but I get,"ask the magic squirrel", Its just the internet, no big deal.
 
#23 ·
F-BIRD'88 said:
The weather is nice there in Florida. Why not take the car to the local 1/4 mile track and test it. That will give you a good idea of where you're at. Just be ready to accept a good dose of reality.....and work from there... I'm 99% sure your motor is making 440 to 460hp at the flywheel (gross BHP) based on the info you gave. I'm close,..... most of the time.
The magic squirrel is less forgiving. You might not like his answer...... :eek:
You're probably on the money with that, but I seriously doubt a 9.5:1 350 is pushing these heads as far as they will go. And the 400 at 10.79:1 is going to create more vacuum and more flow. But if you look back at 327sbc from 68 thay had one at 10:1 comp that made 275hp and one at 11:1 comp that made 350hp a difference of 75hp, both had 4bbl. No doubt the heads and the cam were different but it was factory stuff and it couldnt have been that different.
 
#25 ·
" I seriously doubt a 9.5:1 350 is pushing these heads as far as they will go"

No... ~420HP is pushing these heads as far as they can go...whether it's in a 9.5:1 350 or a 10.8:1 400.

Every given port has a limit to the amount of air it can flow. A well designed 170cc intake port will only flow so much, no matter how big of an engine you bolt it to. That amount of air mixed with the proper amount of fuel is how much energy will be driving the cylinder.

Your theory earlier that because you had high compression your engine is going to create more vacuum and therefore more flow is off the mark. The compression ratio of an engine has NO impact on that engine during the intake stroke. How much air is taken in is dictated by the volume of the cylinder, the speed of the piston, and the flow characteristics of the intake tract. The compression ratio of the engine doesn't change any of that. Think about it....

Air actually doesn't "pull" well. It starts to stretch and come apart. The harder you pull the air through a restriction the less dense air you get. What makes power is the number of O2 molecules you get in there. More pull = more vacuum = less molecules = less power. A head will only flow what it'll flow and more compression won't change that.

F-bird and Automotive breath are giving you solid advise and help here. Take it even if it isn't what you wanted to hear. There are plenty of forums where you can ask question like this and get BS answers like "ya man, my brothers cousins uncle had that exact setup..your making 800 HP fur sure"
These folks are trying to give you honest advise that I imagine comes from from plenty of engines that didn't work out as planed the first go 'round..

If you want 550HP you need a head that can support it. You could try to have the RPMs ported to that but you may end up spending close to what the right heads would cost anyway and unless you have someone you know does good work, it can be a crap shoot. I would just buy "right" heads and move on.

I can't count how many times I've lost money "saving" money.
 
#26 ·
SlowGTA said:
" I seriously doubt a 9.5:1 350 is pushing these heads as far as they will go"

No... ~420HP is pushing these heads as far as they can go...whether it's in a 9.5:1 350 or a 10.8:1 400.

Every given port has a limit to the amount of air it can flow. A well designed 170cc intake port will only flow so much, no matter how big of an engine you bolt it to. That amount of air mixed with the proper amount of fuel is how much energy will be driving the cylinder.

Your theory earlier that because you had high compression your engine is going to create more vacuum and therefore more flow is off the mark. The compression ratio of an engine has NO impact on that engine during the intake stroke. How much air is taken in is dictated by the volume of the cylinder, the speed of the piston, and the flow characteristics of the intake tract. The compression ratio of the engine doesn't change any of that. Think about it....

Air actually doesn't "pull" well. It starts to stretch and come apart. The harder you pull the air through a restriction the less dense air you get. What makes power is the number of O2 molecules you get in there. More pull = more vacuum = less molecules = less power. A head will only flow what it'll flow and more compression won't change that.

F-bird and Automotive breath are giving you solid advise and help here. Take it even if it isn't what you wanted to hear. There are plenty of forums where you can ask question like this and get BS answers like "ya man, my brothers cousins uncle had that exact setup..your making 800 HP fur sure"
These folks are trying to give you honest advise that I imagine comes from from plenty of engines that didn't work out as planed the first go 'round..

If you want 550HP you need a head that can support it. You could try to have the RPMs ported to that but you may end up spending close to what the right heads would cost anyway and unless you have someone you know does good work, it can be a crap shoot. I would just buy "right" heads and move on.

I can't count how many times I've lost money "saving" money.
I dont need a B/Sforum, I need the truth no matter how difficult it is to take. I can do without the magic squirrel though. I'll get better heads. Preciate the advice everyone :spank:
 
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