Please help me to understand the importance of this number. My research I have found on this says that a ratio of 80% is optimal, but more power is thought to be delivered in the 70% to 75% range. Please elaborate and also, what should I shoot for here? The reason I ask is that the 3 versions of the head that I am considering show the following:
(each column goes with respective head)

.2-0.83;0.70;0.79
.3-0.80;0.74;0.78
.4-0.74;0.77;0.79
.5-0.75;0.78;0.80
.55-0.74;0.78;0.81
.6-0.75;0.79;0.81

These #'s are for AFR 180 heads street, competition, and nitrous exhaust respectively. The nitrous heads have a consistent 80% ratio which is considered optimal, yet the street port is in the range considered to make more power.

Thaks,
Doug

 

There is no short answer to this, lots of opinions. In general the better I to E ration the better, but not always. Pro-stock heads are down in the high 60's.

For guys like us building street / strip motors, the better I/E the better the motor will run.

 

So basically the port pattern that flows consistently at 80% is the better one. Is +5% E/I to consistently be at 80% worth a 15% upcharge performance wise?

Thanks,
Doug

 

The I-E ratio is of very little useful value. It can be thrown out of whack by header design and how restrictive the exhaust is after the collectors.

So don't think about ratios. Just look at the CFM for your net cam lift numbers.

As to N.O.X. RATT's statement. The old prostock truck class had the highest HP of any 358 ci motors made. Millions of dollars in R&D. The heads were using 2.300-2.400 intake valves and little tiny 1.5 or less exhausts just because of the bore limited the valve sizes. So in building these 850 hp 358 ci motors it was determined that massive intake flow made more hp than a more balanced I-E ratio with larger exhaust valves

 

knowing would help you pick a cam wouldn't it ???

 

I have a hard time buying that the I-E flow ratio is of little value, just doesn't seem intuitive. What about Intake valve to Exhaust valve ratios? Aren't those supposed to be in the same range? After all is not flow going to be a direct relationship to valve size? Granted it may not be a linear function but wont the the size have a direct impact? Everything I have read is stating that, maybe I am reading the wrong stuff? The more questions I ask, it seems the more questions I have!

Also when you are stating look at the CFM for net cam lift numbers, what about the midlift #'s? Don't I want to take all of this into account? Or am I just making this whole process alot more involved than it needs to be.
For the record, I have it narrowed down to AFR 180's, and cam is looking to be the GM 846. I plan on running this with a 1.6 Rocker Ratio, and was trying to decide if the ooutlay was worth the competition or nitrous porting on the AFR Heads. I plan on having the heads milled to 58cc's like the DPort 113's I have now keeping compression to 10.1. If I didn't get the milling done and ordered a set of 64cc heads, what would that to to my compression and power? Big hit or no? Cost me $250 and 14 months wait time to get a milled set, or no time and no money to get the regular set. By the way there are no machine shops locally that I know of willing to do head work.

Thanks for all of the input, I am trying to learn.
Grashopper out.....
Doug

 

As mentioned...lots of variables here. AFR touts the 80% number and I am sure that is a good target. Generally, an engine that makes good power has a nice intake flow, BUT an engine that HANGS on for a long time is "living on the exhaust port" so to speak.

It is much easier to get rid of exhaust than it is to get mixture into the cylinder. That's why high rpm Pro Stock stuff is happy with the 60% range...they have to do all they can to get the cylinders full at high rpm.

But, the reason you see dual pattern cams is just to address these issues. In serious race heads, on motors with open headers, you will see a cam with more lift/duration on intake side. On most street/strip stuff, or something with stock type heads, you will see a cam designed just opposite..the exhaust will be longer and lift higher. This helps with mufflered exhaust. When you talk to AFR they tell you they optomize the flow numbers for full power deals...they have no way to really control what you put in it for exhaust. I've seen killer race heads "killed" with a set of too small headers that restict ports.

The better the I/E ratio the more likely a single pattern cam "might" do well for you. But again..there's that whole full exhaust deal that changes the whole picture.

One way they "help" the I/E ratio is to play with intake flow. If you use the same ex port on a 180cc and on a 220 cc head, the I/E ratio will obviously be better with the smaller port. Which one do you figure will make the most power??

Also don't assume that bigger valves automatically means more flow. Often smaller ones allow you to recontour the approach angles to port and actually flow better with a smaller valve. You have to watch how close valves are to cylinder wall too. Think about a 2.02 and a 1.60 valve set. That's 3.62". The bore is only 4.00 so you have only .380" to split between the edges of the two valves and the margin area between them. Now add in a set of 2.05's and some 1.625's. Now you're at 3.675 total and .325 to split 3 ways. Often the flow will completely die on the cylinder wall side of the valve as it opens. That's where you see all the work relieving the chamber walls etc.

I also know some winning racers who installed smaller valves in a 9500 rpm 476" race motor and went faster..just for the above reasons. Now you can see why big block Chevy's and Cleveland Fords have "canted" valves and why Hemi's run so well. Also why TFS sells "twisted wedge" small block heads for Fords and Chevy's.


All this said will hopefully give you a little insight. The Nitrous ports are going to be larger to allow the "artificially" enhanced motor to get rid of all the extra exhaust residue. On the street, with full exhaust and a cam not designed for them, I doubt you would see much.

Not sure of the specs on that cam..can you list them? A 350" motor with 180cc ports and a GM cam is just going to make "X" amount of power.

JIM

 

There is no magic number, but 75% E/I ratio is sometimes referred to as "ideal" because valve timing of equal duration and centerlines will usually provide the best torque bandwidth.

For high output 2V engines, you are better off compromising exhaust flow to achieve more inlet flow, and this is the case with vintage OE high performance SB heads and modern LS heads. To compensate for the relatively restrictive exhaust port you open the exhaust valve early, and this is the case with most vintage OE high performance cams. This early opening valve also usually means longer exhaust duration. The best example is the LT-1 cam with durations of 231/239 at .050" and centerlines of 110/122. The longer exhaust duration and very early centerline indicate how very early the exhaust valve opens!

A modern example is the new LS7. The exhaust port was compromised to get as much inlet port araa as possible and a 2.2" valve. To compensate, the exhaust valve is opened early and this shows up as extra duration - 230@.050" - all on the front end relative to inlet duration of 211.

When you rework typical OE or aftermarket 2V heads, things change! Because the exhaust port is short, the relative improvment in exhaust flow is usually greater than inlet flow so a head that flows 75% out of the box will achieve 80-90 percent after a mild pocket port and multiangle valve job or a full racing rework. The ideal valve timing for this setup (street engine) will have a delayed exhaust valve opening, which would show up as less exhaust duration than on the inlet side. This will improve low end torque with virtually no impact on top end power, so you get broader torque bandwidth. On a racing engine with headers and open exhaust a more conventional exhaust valve opening point may be advantageous to take advantage of the higher exhaust pressure to create higher negative pressure at the inlet valve during the overlap period at high revs.

4V heads usually have more flow per unit of displacement than 2V heads and a relatively high E/I ratio, which is improved further with rework, so they also respond well to a late opeing exhaust valve and less exhaust than inlet duration in either production or modified form.

Valve timing should be selected based on head flow and understanding exhaust wave dyanmics (if any), but these issues are usually overlooked by all but the best engine designers and tuners.

Duke

 

Instead of worrying about ratio. I just went out and bought the Dart 227cc 2.08/1.625 and had 306/230 I/E cfm I wasn't worried about the ratio. AFR 227 cc are also a good choice in the 23 degree heads. The 60/40 altered valve arangement does wonders for supposed cylinder wall shrouding

 

thanks gkull! I appreciate everyones help here....I am just trying to figure out what will work best with a 350 as I have no near future plans in punching her out. I wanna get the most bang for my buck! My meager understanding so far has led me to the following conclusions:

1. Max inlet flow in the smallest volume port to maximize low end torque
2. Don't overdo valve size, yet maintain a semblance of the 75% ratio between the sizes for a street motor.
3. E/I is not applicable in my situation, given that I am currently N/A no plans for NOS, but Turbo is a possibility, minor exhaust porting can easily raise the effeciency of the exhaust flow.
4. As the exhaust is heated and also being "pushed" out by the piston, heat, expansion, and also "sucked out" by the previous exhaust gasses flowing out(pressure differential), it has a more efficient flow rate to begin with. So pay more attention to the intake charge, as it has a less effecient flow rate.
5. Bigger is not always better, especially with ports, valves, lift, ramp rates, duration etc. Maximizing the flow while maintaining maximum velocity is ideal. The torque gains are great, and the HP losses are minimal.
So what I should be looking at are the intake flow rates of my intended heads with respect to the lower and middle ranges and try to keep the upper end as well. This will cost me a bit of HP, yet increase my usable torque band.

The 846 specs are as follows:
GM 12370846 - Hydraulic Roller Design

This hydraulic roller design contains eccentric for mechanical fuel pump. It is for off-road use only. The duration at .050" tappet lift (intake/exhaust) is 222/230; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 509/528. Valve lash is zero/zero and lobe centerline is 112 degrees.

Max lift would be 543/563 with 1.6 roller rocker.

So with the AFR 180 head and a spring upgrade as they are only good for .55 lift, I would get a fairly good comprimise with this setup. Flow for the 180 w/o any extra work and not taking into consideration the milling down to 58cc chambers is as follows:
.2-129/108
.3-195/156
.4-240/178
.5-255/190
.55-258/192
.6-260/194

These numbers are almost exactly the same as the AFR 195. I think I am giving up 5 or 8 CFM at .6 lift which is a non-issue since I wont reach that point.

More questions:

How do I determine the loss in compression if I did not mill the heads to 58cc? (I am curently 10:1 with a 58CC chamber) If the change is minimal, I can buy a set off the shelf, save a year wait and 250 bones. From what I have learned here thanks to everyone is that the 180's are a good match with this cam. I am really just trying to do this right and do it once, not wish I had done more when it is over like the setup I currently have. I have a few regrets, but hey I guess it takes time to get it exactly the way you want it right? I also don't want to just follow in everyones footsteps and do what they did, ie 219 cam etc if I can find a better or cheaper option to meet or exceed the same results.

What effect does lift have on duration? i.e. going to a 1.6 RR vs a 1.5, it gets you to max lift quicker, does it hold you there longer also? How do I figure this into the mix? My understanding of the superram is that anything over 230deg on the intake side begins to kill the velocity.

Thanks everyone, I appreciate all the advice you have given in my various threads here. I am determined to learn, so just bear with me.....



Doug

 

Aren't those a bit big for a 350 though? Any bottom end modifications required to run those heads?

 

I once used some race ported 230 cc heads on 355 ci in my Vette and it didn't run very well below 2500 rpm. It had lots of power in the 5000 - 7500 rpm range. Not a good choice at all. I used the 215 & 227 cc on my 383. Very good heads for 7500 rpm 383's and larger ci. I now am driving a 427 Motown small block

 

Try this site for a compression calculator to play with. Don't guess..you need real numbers for deck height and stuff.

http://www.angelfire.com/fl/procrastination/motor.html


If you decide you need heads milled..there are plenty of shops to get them from. Try Mike Lewis Racing..tell 'em I sent you over. He can get you killer deals on the AFR and Brodix heads and could probably either get them faster from AFR already done (he's buddy's with the designer) or he could mill them for you and ship them to you. Great guy.

IF you mill heads, make sure you use a good shop, like Mike who knows that the intake face of heads needs to be milled also...NOT the intake itself. That way heads will always fit any intake no matter what.

You might also check Brodix..they have some killer Race Rite heads out right now.

I think Vettemaniac here on the Forum has a new set of CNC 180 AFR's that you might be able to get from him. Drop Nick a note. He also has a great head porter and machinist handy where he could get them milled and ready to ship to you.

You appear to be designing a low rpm TQ type motor.....so the 180's will work. I can tell you I ran a nice set of 207cc heads on a pump gas 350 once that ran killer even with 3.36 gears. Bigger heads aren't always bad. You want a motor that doesn't nose over as rpm climbs. Too small heads will die at higher rpm. Make sure you gear and cam it to like the rpm range you are planning.

If you are planning turbo stuff someday...the larger exhaust stuff is an advantage as well as going to larger intake ports. No worry about velocity when you stuff some boost into the picture.

What is the adv duration of that cam? It can give a slight idea of manners and ramp speeds. The .050 number isn't really the issue..the actual opening and closing points are what matters. People associate .050 numbers with certain characteristics as a "norm", but there are a gazzilion different cams out there with the same .050 numbers. You can have the same .050, but have 10*+ more @.200...or 12* more at .300 or whatever. So even though .050 is the same, the ones with the larger .200 and on and on will flat outrun the other cams and still have similar manners. It's the rate of lift that makes one faster...how fast it gets valves open the most.

Of course there are physical limits to how fast you can do this, and that's what separates the good cams from the ones with broken parts. That's why roller cams do better than flat tappets. While flat tapper initially accelerates valve quicker, the roller quickly will overtake it and get valves open faster. You can see all the issues with the Comp Xtreme cams..they are really pushing the physical limits for street type cams that have to live. But they do make power. The new Voodoo line from Lunati is using extremely high acceleration rates (doesn't hurt parts much), strong .200 duration numbers and soft closing ramps. This is where parts get hurt...the closing side. They are using ramps almost identical to stock GM stuff on the end of the closing ramp.

Lift isn't a terrible killer..it actually allows cam designer a little more time to accelerate, then slow down the lifter at the nose and stop it, change direction and accelerate to close and stop it again. Lift is always a good thing as long as you have clearance and you keep it in a range where insane spring pressures aren't needed.

In fact, the ultimate would be a spring with lots of seat pressure and not as much open pressure as you typically end up with. You don't need much spring to keep lifter in contact with lobe at full lift, it's the closing and bouncing that happens that needs the high pressure.

The 1.6's will change duration slightly, but it depends on where you measure it. It will open slightly quicker and at certain points might pick up 2-3* or so at the most, again depending on cam design and where you measure it.

Hopefully this helps some...


JIM

 

My TFS heads are a little less than the optimum 80%. That is why I went for just a little more ex dur (218-224) HR w/dual ex. I see now that the Rams Horns ex man are the plug in the system. After reading the posts about how hard it is to open up the ex man, I'm sure mine were never touched. I will get dynoed before and after headers. I'm guessing headers will be worth 40+ hp. I'll keep the forum posted.

Rick

 

How do I figure deck height? My motor is currently assembled and installed. I have 58 cc heads on right now with an advertised compression ratio of 10:1.
How are the race rite heads? I was considering those as an alternative.
I am geared with an Auto 700R4 through 3.55 gears, my stall is curretnly at about 2200-2400, thinking I may need to go bigger there too. How does that affect my picture? I am trying to get something I can drive around town, and smoke down the strip. Best of both worlds if you will. I don't want to kill the all around performace of the Vette as far as shooting the twisties, blasting a decent 1/4, etc. I am trying to boost both torque and HP. I am shooting for a long, smooth, and flat torque band. And trying to get decent HP numbers as well with a peak around 6k since I am using hydraulic lifters. I have been using Dyno 2K to help model these combos, I understand it is not the most accurate, but will help me get into the ballpark. Just want to do it right with no regrets, a good street/strip combo. Am I trying to do too much? Am I taking the right approach?
Are there any sites online with cam cards? I have been trying to find more detailed information on this cam but with no luck. What I have posted is all I have been able to find so far.
Thanks Jim, I appreciate your info. My current motor is a crate GMPP engine so I will have to see if I can figure out alot of this stuff without tearing it all apart. My understanding is Heads and Cam are where the most power gains can be made, and I want to transform my 350 as best as I can with the heads and cam. I also do like the lopey idle of a cam, just need to make sure it all fits together. Since the closest track is now 2 hours down the road, I need to be able to drive her there, run a few passes, and get her home. I also like to occasionally light them up, and make a few stoplight to stoplight runs. I have been reading the Lingenfelter book on the SBC, and the David Vizard Cylinder Head book and SBC Chevy power book, and another fellows book on Cylinder heads. Figure if I do my research, spend some time learning about it, I can spend my funds wisely and not waste any money or time.

 

Sorry..I read you PM first before I read the thread...let me study on all this...it's late and I'm a little tired to try and think!

See ya,

JIM

 

ported super ram - You need to find out the port dimensions and then go to what ever vendor s head sight and look in the specs area as to what the heads intake port dimensions are also.

Fuel injection can utilize larger ports than a carb because the intake is dry flow (less dense) and injectors do a better job of atomization.

If you have 10:1 compression with 58 cc you must have some type of dished piston. 64cc would drop you into the low to mid 9 C/R That much compression drop might be around 3% power change at every rpm. Without a piston change I would be looking for some type of head with 58 or less cc.

IMO 10.7 to 11 C/R is about the best for aluminum heads and pump gas.


I can also tell you right now that if the speed bug has bit you just a few years down the road your going to be installing a bigger ci motor. So it's best to buy bigger heads with that in mind. Of course matched to your super ram is you objective now.

 

10:1 comes stock on the ZZ4 block w/valve relief flattops and 58cc heads. THere is a carcraft article from 01 using the ZZ4 with AFR 195's @58cc's, a Comp Cams HR280R mech roller making about 550HP/575TQ on an 800 or 850 cfm carb on a Victor Junior.

And yes I think the bug has finally taken ahold!!! I need to hurry up and graduate so I can afford this!!!

Thanks,
Doug

 

They made 525hp, and no where near 575TQ. But still quite impressive for a 350. Thats not a terribly large cam either.

 

I was just lookedat it last night, couldn't find the link, thought I was close. Still was an impressive motor though.

Thanks,
Doug