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I think I would go with a shorter cam duration with 3.08 gears, I would shoot for ~214-220 duration . I think with those heads you will run out of air by 5k, so a longer duration is going to shorten your power band from ~2500-5000k. A cam that pulls hard from 1200-1500 to 5k will make it faster off the line and harder on your tires.
I just had a 383 built, 11.3:1,ported brodix ik heads, 230/236 110 lsa, 3k stall , 3.70 gears. It should make pretty flat torque from 3000-6000 rpm . My previous motor was running H268 (~220 duration) and with 3.08 gears it was soggy until about 2800 rpm. That made it pretty sluggish off the line, then the stock heads were done by 4500rpm which made the power band really short. I really needed a shorter duration rv type cam with that combo.
I think I would go with a shorter cam duration with 3.08 gears, I would shoot for ~214-220 duration . I think with those heads you will run out of air by 5k, so a longer duration is going to shorten your power band from ~2500-5000k. A cam that pulls hard from 1200-1500 to 5k will make it faster off the line and harder on your tires.
I just had a 383 built, 11.3:1,ported brodix ik heads, 230/236 110 lsa, 3k stall , 3.70 gears. It should make pretty flat torque from 3000-6000 rpm . My previous motor was running H268 (~220 duration) and with 3.08 gears it was soggy until about 2800 rpm. That made it pretty sluggish off the line, then the stock heads were done by 4500rpm which made the power band really short. I really needed a shorter duration rv type cam with that combo.
He can always choose the same cam but go with a 108 LSA to shift the power curve down. However, his 2500 converter matches the 110 LSA cam well.
I tried 3 different roller cams in my first 383. All of them 112.
You have been getting some bad advice from your mechanic and here.
Rod to cam clearance is determined by the size of the rod beam near the base. It has nothing to do with the cam lobe lift. If you look inside the motor when you rotate it over the cam lobe is always on the low NON lift side at its nearest position to the big end of the rod. That was engineering from GM.
The higher hp LARGER H beam rods and to a lesser extent the higher hp I beam are when you need to think about the base circle diameter of the cam lobes.
People that are inept don't understand roller rockers and valve retainer clearance issues or roller design. You do things like. 100 longer valve stems or even. 200 longer valve stems and push rods. I also built my motors with LASH CAPS. That gives additional rocker to retainer clearance and more surface area for the roller tip to roll on.
I also disagree with jebby on valve lift. It shows a lack of understanding of Volumetric Efficiency. Just because a head doesn't increase cfm lifting a valve past max cfm doesn't mean that it doesn't increase total cylinder filling.
As rpm goes up the amount of time to fill the cylinder goes way down. That's why on a dyno you see the power just drastically drop off at higher rpms. Lifting the valve higher has the valve event flowing at maximum CFM for a longer period of time. That's why your typical flat lifter street motor has 80% VME and a racing engine can exceed 100%
Roller lobes create more engine vacuum because of superior cylinder filling. So don't even compare some 268H flat tappet cam to a roller cams duration. More bad information.
I have posted this many times because this cam works in a 327 or 383. Skip White only made by Comp Skip calls it the Magic cam. I am running Pro Max heads also from Skip.
Higher lift opens the valve higher for the same exact period of time as lower lift if the duration and the ramp are the same. Higher ratio rockers add a very marginal amount of duration, almost not enough to mention or make a difference unless you are class racing.
My understanding of VE is absolute and lifting a valve higher than necessary for the same amount of time after the intake port stalls does squat. Period. You can cheat duration....but you cannot cheat airflow through a port at a given valve lift. You lift the valve to the stall point and no further, ever.....all it does is create more valvetrain stress. This is why LS cams always have so much more lift than Gen 1 small blocks for a given duration.....an LS head flows much better than a 23 degree small block head, so you lift the valve higher to take advantage of it.
Most 383 setups now are I-Beam rod...which Scat and Eagle have addressed the cam clearance on by relieving those areas in the forging. A flat tappet will clear no problem but most rollers require at least a .990 basecircle.......some need more or less depending on the rod and how the shelf part# grind basecircle is set......some grinds are small, some not.....most start out at a nominal 1.050, but not all.... The bottom of the cylinder usually needs to be rod clearanced. The 400 block has less meat in this area so no mods needed with a 5.700 rod. And yes....I generally spec a 5.700 rod as the piston pin is lower and makes for a more stable piece all around and keeps the pin out of the oil ring land.
Comparing durations between roller and flat tappets @ .050 is not a fair comparison as the roller has a LOT less area under the curve to open and shut the valve faster.....this combined with friction reduction is the only two things that determine how much power a roller has over a flat tappet. You can't compare them short of seeing how far down the page you go in the catalog.
I believe in lash caps for very high lifts with a ton of pressure as it reduces strain on the valve tip, but the rest of the world doesn't need them.
A stock small block 350 with stock heads is about 75-80% VE.......put a Dart as cast head on it and that number jumps to 90% or a little above.....my 421 inch 227CNC headed stuff makes 104% VE.....my 477 BBC with a Brodix race oval CNC is 109%. LS engines are about 90%....and so you get the idea.
Where is my lack of understanding? Point it out.
Jebby
Last edited by Jebbysan; Jun 23, 2021 at 10:24 AM.
It is easiest to see on sophisticated modern engine simulation software that actually come out very close to real world dyno results. But it is easy to see on this AFR 180 cc head flow chart.
they didn't bother to show the .550 .600 .650 .700 because the head runner is the limitation. So it continues on at @ 260 CFM Max
180cc Street Head Flow Chart
.200 .300 .400 .500 valve lift
138 198 240 260 Int
110 158 190 207 Exh
To make engine simulation software work the more correct data you put in the more accurate it becomes. So one point that you brought up is duration. .006 advertised doesn't tell you much. .050 lift tells you a little more. But comp cams list's their durations out to .200 lift and you can map out on your own to what ever lift you want and that tells you how much duration a valve is at at given lift. So for engine simulation purposes you input the CFM at all the .050 incremental valve lifts up to say .700 and the duration numbers clear out to say .400 lift You can make a cam with with say 230 degrees @ .050 with only .500 lift or you can have a radical lobed solid roller with steep ramps with the same 230 dur @ .050 and give it .700 lift. I'm also using the Same 1.5 rockers to get the .700 lift
It's very obvious that the .700 lift cam will spend lots of time (degrees of duration) at the 260 cfm of flow. Filling the cylinder at much higher rpm.
So when I am researching a cam lobe for a high VME engine I look at the listed .200 lift degree numbers. 236@ .050 cam .644 lift has a Duration of something like 168 degrees at .200 lift. It spends 168 degrees at the higher listed CFM for what ever head it has to work with. If it was a 236@ .050 and .520 lift it might have such mild lobe rams that it's .200 lift duration numbers might only be 100 degrees. Spending very little time at higher cfm of flow. The low lift cam would fall on it's face on a dyno run at say 5000 rpm where the higher lift cam with vastly superior cfm of flow might continue to rise in power over 5000 rpm.
Lot's of this 30 - 40 - 50 year old BS came from books like David Vizard's (SP?) It was written back before lots of technology came into heads, valves, valve spring, cam lobe designs..... It very obvious to look at flat tappet cam lobe and a modern roller lobe. The roller lobe keeps the valve lifted to higher CFM faster and longer. Making more power and vacuum.
The .700 vs. the .500 would make a marginal increase in power at the expense of longevity......so if I spec a cam for the street, it doesn't go much further than where the head stalls. Street cars are not looking for every ounce of power......class racers and street racers are. I would never put a .700 lift cam in an engine with a head that stalls at .500 lift because it simply isn't worth it......not enough gain to justify it. Now if your head kept going and flowed 300cfm @ .700 lift then yeah.....the question becomes more viable. I do not totally disagree with you but there are a LOT of different aspects besides all out power that determine an engine build....there fore a max lift camshaft is not a consideration.....especially if the cylinder head has awesome low lift numbers, like we see now in the industry with street 23 degree stuff......
The Pro's think the same way......I know because I worked next to a few of them, and the first thing they will tell you when they spec an unknown setup for a camshaft is where do the heads stall? Go ahead, call one.....see what they say. They will also give you a couple of different recommendations depending on how long you want your springs to live.....and it is your choice, one will make 20 more hp on a 900hp N/A engine but your spring life is cut in half........
There is no free lunch......if there was, then all engines would have .700 lift.......
I stand behind my statement of a lift spec that matches where the head stalls. I know how and why roller cams work and it is a whole different world of cam design than FT......
Dick Maskins once told me that if you do not see the car racing on TV then you are building a compromise.....and he is 100% correct.
I tried 3 different roller cams in my first 383. All of them 112.
You have been getting some bad advice from your mechanic and here.
Rod to cam clearance is determined by the size of the rod beam near the base. It has nothing to do with the cam lobe lift. If you look inside the motor when you rotate it over the cam lobe is always on the low NON lift side at its nearest position to the big end of the rod. That was engineering from GM.
The higher hp LARGER H beam rods and to a lesser extent the higher hp I beam are when you need to think about the base circle diameter of the cam lobes.
People that are inept don't understand roller rockers and valve retainer clearance issues or roller design. You do things like. 100 longer valve stems or even. 200 longer valve stems and push rods. I also built my motors with LASH CAPS. That gives additional rocker to retainer clearance and more surface area for the roller tip to roll on.
I also disagree with jebby on valve lift. It shows a lack of understanding of Volumetric Efficiency. Just because a head doesn't increase cfm lifting a valve past max cfm doesn't mean that it doesn't increase total cylinder filling.
As rpm goes up the amount of time to fill the cylinder goes way down. That's why on a dyno you see the power just drastically drop off at higher rpms. Lifting the valve higher has the valve event flowing at maximum CFM for a longer period of time. That's why your typical flat lifter street motor has 80% VME and a racing engine can exceed 100%
Roller lobes create more engine vacuum because of superior cylinder filling. So don't even compare some 268H flat tappet cam to a roller cams duration. More bad information.
I think this picture better explains why people think lobe lift may create a clearance issue. But what works for one may not work for others… So who knows until you try it.
I totally agree that spring life goes way down as lift goes up. I actually consider sub .600 lift to be very mild for roller cams. If a head stalls out at .500 lift a .540 to .580 lift is a good option. It just gives you an extra 500 rpm wider power band. But that means that it might be making power clear out to the red line.
All modern cars have rev limiters. Our old stock chevy's especially the base models couldn't spin their self fast enough to blow up
I totally agree that spring life goes way down as lift goes up. I actually consider sub .600 lift to be very mild for roller cams. If a head stalls out at .500 lift a .540 to .580 lift is a good option. It just gives you an extra 500 rpm wider power band. But that means that it might be making power clear out to the red line.
All modern cars have rev limiters. Our old stock chevy's especially the base models couldn't spin their self fast enough to blow up
I think this picture better explains why people think lobe lift may create a clearance issue. But what works for one may not work for others… So who knows until you try it.
That picture is just a drawing and not showing correct cam to crank like real life. It just showing where on the rod to be looking
Take a look it's cylinder #2. It shown somewhat before TDC. the crank and cam run Counter Clockwise. That tappet for #2 is shown on the heel. I just pulled a random cam card out of my work desk. If that is a intake tappet they start to lift the valve at open 9 degrees before TDC. If that is an exhaust tappet it opens 3 degrees after TDC. So the real cam lobe is already opening at the rods closest point before it reaches TDC
As you can see the cam lobe for the drawings sake is not in actual relationship.
An example. You could take a stock 350 cam with it's 1.085 diameter base circle and crash into it by installing 6 inch H beam rods and it hit's down on the heel of the cam lobe without increasing the lift because that's not what hits. The lobe is rotating CCW and away from the rod. This cam card of mine shows max lift happening at 154 degrees after top dead center.
I’m gonna let you guys duke it out lol.
You guys are way over my head, but that’s why I ask questions on here.
I greatly appreciate all you guys’ input.
Like I stated from the beginning, I’m just a carpenter trying to gain a better understanding of how these engines work, and which parts will work best together.
Yes, it is just gonna be used as a street car, weekend cruiser and from time to time I may drive to work or to look at prospective jobs.
I am not interested in redlining the car or squeezing every ounce of power out of it at the expense of longevity, but an occasional burnout would be fun (but don’t want to break other parts in the process) 😬.
I plan on this being a “once in a lifetime” build, as I do NOT want to do this again. I simply do not have the time or resources to keep tearing into the engine or spending unnecessary $$ re-buying parts on account of my screwups.
On the flip side: since it is a one-time build (and for Gods sake I hope it is), I don’t want to cut corners, either.
If I have to spend a couple thousand more to make it right the first time, I’ll have to bite the bullet, shell out the cash, and accept my ****-whoopin by the wife and make myself comfortable in the doghouse.
Again, I’m not going for the fastest car or highest hp, but DEFINITELY don’t want a slouch, either.
Im looking to you experts for advise on what would make a good, RELIABLE setup while making the best compromise between power output/torque and longevity….leaning heavily towards longevity.
I understand that my 3.08 gearing is not ideal for this build, but when the time comes, I may be willing to upgrade.
What would be the all-around best cam setup that would work considering my current gearing, with the possibility of an upgrade (way) down the road?
Id love to port the heads, but I’m not sure I’d be willing to tackle that job on my own. MAYBE down the road, but then again, I’d prefer not to tear into the engine unnecessarily if I can help it.
There’s still a plethora of items on my to-do list, such as rewiring, replacing body mounts, suspension bushings, borgeson upgrade, trans overhaul, etc, that I’d like to do before installing the engine.
Thank you ALL for your input!!
Given everything you just said (remember it’s the combination that counts) look for a setup that produces lots of torque in a usable rpm range. Forget about hp and flow etc. Seat of the pants fun driving on the street comes with torque production in the 1500 to 5500 range. It will help out your rear gear ratio also. Have fun.
I’m gonna let you guys duke it out lol.
You guys are way over my head, but that’s why I ask questions on here.
I greatly appreciate all you guys’ input.
Like I stated from the beginning, I’m just a carpenter trying to gain a better understanding of how these engines work, and which parts will work best together.
Yes, it is just gonna be used as a street car, weekend cruiser and from time to time I may drive to work or to look at prospective jobs.
I am not interested in redlining the car or squeezing every ounce of power out of it at the expense of longevity, but an occasional burnout would be fun (but don’t want to break other parts in the process) 😬.
I plan on this being a “once in a lifetime” build, as I do NOT want to do this again. I simply do not have the time or resources to keep tearing into the engine or spending unnecessary $$ re-buying parts on account of my screwups.
On the flip side: since it is a one-time build (and for Gods sake I hope it is), I don’t want to cut corners, either.
If I have to spend a couple thousand more to make it right the first time, I’ll have to bite the bullet, shell out the cash, and accept my ****-whoopin by the wife and make myself comfortable in the doghouse.
Again, I’m not going for the fastest car or highest hp, but DEFINITELY don’t want a slouch, either.
Im looking to you experts for advise on what would make a good, RELIABLE setup while making the best compromise between power output/torque and longevity….leaning heavily towards longevity.
I understand that my 3.08 gearing is not ideal for this build, but when the time comes, I may be willing to upgrade.
What would be the all-around best cam setup that would work considering my current gearing, with the possibility of an upgrade (way) down the road?
Id love to port the heads, but I’m not sure I’d be willing to tackle that job on my own. MAYBE down the road, but then again, I’d prefer not to tear into the engine unnecessarily if I can help it.
There’s still a plethora of items on my to-do list, such as rewiring, replacing body mounts, suspension bushings, borgeson upgrade, trans overhaul, etc, that I’d like to do before installing the engine.
Thank you ALL for your input!!
I build mine just as a rowdy street cruiser/tire burner, but it's probably on the edge of being decent on the street. For something fun to drive around town I would have gone down in duration to 218-224 and 9.5-1 compression. With vortec heads and 3.08 gears, you might want to look at something like comp XR270hr. Comp has some dyno graphs from a 350 that might give you an idea of power band on a bunch of different cams. Those vortecs will make good power with the right cam. A cam that puts down good power from 1200 rpm - 5k rpm is just going to work better on the street than one that pulls from 2500-5000.
FYI : I had vtec rebuild my diff and install 3.70 gears, I think it was $1100 plus a couple hundred shipping. Jim at vtec is good guy to talk to and does great work.
Crower makes a real nice one for that its 220/230 .5xx lift, 112 lsa Ill have to look for the PN
Decent manners youll still be able to tell it has a cam but will run hard in that 383. They can soak up more cam than a 350
If you’re already planning to rebuild that turbo 400, put a built 700R4 in instead. That lower first gear makes it MUCH more fun to drive, and could eliminate the need to put lower gears in.......plus, you will have overdrive. And if you decide to put lower gears in.......well, you will have overdrive!
Crower makes a real nice one for that its 220/230 .5xx lift, 112 lsa Ill have to look for the PN
Decent manners youll still be able to tell it has a cam but will run hard in that 383. They can soak up more cam than a 350
Would you mind looking up the part number for that cam?
Thanks!
If you’re already planning to rebuild that turbo 400, put a built 700R4 in instead. That lower first gear makes it MUCH more fun to drive, and could eliminate the need to put lower gears in.......plus, you will have overdrive. And if you decide to put lower gears in.......well, you will have overdrive!
Id love to have the overdrive, but I hear 700r4 are not as reliable as the 400. What’s your thoughts?
Id also consider an aftermarket overdrive that can be installed on the 400, but I’d definitely have to research that.
I like the 110325-10 suggested above......I am using this exact cam in an engine soon (357ci)
I wouldn't go 1.6 on the rocker simply because the Vortec head doesn't flow any better at that lift.....opening the valve further would not achieve much.....and you need to watch retainer to boss even if the heads were cut for it. Call PAC for a spring or.....find the right spec in the Howards catalog. A beehive would work here as the lift is not too severe.......
This is a strong running cam and has a lot of midrange.....right where the Vortec heads do well......should be all done by about 5700 rpm.....
Jebby
Are you saying the 1.6 rockers are not worth the extra $ or would be detrimental to my combo? Reason I ask is I already have a set of 1.6 stamped steel roller tip rockers on a ball pivot. Just wanting to clarify if you recommend I purchase a different set of rockers, and if so I’ll just try to sell this set on CF.
Thanks for your input!
