Thinking about a new cam - help please
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Senior User
Joined: Apr 2007
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From: Glenwood, IA
Thinking about a new cam - help please
As you know I am running a 428 witch is around 400HP?! My cam now is a Hydraulic Flat Tappet, Advertised Duration 262/ 270, Lift .513/ .520. In my class of mud drags one guy is running a 351C with 550+HP and still pulling the required 17" of vacuum @ 1k rpm. I am pulling right at 17" now????
Another thing that I just found out is we can rollers now!!
Is there someone that really knows FE's and cam grinds? Is it possibe to go to a real high lift and short duration in order to keep vacuum?
Can anyone help?
Another thing that I just found out is we can rollers now!!
Is there someone that really knows FE's and cam grinds? Is it possibe to go to a real high lift and short duration in order to keep vacuum?
Can anyone help?
Fleet Mechanic
Joined: Aug 2007
Posts: 1,823
Likes: 252
From: Piney Woods of East Texas
I would contact the mfg of the cam you interested in. Mfg have all of those numbers. Roller will allow a quicker ramp on valves so higher lifts are not required. I would check for clearance before going any higher though. I looked at a roller for my setup and stuck with a std hydraulic. My Crane Kit came with variable lift lifters, to help maintain manifold vacuum. I have 3 that make noise 1/2 the time, making me wish I went with solids.
Are you running stock heads or AL with a modern design?
Are you running stock heads or AL with a modern design?
Fleet Mechanic
Joined: Aug 2007
Posts: 1,823
Likes: 252
From: Piney Woods of East Texas
You have good heads then.
What compresson ratio are you running?
I have a bigger cam than that in my 360.
Crane came out with variable bleed rate hyd lifters. The way these work is at idle they bleed down so you don't have as much lift generating higher manifold pressure. My spec on my cam is 270/270 duration with .533/.533 lift, 216/216 duration. I run 15" vacuum at 650-700rpm. The truck is not running right now or I would run a vac curve for you. It's stripped down for paint.
What compresson ratio are you running?
I have a bigger cam than that in my 360.
Crane came out with variable bleed rate hyd lifters. The way these work is at idle they bleed down so you don't have as much lift generating higher manifold pressure. My spec on my cam is 270/270 duration with .533/.533 lift, 216/216 duration. I run 15" vacuum at 650-700rpm. The truck is not running right now or I would run a vac curve for you. It's stripped down for paint.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,823
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From: Piney Woods of East Texas
What compression ratio are you running? You may gain more power by boosting compression. And or a gear change. Boosting compression also helps with vacuum. You will be capped on overlap, due to 15" at 1k. Rollers will cost you about ~$1500 by the time you get all the necessary parts. I would think you would get more gain from a compression change. Boost timing will help too.
Is the other guy using one of the mainfold pumps to boost manifold vacuum? These are added for just that. Also EFI will add more than carb.
Have you dialed in your carb? Is it stock or after market? The reason I ask if your running a carb from the 60-70's you are probably running lean. Back in that error, the main jets use to be around 48-54. Now it takes around 65-70 with the unleaded LOW octane fuel. Besides you want to be running a 12.6:1 vs a std 14.7:1 for max power. Running lean can and will burn a piston out.
I would contact Crane and other and tell them your requirement. They may have a cam grind just for your application.
Is the other guy using one of the mainfold pumps to boost manifold vacuum? These are added for just that. Also EFI will add more than carb.
Have you dialed in your carb? Is it stock or after market? The reason I ask if your running a carb from the 60-70's you are probably running lean. Back in that error, the main jets use to be around 48-54. Now it takes around 65-70 with the unleaded LOW octane fuel. Besides you want to be running a 12.6:1 vs a std 14.7:1 for max power. Running lean can and will burn a piston out.
I would contact Crane and other and tell them your requirement. They may have a cam grind just for your application.
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From: Glenwood, IA
Well my compression is 9:1. This is also a street driven truck. And the limit is 17" @ 1k. I have my timing advanced as far as I can go.
I dont believe he has a pump, they are forbiden.
My carb is a Holley street advenger 770cfm. And yes I have it dialed in Good! I have uped the jets to 65/69.
When I built this engine this spring, I called comp cams and this is the cam they said would work best for my app. And it does pull 17" @ 1k. But I believe there is more power to gain. That was why I was wondering if I went with a higher lift and short duraton to gain more power and maintain vacuum.
I dont believe he has a pump, they are forbiden.
My carb is a Holley street advenger 770cfm. And yes I have it dialed in Good! I have uped the jets to 65/69.
When I built this engine this spring, I called comp cams and this is the cam they said would work best for my app. And it does pull 17" @ 1k. But I believe there is more power to gain. That was why I was wondering if I went with a higher lift and short duraton to gain more power and maintain vacuum.
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Fleet Mechanic
Joined: Aug 2007
Posts: 1,823
Likes: 252
From: Piney Woods of East Texas
You should be able to use pump gas with a 9.5-10.0:1 compression range. Mine is in this range. Your only options for higher/quicker lift is with a roller cam. I looked at them when I built my engine. The roller lifters are ~$500, cam is the cheapest ~$420. With the higher lift you may need to change pistons. I would recommend using a roller rockers. These will give you adjustable rockers if you do not have any. Valve springs will probably need replaced to to handle the higher lift. I really think the boost in compression may give you the best gain.
I would use the HP calculators and start changing values and see what gives you the best punch for the money.
Just out of curisity what rear end ratio are you using. I assume you are going through the transfer case (automatic or manual), using Low ration or first gear high. What rpm are you tring to maintain during the pull, 4000rpm? with a max speed of 5-10 mph.
Are you allowed to use after market ignition? MSD has a control module that allows you to control the timing up to 15 deg. I use this to tune for pump gas. Are you allowed to run cool tanks (fuel), water injection..... ?
The use of syn fluids throughout will help too.
I would use the HP calculators and start changing values and see what gives you the best punch for the money.
Just out of curisity what rear end ratio are you using. I assume you are going through the transfer case (automatic or manual), using Low ration or first gear high. What rpm are you tring to maintain during the pull, 4000rpm? with a max speed of 5-10 mph.
Are you allowed to use after market ignition? MSD has a control module that allows you to control the timing up to 15 deg. I use this to tune for pump gas. Are you allowed to run cool tanks (fuel), water injection..... ?
The use of syn fluids throughout will help too.
Last edited by blue68f100; Aug 22, 2007 at 06:10 PM.
Senior User
Joined: Feb 2007
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From: idaho
also the stock heads will not handle more than .600 of lift without machining the spring seats. if you did boost your compression you could run more cam timing and still have your vacuum you need. what is your actual running cyl. pressure? maybe it works out that with the timing in your cam already you have less compression than you think, and the bleedoff of the advanced timing will cause low vacuum.
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Senior User
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From: Glenwood, IA
Well first off I wanted the machine shop to not go lower than 9.5:1 but that isnt what I got.
And man thats alot of money!!!!!!!
I am running the stock 4.10 gears front and back, using low range drive. So that is about 8.20 gears or there about.
I run through first and secound and shift into third about 30' from the end.
I am limited to factory ignition. However I have heard that ford used MSD on trucks around '90? I havent found anything on that.
And man thats alot of money!!!!!!!
I am running the stock 4.10 gears front and back, using low range drive. So that is about 8.20 gears or there about.
I run through first and secound and shift into third about 30' from the end.
I am limited to factory ignition. However I have heard that ford used MSD on trucks around '90? I havent found anything on that.
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From: Glenwood, IA
Originally Posted by 390cobrajet
what is your actual running cyl. pressure? maybe it works out that with the timing in your cam already you have less compression than you think, and the bleedoff of the advanced timing will cause low vacuum.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,823
Likes: 252
From: Piney Woods of East Texas
Run a compression test, will tell you what your actual cylinder pressure is. Run this on a hot engine if you can for a more accurate reading. You may be able to vary the cam timing. This will move the power band up and down. A common practice in the 60's.
Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
There is static compression(use a guage and crank motor over), then there is cyl pressure(when running). With a big cam, it will actually loose pressure since there is overlap in camshaft(both valve open at same time).
Senior User
Joined: Feb 2007
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From: idaho
yes, and intake starts opening when piston is still coming up to top dead center as well.
or the other way would be a retarded timing with the intake valve opening later as the piston has already started down, and usually in this case is still open when started back up on the compression stroke but only for a very short travel distance of the piston. that scenario works well on the bottom end because it creates a lot more vacuum at lower rpm speeds so the air/fuel is moving fast and allows the rush of air/fuel to continue in the cylinder even after the piston has started coming up in the bore. this usually gains cylinder pressure.
at higher rpm speeds the air speeds in the manifold force it into the cylinder so it works better to turn the cam timing advanced and open that valve early. the higher speeds of the air in the manifold overcome the tendency of the piston forcing the air back out of the cylinder when the valve opens early. high rpm useage is when you see the benefits of this. now I probably made it worse!
or the other way would be a retarded timing with the intake valve opening later as the piston has already started down, and usually in this case is still open when started back up on the compression stroke but only for a very short travel distance of the piston. that scenario works well on the bottom end because it creates a lot more vacuum at lower rpm speeds so the air/fuel is moving fast and allows the rush of air/fuel to continue in the cylinder even after the piston has started coming up in the bore. this usually gains cylinder pressure.
at higher rpm speeds the air speeds in the manifold force it into the cylinder so it works better to turn the cam timing advanced and open that valve early. the higher speeds of the air in the manifold overcome the tendency of the piston forcing the air back out of the cylinder when the valve opens early. high rpm useage is when you see the benefits of this. now I probably made it worse!
Last edited by 390cobrajet; Aug 24, 2007 at 11:12 PM.