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Discussion Starter #1
Wanting to install a ramjet 350 cam into my carbureted L31 vortec 350. I was thinking of also installing 1;6 ratio rockers at the same time. Any reason not? heads have been setup with LS beehive springs and comp cams retainers so lift clearance is no problem. Or just stick with the 1;5 rockers?
 

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The RamJet cam isn’t a big enough wow over the original L31 cam to bother with. It’s claim to fame is mostly a tight LSA which given its duration does not add power compared to the stock L31 cam but gives a nasty idle note it can’t backup. If you want shake, rattle and roll plus power to prove it get an LT4 HOT cam or reasonable facsimile from the aftermarket.

1.6 rockers make any cam think it’s bigger than it is with delivering at the valve both a faster rate of lift and more lift per crank degree. The problem they present is often you don’t see much if any performance improvement but this is usually the result of 3/8ths rocker studs and or stock springs wandering around with the faster and heavier loads being imposed. There are multiple answers here that include aluminum roller rockers to get the mass dynamics down, a stud girdle on the existing tiny studs to stiffen them up or a conversion to 7/16ths screw in studs, which of course, also, needs machine work to the head and the selection of 7/16ths bore trunnions of the rocker arm. The down side of stud girdles is they don’t work with center bolt covers. Given the flow of the L31 head more lift at a faster rate is useful to making power with these heads. You already have beehives which do more valve control with less force which is a big step in the right direction of keeping the valve tracking the cam lobe without using so much force the stud starts wandering around, so this buys you some better control with 1.6 rockers without a lot of re-engineering the rest of the valve train for revs that don’t crowd 6000 too hard.

Bogie
 

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Discussion Starter #3 (Edited)
The RamJet cam isn’t a big enough wow over the original L31 cam to bother with. It’s claim to fame is mostly a tight LSA which given its duration does not add power compared to the stock L31 cam but gives a nasty idle note it can’t backup. If you want shake, rattle and roll plus power to prove it get an LT4 HOT cam or reasonable facsimile from the aftermarket.

1.6 rockers make any cam think it’s bigger than it is with delivering at the valve both a faster rate of lift and more lift per crank degree. The problem they present is often you don’t see much if any performance improvement but this is usually the result of 3/8ths rocker studs and or stock springs wandering around with the faster and heavier loads being imposed. There are multiple answers here that include aluminum roller rockers to get the mass dynamics down, a stud girdle on the existing tiny studs to stiffen them up or a conversion to 7/16ths screw in studs, which of course, also, needs machine work to the head and the selection of 7/16ths bore trunnions of the rocker arm. The down side of stud girdles is they don’t work with center bolt covers. Given the flow of the L31 head more lift at a faster rate is useful to making power with these heads. You already have beehives which do more valve control with less force which is a big step in the right direction of keeping the valve tracking the cam lobe without using so much force the stud starts wandering around, so this buys you some better control with 1.6 rockers without a lot of re-engineering the rest of the valve train for revs that don’t crowd 6000 too hard.

Bogie
Hey Bogie, I'm not looking for just some shake rattle and roll, I'm looking for some more low end grunt 1000 to 5500 rpm. The stock cam is just that stock, i installed this cam listed below and it is a real let down, but at least i got it cheap so i thought i would try it. Disappointed. I'm running a 700r4 trans 3:73 RG and a 2050 torque convertor. 600 cfm summit carb Holley look alike, and a summit racing intake manifold low rise and a msd large body hei, and shorty headers which i believe are part of the problem, so I'm going to be installing a MSD ready to run dizzy, a edelbrock high rise rpm intake and full length headers, and a new carb. And I'm going to be getting a converter to match these upgrades. Would the LT4 Hot cam fit the bill, or should i look elsewhere? Anybody. This is all going a L31 vortec 350 which has 5000 miles on it so basically new.

Lunati 20080130 219/229 dur. @ .050 lift .503/.503 lobe sep 112 108 centerline.
 

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With that cam you need some rpm to get it going. That also seems like a lot of valve lift for Vortec heads.

Your trans and rear end are probably fine for street use, but I think you would be happier with a higher stall converter. I would also crank up the base timing to about 14-16 degrees and then have about 20 more mechanical in by about 2000 rpm. Just monitor it carefully for pinging, since I’m not sure what timing advance iron heads will tolerate. You may also need an adjustable vacuum can to keep highway cruise timing from being too advanced at part throttle.

Bruce
 

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Why is the Lunati a let down? It is pretty close to the LT4 HOT which is 272/219, lift is .492 with 1.5/.525 with 1.6 intake; 282/229, exhaust lift is .492 with 1.5/.525 with 1.6 exhaust. LSA is 113. This is pretty close to the Lunati you have.

The Ram Jet cam intake is 288/196 with .431 lift on a 1.5 rocker; exhaust is 308/206 with .451 lift on a 1.5 rocker, with a 109 LSA.

The stock Vortec L31 cam is intake 255/190 with .412 lift on a 1.5 rocker; exhaust is 266/195 with .428 lift with a 1.5 rocker. On a 111 degree LSA.

For lift on these with 1.5 rockers where you want 1.6 rocker lift multiply the 1.5 lift by 1.067.

I run the HOT cam in my S15‘s 350 using modified 1994 LT1 heads (some welding, milling and external coolant returns) with 1.6 roller rockers, a GMPP LT1/4 intake and an 800cfm Edelbrock AVS-1 Thunder carb with short headers into duals, distributor right now is a ProComp 7000 and PCE 91 coil, tranny is a built 700R4 with a 2800 rpm stall lockup converter, with rear axle is 3.08 posi. It is very well behaved on the street and packs a lot of power. When new it laid down 400 hundred ft lbs of torque and over 410hp and that was with a reprogrammed chip running a 454 large bore TBI. The big difference between the TBI and the carb is I have to work at getting the kind of gas mileage it just simply got with the injection.
 

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Discussion Starter #6
Why is the Lunati a let down? It is pretty close to the LT4 HOT which is 272/219, lift is .492 with 1.5/.525 with 1.6 intake; 282/229, exhaust lift is .492 with 1.5/.525 with 1.6 exhaust. LSA is 113. This is pretty close to the Lunati you have.

The Ram Jet cam intake is 288/196 with .431 lift on a 1.5 rocker; exhaust is 308/206 with .451 lift on a 1.5 rocker, with a 109 LSA.

The stock Vortec L31 cam is intake 255/190 with .412 lift on a 1.5 rocker; exhaust is 266/195 with .428 lift with a 1.5 rocker. On a 111 degree LSA.

For lift on these with 1.5 rockers where you want 1.6 rocker lift multiply the 1.5 lift by 1.067.

I run the HOT cam in my S15‘s 350 using modified 1994 LT1 heads (some welding, milling and external coolant returns) with 1.6 roller rockers, a GMPP LT1/4 intake and an 800cfm Edelbrock AVS-1 Thunder carb with short headers into duals, distributor right now is a ProComp 7000 and PCE 91 coil, tranny is a built 700R4 with a 2800 rpm stall lockup converter, with rear axle is 3.08 posi. It is very well behaved on the street and packs a lot of power. When new it laid down 400 hundred ft lbs of torque and over 410hp and that was with a reprogrammed chip running a 454 large bore TBI. The big difference between the TBI and the carb is I have to work at getting the kind of gas mileage it just simply got with the injection.

As Bruce mentioned the Lunati cam needs a higher stall and a better set of headers, is what i,m thinking. The let down as of now is there is no low end torque, with how the car is setup now, there was more low end torque with the stock cam. But still not to my liking.
 

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I don’t know what you’re searching for in absolute terms, bigger cams net much bigger torque numbers but like horsepower these cams push the peaks up the RPM range. But a 700R4 has a pretty deep low, with A 3:73 rear axle I’d expect your problem would be getting traction. I guess we need to know your tire size what gear the transmission is in that is disappointing and the geographical and environmental conditions.

Bogie
 

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Discussion Starter #8
I don’t know what you’re searching for in absolute terms, bigger cams net much bigger torque numbers but like horsepower these cams push the peaks up the RPM range. But a 700R4 has a pretty deep low, with A 3:73 rear axle I’d expect your problem would be getting traction. I guess we need to know your tire size what gear the transmission is in that is disappointing and the geographical and environmental conditions.

Bogie
Ok Bogie i am looking for help, here is what i have 56 chevy 373 rg 700r4 trans 2050 stall converter. summit racing low rise intake manifold, 600cfm summit racing carb, large bodied Hei dizzy, shorty headers H pipe 2 1/2" exhaust with dynomax turbo mufflers 26 1/2 tall tires estimating 10" tread width. As stated before in a earlier post it had more of the line torque with the stock computer. I, m looking for more low end torque not upper end this is a street car looking for off the line power. Don't upper end power on the street. Needs to pull 5000 grand that's all. So was thinking to lower the lift to a lower low end torque cam, change converter to a highewr stall , change intake manifold to a hi rise and change to a better performance carb, and will get a msd ready to run dizzy.
 

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Tires are pretty wide, it takes more to light them up. Where you live counts, torque and power for the same engine build is substantially different between the altitude of Denver compared to Cleveland, Ohio or Texas. Temperature and humidity come to play as well a summer day on the Gulf Coast or the coast of the southern Atlantic states will be different than Seattle or San Diego.

Torque like horsepower is among other things RPM dependent. For the same engine otherwise a bigger cam makes both more torque and horsepower and moves them up the rev range compared to a smaller cam. So in your case a smaller timed cam will lower both the amount of power and the RPM where it peaks. Especially where torque is concerned engine size makes a huge difference, a 383 stroke of .28 inch compared to a 350 is a day to night experience. More stroke on the same displacement engine does not make more torque but brings it up at a lower RPM.

A bit looser converter would let the engine get further up its power band. The LT4HOT cam being similar to your Lunati is recommended with a 3000 stall. I run a 2800 stall in my S15. Stall like the speed of light is relative to the ratio of applied power to the load. Less power against a starting load will exhibit a lower stall than a higher power engine against the same load. So when you read stall speeds they are a specific power input against some usually unspecified load, they like to talk about flash stall but in reality it’s just a place in the same problem, your experience will differ from the book values.

I happen to like street cams in the range of the Comp XE268H flat tappet cam. Which as roller cams go the Lunati you have and the GMPP LT4HOT are of similar timing. This is a good range for a performance engine this timing is happy across a very wide range of engine builds particularly in the zone of 350 inch displacement. Cams in this area tend to have a long, full torque curve and peak power occurs in a nice range under 6000 RPM. I run in a range of 18 to 22 degrees at idle. That is a mix of base and vacuum. The set base is 14 to 18 with vacuum putting in the difference. The vacuum plate is constrained, the vacuum adjustment is unrestricted. The centrifugal is limited to 20 degrees which allows a max between 34 to 38 degrees, vacuum advance falling out before max mechanical input. Dinking around with where the vacuum curves out and the centrifugal curves up can take some time. I don’t run a GM style distributor so I dont have a specific process for you, but there is plenty of parts available and advise on the web for those.

Compression and timing count for a lot but cams in this range are tolerant of compression ratios say about 9.5 to 11 the higher being a aluminum head for sure. I run 10.7 using a modified for cooling LT1 aluminum head. Ignition timing also comes in this

The RamJet is going to lower your torque curve. It will peak where the Lunati is just coming on the curve. GMPP sells a lot of other cams that are standard to the LT1 or LT4 which use a wider LSA that will have a smoother idle, but all of these time in duration pretty similarly. GM spends a lot of time inside a 10 degree band duration band with about .025 lift differences chasing Federal EPA regis. The RamJet in timing duration and lift doesn’t leave that range, all they do is twist the lobes closer together which increases overlap but closes the intake earlier. This adds some lope sound and increases cylinder trapped pressure but basically provides a loss at one end for a gain at the other. Probably the best production cam for getting the most of all the competing elements is the production LT4 roller part number 12551142. It times at .050 203/210 with lift at the valve on a 1.5 rocker of .446/.450 or with a 1.6 rocker of .476/.480. The LSA is 115 degrees. Remember that increasing the overlap allows mixture to escape unused so you use more fuel for miles travelled. This doesn’t effect power other than spending from your wallet.

Long tube headers offer substantial lower end torque gains without any penalty on top end power which is why they are so popular. Then inject 15 to 20 foot pounds pretty early in the rev range. Rather than camshaft this would be my first investment. Then decide if it moves your happiness needle enough.

Bogie
 

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The 82 C10 pickup I recently sold had a 355 with around 9.4:1 compression, .043" quench height, and Vortec heads. It had a RamJet/HT383 cam with LS6 valve springs @ 1.750" installed height. I went with 1.6 rockers on the intake side only. The engine worked well with the stock 2.73 axle and 29" tires. Lots of low-to-mid range torque that would even spin the heck out of the tires with a TH350 and stock converter. Idle vacuum was 18-19" and was fairly smooth. Even with the cam's 109 LSA, there is very little overlap with only 196/206 duration. It's actually less than a 204/214 cam with 112 LSA.

I never drove a truck with a stock L31 engine with 191º/196º , 0412"/.428" cam, but I'd be surprised if the RamJet /HT383 cam's additional duration and lift didn't make more torque and horsepower.
 

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Discussion Starter #11
Tires are pretty wide, it takes more to light them up. Where you live counts, torque and power for the same engine build is substantially different between the altitude of Denver compared to Cleveland, Ohio or Texas. Temperature and humidity come to play as well a summer day on the Gulf Coast or the coast of the southern Atlantic states will be different than Seattle or San Diego.

Torque like horsepower is among other things RPM dependent. For the same engine otherwise a bigger cam makes both more torque and horsepower and moves them up the rev range compared to a smaller cam. So in your case a smaller timed cam will lower both the amount of power and the RPM where it peaks. Especially where torque is concerned engine size makes a huge difference, a 383 stroke of .28 inch compared to a 350 is a day to night experience. More stroke on the same displacement engine does not make more torque but brings it up at a lower RPM.

A bit looser converter would let the engine get further up its power band. The LT4HOT cam being similar to your Lunati is recommended with a 3000 stall. I run a 2800 stall in my S15. Stall like the speed of light is relative to the ratio of applied power to the load. Less power against a starting load will exhibit a lower stall than a higher power engine against the same load. So when you read stall speeds they are a specific power input against some usually unspecified load, they like to talk about flash stall but in reality it’s just a place in the same problem, your experience will differ from the book values.

I happen to like street cams in the range of the Comp XE268H flat tappet cam. Which as roller cams go the Lunati you have and the GMPP LT4HOT are of similar timing. This is a good range for a performance engine this timing is happy across a very wide range of engine builds particularly in the zone of 350 inch displacement. Cams in this area tend to have a long, full torque curve and peak power occurs in a nice range under 6000 RPM. I run in a range of 18 to 22 degrees at idle. That is a mix of base and vacuum. The set base is 14 to 18 with vacuum putting in the difference. The vacuum plate is constrained, the vacuum adjustment is unrestricted. The centrifugal is limited to 20 degrees which allows a max between 34 to 38 degrees, vacuum advance falling out before max mechanical input. Dinking around with where the vacuum curves out and the centrifugal curves up can take some time. I don’t run a GM style distributor so I dont have a specific process for you, but there is plenty of parts available and advise on the web for those.

Compression and timing count for a lot but cams in this range are tolerant of compression ratios say about 9.5 to 11 the higher being a aluminum head for sure. I run 10.7 using a modified for cooling LT1 aluminum head. Ignition timing also comes in this

The RamJet is going to lower your torque curve. It will peak where the Lunati is just coming on the curve. GMPP sells a lot of other cams that are standard to the LT1 or LT4 which use a wider LSA that will have a smoother idle, but all of these time in duration pretty similarly. GM spends a lot of time inside a 10 degree band duration band with about .025 lift differences chasing Federal EPA regis. The RamJet in timing duration and lift doesn’t leave that range, all they do is twist the lobes closer together which increases overlap but closes the intake earlier. This adds some lope sound and increases cylinder trapped pressure but basically provides a loss at one end for a gain at the other. Probably the best production cam for getting the most of all the competing elements is the production LT4 roller part number 12551142. It times at .050 203/210 with lift at the valve on a 1.5 rocker of .446/.450 or with a 1.6 rocker of .476/.480. The LSA is 115 degrees. Remember that increasing the overlap allows mixture to escape unused so you use more fuel for miles travelled. This doesn’t effect power other than spending from your wallet.

Long tube headers offer substantial lower end torque gains without any penalty on top end power which is why they are so popular. Then inject 15 to 20 foot pounds pretty early in the rev range. Rather than camshaft this would be my first investment. Then decide if it moves your happiness needle enough.

My timing is set to 14 initial with vacuum at idle is 18-20 with a total timing of 32 , I'm living at and elevation just under 5000ft, i believe what's hurting my low end is my 2050 stall converter, as you stated the Lunati similar to the LT4 HOT needs a higher stall. So i think my plan is while i will have the engine removed for clean up and paint, i will be installing a different converter with a higher stall, long tube headers, msd dist. different intake manifold and carb, and then give the cam a chance with the proper items to go along with it's spec's.


My timing is set to 14 initial with vacuum at idle is 18-20 with a total timing of 32 , I'm living at and elevation just under 5000ft, i believe what's hurting my low end is my 2050 stall converter, as you stated the Lunati similar to the LT4 HOT needs a higher stall. So i think my plan is while i will have the engine removed for clean up and paint, i will be installing a different converter with a higher stall, long tube headers, msd dist. different intake manifold and carb, and then give the cam a chance with the proper items to go along with it's spec's.
 

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Your idle vacuum seems very high for that Lunati cam and 5000 feet of altitude. So what is in the engine cam wise that gave 18-20 inches at idle?

Bogie
 

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Discussion Starter #13
Your idle vacuum seems very high for that Lunati cam and 5000 feet of altitude. So what is in the engine cam wise that gave 18-20 inches at idle?

Bogie
Should worded that differently timing is around 18 to 20 degrees with vac hooked up. Not 18 to 20" of vacuum at idle.
 
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