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Hey fellas, let's keep it constructive. 2 degrees is what we use for our original T4 turbo lineup. Folks with T4's are likely running an inexpensive T4 with pretty poor turbine flow and really high reversion from backpressure- whether it be at the wheel or the end of the tailpipe. Our SUM-8722R1 through SUM-8726R1 T6/Twin cams start at 6 degrees and run as high as 14. By the time someone is at this level, we hope they are measuring turbine inlet pressure to boost ratios to prevent engine damage from excessive overlap.
Hey fellas, let's keep it constructive. 2 degrees is what we use for our original T4 turbo lineup. Folks with T4's are likely running an inexpensive T4 with pretty poor turbine flow and really high reversion from backpressure- whether it be at the wheel or the end of the tailpipe. Our SUM-8722R1 through SUM-8726R1 T6/Twin cams start at 6 degrees and run as high as 14. By the time someone is at this level, we hope they are measuring turbine inlet pressure to boost ratios to prevent engine damage from excessive overlap.
Appears that your SUM-8726R1 is right around 19-20 degrees of overlap. Its spec wise close to my cam, yours is on a wider LSA. I agree you should be running larger twins or a very large single for a setup like that to work well.
I had an interesting read on the turbo forums about how LSA affects affects a turbos ability to spool up. Having a healthy amount of over lap actually does help the turbo "spool" up much much more quickly. One thing I did not fully understand was how does more overlap allow for more horsepower to be made. I figured that due to the air being blown through the cylinder would mean that boost is being blead off; However, they mentioned about how that this over lap reduced the back pressure, keeping all of it low and I suppose it allowed for more power.
This makes me think of something like lowering compression (then making less power) to add more boost (which then increases power.) Is the reduction of back pressures making up for the bled boost ? Could it be for another reason ? Im really interested in how this works because I had typically believed the opposite when it cam to lopey cams and turbos. Maybe this only relates to lower boost applications.
Think the important take away is there are exceptions to every rule. You need to give a basic power level for anyone to suggest anything cam or turbo wise. "Fast street car" means different things to different people. If you give an exact power number people can help you select a cam/turbo. You have stated a lot of factoids than can be true or false depending on application. Like most things performance related, there is no blanket statement answer. you can have a great running low or high compression turbo motor. You can also have a great running low or high duration cam turbo motor. I can also tune a "mild" low duration cam to sound like a choppy high duration cam.
Let’s think about this. Intake closing point is the primary event where the powerband begins and ends from charge inertia. The exhaust opening point is where blowdown occurs. Heat and pressure are higher the earlier the exhaust opening begins (spool but not necessarily powerband). There are some downsides to valvetrain life depending on how aggressive one works this with available valvetrain components. The basic lesson is we need to get “Overlap” completely out of thinking and understand “Valve Event Calculation” so we can clearly see what needs to be done and why. Run your favorite cams through our calculator to see the differences. Summit cam timing calculator
Last edited by Summitracing; Sep 8, 2022 at 09:48 PM.
Assume you mean 224/233? What size engine and what size turbine are you going to run?
I actually mean 226/232. Engine size is 355. Haven’t researched turbo since. What I do know based off of another cam which has 13 degrees of over lap; it’s max boost is 5 psi according to com cams.
Last edited by Money_Pit; Sep 9, 2022 at 11:27 AM.
I actually mean 226/232. Engine size is 355. Haven’t researched turbo since. What I do know based off of another cam which has 13 degrees of over lap; it’s max boost is 5 psi according to com cams.
Overlap doesn't have an impact on max boost unless you have high backpressure like noted above. No idea what power level you are looking for but 8 degrees of overlap works fine on a typical 88/96 turbine.
This is interesting, I'm running the Brute Speed Forced Induction cam currently and have been wondering if its tailored more towards supercharger applications since that's what Brute Speed specializes in, plus it says "blower cam" on the cam card.
I tried entering the values into the Summit calculator but it only confused me more lol.
Tried emailing Brute Speed with questions but never heard back, curious to know if this is the best cam for my combo, seems to perform well, pulls hard well into 7,500rpm range and has an excellent lope at idle.
Specs listed below and attached the cam card too, would love everyone's opinion.
______________INT EXH
Gross Valve Lift .595 .608
Dur. @ .050 ___232_ 240
Centerline @ 114.0
Lobe Sep. 115
Valve Timing @ .050 ____Open____ __Close
______________INT_ __2 BTDC ____50 ABDC
______________EXH__ 56 BBDC___ 4 ATDC
This is interesting, I'm running the Brute Speed Forced Induction cam currently and have been wondering if its tailored more towards supercharger applications since that's what Brute Speed specializes in, plus it says "blower cam" on the cam card.
I tried entering the values into the Summit calculator but it only confused me more lol.
Tried emailing Brute Speed with questions but never heard back, curious to know if this is the best cam for my combo, seems to perform well, pulls hard well into 7,500rpm range and has an excellent lope at idle.
Specs listed below and attached the cam card too, would love everyone's opinion.
______________INT EXH
Gross Valve Lift .595 .608
Dur. @ .050 ___232_ 240
Centerline @ 114.0
Lobe Sep. 115
Valve Timing @ .050 ____Open____ __Close
______________INT_ __2 BTDC ____50 ABDC
______________EXH__ 56 BBDC___ 4 ATDC
Did you check your spam folder, I try to get back to everyone who e-mails me. Thanks. Bob
__________________ ATI ProCharger and Moser Sales 260 672-2076
This is interesting, I'm running the Brute Speed Forced Induction cam currently and have been wondering if its tailored more towards supercharger applications since that's what Brute Speed specializes in, plus it says "blower cam" on the cam card.
I tried entering the values into the Summit calculator but it only confused me more lol.
Tried emailing Brute Speed with questions but never heard back, curious to know if this is the best cam for my combo, seems to perform well, pulls hard well into 7,500rpm range and has an excellent lope at idle.
Specs listed below and attached the cam card too, would love everyone's opinion.
______________INT EXH
Gross Valve Lift .595 .608
Dur. @ .050 ___232_ 240
Centerline @ 114.0
Lobe Sep. 115
Valve Timing @ .050 ____Open____ __Close
______________INT_ __2 BTDC ____50 ABDC
______________EXH__ 56 BBDC___ 4 ATDC
Similar specs to the cam my friend had in his car when we took off his PD blower and slapped a turbo on. He was concerned about swapping the "blower" cam to a "turbo" cam, I told him it wouldn't make a bit of difference he would notice. We threw it on the dyno for me to tune and sure enough it made almost 200whp more than the blower on about the same boost, he didn't care about the cam anymore, he went to buy new tires. Not sure what power level you are at but this was at 900whp thru an auto, we only stopped there because he was concerned about his drivetrain. In other cars I've used existing "NA" cams to well over 1000whp in turbo setups. If you like the way it currently drives, spools, powerband range, etc, you aren't going to get much of a gain swapping cams.
Overlap doesn't have an impact on max boost unless you have high backpressure like noted above. No idea what power level you are looking for but 8 degrees of overlap works fine on a typical 88/96 turbine.
Ill look out for that turbo size. Comp cams mentioned on a large came like I mentioned, over five psi would cause problem can occur and even a rich condition. Granted it was for carbureted. I’m only gunning for what ever the stock crank can handle and I’ll leave it at that.
Did you check your spam folder, I try to get back to everyone who e-mails me. Thanks. Bob
You may have Bob and I simply missed it, I've been getting tons of spam lately and with traveling for work its impossible to keep up with, honestly I should have just come here to contact you lol.
While I have you, what would you say is the max rpm I'll get out of this cam?
What is the lobe ramp profile as well, aggressive, soft, etc.?
I only ask about the lobes because I broke a valve spring (unknown age or mileage) shortly after getting the car and just need to know if its something I need to monitor.
Originally Posted by SLOW SEDAN
Similar specs to the cam my friend had in his car when we took off his PD blower and slapped a turbo on. He was concerned about swapping the "blower" cam to a "turbo" cam, I told him it wouldn't make a bit of difference he would notice. We threw it on the dyno for me to tune and sure enough it made almost 200whp more than the blower on about the same boost, he didn't care about the cam anymore, he went to buy new tires. Not sure what power level you are at but this was at 900whp thru an auto, we only stopped there because he was concerned about his drivetrain. In other cars I've used existing "NA" cams to well over 1000whp in turbo setups. If you like the way it currently drives, spools, powerband range, etc, you aren't going to get much of a gain swapping cams.
Its probably pretty close to 650-700whp, it made 732whp @ 12lbs. on the same timing with the trans slipping top of third so I outta be pretty close to that at 10 lbs.
Will be turning it up to 14-15 lbs. on pump very soon, maybe higher if possible.
I've got no complaints about the cam, the chop at idle is killer, drives very nice and it pulls effortlessly to 7,500rpm, the valve clatter seems to be kept to a minimum too.
Sounds like I should save my pennies and buy a set of Bosch 210's instead lol.
Ill look out for that turbo size. Comp cams mentioned on a large came like I mentioned, over five psi would cause problem can occur and even a rich condition. Granted it was for carbureted. I’m only gunning for what ever the stock crank can handle and I’ll leave it at that.
If its a cast crank in that LT1, it won't handle much, proceed with caution....
In fact, I'd LS swap it.....(runs for the door)
You may have Bob and I simply missed it, I've been getting tons of spam lately and with traveling for work its impossible to keep up with, honestly I should have just come here to contact you lol.
While I have you, what would you say is the max rpm I'll get out of this cam?
What is the lobe ramp profile as well, aggressive, soft, etc.?
I only ask about the lobes because I broke a valve spring (unknown age or mileage) shortly after getting the car and just need to know if its something I need to monitor.
Its probably pretty close to 650-700whp, it made 732whp @ 12lbs. on the same timing with the trans slipping top of third so I outta be pretty close to that at 10 lbs.
Will be turning it up to 14-15 lbs. on pump very soon, maybe higher if possible.
I've got no complaints about the cam, the chop at idle is killer, drives very nice and it pulls effortlessly to 7,500rpm, the valve clatter seems to be kept to a minimum too.
Sounds like I should save my pennies and buy a set of Bosch 210's instead lol.
The cam can go well past 7000, but it's really done at 6600 on most engines. Valvesprings tend to last quite a while with this cam. Bob
That's good to know Bob, so running it out to 7500 rpm really isn't necessary then?
I can live with that if that's the case, maybe lower my shift point down to 7 or 7100 rpm perhaps.
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Not sure what power level you are at but this was at 900whp thru an auto, we only stopped there because he was concerned about his drivetrain. In other cars I've used existing "NA" cams to well over 1000whp in turbo setups. If you like the way it currently drives, spools, powerband range, etc, you aren't going to get much of a gain swapping cams.