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Just turn the boost up. Most correctly designed cams and turbo systems will allow the engine to make peak power about 1000rpm higher than you would get out of the same cam duration running a N/A engine.
 

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Just turn the boost up. Most correctly designed cams and turbo systems will allow the engine to make peak power about 1000rpm higher than you would get out of the same cam duration running a N/A engine.
I think that is a good plan. I am freshening the engine now. One area of poor reliability for this combo of all things was the intake gaskets. Long ago the heads were angle milled and the correction done on the intake not ideal. It lines up perfectly, but requires a thicker than ideal gasket, which is more prone to failure. I have considered machining an aluminum spacer to take up the extra space, so I can go to a thinner gasket. Fixing this reliability issue and the tire shake should put me just into the 6's at 17 psi. Sometimes it's the simple stuff that gets ya. All considered, switching to a turbo combination has been about the most fun thing I could have done with my bracket program.
Thank you I really appreciate the info/input!
 

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Discussion Starter #23
It would be ok in a supercharged application. It will be a turd down low and will spool like shit. I just sent a cam to a guy in Australia that had some jackass sucker him into building the engine after a lifter hurt the block/cam. Ran ok on chassis dyno but gave some excuse why two-step wasn't hooked up. Got car home and it wouldn't spool on proven converter even added converter dump but still no good. I spec'd a new Comp Cams solid roller and it is working awesome now. The cam I spec'd was more aggressive than your setup, max effort deal with twin GT4788 turbos on methanol but same cam issues you may
 

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Who's cam is everyone commenting on??? My cam or Tempname's cam???
T2 said that yours would be a turd down low, and that cam would be better suited for a supercharged combo. And that the split was overly large. He said he had the customer in Australia with a similar cam that was a disaster in a turbo combo.

Mine should be fine for my rpm range since turbo charging extends the rpm range by at least 1000 rpm, and I should just raise the boost level.
 

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Discussion Starter #26
T2 said that yours would be a turd down low, and that cam would be better suited for a supercharged combo. And that the split was overly large. He said he had the customer in Australia with a similar cam that was a disaster in a turbo combo.

Mine should be fine for my rpm range since turbo charging extends the rpm range by at least 1000 rpm, and I should just raise the boost level.
OK, thanks for the clarification. The last thing I need is a turd for a street car! Is it a rule of thumb that all higher rpm cars will be a turd down low?? I want to shift at 7500...does this mean that my car will have a narrow power band? Not sure why this cam was recommended?? I'm still wondering if it has anything to do with me running full exhaust and mufflers???
 

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OK, thanks for the clarification. The last thing I need is a turd for a street car! Is it a rule of thumb that all higher rpm cars will be a turd down low?? I want to shift at 7500...does this mean that my car will have a narrow power band? Not sure why this cam was recommended?? I'm still wondering if it has anything to do with me running full exhaust and mufflers???
It does not have to be a narrow powerband if the entire system is designed correctly. 7500rpm is not "high rpm" these days. 7500 is the new 6000, LOL. The full exhaust makes the back pressure even worse which needs the opposite of what was ground. The added back pressure from the full exhaust will magnify the reversion issues with the long exhaust duration cam. Your cam guy was thinking it needed more time to blow down the cylinders due to the added back pressure. The problem is this gives it more time for reversion to occur. The cylinder is going to empty, it doesn't have any choice because the exhaust stroke is truly positive displacement. I'm not a fan of reverse split cams but they do come to mind when discussing an application like yours. I probably wouldn't go quite that far but I will say, I think a reverse split would work way better than what you have. I would probably keep it somewhere between even duration and 5*-6* split depending on size of exhaust and type of muffler used. This is a very general statement since I don't know all the particulars about the combo.
 

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I will add only from what little experience I have. No, high rpm doesn't have to mean narrow rpm band. Mine is that way because I can be....it's a race only lighter car. So no need to lug it and we can run it for the entire run at high rpm efficiently.
It's funny, when it comes to cams, often a good starting place is a STOCK cam. The rpm range will be extended, and you won't have overlap issues that a big aftermarket cam can have. As you go higher effort, obviously the stock cam can hold everything back. But the same cam you would use n/a also may not be the right choice. As with anything high performance, there are compromises. I will say that I started off using the WRONG cam by every person's opinion. And....it ran ok. The world didn't grind to a stop and it did what it was supposed to do. The right cam made everything work better. And remember that my application is pretty forgiving with a very loose converter.
Now, throw in the mix the size and configuration of the turbocharger. Very generally, bigger turbo, smaller engines mean sluggish and slow to light. Big engine and little turbo is more likely to be immediately responsive and have a better chance of running out of breath up high.
If I am doing a street car, error'ing conservatively is going to make for a more enjoyable car....even if it is not the fastest it could be on the track.Giant numbers sometimes aren't as fun as a good combination that is fun to drive.
And let's not forget reliability. A short duration lobe with a lot of lift can be an absolute SOB on valve springs and every valve train component. Why have to deal with that along with the fact that it is less responsive? Plus, it takes every component being up to snuff. Valve springs. Big push rods. Rockers that are strong and supported. And lifters that are larger in diameter.
 

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4.130 bore,racetech pistons thick wall pins 1mm 1mm 2mm ring stack 9.8 comp, 7500 rpm range,have vic jr heads and intake. Still building it.cam was ground for a single 7675 for the nmra class but this engine is getting repurposed as a twin turbo. Probly two s366s.in my 67 cougar
 

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Thoughts on these cam specs for a twin turbo 347 looking to shift around 7500 + and make around 1350 + hp:

I can't say that I've ever ran a turbo cam with so much lobe separation before...any ideas of what the idle quality and lower rpm power response will be, if any, with this cam?? I've also never seen so much extra exhaust duration. My last HR cam that shifted a whole 1000 rpm lower was 241/243 @ .050, .601/.608 on a 114 lsa...had noticeable lope at idle, about 8 inches of vacuum and was very snappy on the bottom end. I made about 1150 hp with the HR cam and 25 psi boost.

Valve Adjustment: .016” .016”
Lobe Lift: .447” .445”
Gross Valve Lift 1.60 Ratio: .715” .712”

Duration @ .050” Tappet Lift: 240* 256*

Lobe Separation: 118*

Recommended Intake Centerline: 114*

Specs at 114 Degree Intake Centerline:
Valve Timing at Open Close
.050” Tappet Lift: Intake: 6.0* BTDC 54.0* ABDC
Exhaust: 70.0* BBDC 6.0* ATDC
My setup is a 427 LSx, TFS HIP’d 245s (setup for Solid roller)
Close to 12:1 compression
Twin Forced Inductions Garrett GTR-88’s
88mm GT5018’s running a dual fuel setup
(E85/M1)

thesolid roller cam that I was spec’d was
268/276 @ 0.50”
.750/.750
116+5 LSA
I’m spinning the motor to 8800-9000 RPM
 
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