Best cam for 80% Street, 20% track?

[cool 84]

I've run stock, 200-200, 206-206, 210-205, and 204-214. The first 3 were great and it was hard to tell a difference but it "felt" like the 210-205 had a little more top end could've been my imagination. Then I tried the 204-214 and the car fell on it's face. It had absolutely no torque and the same or less top end. All the time I was running it I figured since I didn't use a degree wheel I must have installed it a little off. But when I pulled it apart I checked it and it was right.

The things that made the most difference on the mid-top end on my car were big turbo, intercooler, and downpipe a lot more so than the cam size.

 

[faster1]

So does a bigger cam like a 212/212 actually hurt performance or is it just that it is simply uneccessary on say a mid 11 car?

 

[TTA89]

hehehe I missed this thread... Thanks for the laugh

 

[blackshoebox]

Originally posted by faster1
So does a bigger cam like a 212/212 actually hurt performance or is it just that it is simply uneccessary on say a mid 11 car?

Its unneccessary, unless your looking to go deep in the 11's and even then, a 206 comp cam is more then sufficient. I know of three cars in this area running 10's with a 206 flat tappet cam. I run a atr 313b, which is just slightly bigger then stock and my car has went 11.8 @115 with more tuning to go. And my car sees about 150-300 miles per week. Rollor cams are great performers, but expensive if im not mistaken(billet roller is like 1000.00 big ones)

I have also heard from different people who like to run lower boost levels(under 22 psi) they run the larger cams 224/224 and up and get the same performance as a small cam car, but with less boost.

I personally like the quite, innocent sound of a stock cam or close to it, so whomever you happen to run up against has no clue what just flew by him, since he could not here the rumble of a large cam like you hear in big blocks and most fast mustangs.

Basically Ill run more boost before i get a loopy cam.

Shoebox

 

[GNVAIR]

I really wish Mike Licht would jump in here. I remember him talking on the board here about a guy up in the Detroit area that had a big cam in his car and was running high boost on pump gas. The main advantage (atleast on a forced inducted car)to running a cam with more duration is how duration kills cylinder pressure. Its a double edge sword. Cylinder pressure can = more power, but on the other hand cylinder pressure can = detonation.
My advice is if you arent sure, then leave it close to stock. Guys have gone plenty fast on stock or near stock combos.

 

[REDS HOT AIR]

i've ben watching but not saying anything but how many engine builders do we have on here ? seems like a lot ..a engine builder isnt someone that knows how to bolt a motor together but one who knows what everything does and how it affects other things in the motor

cool: if you put a 204-214 in your car and it fell on its face then you definatly had a problem with something else.

 

[UNGN]

Originally posted by quickt


Ok guess you did not have a crystal ball. I did not see the sig.

Actually, I had a crystal ball, but I threw it away when it failed to tell me about the tech stock and telecom meltdowns. Damn POS.

 

[Steve Wood]

Must have been yours I pulled out of the trash...otherwise I would not be comtemplating starting another career. LOL

 

[cool 84]

Originally posted by REDS HOT AIR
i've ben watching but not saying anything but how many engine builders do we have on here ? seems like a lot ..a engine builder isnt someone that knows how to bolt a motor together but one who knows what everything does and how it affects other things in the motor

cool: if you put a 204-214 in your car and it fell on its face then you definatly had a problem with something else.

True, but I checked everything I could think of. It was so slow that I had a new Duttweiler 206-206 waiting to go in because it was unbearable. This was with no other changes and I checked the preload too. Too bad the motor blew before I had a chance to install the other cam so I could know for sure. Now I have a 212-212 for the 4.1 which should be on the conservative side.

 

[blackshoebox]

Originally posted by REDS HOT AIR
i've ben watching but not saying anything but how many engine builders do we have on here ? seems like a lot ..a engine builder isnt someone that knows how to bolt a motor together but one who knows what everything does and how it affects other things in the motor

Enlighten us. ...not to flame you, but if you own one of these cars, chances are you know what a cam does. I know of a few "engines builders" who can build cars, but can't tune them. And we all know, tuning is half the battle.

Also as seen by the diversity of "build ups" on this board, everyone has a reserved opinion on what works and what doesn't.

Shoebox

 

[REDS HOT AIR]

just thinking guys should give their opinion on the way their car acts with a certain cam but no need to say that any thing different wont work...they will all work its just how well they do the job.

full race cams carry more duration and lift on the intake side to create a supercharged affect at higher rpm to cross the 100% ve.

well we have a turbo so we dont need that supercharged affect but better yet need to get the exaust out of the motor.

just say you stuff twice the volume in the cylinder with boost so now you have 462 ci instead of 231 so the exaust side has to be up to par for a 462 ci engine and with no assistance getting out why would you not hold the valve open longer and/or higher if thats what the head likes

the typical person says well the piston pushes the exaust out well the more pressure it takes to push that exaust out the less hp you'll have heading toward the trans.

all the cams will work but the factory sure put more on the exaust side of the cam...but i guess they didnt know what they were doing either..

 

[Steve Wood]

So tell us at what point the backpressure of the PTE51 comes into conflict with the 214 duration and flow becomes negligible or reversion is encountered.

The factory thought about such things.

 

[TurboJim]

Steve,

Alan and Lonnie talked about this a few months ago. The jist was cams with longer exhaust durations were not so good in turbo apps. With the reason being, the exh valve is open longer. This will allow backpressure to push the intake charge back in the intake. Lets say theres 10psi backpressure (just throwing a number out here) It will then take higher boost to make the same power than if, possibly an additional 10psi of BOOST to make the same power than if exhaust backpressure wasnt as large an issue. This is why I listened to them and bought a 214/210 from Lonnie as I thought I understood this was the preffered type of grind (longer intake duration).

Maybe I didnt understand it correctly, or am not explaining it correctly, but it sure made sense to me.

 

[elevensecgn]

Originally posted by TurboJim
Steve,

<Alan and Lonnie talked about this a few months ago. The jist was cams with longer exhaust durations were not so good in turbo apps. With the reason being, the exh valve is open longer. This will allow backpressure to push the intake charge back in the intake. >

Well, just to muddy the waters even more, here are my findings.
Be assured that I am still as confused as anyone

(20) years ago when developing a Twin turbo SBC for marine use I contacted Comp, Crower and a few others. Comp recommended the old 268 h grind. (Quite similar to a popular GN grind today. I could run X amount of boost with it and X mph with the boat. (MPH of a boat is a good way of determining HP without the use of a dyno. ) After running it and establishing a baseline I decided to try a Crower custom grind. They recomended a short side exhaust like many of the grinders do for turbo cars today. It allowed me to run slightly less boost and make the same MPH or make a small (2 mph) increase with the same boost. Any more boost and I got into detonation badly.
(Keep in mind that I did not have the computer control and technology available today.)

After that at the advise of a fellow turbo "tinkerer" I went with a cam quite similar to the 204 214 grind from speed pro. I was able to run 5# more boost and gain 7 mph. This told me I was going in the right direction. I can attest that it definetly did have some reversion as the intake would blacken. I know that is not a good thing, but at the time it seemed to work in spite of what the numbers looked like on paper.

I do know of a few folks who have had great sucess with longer exhaust duration cams in their GN/TRs Bob Slusser has went mid 10s on a 204 214, a lot of guys in the 11s, and Lee Thompson runs a much bigger cam that is also heavy on the exhaust side, and loves it.

There are also guys like Geno who have made it into the 9s with a 208 208 so I guess there is no "right answer" There seems to be different ways to get there, but a "magic cam profile" doesnt seem to exist. For what it's worth I have yet to hear of someone losing a lobe on a 204 214. (No explanation here, just observation)

For now I'll stick with my stock cam, and hope I don't need another cam till this question is answered

Dwight Hayden
87 GN 11.33 with a few bolt ons

 

[Steve Wood]

well, Lonnie and Alan are pretty sharp and experienced guys.

Now, the factory used a low lift cam with a bit more duration. Did they do this because they used a low lift cam? Did they use a low lift cam because they knew the block had misplaced lifter bores and they wanted a gentle cam profile on the exhaust to avoid warranty claims? Did they use more duration because the port does not flow well in stock form? Did they use it because the Stock Turbo is dead at 21# and it never generates enuf backpressure to interfere with the exhausted charge coming out of the cylinder? I have no idea. Like Red will tell you, I am clueless!

I do know that the total combination has to be looked at. Turbo with regard to efficiency and back pressure vs boost, port configuration on both sides, cam timing events and profile, etc.

To say, the factory did it so it must be the way to go might be less than the whole story as those engineers must compromise stock components, performance, and cost of manufacture, plus, cost of honoring the warranty. We have come a long way beyond what the factory envisioned.

Real engine builders understand combination....some may understand modeling software but all learn from experience.

 

[RDavis]

turbo cam

with high boost pressures you usually run a 1.8 or 2 to 1 pressure ratio on your turbo to achieve this. Meaning if you have 15psig of boost you have 30 psig of exhaust back pressure.
So if you have both vavles open then the exhaust pressure is going to win the battle.

 

[cool 84]

Re: turbo cam

Originally posted by RDavis
with high boost pressures you usually run a 1.8 or 2 to 1 pressure ratio on your turbo to achieve this. Meaning if you have 15psig of boost you have 30 psig of exhaust back pressure.
So if you have both vavles open then the exhaust pressure is going to win the battle.

So possibly the longer duration exhaust cams would favor cars with big turbos and free flowing exhaust.

 

[TurboJim]

Originally posted by Steve Wood
Now, the factory used a low lift cam with a bit more duration. Did they do this because they used a low lift cam? Did they use a low lift cam because they knew the block had misplaced lifter bores and they wanted a gentle cam profile on the exhaust to avoid warranty claims? Did they use more duration because the port does not flow well in stock form? Did they use it because the Stock Turbo is dead at 21# and it never generates enuf backpressure to interfere with the exhausted charge coming out of the cylinder? I have no idea. Like Red will tell you, I am clueless!

They did it to meet emissions, longevity, and fuel mileage standards. If they were going for balls out HP/TQ, they'd have done what we all are doing now.

 

[TurboJim]

Originally posted by elevensecgn
After that at the advise of a fellow turbo "tinkerer" I went with a cam quite similar to the 204 214 grind from speed pro. I was able to run 5# more boost and gain 7 mph. This told me I was going in the right direction. I can attest that it definetly did have some reversion as the intake would blacken. I know that is not a good thing, but at the time it seemed to work in spite of what the numbers looked like on paper.

Dwight Hayden
87 GN 11.33 with a few bolt ons

You were ABLE to or HAD to to realize a GAIN. You said you used less boost to make same MPH, thats the same as leaving the boost the same to GAIN MPH.

I wonder what the deal would have been had you raised the boost 5psi on the longer intake duration setup. Would you have gained 7mph? Or, since you lowered it to realize 0 gain, would bringing it back to the original level have netted you the 7mph?

I know, hard to say, its all speculation at this point.

My point is what Alan and Lonnie explained made perfect sense to me, and explains why one friend of mine goes 10.90 on 30psi, and another on 22psi. One has a 205/215 cam and the other has a 218/218. (I think thats whats in it) Both engines I guess are similar, but the 30psi has a 76 and the 22psi has an old hybrid, think he said the equivelant of a 63. (Yes Lonnie, I'm referring to Scott, maybe you know his combo more accurately)

Understand I am not saying anyone else is WRONG. Not my point, sorry if taken that way. I'm no engine builder, probably cant even be considered a tuner, so I guess I also haveta rely on others information in this area.

I went 214/210, guess we'll see how my choice works out.

 

[REDS HOT AIR]

Originally posted by Steve Wood
So tell us at what point the backpressure of the PTE51 comes into conflict with the 214 duration and flow becomes negligible or reversion is encountered.

The factory thought about such things.

when the blades break off the exaust wheel..