Need some "turbo cam" info / help

[donk_316]

I usually harrass Shaun through IM but hes getting sick of my constant questions.

I know overlap is bad (atleast to much anyways) but what about duration and lift?

I love my cam now (Dur 272in/ 284ex Lift .454in/ .480ex) but its got close to 55 degrees of overlap.

Can i get a bumpstick ground but on a wider seperation? Will it run?! lol!

I was gonna post "over there" but the few folks who im looking to answer live here...

[eHoward]

Overlap baaad.

Corky Bell writes that It is hard to find a turbo cam that works better than the stock item. He also writes that turbo cams should be low duration, low overlap.

Having written that, I know honda guys are making more power switching to Integra R cams from GSR or Si ones. Not 4 or 5 horse but in the area of 50.

I usually harrass Shaun through IM but hes getting sick of my constant questions.

I know overlap is bad (atleast to much anyways) but what about duration and lift?

I love my cam now (Dur 272in/ 284ex Lift .454in/ .480ex) but its got close to 55 degrees of overlap.

Can i get a bumpstick ground but on a wider seperation? Will it run?! lol!

I was gonna post "over there" but the few folks who im looking to answer live here...

[The Dark Side of Will]

breathing is good for any engine
highest lift you can get is good
moderate duration... if you go crazy with the duration on a wide lobe sep you can get the exhaust valve opening pretty early and the intake valve closing pretty late. I'm not really sure what the all the negative effects of those two characteristics are.
This is where modern technology comes in... with modern roller cam grinds, you can get a CRAZY ramp rate and spend a lot of duration at max lift, even if your cam doesn't have that much overall duration.

Oh yeah, overlap is measured in degree-inches, not just degrees.

[AkursedX]

So, would a custom regrind cam to stock specifications, but with higher lift be a good way to go?

[The Dark Side of Will]

prolly

You definitely don't want anything that lopes

[admin]

going with a turbo now donk you will need to change the cam to maximize the performance. That 272 is a n/a cam.

You can prob drop to a 260 cam and be ok. It does state that it is suitable for mild turbocharged applications. You prob wont' run more then 10 psi so thats mild by my defintion.

I say 260 with 1.6 rockers and massive port work.

al head head gasket to drop compression a point or two could help a bit as well.

Or just go with a crower turbo cam. I think scca fiero on Fagland bought one of these. Talk to him about it

[eHoward]

I would run a stock cam and concentrate on other areas like manifold design if getting a *turbo* cam is difficult or expensive.

[X86GT]

Here's a couple of turbo cam profiles I've collected from other turbo Fiero owners. Both are special order grinds (of course). I plan on using the Crower grind when I build my 3.4L.


Crower Cam Turbo Profile #E-47655
212/212 @.050"L
444" I /.439" E total lift
113* Lobe Sep.
__________________________
Manufacturer Unknown
INT Duration: 298*@.449 Lift
EXH Duration: 290*@.432 Lift
Lobe Separation: 114*

[donk_316]

Well ive ran about 10 different cam profiles in DD2000 and that program sucks....it just sees "big cam = big powah"

I need to find EngineAnalyzer Pro again...that program rocked.

[Nemesis]

I had a custom cam turned from Crower.

Part Number E-47691
Intake: 298* / .449 lift
Exhaust: 290* / .432 lift
114* seperation

Expensive.... I think it was a bit over $300 just for the cam.

[donk_316]

I had a custom cam turned from Crower.

Part Number E-47691
Intake: 298* / .449 lift
Exhaust: 290* / .432 lift
114* seperation

Expensive.... I think it was a bit over $300 just for the cam.

What made you go with a grind like this? Low lift long duration? not a turbo cam im assuming...

[donk_316]

going with a turbo now donk you will need to change the cam to maximize the performance. That 272 is a n/a cam.

You can prob drop to a 260 cam and be ok. It does state that it is suitable for mild turbocharged applications. You prob wont' run more then 10 psi so thats mild by my defintion.

I say 260 with 1.6 rockers and massive port work.

al head head gasket to drop compression a point or two could help a bit as well.

Or just go with a crower turbo cam. I think scca fiero on Fagland bought one of these. Talk to him about it

The 260 has a SLIGHT advantage under 5000 rpm but from there to 7000 the H272 takes a slight advantage. Only 12* of overlap between the two. The H260 has 42* and the H272 has 54*

The Tq peaks at 500 rpm lower (4500 vs 5000) on the H260. Same #s (288 vs 286)

The Hp peaks 1000 rpm lower (6500 vs 7500) also and approx 25hp diff (318 vs 345)

These tests where performed on a boosted 3400 with 65mm TB...on my computer. LOL! :thumbleft:

[Shaun41178(2)]

ok getting back into this as I am working on getting a cam to use with a turbo, and then to swap to N/A with nitrous and still make good power.

Usually N/A cams work better with nitrous then a turbo grind would but I am trying to find a happy medium to use both setups.


I have my cam book here. THe 272 intake cam opens at 1 degree BTDC. It closes at 35 Degrees ABDC The exhaust opens at 51 degrees BBDC and closes at 3 degrees BTDC.

So the the exh valve is fully close before the intake valve starts to open. The exh valve is actually closed for 2 degrees before the intake valve starts to open. So if I have this right, there is no overlap there.

Now on the intake stroke, the valve opens, the piston reaches bottom dead center and then the intake valve starts to close and is closed as the piston starts up on the intake of the compression cycle and is fully closed 35 degrees ABDC. Plug ignites and as the piston passes TDC its in its powerstroke and 51 degrees before the piston reaches BDC(crank reaches BDC) the exh valve starts to open to help scavenge the exh better at high rpm.

Now I guess I am an idiot here but both valves arent' open at the same time anywhere in that cycle. Now someone explain where the overlap is as apparently I am missing it somewhere.

Compared to a 2030 cam the 272 isn't that much different as far as cycles go. It has more overall duration, but nowhere like the 2030 are both valves open at the same time

2030 is:
intake opens at 3 ATDC and closes at 27 degrees ABDC
Exh opens at 40 BBDC and closes at 6 BTDC.

So the 272 intake valve opens 4 degrees sooner then the 2030 and the exh valve opens 11 degrees sooner then the 2030. But still are neither valves open at the same time anywhere.

So it seems to me that the 272 cam can still be used as a turbo cam.

Unless I am going about this all wrong someone please tell me. I might not be thinking this out properly even though I have gone over cam designs one million times.

I mean GM says the 260 cam is good for mild boost and the 272 is a smidge up from that cam as far as valve events are concerened Also the 272 has a LSA of 112 just like the 260.

The only differences really are the duration numbers. and lift numbers

It seems to me this is a decent cam for a turbo, and it can also be a good cam for nitrous too with more compression.

I am going through all of this as I am thinking of going turbo for a bit and then swap to al heads which will give more compression but do this without having to switch out the cam and get good performance from both.

Of course with the exh valve opening sooner on the exh stroke the turbo will spool a bit later as there will be less burned gas generating heat to spool it, but in the upper rpm band the turbo should scream pretty well as the exh will then need more time to get out of the cylinder.

I think I might go this route unless someone has some objections.

Am I way off here? Sometimes I have brain farts and/or try to overanalyze things and end up just confusing myself.

[Shaun41178(2)]

ok I just realized that all the numbers I gave were at .050 lift for opening and closing points. Damn so how do I find out how many moer degrees it takes to go that extra .050 to open and or close"?

[Indy]

Here's some specs on the turbo cam from Isky. Keep in mind it's for an SD4, with a powerband from 4K-8K. Just giving a bit of a reference.

Lobe Center: 110 DEG.

Overlap: 78* (at .020 before and after)

Intake Duration (at .050)
268*
OPEN 24* before TDC
CLOSE 64* after BDC

Exhaust Duration (at .050)
260*
OPEN 60* before BDC
CLOSE 20* after TDC

There it is, for what it's worth.

[Shaun41178(2)]

hmmm damn. I guess the 272 doesnt' sound too bad. I am still trying to figure out how donk got 55 degrees of overlap.

Where are you donkster?

Meh maybe I will jsut stick to a 260 and go with 1.6 rockers. THat will give me a bit more lift but the same duration.

I HATE MY LIFE... GOSH!!!

[Shaun41178(2)]

Meh I think I am going to go with the 260 and 1.6'r

Its been proven and can go with a turbo as well. That gives me the ability to get ht elfit of the 272 but with the overlap and duration of the 260.

Head porting will be extensive to get as much flow out of these as possible. I am hoping to get around 170-180 cfm intake flow and 130-140 cfm exh. High numbers yes but if I can get them close to stock of an aluminum head then that will be sufficient enough for me.

Pistons are on the way. For the price I got them for I will prob get the tops coated. Add some thermal stability in leiu of boost and nitrous.

lots of parts to get, but I think I def want a GT 35 wheel. Do this bitch once and forget about it. T3/61 I think I will go with. Great efficiency at low boost numbers and 10 psi will push some major cfm which will give nice gains.

Or hell I guess I could always go get a t3 off of a saab and spend $1200 upgrading it to "custom" t3 specs. yea thats prob what I will do because its the stupid fiero owner way.