madwolf

I've seen TOO MANY instances were people go with a big cam (847, 306, etc) and they rev or plan to rev the cam to about 6100-6200. DO NOT get a cam that big if you will rev it to only 6100-6200 or even 6300. You will get CRAPPY times if you do. These cams like 6700-6800 shifts!
If you do a 847, 306, 233/239 or even 230/236 and shift at 61-6200ish, you will be in the low 13s! You'll be lucky for a high 12.
There are plenty of cams out there which can take advantage of your targeted range much better and will yield better times than a bigger cam in the same range. Please consider this.

Yes, I've had at least 2 people with a 306 requesting a 6200 rev limiter and a number of other people who shift at 6100-6200ish and that's on the stock tach, which is about 5900 real RPM.

mattybz28

Some people will never understand...

12SCNDZ

Ion,
I thought the 847 only makes power to 6500 RPM's??? I'm building a 6" rod, 847 cammed 355 right now for my '93 Z. The heads are race ported LT1 castings with 2.0"-1.56" valves.
I shift my CC305 cam at 6200. I'm using an Autometer shift lite wired into my 7AL-2 box. The CC305 is only supposed to be good to 5800, though.

How do the '93 computers like big cam/high RPM's?

Thanks,
Frank

madwolf

If a cam peaks at 6050, it doesn't mean that you should shift it at 6200. My 233/239 shifting at 6000 yielded almost stock times on 3.23 gears. (101ish traps or so with long tubes!) With 3.23 gears shifting at 6700-6750, it trapped 106.66.

With 4.10s, shifting at ~6000ish, it trapped about 106. This cam peaked at 6050 on the dyno. Both of these were done in the same day.

With 4.10s, shifting 6700-6800, it trapped 109.33.

The reason it trapped significantly higher with 4.10s shifting at 6000ish than 3.23s shifting at 6000ish is because the 4.10s won't throw your RPM back as much as 3.23 after a shift.

These cam make their power at higher RPM, so you have to shift even higher so that when the RPM fall back in the next gear, they are still in the range the cams makes its most power at.

With an 847, if you want to get the best track times, you will want to shift it around the same RPM I was shifting mine at.

6 speeds are a BIT more forgiving since you go through more gears and so the RPMs will not drop as much, BUT, that is true provided you shift at least as good as an automatic, or else if you shift slow, you will be slower because you have to do 1 or 2 extra shifts. (depending on gear ratio)

Frank, I ran mine on the 93 computer up until now. It works great if it's tuned correctly. I am switching to a 94 PCM now, but I will keep it speed density.

Also, using good/correct springs is also important if you don't want your power to drop like a rock after the cam's peak.

12SCNDZ

Thanks for the info Ion. I've always shifted beyond where the cam is "supposed" to make power to. I also drive a '70 Camaro that I shift at 7600 RPM's...

As long as the computer will work in the 847's RPM range, the rest of the engine should be more than capable of handling the high R's.

As for the springs? K-Motion K800's with titanium retainers.

Frank

madwolf

You're all set then.
The 93 ECM shouldn't have a problem going up to 7000. I didn't have the motor to try it beyond that, but you could give it a try if you want.
Ellis (OneFlyn95z28) on here was reving his 847 to 7100-7200 if I'm not mistaken.

Here's his post:

With Stock heads my car would not peak on the dyno even at 7,000.

With the ported heads it peaked at 6,900

That was a few years ago and I have not stopped yet

Capt'n Two Rotors

I just joined the 847 stock heads club and love it!! The rpm range is up there though, I was still pulling when the pcm shut off at 7000k++ so becareful what ya wish for. When I do get heads won't the power move up even more??

stereomandan

Yeah, guys don't realize that full bolt on LT1's should shift at 6000-6100 rpm. Put a cam in there, any cam, and it shifts it up at least a few more hundred RPM. Even the Hotcam has an optimal shift point of 6500+ rpm.

You definately do NOT shift where the power peak of a cam is. It's much higher than that. My stock cam peaks at 5200 rpm and I calculated my optimal shift point to be 6000-6100 rpm.

Dan

WS6T3RROR

madwolf the 3.23's and the 4.10's will dump you back the same amount of rpms on a shift with the same tranny. the trans gear splits are what defines shift recovery rpms. the rear gearing only defines what mph the shift occurs at, but i believe what you meant to say is the 4.10's make it easier to recover fromt he crappy gear splits of the 4l60e and get back to where you're making power.

TransAm396

..yeah but if you have a 383..doesnt that change things up a bit?(i plan on running my 383 to about 6800rpms..but im going with a custom stick)

madwolf

WS6T3RROR,
yes, that's what I meant. Thanks for clearing it up.

TransAm396,
the same cam will peak earlier on a bigger motor, yes.
I addressed this thread mainly to members of the 350 crowd you often see posting about getting a cam on here.

TransAm396

i figured id ask it for everyone else so you didnt get em later on... wanna tune my car?

slverbullet

i know with my cam i dont shift till about 6600-6650rpm. it kinda freeked me out the first time i did it because i was used to shifting at 5700rpm. once i did though, i'd never shift below that if i'm racing it. the power above 6k is too unreal. just my .02.

Mindgame

I don't think you realize the can of worms you're opening here.

The "rev limit" is not solely dependent on the camshaft duration. What about the cylinder head port? What about the valvetrain??

If I were to take two identical LT1's, one with stock heads, the other with a set of AFR 200's (for comparisons sake), both with identical camshafts and valvetrain components. Think they're gonna shut off at the same rpm?

There are a lot of factors that will determine "where" peak power occurs, the camshaft is only 1 variable in that equation.

BTW, I like the new doo.

-Mindgame

Jameslt1TA

Ya the only reason that i had ion set my shift points at 6200 was because i wanted to get atleast 1000miles on my new motor before i shifted it very high.

Also one other thing ion, when you did my tune did you take into account that im 5500 feet above sea level i think that it is running kind of rich...not sure(im a carburator guy and alttitude makes a big diff). If you didnt could you send me a new tune that is leaned out a bit and has a shift point of 6500rpms. My email is jrmarlt1@hotmail.com

thanks
james