It's getting close to go back out and start playing with my cars. And on my 80 z28 i was wanting to make some changes. It's a driver i take to work when weather is nice and it is raced during the summer at the track when i dont want to haul the "race car" out.

i'm always tinkering with it to improve the e.t. and mph. and i do alot of highway road trips with it too. hence the gear ratio.

my car is 3900 lbs with me in it and about 5 gals of fuel.

i currently have a 2.41 posi in it. but i have another rear end ready to go in that sports 2.73 gears.

last year i was crossing the finish line just at 5,000 rpms using 1st and 2nd gear only with a th350. and was shifting into 2nd gear at 6,000 rpms.

after some caculations i decided to step up the gears to 2.73 to allow me to cross the finish line at over 6,000 rpms to bring it in closer to the cams pulling power. assumming i can pull better mph out of it this summer. i'm looking for around 102-105mph trap speeds.

i know my combination is not the norm. since im running highway gears. and more compression then a street car really should have but it is working out ok. i can still run 87 octane.

my cars specs as follows:

-396 bored to 414ci
-closed chambered heads,oval port, ported and cleaned up thru out the runners. exhaust was polished, intake runners finished with 80 grit, all corners radiaused, bowl blended after 3-angle valve job, chambers polished,2.19/1.88 valves with 20* back cut.
-on the money 10.2 to 1 compression,domed KB hypers. cranking compression 155-160psi
-delta cams recommended a regrind with the following specs.
lobe center sep.....110.3
valve over lap......14.7
intake
valve opening........7.4 btdc
valve closure........45.3abdc
lobe center..........108.5 atdc
duration............232.7
cam lift............318
lift................547
lobe area...............25.95

exhaust
valve opening..........51.5
closure................7.4
lobe center............112
duration...............238.8
cam lift...............320
valve lift.............550
lobe area.........27.04

number are stated @ .050 lift on intake and exhaust.

-torker 2 low rise single plane
-highly modified 3310-2 750 holley with 72/76 jets
-msd 6al box, hei accel coil,timming set at 20* initial and 36* total at 3,000 rpms.
-summit headers 1 7/8" pri. tubes
-2 1/2" exhaust dumping at axle thru turbo mufflers
-cast crank, polished and lighten stock rods,arp bolts everywhere, balanced, crank scrapper,windage tray,rear oil pump baffle. high volume high pressure oil pump from melling.
-heavy duty pushrods,stock rocker arms,single spring with damper, lift good for just over .600
-th350 tranny with 2100 brake stall convertor.
-2.41 posi unit.

as combo stated above it ran a best of 14.47@98 mph with 2.15 60 ft running thru the mufflers on 245/60-15 street tires. shifting at 6,000 rpms and running thru the lights at 5,000 rpm.

since then i have installed/added:
-2800 rpm brake stall convertor
-roller tip 1.72 rocker arms
-K&N filter on my stock air cleaner assy (factory cold air induction set up on the 80 z28's)

now with the cam that is in there it provides little vacuum (5.5 inches @ 600 rpms) at idle. i was thinking about adding Rhoads lifters to increase vacuum and to smooth out the idle since it is rough. from what i understand they would give me my cams full value back around 3000-3500 rpms........i really dont want to give up to much on the top end because this thing pulls hard and i was planning on pulling the 6000 rpm rev limiter chip out and put in 6600 rpm chip to allow me to run it over 6000 rpms. the engine is pulling very hard to 6000 so i know there is more in it..........

i was also thinking about getting me a rpm edelbrock intake and finding a way to make it fit under the hood. from what i understand this should help out with the lower rpms but not give up to 6500 rpms.......

i guess what im looking for is a smoother idle for around town driving giving better street matters........but i dont want to loose the power it has on the top end specially now since im looking at crossing the finish line above 6000 rpms.......

i also thought about advancing the cam 2* to see what that does and even changing out my head gaskets to steel shimmed to raise the compression more about .5 to maybe increase low end torque.

right now i can run the 87 junk fuel and load the motor going up a hill and i dont have any pinging........not sure thou if another .5 in compression would send it over the top with pinging problems even with 91 octane.....

basically the bottom end is soggy to 3000 rpms and im just looking at ways to clean it up with out loosing the top end pull.

comments are welcome maybe even cam change if it doesnt effect to much on top end charge.

ddeennis,

Advancing the cam 2° will help the bottom- and mid-range power. I doubt if it will affect the top-end at all. Running the Rhoades lifters will improve the idle and vacuum system by about 2" of vacuum.
They will work ttogether and compliment each other.

UDHarold

Have you ever tried shifting at a lower rpm? I loose ET shifting at 5500+ with 2.73's..if I shift @ 4800-5000 1/2 shift and 2/3 shift,I cross the stripe at 4100,and get the best time..

thanks ud harold i guess i will give those two things a try..........

i have tried lower shift points i started at 5000 rpms and went to 5500 and to 6000 and the higher i shifted it the faster it goes.........this engine just pulls damn strong on top end......so im sure with a 6500 rpm shift it will go faster...its just at the time i went to 6000 because i was running out of test and tune time......

Try putting a cowl hood on it. Then a RPM will fit.
You might try a Performer intake. They're not too expensive used. I had a 396 with an old original style performer and 1" spacer and a similar cam with more compression. It pulled to 5800 with stock 2.07 heads. And 2.48 gears. ;) I think the old intakes didn't have tapered ports. You'd have to ask Edel. to be sure.

Was the cam degreed in when it was installed? Your idle vacuum seems low even considering the size of the cam and the 600 rpm idle speed. I wonder if the cams retarded a little from the cam opening/closing specs you gave? You could also probably gain a couple inches of vacuum by setting the idle speed to 800-900 rpm.

Originally posted by Scott_68_SS:
Try putting a cowl hood on it. Then a RPM will fit.
You might try a Performer intake. They're not too expensive used. I had a 396 with an old original style performer and 1" spacer and a similar cam with more compression. It pulled to 5800 with stock 2.07 heads. And 2.48 gears. ;) I think the old intakes didn't have tapered ports. You'd have to ask Edel. to be sure. i do have a cowl hood on there.....it is the factory z28 hood with a functional hood scoop.........im also running the factory air cleaner assy.........which makes things fit tight...........

Originally posted by Bob T:
Was the cam degreed in when it was installed? Your idle vacuum seems low even considering the size of the cam and the 600 rpm idle speed. I wonder if the cams retarded a little from the cam opening/closing specs you gave? You could also probably gain a couple inches of vacuum by setting the idle speed to 800-900 rpm. no the cam was put in straight up from the box........the cam was reground and thats what the cam analysis gives for numbers after the regrind......so im not sure if there is any advance built in or not......maybe someone could shed some light on that.......

im kinda stuck with the idle.......it idles about 950-1000 rpms and in gear it idles 600 to 650.....so theres not much choice there......alot of time was spent to get it to idle decent and to close the gap on the in gear and park throw of the rpm's...........at 950 rpms there about 10.5 to maybe 11 inches of vacuum.......

According to the numbers you posted, the cam is ground 2° advanced.

UDHarold

And I think BobT is 'feeling" the answer in AZ. Why don't you pull some plugs so you can roll the motor over by hand and try Harold's 'quick and dirty' method of degreeing ( it works!) and see how the cam is timed in relation to the crank. My bet is that you'll find the exhaust valve closer to the head surface then the intake, i.e., the cam is retarded. I would at least check so you KNOW how the cam is phased.

You should have more idle vaccum. But if you advance the cam and make this puppy pull harder, you can kiss the 87 octane out the window I should think.

God, 6500 rpms with 2.43 ( or 2.73s). Kripes man, I run the equiv of 430s and shift at 6700.

Anyway, neither here or there. I think Bob has a posible answer , and it wont cost you anything but possibly a offset cam pin bushing to fix it. At least check it.

Originally posted by UDHarold:
According to the numbers you posted, the cam is ground 2° advanced.

UDHarold well then thats not good then........you think 2* more advance be enough?

it just seems like 2* is nothing.that it wouldnt show no difference you know.

i guess i could buy a good double roller with multipile settings for advance and retard. and just try 2* with no other changes. and see how that does. and maybe just sneak up on things.

i dont think i want to try to many things at once. ill just do one at a time. thanks for all the reply's.

Dennis,
Before you change anything you should take Gene's advice & find out where the cam is in the engine.
The numbers you posted look like they came off of a cam doctor stand & will tell you what the cam is but until you check it in your engine you will have no idea of phasing (intake centerline)
Also depending on who's software Delta is using you can put the intake centerline anywhere you want on the stand & it really has no bearing on where it is in your engine.
I use one with Audie Technology software & I can make the cam look advanced, retarded or straight up with about 2 keystrokes ;)

Here's what to do----
Do a search on Team Chevelle for 'UDHarold's quick and dirty method'. I've posted it so many times you are bound to get some hits.
Follow this method and it will positively tell you whether your cam is advanced or retarded. If it is advanced properly, you can tell, the intake valve/retainer will be .030" to .060" closer to the head. If it is retarded, and low vacuum can be a sign of a retarded cam, the exhaust valve/retainer will be MUCH closer to the head than the intake is.
The hardest part about this system is taking off a valve cover.....
If the cam is retarded, buy yourself a set of offset bushings, follow their instructions, and put one on. Immediately, recheck using my quick-n-dirty method, to make sure you put the bushing on right.
When the bushing is on right, button everything up and go have fun.....

UDHarold

i did post research under the quick and dirty method.......read to many posts.......lol

looks pretty easy set the #6 at tdc and check out my valve spring heights. im just hoping i see the exhaust retainer lower then the intake........that will explain alot of things.............thats does mean retard right?..........thats the way i got it wrote down............this is the first time ive heard of this method and more then likly i will use it on every motor from here on out..........................

exhaust valve retainer lower then the intake retainer= retarded

even on both sides = straight up

exhaust valve retainer higher then the intake retainer= advance

You got it graemlins/thumbsup.gif
Just remember on overlap the intake is opening & the exhaust is closing so the further the intake is open at TDC the more advanced the cam is.

Dennis, I degreed my cam using this method and it was SPOT ON! ( well OK, I got it on a 103 ICL instead of Harold's 104, but close enough). The machine shop was told to degree it in +6. I just happened to check it while adjusting valves. They apparently put the bushing in backwards, because flipping it around was all it took to get it right! Anyway, hardest part is the measurement, 6" machinists scale was not working well, so I ended up using a 6" dial caliper as a 'depth guage'.

I was wondering why the exhaust valve clearance was so friggin' tight! ( .100 w/o gasket).

If you did this enough you could almost degree a cam visually! You'll see what I mean. The EX is closing and the INT is opening, so, again, you could almost 'eyeball' it.

Wicked time-saver!