Hi everyone, now that ive got my car up and running good, its time to fine tune it (and probably break something) but anyways, Ive tried tuning the car as best as I know how, but I am looking for more input from the experts on this. Here is my set up, 350ci engine, flat top pistons with valve reliefs, roller timing chain, 64cc chamber heads with 2.02 intake/1.6 exhaust valves, summit cam with advertised duration of 272/282, duration at .050 214 intake/224 exhaust. Gross Valve lift .442/.465 with a 1.5:1 rocker arm. I am running crane full roller 1.6 ratio rockers, so I am assuming a .030 increase in valve lift. On top of it all is an edelbrock performer intake with a quadrajet built by Sean Murphy of SMI. (saw him in chevy high performance a few times) the quadrajet has been modified with the following, 74 jets, rods 42k, sec: AU, and flows 750 cfm. This is the from the sheet i was sent with the carb. As for timing, I am running a proform dist. w/50k volt coil and module, my base timing is set at 16 degrees btdc, and total advance with dist. unplugged is 36 at 2700rpm. With the vac. advance hooked up I seem to be getting about 60 degrees advance 3200 rpm. Does anyone have a guess as to what kind of power numbers this combination should be putting out, and is there anything else I can do tuning wise. The car feels fast, but not fast for the kind of power I feel it should be producing. Hopefully the car will be dynoed on sat. to find out for sure.

:steering:

----Chris


[Modified by Today's problem is.., 4:29 AM 5/21/2004]


[Modified by Today's problem is.., 3:18 AM 5/23/2004]

 

Maybe 325-350 at the flywheel?

Everything sounds pretty darn good, but you sure need to get that vacuum advance under control--too much, man. There's a Lars tuning paper around here somewhere that can gove you the optinal figure for baseline.

 

Been checking out Lars paper...for total advance 52 is good, 54 is max

 

Ok, I found the paper lars wrote, extremely informative, as they always are, anyways, i pulled the vac. advance out and after much careful studying, put in the VC1853, and now my advance goes like this, 16 initial, 36 at 2700-2900 rpm, it seems to kinda vary just a little, either that or the ungodly amount of heat coming off the headers was messing with my eyes, with the vac. advance hooked up i am getting a max now of about 50-51 degrees total. I checked it before and it was a 59 degrees, I havent driven the car yet, but hopefully this will help it out a little, seemed like it was running way lean while crusing, and according to the a/f guage, it was. Any more suggestions from anyone, all help is appreciated.

---Chris

 

I had the car dyno-ed this morning, was rather disappointing actually for what i thought the car was pushing, only got 230hp at the rear wheels, but 295lb of torque. I thought that was rather weird. Any suggestions from anyone on how to get the hp up? I ran all my numbers through desktop dyno and it says 351 at the flywheel.

 

You didn't mention if you have headers or true dual exhaust. If you do not have both of the above then you can gain some there.

If you have an automatic transmission then you may want to look at a torque converter with a stall speed of about 2200 to 2400 RPM to let the engine rev a bit.

Get cool fresh air to the engine. The stock late C3 air cleaners work great.

You didn't mention what cylinder heads that you have. Some of the GM heads could be greatly improved by a bit of bowl work and some unshrouding of the valves.

 

I do have headers and dual exhaust, 2 1/4 pipes with flowmaster 40 series. The trans is a turbo 350 with a b&m 1800 stall and a transgo shift kit, although i would like to upgrade to a 700r4. The air cleaner is just the standard 14x3 with an open element k&n filter, im sure it is sucking hot air, I do have a complete dual snorkel set up from an 81 vette, I havent put it on, but im thinking now that summer is here and its 95 already that i should. My heads came from a performance shop, they are GM iron heads that have had the valves enlarged to 2.02 intake/1.6 exhaust. I am thinking my cam is the weak link due to the low duration @ .050. I do however like the way the car idles and cruises, no flat spots. I scanned in my dyno sheets, my a/f ratio looks good to me, but I am new to all this fine tuning a car. So again, any help or suggestion are appreciated.

---Chris

 

Looking at the much higher torque number seems like you motor stops breathing at higher rpm's. Your right that air cleaner is a suspect.
And hey Chris, your just on the learning curve here and now is when you find out what really works. Even if you have to experiment a little with every part/adjustment - from valve/lifter adjustments to throttle cable travel - allways room to improve the system. And IMHO, better now than with a big dollar dream motor that leaves you Teed-Off - and broke. At least now the racers at the track will talk to you and try to help. :yesnod:

 

I didnt think of that, that the engine wasnt breathing, this is my first corvette and although I have worked on a lot of older GM, it was mainly as a teenager with no money when I saved up for a manifold and carb and slapped duals on a car and it automatically became a "hot rod". Now that I know better and am able to really play with a car that isnt a daily driver, I can honestly say Ive learned more working on this car than any other project, and a lot of that is due to this forum. I am considering a larger cam to maybe up the power, but I am on the fence about it because i like the easy start up and good idle capabilities. Does anyone have an idea of what kind of cam would put this motor upwards of 280-300 rear wheel hp and still retain a good street worthy car that is reliable? (all i want is everything) :D


---Chris

 

IMHO, you may pick up a little with cold air ducting, but not a bunch. It looks to me like what is hurting you is the short duration cam. That is what is causing power to peak at only 4700RPM or so. Of course, big cams hurt gas mileage, move the torque peak up, etc.

My motor has a cam with 235 degrees duration @0.050 in a 327, 108 lobe separation, tons of overlap. Torque doesn't peak until 4100RPM, gas mileage is 11MPG on the freeway (4.11 gears too), but it really loves to rev.

The Performer intake bites as well at higher RPM. It works great at lower RPM, though.

You have a good combination for a street motor, stall is well-matched to the cam, etc.

To convert your rear-wheel numbers to flywheel, my Dynojet guy uses 22% loss for an automatic (18% for manual). If we use that, you're getting 294HP, 378lb-ft of torque, and that's through full exhaust, all accessories, etc.

Your setup is good, and if you do change the cam you're going to need more stall to make it come off the line. There probably is something to be gained with tuning and cold air, but you are already close to the potential of the combination, especially on the torque.

I bet that Desktop Dyno number is with no accessories. Many have told me it is optimistic, too. Good for comparisons, but not absolute numbers.


[Modified by L79vette, 10:06 AM 5/23/2004]

 

Your best bet on a cam to get to 280-300HP at the wheels and maintain street manners is a roller. Big bucks, like $800-900 for all the parts to convert.

You can get there with a flat tappet, but you lose manners. My car made 281HP at the wheels with 2.5" exhaust manifolds. Just got the headers done, no new dyno yet, hoping to get close to 300HP. My idle is rough, exhaust smells bad at idle. I can drive around OK at 1600RPM or so, probably because of the deep gears.

With a flat tappet, you have to trade off. With a roller, you can get a bunch of performance without hurting manners. Here's a great article on the conversion benefits: http://www.idavette.net/hib/camcon.htm .
Not sure you can get there with that intake, but maybe. With better heads and the roller cam, you could get there for sure even with the Performer, but now you are talking even more money.