Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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I just recently bought this car, and 1986 S/C with a low miles driveline, 20k on the 225hp 305 crate motor, 10k on the trans and rear. The trans and rear are awesome, 2500rpm stall, good shift kit, 3.73 Richmonds in back with factory posi. Better launching car than my 350TPI IROC was... seriously, its good.
What I'm considering is what my next mod might be. The motor's got a L69 dual snorkel intake, CC Q-Jet going into a ZZ3 intake, with what I think are stock heads operated by a K1102 Summit cam 204/214 .423/.442 at .050, ZZ3 intake, slp 1 5/8" headers, smog crap, 3" cat, 3" catback. All ignited by a DUI ignition, still pcm controlled. Where would I look for more power? Obviously CID would help (ie 350), I'd like to start simpler, but I'm not gonna throw too much money at a 305. I feel like good heads might really go a long way with an otherwise well breathing motor. Some compression can't hurt either. It pulls pretty good right up to 5500rpm, I'm not sure I should be trusting a stock valvetrain to do that day in and day out. Thoughts on that?
Barring the obvious, get a 350, or power adder, what would you do for some power on this if it was your ride? I probaby will spray it, but I don't need that suggested to me, its already in the plans. Heads? More cam? Something else?
You've almost duplicated what I did. See sig. It was basically the same with the 305 except it had a Crane 2050 Compucam in it. I discovered when I pulled it apart to put the 350 shortblock in that the heads actually measured 64cc chambers. Really bizzare, because they have "58cc" cast right into them under the valve covers. So, I thought I had 9.5:1 compression with the 305, actually had closer to 9.0:1.
It ran well. A little weak in the low RPMs. I never had the transmission operating properly, so real performance #'s were never obtained, but it ran a best of 15.70 at 5800' elevation.
I would suggest you pull the heads and have 1.94" intake valves (and 1.60" exhaust valves, if you like) installed, then port them per the do-it-yourself guidelines available here and on the Standard Abrasives website. Get new valve springs & retainers, have the guides cut for positive-sealing valve stem seals.
After doing that, your Summit cam is the next thing that needs to go. Since you have a CC carb, you don't want to go overboard with overlap, so look for something in the 268 advertised duration range and 112 LSA. The Crane Z Series ( Summit Racing - High Performance Car and Truck Parts | 800-230-3030 , p/n CRN-113521) looks pretty good. It would really wake that puppy up with ported heads and your other mods, while keeping the computer happy.
FWIW, I took off over a second from my 1/4 mile ET while maintaining the same fuel economy when I put the ZZ3 shortblock in mine. The ZZ4 cam has just as smooth of an idle as the Compucam in the 305 (maybe smoother), has more lift with slightly less duration. The end result was a lot more torque (and therefore power) than the 305 had. I just flat-out love it.
These are all fairly similar. Crane has 112 LSA, comp has the 110 and 114 version, and lunati's is 110LSA. The reason I like the lunati most is that it has the most lift, and comparable duration. More duration @.050, but same advertised duration. See if these links work here:
The heads really are probably the next step, might touch the cam while I'm there. What do you think about running the stock valvetrain up to 5500rpm on a regular basis? I'm not positive if the guy did the springs when he did the cam, I know the cam was put into the crate motor before it went into the car. Also, what about 1.6 rocker, that might cheat me into a little more lift, but would the heads and springs tolerate that?
I think that I'd just swap out the rockers and call it good. With 1.6 rockers you'd be at .451/.471 lift which the stock heads should support.
If you want to go cheap then just get some stamped rockers. Summit Steel Rocker Arms: SUM-G6801 - summitracing.com
An 86 S/C would have only come originally with the milder LG4 engine. I assume you're still using the cc-HEI distributor along with that cc-Qjet? If so, you might actually want to look into a better chip to help with your ignition advance curve. Stock LG-4 chips are really mild. Now, you could bump up the initial quite a bit as a crutch, but a more performance-oriented advance curve would probably be a better answer. That's really the only area of engine performance at WOT that the chip affects on these computer controlled carb motors. Just about any chip you could get for it would be more aggressive than stock. Don't overlook this- it can make a "holy cow!' kind of difference.
Other than that it looks like a well balanced combination of parts. I'm not surprised it runs as well as you say.
Not sure I'd do anything to the heads if you're not into throwing money at the 305. However, if you can install a set of Comp 981 valve springs in place of your stock ones (you do the work- just the cost of the springs) you will probably find it pulls even better on the top end. Comp 981 springs are drop-in replacements for stock but much stronger and much better suited to over-5000 RPM use. With even a mild performance cam they should be just about mandatory.
An 86 S/C would have only come originally with the milder LG4 engine. I assume you're still using the cc-HEI distributor along with that cc-Qjet? If so, you might actually want to look into a better chip to help with your ignition advance curve. Stock LG-4 chips are really mild. Now, you could bump up the initial quite a bit as a crutch, but a more performance-oriented advance curve would probably be a better answer. That's really the only area of engine performance at WOT that the chip affects on these computer controlled carb motors. Just about any chip you could get for it would be more aggressive than stock. Don't overlook this- it can make a "holy cow!' kind of difference.
Other than that it looks like a well balanced combination of parts. I'm not surprised it runs as well as you say.
Not sure I'd do anything to the heads if you're not into throwing money at the 305. However, if you can install a set of Comp 981 valve springs in place of your stock ones (you do the work- just the cost of the springs) you will probably find it pulls even better on the top end. Comp 981 springs are drop-in replacements for stock but much stronger and much better suited to over-5000 RPM use. With even a mild performance cam they should be just about mandatory.
Nice food for thought. Yep, still the CC-HEI and CCQjet, its a DUI cap and module, but still computer controlled. I haven't even checked the initial advance yet, I was thinking to see how much it would tolerate, I've heard 8-10* of initial isn't unreasonable, especially with relatively low compression, and generous jetting. I'll do some research, any good reccomendations for getting chip burning done, or a generic program that I might look for? Now that you mentioned it, the car really does feel like it could benefit from some more advance.
Comp 981's might be on the list as well, I'd really like to make this pull the top end for all its worth, it really starts coming alive at 4000rpm, and pulls up as far as 5500, that as far as I've taken it, and it wasn't falling off. Shifting there as opposed staying in drive and letting the trans shift at 4900 makes an incredible difference in acceleration, you're in the power much better for the next gear. The 700R4 ratios really do need to be pulled as long as possible to avoid a bog between gears.
