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Old 11-05-2007, 11:34 AM
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SBC Questions. Help Please!

Forgive me, but think I need more expertise. I have done a search on the forum, but would like more imput. I have a 56 Chevy 1/2 Ton with a freshly rebuilt 350 SBC and TH350 in it. The shop I bought the engine from is a reputable shop in the Dallas area. The engine has iron heads, two bolt main, MSD HEI Street Fire Distributor, 85 Quadrajet 4 bbl carb and stock intake. The shop installed a CC 280H in the engine, which I did not order. They assured me it would do great and that I did not need to change the stock torque converter. The engine runs great, but the idle is rough. Right now I have it set at 10d-12d BTDC with distributer vacuum plugged. I also have the idle set at 1000 rpm in park. When I shift into gear it drops to 650 or so and rumbles roughly while I hold the brakes. It does not stall out, but it is rough. MSD says to use ported vacuum, but reading posts here, it appears that manifold vacuum might be best.

How much vacuum should I have at idle with my setup? Should I go ahead and hook up my vacuum advance to manifold vacuum? Also, checking the MSD site, they say that from the factory, the 8362 Street Fire Dizzy has 20d mechanical advance at 4000 rpm. To get it in at 3000 rpm I will need to change the springs. Should I do so?

Everything I read says the stock torque converter should be changed, but doing so will be a real PITA. What complications might arise from retaining the stock torque converter?

BTW, I have a 3.73 rearend from a 79 Z-28 in the back and 2 1/2" Dual exhaust with headers and flowmasters.

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Old 11-05-2007, 12:26 PM
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Quote:
Originally Posted by oscarlovel
Forgive me, but think I need more expertise. I have done a search on the forum, but would like more imput. I have a 56 Chevy 1/2 Ton with a freshly rebuilt 350 SBC and TH350 in it. The shop I bought the engine from is a reputable shop in the Dallas area. The engine has iron heads, two bolt main, MSD HEI Street Fire Distributor, 85 Quadrajet 4 bbl carb and stock intake. The shop installed a CC 280H in the engine, which I did not order. They assured me it would do great and that I did not need to change the stock torque converter. The engine runs great, but the idle is rough. Right now I have it set at 10d-12d BTDC with distributer vacuum plugged. I also have the idle set at 1000 rpm in park. When I shift into gear it drops to 650 or so and rumbles roughly while I hold the brakes. It does not stall out, but it is rough. MSD says to use ported vacuum, but reading posts here, it appears that manifold vacuum might be best.

How much vacuum should I have at idle with my setup? Should I go ahead and hook up my vacuum advance to manifold vacuum? Also, checking the MSD site, they say that from the factory, the 8362 Street Fire Dizzy has 20d mechanical advance at 4000 rpm. To get it in at 300 rpm I will need to change the springs. Should I do so?

Everything I read says the stock torque converter should be changed, but doing so will be a real PITA. What complications might arise from retaining the stock torque converter?

BTW, I have a 3.73 rearend from a 79 Z-28 in the back and 2 1/2" Dual exhaust with headers and flowmasters.
The cam you have is right on the line for a stock converter stall if not a step over. You need a higher idle in gear which will make the drop into gear more severe than it already is.

Bogie
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Old 11-06-2007, 08:34 AM
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Quote:
Originally Posted by F-BIRD'88
While you can get away with a stock converter that cam really needs a 11" 2800stall at minimum. A 10" 3500stall is not too much.

That cam will idle better if you give it more initial timing at idle.
Needs 24deg at idle and a short curve to 36deg at 3200.
In order to achieve this curve you must limit the advance travel in the distributor from 20deg stock to around12-14deg.

Then use a medium tension curve spring.

Probabily not the best choice for a truck.
if you want a more suitable truck cam that will idle and drive fine with a stock converter swap to a Comp Cams 265DEH #12-208-2

You'll have a lot more low/mid range power right where you use it the most in a truck application and not give up too much top end.
Its a much better match to your combination and application.
This truck friendly cam is strong from idle to 5500rpm.
You'll probabily like it a lot better overall. 1.6 rockers are a nice addition.

look here for the specs

I realize that means tearing the motor half apart but if you have the wrong cam you'll never be happy with it. "Drivability" is very subjective. The most common error people make is overcamming for the intended application.
Its your truck. Your overall satisfaction is paramont.
This is the cam I would have recomended for you.
Yeah, I agree with you about the overcamming. This is not the cam I would have chosen myself. By the same token, I've already had to pull a 305 from the truck that turned out to have bad rings, and I just got the 350 in. My inclination is to get it running now and do a cam change down the road when I'm in a better frame of mind.

Your timing recommendations make sense. I'm wondering about setting say 18d initial, then using manifold vacuum (which I can adjust on the MSD). Would this work in lieu of switching out the 20d mechanical advanbce that is built in? I have ordered the advance curve kit from MSD. It should be here in a few days. If I set the initial timing to 18-24d BTDC as suggested, will starting be difficult? And is my Quadrajet and stock intake up to the challenge this cam presents?

I know these are lots of questions, but frankly, I've been a Mustang guy and this is my first venture into Chevy V8's. Thanks.
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Old 11-06-2007, 12:01 PM
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Actually, I have a new Summit 1102 cam & lifters in the 305 I removed. Breakin time only, so I could switch them out with no cost involved. I just hate to remove the front end of my truck again and have to drop the pan and all that is involved. To be honest, I'm almost ready to light a torch under it and say goodbye, but I have too much invested in time and money.

Frankly, I don't like the bad boy idle. I'm 51 years old and those days are long gone for me. I've had my share of hot Mustangs over the years. I also have a stock 42 Chevy 1/2Ton Pickup that will be cherry real soon --- Actually, as soon as I get this 56 on the road, out of the shop, and can finish the final painting and reassembly. That 216 is certainly not a hotrod! LOL!

Decisions, Decisions!
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Old 11-06-2007, 06:47 PM
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Just curious, what do I gain with the 1103 over the 1102? Not being cheap here, just trying to learn something.
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Old 11-07-2007, 08:56 AM
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OK. I bumped the timing up as you suggested. Since my timing light doesn't have a dial-in advance, I just ordered one from Summit. I'm probably close to 24* BTDC. Used a vacuum guage and adjusted to max vacuum, then backed the timing down 1/2" of vacuum. That leaves me right at 14" vacuum at idle parked. She idles fine now when I drop it in gear, though still lopey. Hot starts no problem at all. In fact, seems to start better than ever. Distributor recurve kit should be here in a couple of days. I'll recurve as you advized and give it a go. I may look at a new torque converter and intake. Can I use the Quadrajet 4bbl I have?

I'm also going to call the builder this morning and try and find out what specific things they did to accomodate this 280H in this engine. If all else fails, then I'll tear everything apart and go with the 268HE you suggested or the Summit 1103.

Thanks and wish me luck.
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Old 11-09-2007, 09:02 AM
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I know you are right about the cam switch, but there is one other issue. If I cahange the cam out, I'm sure to void the warranty from the shop I bought the engine from. So I'll try and make the current setup work. Just got the MSD recurve kit in and should have the new timing light and timing tape in this afternoon. Will let you know how things turn out.

BTW, should I change the intake to a dual plane, will my Quadrajet still be useable, or should I get another 4bbl carb as well?
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Old 11-10-2007, 04:12 PM
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Quote:
Originally Posted by oscarlovel
I know you are right about the cam switch, but there is one other issue. If I cahange the cam out, I'm sure to void the warranty from the shop I bought the engine from. So I'll try and make the current setup work. Just got the MSD recurve kit in and should have the new timing light and timing tape in this afternoon. Will let you know how things turn out.

BTW, should I change the intake to a dual plane, will my Quadrajet still be useable, or should I get another 4bbl carb as well?
What did you want from this engine in the first place?

-As an everyday work engine where hauling a load or trailer is expected of some if not all the time.

- A simple get me to work and home truck, maybe hotted up a little but not a racer.

- A racer, hot street, Saturday night brawler, semi hot lower end race motor, cause this is what you've got and all the quirks that go with it.

-The cam, compression and intake all are driving toward upper end
power at the expense of "cruisablility" to some degree and if this was
to be a work engine, that's really been compromised.

So you need to choose what you want; if you want the big lumpy cam then the torque converter's stall speed needs to go up. That means a new converter, which means at the least the tranny has to come out. High stall converters do not like to be used in a "working" truck. They want to run with a lot of RPM, if you don't they make lots of heat which ends in a fried transmission. They always need extra cooling capacity added for the transmission oil, that means a good oil cooler, maybe even one with a fan if you have to idle or drive slowly a lot. This has to go in ahead of the radiator heat exchanger to take some of the heat load off the radiator itself or can be plumbed without the old in radiator cooler.

Tricks you can try are pretty limited, if the heads have 1.6 rockers you can drop back to 1.5s. You could try Rhoads lifters, the allow a little variable duration which calms the idle a bit. This might get you around the harsh drop into gear by allowing the engine to idle slower than 900-1000 RPM. The harsh drop into gear will accelerate wear inside the tranny and could eventually break something.

Bogie
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Old 11-12-2007, 06:34 PM
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OK. Much as I hated doing it, I tore everything down this afternoon, removed the 280H cam & lifters and replaced them with the Summit cam & lifters. Did not get everything back together, but am happy with the progress. BTW, it was a royal PAIN. I called the shop that built the engine this morning and they agreed to continue the warranty if I changed the cam, so I went ahead. Chances are, they could find a way out no matter what I did or did not do, but at least I have it in writing. Guy at the shop was puzzled. Couldn't understand why this would not work for me. After all, it's the same cam (280H) that his kids always wanted, and it works for the circle track guys. Makes me wonder about the build, but all I can do now is put it back together and see.

Will post a report after it is running again. Hopefully tomorrow or the next day, depending on whether I get some time to work on the truck or not. Thanks for the advice and prodding. I believe in the end I will be happier with the cam switch. My wallet should be for sure!
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Old 11-27-2007, 12:53 PM
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Success

Was out of town for a week or so, but just fired up the 56 with the Summit cam. WOW! What a difference. Thanks to all -- you were right, I will be much happier with this than the Comp 280H the shop originally put in.
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