Small Block & Big Block Chevy Specific - Track Trip

So here is how it went down, just messin around with the 1983 C-10 tow truck with some friends and seeing what i could get out of it.

-The motor in the truck is a 350 290hp crate motor, and the trouble i kept having was it cutting out at about 4K rpm in second gear, it would come back on after i let out of it.

-The motor has the 305 intake manifold, rochester Q-Jet, stock GM HEI, nothing special.

The fuel pump is an 80 gph Holley mechanical pump.

Just wondering if there were any ideas out there?

So first gear is fine? How about third?

well 1st automatically shifts at 4800 with my 700R4 but as it gets near 5K rpm in first, it does feel down on power, and when i go through the traps in 3rd gear it feels down on power in the top end. It almost felt like it was starting to miss. idk how many rpms i was turning through the traps but it was hardly pulling and falling on its face.

Some of my friends were saying it could be a bad vacuum advance because it is ok in the bottom end, but idk if that makes sence...

Just looking for suggestions.:angel:

Well, it could be starving for fuel, check your timing. Your vacuum advance is only functional under part throttle, has nothing to do with WOT. So, make sure your timing is not way back, toy might want to get a electric fuel pump but what you have SHOULD be good enough. Male sure you have your carb adjusted correct if it is a holley, the floats might need to be set higher.

alright i will check timing... how much should i be looking at... about 32*? and the carb is a Rochester Q-Jet.

Well, timing should be about that at total advance, so make sure you disconnect the vacuum advance and plug it off at the carb while tuning. I hate to say it but that carb might not be in tune ither.

i agree with carb. being a part of the problem also, but i can never get a straight answer ever, when the truck is at idle with the vacuum disconnected... how many degrees of timing should i set to when i throw the light on it.

bump... help me with timing this motor!!!!!!!!

I would 36 degrees of total timing.

so your saying, when it is idling... with the motor warm... put a timing light on it and set to 36 degrees?

Sorry for my ignorance.

the vacuum advance won't affect much at WOT. it's for part-throttle driving.

here's a great write-up to set your timing. (http://www.stevesnovasite.com/forums/showthread.php?t=11689)

It would be a good idea to get a long piece of tubing and hook up a vacuum meter to your carb. drive it around and note your vacuum at various speeds and loads. this will help with tuning.

by chance, were you in the truck with giant rear meats out at firebird last friday?

thanks for the help man, and no it wasnt me, i live in NC.

so... im still looking for an answer... with my VA disconnected at idle... what # should i shoot for on the balancer?!

I almost NEVER post on forums, but I thought I would try to help you out with some general timing info. Your base timing (what you will read on the balancer with the engine warm, vacuum advance disconnect and idle) is controlled by the position of the distributer only (unless your distributer is worn...that's a different topic!). Generally speaking, you should set it in the neighborhood of 8 to 12 degrees advance. Your total timing is the amount that is built into the system as the RPMs go up and the distributer internals turn faster. Now, the total mechanical advance can vary. If you have a smog era distributo, you might only get 20 degrees of mechanical advance. That 20 degrees plus the base timing (say 12 degrees) would give you 32 total. The advance curve determines how fast this extra mechanical advance comes in. With a performance motor, you want it all in by 3000rpm (give or take...all engines are different). If you are measuring the mechanical advance with an adjustable timing light, make sure the vacuuum canister is disconnected. Lastly, the vacuum advance is controlled by the engine vacuum built up at part throttle. It can be quite a lot in some circumstances. I have my engine puttin in 45 degrees total at some points. Again, each engine wants what it wants. Hope this helps!

I never use the vac.advance on the older SBC i just use a dial timing light and set it to the total timing i want and zero it on the timing tab.

Locking out the vacuum advance is another approach, but I wouldn't recommend it on something you plan on driving a lot (unless you don't mind a drop in gas mileage). I did this on the 406 in my old 1975 Nova. When I switched back to a dedicated vacuum advance distributer, it was the difference between 8MPG and 12MPG. Of course, if you have high compression and are up against it with pump gas, you may want to stay away from the vacuum advance (to be safe) and live with the poor MPG.

There is also the concept of totally locking out all advance. This is a racecar only procedure that has been carried over to the street. I know guys that lock their distributer at 35 degrees advance. This means it is ALWAYS at 35 degrees advance (idle...WOT...etc). It makes for a hard starting car and will also do nothing good for MPG. On a racecar, you really don't care because it is always at WOT.

thank you fine sir! I suggest you post more often, your knowledge is useful!

Glad I could help. I was reading back through your posts. You said the engine was feeling down on power at around 5000rpm. It could be valve float. If the valve springs aren't up to snuff (or they were installed wrong), they could be going into float...it actually feels like the engine is missing and can be easily mistaken as timing or carb problems.

Another poster suggested getting a vacuum gage and hooking it to the motor. I couldn't agree more. It is the poor mans oxygen sensor!!

See i was thinking the same thing but i was always told it probly not... it is a crate motor, a cheapy 290hp 350, what would i see on the vacuum guage when the valves begin to float?

bowtiescottsdale,

Good question. I have never tried to diagnose valve float with a vacuum gage (i use them more for setting up timing and carb adjustments). However, it would make sense that the gage needle would start to flutter when the engine goes into float. At WOT you should be seeing little to no vacuum (if you are hooked to the port that your vacuum canister is hooked to). If at 5000rpm (under load...try doing this test in low gear going up a hill) the needle starts bouncing around, I don't think that could be traced to the carb. Maybe timing, but not the carb. The timing you can check in park with an adjustable timing light. I doubt the engine will go into float with no load on the engine.

I don't know anything about the GM 290HP motor. You could probably get some info from the SDPC2000.com website (or other GM dealer websites). My guess is that it has a very mild cam and small springs (doesn't take much to make 290hp with a 350). The power band may only stretch to 5500rpm. Let me know what you find out.

The 290 HP 350 is almost the same as a LO5 truck 350 with 76CC heads. The cam is a little different though.

I guess when i get home this weekend I will throw the vacuum guage on it and see what's up with it, if i do think it is floating the valves would it be worth throwing new springs in it? Im bout to pull the motor but when i sell it i want it to run correctly.

What springs would you recomend?

The GM 350/290HP/326TQ W/A Hyd. flat tappet cam222/222Dur 450/460 lift.

That cam is very similar to a comp 268H grind. Comp recommends the 981 or 983 single spring (1.25 OD). Also, I looked up the 290HP motor and it is rated for power up to 5100RPM. That means you should be shifting at about 5400-5500RPM.

How many miles are on the motor? If there aren't many miles, and your vacuum gage shows what appears to be valve float, it could be the lifters also.

it has about 15K miles on it, i went back and got dad to pull out the receipt and it is the 260hp model... hell right now it wont even make it to 5500rpms.

I thought about throwing some heads and a cam in it but idk if that bottom end would hold any power.

The 260HP motor appears to be a stout piece (4-bolt mains, cast crank, LT1 rods and decent pistons). I have a completely stock 1990 L98 short block in my IROC. It runs 11.60's at 117MPH and I have the rev limiter set at 7000RPM. That short block isn't as good as the one you have. That crate engine can take more than 260HP and 5000RPM.

The cam specs are real mild and the compression is pretty low on that crate engine. I think it will be all done by about 5000RPM. Super Chevy did a test with one of these engines. In base form it peaked at 264HP at 4400RPM. They then bolted a blower on it and made some serious power (383HP at 5500RPM on 7psi of boost).

If it were me, I would go over the motor good. Use your vacuum gage. Try to diagnose what is going on at the 5000RPM. Get the carb in tune and play with your timing. The secondary valve on the quadrajet (the plate that covers the top of the secondaries) can be a great tuning aid and there is power to be found there (you want it to open as fast as possible without bogging the motor down). Also, many smog era quads were limited in how far the secondary throttle blades could open. Verify that they are making it to full-open.

The short block is a decent foundation to build from. If you plan on keeping it, I would go with a head and cam swap.

The cam in the 350/260hp is tiny 383/401 rpm1000-3100 not much of a range of rpm.

I've thought about building off it, i just didnt know how stout it was and also I bought a nitrous kit to spray it but with it acting up backed out... so i guess i will go over it and see what I can do with it.

Just a camshaft change w/ wake your motor up.Go w/ something like a Comp Cam 218/218-454/454 RPM range1500-5500.I think your over reving your motor which is not hard w/ the little cam that is in it now.

If you are looking for something to just have fun with, stick with the shortblock you already have. Its free, has low miles and you know the history of it. Getting 1HP per cubic inch is pretty straight forward. I would look at EQ cast iron cylinder heads with 180cc runners and 64cc cumbustion chambers. This will bump your compression up. I would then throw a comp XE268 hydraulic cam in it. Get a set of 1 5/8 headers and dual exhaust (if you don't already have them). Put a high rise dual plane manifold on it (like a Performer RPM). Keep the quadrajet and the HEI. This should get you around 325HP and decent low end torque. I wouldn't be afraid to hit it with a 100HP shot of nitrous...just be careful with the timing (high compression/cast iron cylinder heads). You will also want a higher stall convertor (2800-3000RPM) and decent rear gears (3.55:1). Take as much weight out of the truck as possible and then plan on finding a way to hook it all to the pavement (Cal Track bars and new front springs and shocks). All of this will cost you money...but you can do it in steps. Thats the fun part! Going back to the track week after week and getting a little faster every time!

well i have the money to do aluminum heads, i was thinking AFR 195s, and id like to go with a cam with a pretty good bump to it... also i already have 1 5/8s headers, and 3.73 gears out back with a Torsen locker!

so do you think all that and a 75-100 shot would work on that bottom end?

how fast do you think it'd run in the 1/4?

Tell me a little more about the truck. What does it weigh? Is it a 4wd? Is it only for the track?

the AFR 195's are hard to beat. They are worth the money!

The truck is an 83' C-10 and it needs to be able to be weekend driven, i refuse to trailer it to a track, it weighs about 4500 lbs.

Im kinda leaning toward building a motor cuz i want something very reliable idk though.

4500lbs isn't as bad as I thought. No reason you can't get it into the 12's. There is a guy with a similar truck at the track I race at that is in the high 12's. He has a 406 with iron heads and a mild cam. The truck also doesn't hook well (lots of tire spin!). I think the formula I gave you above can get you there with the short block you have. Suspension tuning will be the key. You'll want a tire in the neighborhood of 27" tall and as wide as you can fit/afford. I would put them on 15" rims (no bigger). You're going to want some sidewall flex to get weight transfer to the rear. I'm not sure if Cal Tracks are made for your suspension, but if they are, they work good. You could also remove a leaf or two from the rear springs (you wont be hauling anything with it?). For the front, find a lower rate spring (maybe from a 2wd with a 6cyl). You can also whim the swy bar at the track to get a little more front end rise.

very nice, i think i will soon order AFR 195s, comp. 272H cam (or bigger?) thinking of going roller, recommend me an intake manifold and carb.

What kinda valve train set-up would u go with?

and Cal-Tracs are made for my suspension... like 85 bucks!

Looks like you are thinking of going all out. If you are thinking of a roller, I would look at the Comp XR288HR. You will have great flow with the AFR's. Just make sure you get them with a 64cc or 60cc chamber for good compression to go with that cam. Get yourself a performer RPM Airgap and as good of a carb as your budget can swing (something in the 750-850 range). The right carb will make this streetable (look into AEM...they have good stuff but it is pricey). This will all get you some major horsepower (probably in the 450HP neighborhood). Sell the nitrous kit to fund the carb if you have to.

i think im gonna type up a list soon, so ill post it so you guys can see what you think.

Im excited!

What is good stock replacement valve spring that would work for a GM 260HP crate... needs to be a little stiffer then stock, im gonna spray this bitch lmao.

The bottom end is fine, I was spraying a 150 shot on it.

ever float the valves on urs?

No, but I didnt push the stock heads just used them to get the car up and running. I have some really nice Vortec heads that were on it when spraying.

for sale?