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Old 10-16-2012, 07:17 PM
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my 355 after cam swap sluggish help

I have a 355 with lunati 285 235@50 510 lift 108degree lobe sep edelbrock performer eps intake 305 heads runnin very sluggish cant figure out why it seems to take very long time to get any speed at all edelbrock 600 carb could this be my problem is not enough carb??? LOST if anyone could give me any ideas would greatly appreciate it i know the 308 gear isnt helping but truck was alot quicker before cam intake and headets thanks for the help

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Old 10-16-2012, 07:31 PM
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sounds like the ignition timing is slow or if you have vacuum advance it may not be responding properly...you will loose vacuum sometimes when you change cams..and if this all checks out ok you will need to put the cam in at a 106 lobe center...
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Old 10-16-2012, 07:38 PM
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Quote:
Originally Posted by chvy285 View Post
I have a 355 with lunati 285 235@50 510 lift 108degree lobe sep edelbrock performer eps intake 305 heads runnin very sluggish cant figure out why it seems to take very long time to get any speed at all edelbrock 600 carb could this be my problem is not enough carb??? LOST if anyone could give me any ideas would greatly appreciate it i know the 308 gear isnt helping but truck was alot quicker before cam intake and headets thanks for the help
This can be a lead in to a lot of tuning issues but this is a pretty big cam that has moved the power band way up the rev range. For sure the 3.08 gearing isn't helping because the engine's power band and the gearing to get up to it no longer match. The 305 heads unless you put in 350 valves and did some porting aren't helping either as about the time the engine revs to the cam's power band unmolested 305 heads are out of breath. You may also be looking at detonation with these small chamber heads, they have the spark plug way off to one side with a lot of compression on a 350, the plug location brings the slow burn of large chamber heads with a lot of compression. This will put the point of maximum pressure late in the power cycle where it isn't effectively pushing the piston and creats a situation where the piston has moved so far down the bore that the quench function is no longer a viable method of damping the excess temperatures that cause detonation of the unburnt mixture ahead of the flame front. More advance that comes in quickly will help getting the peak cylinder pressure earlier but will increase any detonation tendency. There are some cures for that of which richening the mixture is the quickest without backing down the advance. The 600 cfm carb won't be the best at feeding the engine where it has to go for max power on this cam, but that's probably the last issue to chase as it will do well enough to at least tickle your fancy for power but won't satisfy it.

Bogie
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Old 10-16-2012, 09:24 PM
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The cam you ahve does not make power till 3000++ rpm.
For a truck, needs 4.30++ gears and a 3000++high stall. More if the tires are tall.
The stock distributor advance curve will not work with that cam.
Such a cam needs a totally different timing curve. Much more initial at idle 26+deg and 34-36deg at max advance.
Shorten the mech timing curve to around 10deg to allow this.
Verify the TDC point on the timng tab/balancer is true TDC. There are 3 or 4 different timing over/balancer combos with differnt timing tab loations. Ya it mtters.
Which 305 heads. Casting number undr valve cover.
For a truck with 3.08 gears I would forget that cam. Replace it with a short duration cam.
That makes low end Truck torque. That cam is all top end.
Pick a cam with 203 to 218@.050" duration. Your truck wil make much more low rpm torque and accelerate much faster with 3.08 gears. Tall tires need more rear gear reguardless.
What rear tire diameter?
With that big cam you want to cruise at 3000 to 3400 rpm @60MPH.
30" tires wants n less than a 4.30 gear
32" needs 4.56 gears.
28" needs 4.10
35" tires 4.88 to 5.38 gears
Your 3.08 gears wants a 22" tall tires on your truck.... Got 22" tall tires on it?
Anything less than this will result in lame accelertion with this cam.
Its very easy to over cam a heavy truck.

The 305 heads are not likely the problem. But some don't have much power potential
small valves small ports on some. They are not all the same.
the 416's are not bad at all with porting and larger 1.94 valves. But not great in stock form.
The carb is not a big problem should be a 750 for power thu. may need jetting too.

The biggest problem is the cam/axle ratio mismatch. Start by fixing the timing true TDC point and timing curve.
Get your head around a gear change or a cam change.
Big cams need big gears. Big truck tires need even bigger gears.

it is also possible that this cam (which is just too friggin big) is also installed wrong (retarded) making for even worse low end power. Bad cam choice for a truck with 3.08's.

Last edited by F-BIRD'88; 10-16-2012 at 09:40 PM.
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Old 10-16-2012, 09:53 PM
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with all the parts you have in the engine,its the cam thats a little big.The carb could be a little bigger.The heads could use some work. Im sure with some tuning it will improve.Is that a hydraulic flat tappet cam. when the engine reaches 2500 rpm does it get a lot better?
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Old 10-17-2012, 05:46 AM
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355 slow

Thanks to everyone who answered it seems the cam is to big for the stock 305 headsand my 308 gear it seems a head swap to maybe a good set of double humps and a lot more gear would be a huge help as i am really new to all this i never realized u could overcam one that easily this is in a 1983white gmc swb also runnin a 10/31/50 tire also seems to be killin it what would be a good tire size lookin for at least a 410white gear now
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Old 10-17-2012, 06:07 AM
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Its in my post .Why not just keep the tires and get some 4.56's
You need a 10" 3500 stall converter too, for that cam.
You still need to get the timing curve in order.
Thats where to start.
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Old 10-17-2012, 06:43 AM
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Does it hit hard up top and in the top of first gear?

Any chance you didnt get the cam in at 0 its easy to do. A one tooth mistake in installing a cam can lead to this behavior. It will run a like its dont have a cam and will not rev right.

Also to far advanced will make the car run like crap down low and only pull in a very narrow rpm band.

You can check the cam without removing the engine or cam covers. You can grab a degree wheel off ebay and dial indicator. Just need to make sure its close. I would call make fo that cam and ask if they can help you make sure its installed right before you go and buy gears and make any other major changes.

I have seen big cams in heavy cars with wrong gears they usally are still fast just got to wind them up first. Its rare that a cam like that will not put you back in your seat.

If I had to guess i would say you got the cam a tooth off during install. Its easy to do and hard to notice. There are a bunch of good guys on the forum that can help you check the intake opening degree to make sure the cam is at least close.


Hope this helps.
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Old 10-17-2012, 08:41 AM
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It starts pullin around 2700 pretty hard but nothin like it shouldat the top if first gear its pullin hard if u hold it to around 5500 before shiftin when u shift it barks tires just takes forever to get it there was just very disapointed in the petformance but i am new at this and learning some things i am learning are turning out to be expensive lessons lol
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Old 10-17-2012, 09:03 AM
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if it's an 67-72 p/u they are not heavy by p/u standards my long bed is 3890. lb
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Old 10-17-2012, 07:29 PM
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Just thought of something. What timing chain did you use. Did you use a true double roller high performance timing chain. Or a stock style for your year truck. That might be the -5 retard style that will kill your cam and make everything out of whack.

If you have hei just unhook vacum advance and restric the wieghts movement and set intial advance higher and go drive it for a short distance. If ot runs better you need to tune the hei. If not its wiped cam or wrong chain/timing.

I helped a friend install a big cam in his car it was a chevy caprice 4 door with 400. The car without the cam could pull 50 in first gear from a turbo 400. He got a race cam against all the salesmans advice. It was fine it did not idle well but ran fine and it callled for low gears high compression and 2500 stall. He had none of that. But the car was still fast. It surely was not slower. Just did not rip off the line like it could of with the right setup. It does not sound like This is your problem.
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Old 10-18-2012, 04:56 PM
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I installed a cloyce heavy duty double roller timing chain and gear at first had it all out of whack and had to tear it all down and reset it i had it set on wrong timing mark and wouldnt hit a lick
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