318 wont rev above 5,300

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Mopastor

Mopastor

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I have a quick question


I put a turbo on my 318 and used the summit cam SUM-6901

I am having issues with the car running above 5,300 - it breaks up.

I was wondering if anyone had an Idea. I have tried a different coil, but maybe its a broken valve spring. Could the cam keep it from reving above a certain RPM?

THe car runs great up to then. It ran a 12.32 @ 105 short shifting at 5,000 and the car has 3.91 gears so it needs to go through the traps at 6,000. Its puking at the finish line.

Should I get a bigger cam? or do you think its electrical? Im running an MSD and a boost controller.

Thanks for your insight!
 
check your valve springs....and secondly can the fuel system support 6000 rpm...
 
Not sure what valve springs you are using, sounds like they may be floating and could be to weak.
A tech will jump in here and help you out soon, but I do know this can happen
I have been there years ago :thumleft:
 
well as said above... check you valve springs, like was said in another post with boost you have to figure that much spring pressure is taken out of the equation...

as for me im sure that cam you bought is not a boost profiled cam and those springs either... so i would look into that first...

second, did you have the dizzy curved? are you running "lots" of total?? maybe to much...

also fuel, running out of it? fuel line size ect

tell us your combo plz!!

P.S. you took the chance of running the car when you knew there was a problem?
 
Looks to me your cam is tapped out!! These are the specs below that I googled,

Basic Operating RPM Range 1,800-5,500
Intake Duration at 050 inch Lift 218
Exhaust Duration at 050 inch Lift 228
Duration at 050 inch Lift 218 int./228 exh.
Advertised Intake Duration 276
Advertised Exhaust Duration 286
Advertised Duration 276 int./286 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.441 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.441 in.
Valve Lift with Factory Rocker Arm Ratio 0.441 int./0.441 exh.
Lobe Separation (degrees) 114
Computer-Controlled Compatible No
Valve Springs Required Yes
Camshaft Manufacturers Description Fair-smooth idle, low-midrange power. Works with stock-2,000 stall, 9:1


I would suggest to get that 3.91 out of it and install a 2.91 or a 3.23. Turbo's like "load"....Bet with this gear change you could see high 10's low 11's!!
 
I doubt that it is the valves floating at 5300 RPM. Unless you used some really old wore out springs.
My guess is that it's fuel or ignition related.

How much boost are you running?
 
I'm running the Aeromotive A2000 pump with 8 an braided line.

I ran it with 10lbs of boost, but I tried driving it without any boost and it still breaks up at around 5,300 Im sure its not boost related.

I have a 7,000 pill in the MSD

I will check on the valve springs, I bought the motor from someone who built it for turbo (you know how that goes sometimes) and I know it had new springs. The CR is 8.5 I will ask him for the specs on the springs themselves.

I just want sure if a cam could keep a car from reving over a certain limit.

Thanks guys
 
CUUDAK said:
Looks to me your cam is tapped out!! These are the specs below that I googled,

Basic Operating RPM Range 1,800-5,500
Intake Duration at 050 inch Lift 218
Exhaust Duration at 050 inch Lift 228
Duration at 050 inch Lift 218 int./228 exh.
Advertised Intake Duration 276
Advertised Exhaust Duration 286
Advertised Duration 276 int./286 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.441 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.441 in.
Valve Lift with Factory Rocker Arm Ratio 0.441 int./0.441 exh.
Lobe Separation (degrees) 114
Computer-Controlled Compatible No
Valve Springs Required Yes
Camshaft Manufacturers Description Fair-smooth idle, low-midrange power. Works with stock-2,000 stall, 9:1


I would suggest to get that 3.91 out of it and install a 2.91 or a 3.23. Turbo's like "load"....Bet with this gear change you could see high 10's low 11's!!
Click to expand...


Again,
cam is tapped out!!!
 
The cam being "tapped out" doesn't have any effect on the engine "breaking up" (missing) at high rpm.

The weak valve springs that aren't matched to the cam are a problem, along with not having enough fuel and ignition to support that kind of power.
 
rnaz said:
The cam being "tapped out" doesn't have any effect on the engine "breaking up" (missing) at high rpm.

The weak valve springs that aren't matched to the cam are a problem, along with not having enough fuel and ignition to support that kind of power.
Click to expand...

A stock ignition will survive 5500 rpm as well as a stock pump. Been there done that.

The springs are more than likely the same chinese **** as the cam so there too could be a problem.

It is still in his best interest to get rid of the 3.91 gear! TOOOO much gear for the turbo!
 
It could also be from too much boost for the springs. Alot of boost and weak springs could mean the the valves are being held open by pressure up in the higher RPM's!
 
Mopastor,

You got any pictures of your engine bay & set up? I am sure everyone would like to take a peak!

I know I would.
 
What are your spark plugs Brand/Range...and what are they gapped to? Boost tends to BLOW the spark out under High Load situations.
I recommend nothing but NGK Copper Plugs.

If your plugs are gapped like stock specs....close them up to .028 and report back.

I agree with everyone else....you need less Final Drive Ratio to fully load that bad boy on the big end....mmm SG 3.23's

Good luck.
 
It was limmiting at 5,300 without boost too, so it must be springs or cam.

Mad Dart - I have a pic or two on my members gallery. I will have to take some more pics and post them. I love your set up, do you have any vids of the thing runing? Have you raced it at all?
 
Mopastor said:
It was limmiting at 5,300 without boost too, so it must be springs or cam.

Mad Dart - I have a pic or two on my members gallery. I will have to take some more pics and post them. I love your set up, do you have any vids of the thing runing? Have you raced it at all?
Click to expand...

Ok, I will check them out.

The Twin Turbo build is not finished yet.
 
not enough cam, it just slowly slows down.Springs, it refuses to rev higher. Breaking up either ignition or fuel. Lack of fuel slows down, maybe some pops in exhaust.
I would say ignition.
 
Did it always do that? I would check and see if the intermediate shaft bushing failed, or the gear. Just grab the distributor shaft and see how much play if any by trying to turn the distributor rotor back and forth.
 
How much if any play should there be in the distributor?

It has always done it since putting it in, but the whole combo is new. I didnt realize it till the track because I didnt wind it up that high on the street.
 
I had a worn out distributor bushing in my cuda that did what you are describing. Once I got a new distributor, it ran perfect.
 
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