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wont rev past 6k

4K views 33 replies 12 participants last post by  406 ss monte 
#1 ·
ive posted this thread before but couldnt find a problem so im posting it again to see if anyone can tell me why my motor wont spin past 6k... 355sbc, holley aluminum heads (190intake runners, 2.05 valves) holley dual plane intake, lunati solid roller cam (.502/224deg@50 in.... .502/232deg@50 ex) cam (slightl;y retarded... roller roller rockers (1.5) holley 650 double pumper w/ proform 750 centerstock block .040 over. msd billet distributor, msd digital6, blaster 3 coil w/ 45deg advanced timing.... everything should turn past 6 fine.. but when you hit 6k it just flat lines... wont rev past.... feels like a rev limiter.. the motor turns hard all the way up.. no dieing off... ive checked the rev limiter and thats not the problem... any ideas?? also i was thinking of going to a victor jr intake... but if it wont turn 6 i was thinking im better with a dual plane right?? or could that be the limiting factor??
 
#4 ·
most dual planes are only good to about 5500.
some "rpm models" will advertise flow up to around 6500. i don't believe that one though. are you regularly in the 6000 or higher?
or better yet, rarely in the idle to 2500, if these are both yes; you need a different intake

i am not sure about the hard line that you are hitting that sounds like either cam or distributor breaking down.
you mentioned a rev limiter, what is the model of your msd?
is the limiter built in like in the 6al or is it in a seperate rev box?
msd stuff will run without the limiter pills.
can you test run it without any pills or limiter hardware?

31
 
#5 ·
"most dual planes are only good to about 5500.
some "rpm models" will advertise flow up to around 6500. i don't believe that one though. are you regularly in the 6000 or higher? or better yet, rarely in the idle to 2500, if these are both yes; you need a different intake."


While most dual plane intakes don't make power past 5500-6500 rpms, they will surely rev past that if everything else is right. I've revved my 327 and 350 well past 7000 with the factory Z-28 dual plane intake. I think his problem is with the valve timing or as mentioned, valve spring float.

tom
 
#6 ·
I agree it sounds like valve float. Did you buy the recommended springs for the cam?

What do you have for a timing chain? You might want to try borrowing a larger carb to see if that helps as well.

Royce
 
#7 ·
i was not implying that it would hit a wall @ 6000 with a dual plane ,
i was responding to his question of wheteher he had the right intake. i was trying to contribute to a question that no one had answered for him. that is why i asked what range he would normally run in
also i was thinking of going to a victor jr intake... but if it wont turn 6 i was thinking im better with a dual plane right??
if you read my post, it also talked about other components that might be breaking down.

31
 
#9 ·
theyre dual valve springs.. not sure exaccally of the brand and such but i know theyre good quality and dont see why it should be the springs... im going to try backing off the timing a little tomorrow... i didnt degree in the cam... im running a gear drive so it was slightly retarded when we installed it (couldnt get it dead on)....

as for the intake its a street car kind of... as in its a drag car that i drive on the street... should stay near 2500 in regular driving... but my main question is will i bennifit at the drag strip??
 
#10 ·
Well you answered with what I expected, for a high rev'ing engine I do not think a gear drive is the best choice. It could be a harmonics problem due to the gear drive. Don't get me wrong I don't have anything against them I have run them in the past and will again but, not on a high winding (6500 ++) engine. Since you are falling on your face at 6000 I doubt it is the gear drive and more than likely the springs.

Just because they are dual springs that doesn't mean they are going to work with a big solid roller. The spring pressures are more important than being single, dual or triple. If the springs are not controlling the lifters then you will have valve float and this will limit your RPM level. Not to mention if the springs are not up to the task you run the risk of stressing/breaking them and that will get expensive in a hurry. Solid rollers typically have aggressive ramps this means the springs take a beating and need to match the cam very well.

Royce
 
#11 ·
corona jon said:
theyre dual valve springs.. not sure exaccally of the brand and such but i know theyre good quality and dont see why it should be the springs... im going to try backing off the timing a little tomorrow... i didnt degree in the cam... im running a gear drive so it was slightly retarded when we installed it (couldnt get it dead on)....

as for the intake its a street car kind of... as in its a drag car that i drive on the street... should stay near 2500 in regular driving... but my main question is will i bennifit at the drag strip??
[/QUOTE
They may be very good springs but if they are for a flat tappet cam they might be no good for your solid roller. To add to what camaroman said roller lifters normally are quite a bit heavier than flat tappets. It takes a lot of spring pressure to keep the rollers on the cam rather than fly over the nose and bounce when the land. This is why many people run a rev kit with solid rollers.
 
#14 ·
I garantee it is valve float. If it is the dual spring that comes on hollys heads, it is 125# and for a hyd. roller. You need something in the 180#on the seat and around 500# open.

Now for the bad news, if you have rapped this thing a few times or have some run time on it. The valves have probly tuliped and will need to be replaced due to the bouncing on the seat that incurred. I would take this thing apart and check.

Chris
 
#15 ·
Cstraub said:
I garantee it is valve float. If it is the dual spring that comes on hollys heads, it is 125# and for a hyd. roller. You need something in the 180#on the seat and around 500# open.

Now for the bad news, if you have rapped this thing a few times or have some run time on it. The valves have probly tuliped and will need to be replaced due to the bouncing on the seat that incurred. I would take this thing apart and check.

Chris
Chris,

It is only a .500 lift cam. There is no way he needs 180# springs IMHO. The #125 should be more than enough concidering it is a hydraulic flat tappet and the cam will crap out by 6500. It does sound like valve float, but I cant imagine #125 springs being the problem. I run #115 springs on my .500 solid cam with 6500RPM shifts and no float.

Chris
 
#19 ·
One other point it is not always the amount of lift but, how fast it gets to that lift number. Aggressive ramps need stronger springs.


As far as spring recommendations, look up the spring specs for your specific cam and then buy a set of springs from your favorite manufacture (K-Motion, Isky, Crower, Comp, etc...).

Cstraub, I agree I would pull it apart those valves have probably taken a beating (along with the seats).


Royce
 
#20 ·
called up jegs and ordered some springs for it.. i talked to the guy i bought the heads from and they were the springs that came wit the head... the new ones are 190#seat/515# open...

now as far as installing springs on the head still on the block hows that go?? air pressure in the spark plug right??
 
#22 ·
what about using the piston compression to hold them?? changing a pair at a time and turning the motor to compress each cylender... bad idea?? kind of a crowded work area.. looking for the easiest way (hoping im not going to have to pull the motor to take off the valve cover :))
 
#23 ·
You can use a length of nylon/cotton rope as well. Remove the rockers and spark plugs, feed the rope into the cylinder rotate the engine until the rope is pressed against the valves, remove and replace the springs, rotate the engine backwards and pull the rope out, move to the next cylinder. Make sure you leave a pig tail hanging out so you can pull the rope out. You want to use enough rope so that it bunches up on top of the piston. Keep in mind the rope has to be a small enough diameter to fit through the spark plug hole.

I prefer that method because you don't have to worry about breaking the seal (as with air) and dropping a valve into the cylinder.


Royce
 
#25 ·
it surprises me that it ran as long as it did without screwing something else up bad. you are going to check out your valve's an't you? look at the seats too, they might have been trashed. as fare as the cam goes, how heavy is the car? what size stall? street car or drag car? what rear gears? you could just go to a 1.6 rocker & gain more lift with the same cam you have.
 
#26 ·
YOu just ordered the springs for your current cam, correct? If this is the case why would you change cams? Does the new cam you are looking at require the same springs? You don't know how the car is going to run with the proper springs, it might be just what you are looking for. It's your car do what you want but, personally I wouldn't change the cam (yet), unless you have a specific reason/goal.

Royce
 
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