408 stroker rpm questions

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Jake1974dart

Jake1974dart

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Ok this is my first post so hope this works. I have a 408 striker that I recently built but the motor seems to fall on its face at 4900 to 5000 and I don’t want to rev past that it has a carter 600 afb carb with an edlebrock LD340 intake and stock 360 smog heads with comp pro comp rocker arms with a .480 lift comp can a 2.5 inch exhaust with headman headers. Do any of you guys know what rpm it should fall off at ?
 
take a pick.....smog heads....600 cfm carb with ld340.....being chocked to death.....motor needs to breath....put a straw in your mouth and run 440 yd dash......

duration on camshaft....???
 
70aarcuda said:
take a pick.....smog heads....600 cfm carb with ld340.....being chocked to death.....motor needs to breath....put a straw in your mouth and run 440 yd dash......

duration on camshaft....???
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226 duration at 50 Andy I have a set of non smog heads that I want to do a gasket match port job on and what’s the difference between the smog heads and the non smog heads ?
 
There is no better to expect with stock heads and a small carb. What works on a 318 is MUCH to small on a 408.
Almost no matter what cam you put in there... it will just make the midrange peak higher (someone said light switch power
recently).
In order to make the engine rev higher you have to do something to make it breathe... and that is cylinder heads. Ported iron
or some aluminum heads would be the first step. Even stock aluminum heads like the ubiquitous Edelbrock heads will be done
by 5500RPM most likely ... so you are getting the picture.
 
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Jake1974dart said:
Ok this is my first post so hope this works. I have a 408 striker that I recently built but the motor seems to fall on its face at 4900 to 5000 and I don’t want to rev past that it has a carter 600 afb carb with an edlebrock LD340 intake and stock 360 smog heads with comp pro comp rocker arms with a .480 lift comp can a 2.5 inch exhaust with headman headers. Do any of you guys know what rpm it should fall off at ?
Click to expand...

It falls off where you built it to fall off; small cam, small heads, small exhaust, small intake........will say this, you built a good truck engine
 
If it’s really falling on its face at 4900-5000, it’s more than likely a “problem” other than a combination issue.
Without knowing how the heads are set up, I’d lean towards floating the valves myself....... especially if it feels the same, at the same rpm point, in every gear.
Other possibilities are fuel or ignition woes.
 
That cam is ridiculous small and if you have the matches springs on the ridiculous small head, your getting what I would expect.

Your short comings are huge and it’s all the equipment that your using. Everything is to small.
Everything.

Carb, go to a 750
Intake, if it isn’t modified, modify it or swap to a RPM. Port the runners.
Cam; You can use a better cam with way more lift on better....
Heads; Smogger heads will perform like smogger heads unless you dump in $2500. Save money and step up to the new Trick Flow heads.

After all this spending, you’ll add a hundred hp and 1000 - 1500 rpm.
 
Does the engine still have factory connecting rods, also? If it does it won't survive at more than 5000 rpm, for any length of time. Maybe leave it alone and call it done?
 
PRH said:
If it’s really falling on its face at 4900-5000, it’s more than likely a “problem” other than a combination issue.
Without knowing how the heads are set up, I’d lean towards floating the valves myself....... especially if it feels the same, at the same rpm point, in every gear.
Other possibilities are fuel or ignition woes.
Click to expand...
PRH said:
If it’s really falling on its face at 4900-5000, it’s more than likely a “problem” other than a combination issue.
Without knowing how the heads are set up, I’d lean towards floating the valves myself....... especially if it feels the same, at the same rpm point, in every gear.
Other possibilities are fuel or ignition woes.
Click to expand...


valve springs sounds likely to me , lots of parts need upgrading as stated in other posts in order to get the most performance from your stroker . Also lifters could be a problem causing valves to float .
 
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True, valve springs control rpm to a large degree.
 
Many times there can be problems in how someone perceives what’s happening, and then trying to describe that to someone else.

My interpretation of “falls on it face” is not what would typically be experienced by a motor combo just having a small cam and carb, and a mild dual plane intake(not including stuff like the sp2p or offy dual port 360).
The combos where the cam, carb, intake, etc are just “small” feel like they just “flatten out” when you start to get beyond the normal operating range of the combination.

I used to be involved with some 360 oval track motors that had to use unported stock heads(1.88/1.50 valve rule), stock 2bbl intake manifolds, and a 2bbl carb.
Granted they didn’t have small cams in them....... but the stock heads and 2bbl intake and carb were still making reasonable power at 7k, which is how high the motors were run in the car.

“Runs into a wall” is usually indicative of a “problem”.

I just did a little work on a 360...... that had the “runs into a wall” condition.
Owner said it just wouldn’t go over 5100.
Even had it on a chassis dyno...... power dropped off a cliff at 5100.

Hyd cam..... unhappy lifters.
Had plenty of spring.

I put in a solid cam..... peak hp now around 6100...... power hangs on good to 6700....... same springs and rockers, intake, carb, etc.
 
Ok I finally got logged back in and I have a 750 Holley I going to rebuild and the LD 340 intake has been ported and massaged already and I have a set of iron heads I want to port match. I don’t know what spring pressure I am running but I know it matches with the cam. The rods and crank are from scat with Keith black pistons. I am trying to stay low budget with this build thank you guys for your input this is my first built motor and needs improving obviously. I greatly appreciate your input.
 
RedB. said:
valve springs sounds likely to me , lots of parts need upgrading as stated in other posts in order to get the most performance from your stroker . Also lifters could be a problem causing valves to float .
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rumblefish360 said:
Did you degree the cam in ?
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no I had a shop build the bottom end and put the cam in I put the heads and intake on
 
Jake1974dart said:
no I had a shop build the bottom end and put the cam in I put the heads and intake on
Click to expand...
You're doing fine. I started the same way. Almost the same way I should say I went with two Edelbrock carburetors on a dual quad intake that I still have and love. The important part is you have a nice quality short block and can build from there as time goes by. You don't have to do it all at once. It's expensive that way. There's many people out here will tell you to buy this and buy that and buy this and buy that like your money comes off a tree out in the backyard. I say to them why no s*** Sherlock if I had that budget I would I would have bought all that crap to begin with... read on what other people are doing take other people's suggestions with a grain of salt and continue to do what you can when you can. I'm personally have reground my cam three times trying to find The Sweet Spot of where I like things to be. It becomes part of the fun of the hobby. The one thing I did like you did was have a machine shop build the bottom end and balance it nicely so you have a nice Foundation you can play with. I do agree whatever you can do to make it breathe better or improve..
 
j par said:
You're doing fine. I started the same way. Almost the same way I should say I went with two Edelbrock carburetors on a dual quad intake that I still have and love. The important part is you have a nice quality short block and can build from there as time goes by. You don't have to do it all at once. It's expensive that way. There's many people out here will tell you to buy this and buy that and buy this and buy that like your money comes off a tree out in the backyard. I say to them why no s*** Sherlock if I had that budget I would I would have bought all that crap to begin with... read on what other people are doing take other people's suggestions with a grain of salt and continue to do what you can when you can. I'm personally have reground my cam three times trying to find The Sweet Spot of where I like things to be. It becomes part of the fun of the hobby. The one thing I did like you did was have a machine shop build the bottom end and balance it nicely so you have a nice Foundation you can play with. I do agree whatever you can do to make it breathe better or improve..
Click to expand...
Thank you just on step at a time honestly just gotta get the heads ported now n let this thing breath better while I save now lol definitely happy I joined here so I can get advice though
 
It will end up being a restriction, but your intake should be good until you have some pretty good flowing heads/cam. For instance my combo has almost a full effort cast x head with eddy 800 cfm avs and a moderate to serious flat tappet cam running high 11’s through a 68-69 340 stock intake with the divider cut out. Of all the top end parts you have you could live with the intake the longest. I chased a bad hyd lifter for awhile also. Would stop pulling at 4800 rpm. Went to solid lifter and problem solved.
 
furrystump said:
It will end up being a restriction, but your intake should be good until you have some pretty good flowing heads/cam. For instance my combo has almost a full effort cast x head with eddy 800 cfm avs and a moderate to serious flat tappet cam running high 11’s through a 68-69 340 stock intake with the divider cut out. Of all the top end parts you have you could live with the intake the longest. I chased a bad hyd lifter for awhile also. Would stop pulling at 4800 rpm. Went to solid lifter and problem solved.
Click to expand...
The intake has a gasket match and the plenum removed already so that’s good to know that it will still work later on down the line
 
My suggestion is...... before changing any parts....... bring the car to a chassis dyno and make a few pulls.
Let’s see what the power curve looks like from 4000 and up.
 
PRH said:
My suggestion is...... before changing any parts....... bring the car to a chassis dyno and make a few pulls.
Let’s see what the power curve looks like from 4000 and up.
Click to expand...
I am going to a dyno after I swap to a 8 3/4 with better gears once that happens I’ll post the dyno graph here
 
what distributor do you have in it.?
what is your base timing ?
and what is your ignition timing reading at 3500 rpm?
 
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