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90caprice408 02-20-2013 01:46 PM

very lazy 400
 
I recently built a sbc 408 for my chevy caprice but for some reason it seems to have no bottom end grunt....this is the cam i used for my build Lunati Hydraulic Flat Tappet Camshafts 10120412 - SummitRacing.com ....i used flat top pistons and 64 cc aluminum heads so my compression is around 11:1..i'm running a 3k stall converter with 3:73 gears th350 and a 750cfm carb and air gap intake...I have my timing set at 16 base and 32 total...My question is can anybody point me in the direction as to why this setup has such a lazy low end? it is also my first build so take it easy on me

F-BIRD'88 02-20-2013 02:05 PM

this cam does not get budy till 3000+ rpm. It will have a lot more grunt if you lock out the distributor timing curve. Set the locked timing at 34 to 36deg BTDC.

11:1cr is too much cr for pump gas. thats why you can only run 32deg timing.

The increased idle and low speed timing will really help with this cam.
if it will only take 32deg than you will have to settle for that.
Should have built with lower compression. 10:1 for pump gas.

16deg base timing is going to really suck with that cam.

100 octane unleaded Sunoco GT260 is what this motor needs.


the motor will like a locked fixed timing, with that cam.
The idle and low rpm throttle response will be a whole lot better.

vinniekq2 02-20-2013 02:42 PM

what heads and intake?what headers?

90caprice408 02-20-2013 04:04 PM

Quote:

Originally Posted by vinniekq2 (Post 1648491)
what heads and intake?what headers?


pro comp heads 210 heads with 64 cc and air gap intake....and i used these headers Summit Racing® Headers SUM-G9001 - SummitRacing.com

90caprice408 02-20-2013 04:05 PM

Quote:

Originally Posted by F-BIRD'88 (Post 1648469)
this cam does not get budy till 3000+ rpm. It will have a lot more grunt if you lock out the distributor timing curve. Set the locked timing at 34 to 36deg BTDC.

11:1cr is too much cr for pump gas. thats why you can only run 32deg timing.

The increased idle and low speed timing will really help with this cam.
if it will only take 32deg than you will have to settle for that.
Should have built with lower compression. 10:1 for pump gas.

16deg base timing is going to really suck with that cam.

100 octane unleaded Sunoco GT260 is what this motor needs.


the motor will like a locked fixed timing, with that cam.
The idle and low rpm throttle response will be a whole lot better.

how do i go about locking the timing? and i run a mix of pump gas and 110 octane

vinniekq2 02-20-2013 04:17 PM

very big heads,there you go,,,,and that flat tappet hydraulic is not very good at low RPM. I really dislike big hydraulic flat tappet cams.
you are better off by far using a solid cam when you get this big,or step up to a roller,

90caprice408 02-20-2013 04:28 PM

Quote:

Originally Posted by vinniekq2 (Post 1648526)
very big heads,there you go,,,,and that flat tappet hydraulic is not very good at low RPM. I really dislike big hydraulic flat tappet cams.
you are better off by far using a solid cam when you get this big,or step up to a roller,

so you are saying that the setup i have isn't good for low end torque? and what are the benefits of a solid cam over a hydraulic flat tappet?

cobalt327 02-20-2013 04:32 PM

Quote:

Originally Posted by 90caprice408 (Post 1648460)
I recently built a sbc 408 for my chevy caprice but for some reason it seems to have no bottom end grunt....this is the cam i used for my build Lunati Hydraulic Flat Tappet Camshafts 10120412 - SummitRacing.com ....i used flat top pistons and 64 cc aluminum heads so my compression is around 11:1..i'm running a 3k stall converter with 3:73 gears th350 and a 750cfm carb and air gap intake...I have my timing set at 16 base and 32 total...My question is can anybody point me in the direction as to why this setup has such a lazy low end? it is also my first build so take it easy on me

It's a shame you didn't ask about this combo before you built it! Not ragging on you- just saying.

The best thing to do would be change either the pistons to a d-shaped dish or swap to a larger combustion chambered head, along w/swapping out the cam for something designed to make good low end torque. But if that's not happening, you are going to be saddled w/a camshaft that cannot give the kind of bottom end torque the car would really like to have (big, heavy car = big torque, not necessarily big HP), along w/not being able to give it max power total timing, AND still needing premium gas, possibly mixing in some race gas.

This is one time I will agree to give it a ton of initial timing, even if that means locking the mechanical advance. You can still use (and should use) a vacuum advance. Hook it to ported vacuum if you lock the mechanical advance. Limit the vacuum advance to around 10-12 degrees.

More on locking the mechanical advance, setting up a vacuum advance, wiring an ignition interrupter switch, and timing info in general is here.

vinniekq2 02-20-2013 04:36 PM

When you talk about lazy performance,the first thing I think of is a long duration flat tappet hydraulic,

they idle quite rough and just dont respond as quickly with just off idle throttle response compared to solid flat tappet
Then the top end of a flat tappet hydraulic rolls off at a lower peak rpm and are usually limited to 6500 rpm as far as making good power.
the lobes are more aggressive in a solid lobe and even more aggressive with a roller.

mid range power say 2k - 5500 is about the same with a hydraulic flat tappet and an equal solid

the solid just has a little more on the bottom and a little more on top.

hydraulic cams work good enough for 75% of the people

F-BIRD'88 02-20-2013 04:44 PM

fix the distributor..how you do that depends on which distributor you got. .The cam is fine.

and will really respond well to the locked timing, allowing more idle advance.

post your results when you get the distributor locked out and the carb resadjusted.

Don't forget the GM starter motor brace. If yours is missing get one.

The fact that you are mixing your fuel to get the required octane for this 11:1cr motor
shows you are on the ball. It won't take much to get er dialed in.

re: solid cam. Solid cam rev higher and make more ultimate power.
A big solid cam of comparable .050" duration won;t have any more low end power than the hyd you got now.
a big cam is a big cam.
And 16deg inital is your main problem. It will be a whole different beast with locked out timing 32 to 36deg at idle.

I prefer a solid lifter cam too but my 400 with a very similar hyd cam has a ton of low end response
and will yank the wheels on launch. It has lightning fast and smooth throttle response and plenty of low end.

Big cams, whether hyd or solid, want and need a lot more idle timing than 16deg or they are very lame off idle .

vinniekq2 02-20-2013 05:08 PM

solid Vs hydraulic
 
Quote:

Originally Posted by F-BIRD'88 (Post 1648541)
fix the distributor..how you do that depends on which distributor you got. .The cam is fine.

and will really respond well to the locked timing, allowing more idle advance.

post your results when you get the distributor locked out and the carb resadjusted.

Don't forget the GM starter motor brace. If yours is missing get one.

The fact that you are mixing your fuel to get the required octane for this 11:1cr motor
shows you are on the ball. It won't take much to get er dialed in.

re: solid cam. Solid cam rev higher and make more ultimate power.
A big solid cam of comparable .050" duration won;t have any more low end power than the hyd you got now.
a big cam is a big cam.
And 16deg inital is your main problem. It will be a whole different beast with locked out timing 32 to 36deg at idle.

I prefer a solid lifter cam too but my 400 with a very similar hyd cam has a ton of low end response
and will yank the wheels on launch. It has lightning fast and smooth throttle response and plenty of low end.

Big cams, whether hyd or solid, want and need a lot more idle timing than 16deg or they are very lame off idle .

fbird you know better than that,you know how a hydraulic lifter works and the compromise you get

painted jester 02-20-2013 05:53 PM

Quote:

Originally Posted by vinniekq2 (Post 1648533)
When you talk about lazy performance,the first thing I think of is a long duration flat tappet hydraulic,

they idle quite rough and just dont respond as quickly with just off idle throttle response compared to solid flat tappet
Then the top end of a flat tappet hydraulic rolls off at a lower peak rpm and are usually limited to 6500 rpm as far as making good power.
the lobes are more aggressive in a solid lobe and even more aggressive with a roller.

mid range power say 2k - 5500 is about the same with a hydraulic flat tappet and an equal solid

the solid just has a little more on the bottom and a little more on top.

hydraulic cams work good enough for 75% of the people



I agree:thumbup:


Jester

F-BIRD'88 02-20-2013 07:43 PM

Quote:

Originally Posted by vinniekq2 (Post 1648557)
fbird you know better than that,you know how a hydraulic lifter works and the compromise you get

And you know better (or should know) than to suggest that the problem
here is the camshaft in the motor...hyd solid or other wise.
It was a bad bit of confusing advice for the problem.
Poster: you do not need a new camshaft.
This is simply the nature of a cam this big.

The problem is the 16deg initial timing.

A 246@.050" 108LSA solid lifter cam will very near run the same and needs the same simple cure.

A lot more initial advance.

locking out a HEI distributor: it don't get much simpler. you have to drill and tap a new hole for the Lock out screw, if/when locking out the mech advance. The weights and springs are not re-used
http://www.crankshaftcoalition.com/w...limitlock2.jpg

If you got a MSD billet distributor SMall cap: download and read the directions from MSD on how to disassemble it and lock
the advance system.

F-BIRD'88 02-20-2013 07:57 PM

This has no effect on the vacuum advance system.

two different things.

Use ported vacuum as a source for vacuum advance. Or leave it disconnected if you are not willing to fine tune the vacuum advance system.

painted jester 02-20-2013 09:34 PM

Timings a good guess if the blue print is right, We are assuming the cam was degreed and checks out right but don't know if its advanced, straight up or retarded, Or if the cam has an advance already in the grind, His gears are small should be at the least 4.11s, we don't know if the convertor is washing away his torque, We don't know if the flash torque is too low to use the converter to its potential! Trouble shooting this or any other thread is a guess and elimination puzzle! Ive installed these cams and 16*to 18* initial to 25 or 28 off idle and 34 to 38 in at about 2800 was plenty and never had to lock out the distributors to get good response, With a good flash stall converter, taller gears and the right diameter tires. And lets consider the carb Jetting, power valve, accelerator pumps duration and squirt, timing the secondary linkage! All this seems to be taken for granted its dead on! and narrowed to locking out the dist.

Lunati Hydraulic Flat Tappet, Advertised Duration 300/300, Lift .515/.515, Chevy, Small Block, cam: I dont know why but for some reason a comp or isky etc. of comparable size and specs hyd. or solid blow it out of the water on a naturally aspirated engine at 11 to 1 compression, bring the gears and stall up and that cam will really wake up! Im not saying you cant wake up that engine with that cam but I agree that a solid cam would have been a better choice and I could suggest others!

He never even stated his complaint Is it non responsive off idle when leaving a stop light idling at 600 rpm or is it non responsive at the track leaving the tree staged at 2800 rpm and it falls on its face! Does he stomp it at idle and its sluggish till it hits 2500 rpm! If he could explain his problem better and exactly what his complaint was I think I could come in on this thread with you other guys!

How did you come up with the 11 to 1 compression 90 caprice 408? What brand converter do you run #s? Where are you located (elevation)?


And no that cam is not for low end torque, and it was designed for mid to top end and a shot of N. Its gutless at bottom end, Do you bracket race or did you build for power on the street!

Why did you plan a build like this for your first (just curious) Its one hell of an accomplishment for your first build:thumbup: Who suggested that cam to you?

Jester


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