Too much gear?

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gtsdude said:
Is it possible I am just reving right through the power and I need a 4.10 or 3.91 gear?
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Seems like there's a lot of "let's throw parts at" solutions here. It's all just speculation without real data.

Getting the thing on a chassis Dyno would tell you exactly what the Hp curve looks like and where you should be shifting. It would also give you an opportunity to play with timing and A/F. You might find out you have a completely unrelated issue causing the power loss.
 
JBurch said:
Interesting hypothesis......spelled out like that it makes sense; how would you prove it?
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Have some one put it on a flow bench to prove it is crashing at or after .500 lift. Then get them to port it so it don't crash (loose flow) at his lift (.557)... test on car. (There is so much more to this)
That is, making the bowl/valve/chamber hold above .500 lift.
Install it. If the et mph jump, probably the problem. (or you could do like i did and buy a better flowing, more efficient head the flow above .562 lift, my lift)
Then you would have to put to old cam in and see if it make less HP BUT make more them before.
Dont mistake me for a head porter, or someone that knows what he is doing.......I'm not that guy. I have experiment on the j head for 2 years(back in 2012) and never installed it on anything. so i really don't know.
 
if he is running out of gear...the car will still et pretty close to what it had run previously but the mph will be down....in his case both are off.....lack of power or something not right
 
After lash the cam is around .535 lift if I remember right. And it was pretty close to same et, 13.42 to 13.55
 
gtsdude said:
Yep matching springs with cam change. I checked timing at the track. 18 initial 34 total. I did use a new dial back light. Going to double check with my old light to make sure it reads the same
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Could it be that the "matching springs" were not set at the recommended installed height? like using longer valves than stock(gm .100 longer valves) and spring install height was designed for standard height?
Valve starts to float, top rpm lost, slower mph.
 
They were set at 1.66 and they usually seat in another .10-.20, it's stock 1.68
Valve height springs. Going to pull valve covers and check them as well
 
gtsdude said:
They were set at 1.66 and they usually seat in another .10-.20, it's stock 1.68
Valve height springs. Going to pull valve covers and check them as well
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Did you have the guids cut down? running a valve seal? how much more lift do you have before it hits the valve seal?
 
Yeah guides were cut, has valve seals too, I can't recall how much room there was, might have it wrote down some where.
 
gtsdude said:
Yeah guides were cut, has valve seals too, I can't recall how much room there was, might have it wrote down somewhere.
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ok, just make sure you have valve retainer clearance at max lift.
 
do you have 60 ...330 ...1/8 and 1000 ft times to compare to the old combo?
 
Yeah I did check the retainer clearance before the cam went in. Yes I have some slips, I'll pull them out when I get home.
 
I ran the same cam (296/557) in my Demon. It had ported J heads, Holley Strip Dominator intake ,750 Holley, Carter mechanical fuel pump,1 5/8 headers , 4.88 gears. The car was stock weight with bench seat full interior , 3 inch exhaust with Flowmaster mufflers driven to track.It ran a best of 7.10 @ 95 mph in the 1/8 shifting at 6300 rpm. According to the Wallace calculators that should be around 11.18 at 118 mph. I think you have something holding you back.
 
I am hoping I find something simple, throttle not wide open or new timing light not right.D50 what size rear tire
 
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A fresh 340 with a 280° cam that is struggling to reach mid 13s with exhaust, and can't rev? You have a problem with the combo. My opinion is the heads. I'd expect that combo to be 2-3 tenths faster than it is with the exhaust on it and it should rev way past 6500 as is.
 
Just my thoughts. You have advanded the cam 4 degrees and my understanding is now days most cams are ground with around 4 degrees advance so if you're running 8 degrees advance that will kill your top end.
 
Retroboy said:
Just my thoughts. You have advanded the cam 4 degrees and my understanding is now days most cams are ground with around 4 degrees advance so if you're running 8 degrees advance that will kill your top end.
Now a days is correct, except the old MP 557 cam grind is 30 + years old...LOL...Have used several of them...also advance them 4 degrees..
a lot of times the 1st time out with a new combo..It never runs what you thought or hope it would....Start checking the basic
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gtsdude said:
Exhaust is 2.5 to muffler, choke
Masters, factory tail pipes on it. 2 1/4 or smaller in the bends. I knew it killed the old cam a little, didn't think it would kill this on that much. I am going to check the throttle again to make sure.
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This is definitely an issue.
 
The exhaust is not a major contributing factor IMO. My stock everything but cam and headers 340 with a smaller 268° advertised hydraulic would pull to 7K. Not just rev, but pull. Stock Thermoquad intake, Thermoqaud carb, '68 long block, stock electronic distributor and Jacobs Energy Team running it. In an E body it went 13.0s with me rowing it. That was in the 80s before really good mufflers or pipe larger than 2.25" was the norm. Yes, gains are to be had - but there's something sick with it if it can't go into the 12s even without the pipes and the smaller cam. I think it's a porting or valve job issue.
 
Well I checked timing with my other light, it was same as the other one. Throttle is going wide open also. Valve Springs all look good, measured with caliper are still 1.68-1.70 installed height. The lash however was off on the few I checked, like over .030, didn't have a lot of time to mess with it but I will run all the valves and check where they were at. I also checked my header gaskets, passenger side had a leak on #2, will have to put news ones in. I also did a compression test and got 190-200 with one at 185. Does that seem high? My old cam was advanced 4 degrees and was [email protected], compression test on that was 180-190, I thought this cam would be lower with more duration? Will too much lash cause more cylinder pressure? Making a bigger cam act smaller? Think I will check it again after lash is set.
 
roccodart440 said:
This is definitely an issue.
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Op said that his et is better by .2 to .3 tenths better when he uncorks it. Sooo there is an issue!

Just to Throw Mud in the water....... My 408 has/had a 2.5" exh, full lenght, up and over the axle and dumped at the bumper. I showed NO improvement with or without the headers open.(just made more noise) Added a 10.5" collector to header(open exh) and killed a tenth.
His .2 to .3 improvement was with his old cam, don't think he has tried it with new cam.
open exh or a better exh system(3") will help his ET, But is not why he lost 4 mph.

Gears? could be. Head flow? could be Or maybe this cam just wants more timing.(ignition timing)
before and after ET slip could really shed some light on the problem. ET slip is a Cheap Dyno! LOL
 
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Your cylinder pressure is fine. Do you degree your cams when they are installed (sorry if I missed that)? More lash will add cylinder pressure, but don't go too crazy because you can have problems with too much rattle space in the valvetrain. The rest of your stuff sounds good. It seems like you're just not getting air through the heads effectively.
 
Cudafever said:
His .2 to .3 improvement was with his old cam, don't think he has tried it with new cam.
open exh or a better exh system(3") will help his ET, But is not why he lost 4 mph.
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Agreed. IMO even the smaller cam should have gone the number. Bigger just made the problem worse. Also agree on some track testing. Compare incrememtals too.
 
Yeah I degreed the cam. I wonder if it is getting into a little detonation and I just can't hear it with the solid cam?
 
gtsdude said:
Well I checked timing with my other light, it was same as the other one. Throttle is going wide open also. Valve Springs all look good, measured with caliper are still 1.68-1.70 installed height. The lash however was off on the few I checked, like over .030, didn't have a lot of time to mess with it but I will run all the valves and check where they were at. I also checked my header gaskets, passenger side had a leak on #2, will have to put news ones in. I also did a compression test and got 190-200 with one at 185. Does that seem high? My old cam was advanced 4 degrees and was [email protected], compression test on that was 180-190, I thought this cam would be lower with more duration? Will too much lash cause more cylinder pressure? Making a bigger cam act smaller? Think I will check it again after lash is set.
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Just something to think about.
If you are gaining clearance, something is wearing. rocker shaft, rocker arm bushing, pushrod bending, adj getting pounded to death or cam lobe is bad.

Losing adj clearancing? Valve is receding into the seat.

OR you were not as precise setting the first time as you may have thought.
 
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gtsdude said:
Yeah I degreed the cam. I wonder if it is getting into a little detonation and I just can't hear it with the solid cam?
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Pull some spark plugs and see if there is spec's on the ceramic. if so you are detonating. If the ceramic is dark, you're too rich!
 
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