Valve Float?
Sorry to say this, but I think your restriction is the headers. I mean the primaries are only 1 1/2" on those things with a 2 1/2" collector. Doesn't matter that you stepped it up to 3 further down the line, it will only flow as much as your highest restriction. With a higher cube motor with more cam it really must be having a hard time breathing. I would look more into headers. Remember to also compare fitment of Ford 302 and 351 headers being the tube spacing is identical. You would just need to shape the port and weld the LS flange to it.
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Thread Starter
Teching In
Joined: Sep 2012
Posts: 40
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yeah...Im trying to find a decent set of used pacesetter headers. I will have to modify them a bit to fit. header choices for my "car" are difficult and these are really the only ones people use on this swap
Thread Starter
Teching In
Joined: Sep 2012
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to me these numbers seem low. I have just been looking at all the other 383 with ms4 and they are getting high 4xxhp & tq. Its hard for me to believe that my shorties are holding back 60-70 hptq. My power is dropping off so early and all the others are pulling into mid 6k rpms
Thread Starter
Teching In
Joined: Sep 2012
Posts: 40
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You have to call them to get these. They have some sort of deal with broken kitty and johns cars. It was a hassle to get these without getting them through those guys. I had to actually get johns cars to call them. I will snap a picture of
Me measuring the primaries. My spark plug wires barely fit in between these things
Me measuring the primaries. My spark plug wires barely fit in between these things
TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
The problem doesn't look to be valve float to me. Power is peaking about 5400 RPM, thats about 1000 rpm before it should be. Max torque is about 4900 and max power at 5400, only a 500 RPM spread indicates a problem, it should about 1500. Even if you springs were a little too light, I would not expect valve float so early. It looks choked. Are you running a free flowing exhaust after the headers? It is either somthing on the intake side, exhaust side, or somthing drastically wrong with the valve train.
I have had underperforming engines before, but usually the power peak lies close to the peak I would expect for that cam profile. MS4 is a monster stick IMO even on a 383, and should be sidnificantly higher.
I have had underperforming engines before, but usually the power peak lies close to the peak I would expect for that cam profile. MS4 is a monster stick IMO even on a 383, and should be sidnificantly higher.
Scotty just triggered a thought. Did you degree or cam doctor the cam prior to installing it? It's possible your cam grind isn't what you think it is or something in the cam timing isn't right IE wrong advance ground in or a miscut keyway on the crank etc.
yes that is exactly what mine looks like on the dyno above. My shorty headers I know are holding me back but with the same build with the same headers on other 280z they are making high 400and close to 500hp. I only have so much space on the sides of my engine bay. I am currently modding some longtubes. but yes I almost thought that you somehow got ahold of my dyno sheet. My pushrods are also 11/32 7.57. I wonder if the extra weight may be putting extra stress on the springs...next time i go back to the dyno Im going to go with my 7.55 5/16 pushrods as well.
Also these super high open pressures over 400lbs will over time chew the valve stem tips up from an improper wipe pattern on the tip of the valve. This is why Brian Tooley recommends no more than 400lbs of open pressure on stock rockers. With a stock rocker it is so light that even with some of the most aggressive hydraulic lobes available today it is still plenty sufficient for controlling them.
Also more than 400lbs open pressure with aftermarket rockers on 5/16" push rods will start to "pogo" the push rod as it deflects from too much over the nose weight and too much spring pressure. I know you don't have aftermarket rockers, but it's good information to put out there.
I might of missed it but what intake manifold are you using?
I agree the headers are choking it and not allowing it to pull to the rpm peak it should with that cam. I don't see any valve float in that graph either.
No one asked what kind of dyno was this? SAE correction factor being used?
What ICL did you install the cam at or is it straight up? If it hasn't been degree'd in with a degree wheel I'd do that and see if it's correct.
Well I wasn't too concerned with dyno brand or model, as both his combos were on same one , so apples to apples in my eyes.. Something's off , and i don't quite believe its the headers.. But anything is possible.
Just was trying to cover all scenarios. Human's operate the dyno and things can be overlooked.
humans ? Wtf are th0se?