Dyno #'s LT4 w Hot Cam
Safety Car
Joined: Apr 2005
Posts: 3,624
Likes: 431
From: Dale City VA
You can see it plain as day on the dyno graph starting at 5200 rpm.
I would first suspect old valve springs or inproper spring set up... but something as simple as the rocker/valve train geometry not being correct would also cause it.
Will
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Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 79
From: Monroe OH
NCM Sinkhole Donor
Its got valve control problems.
You can see it plain as day on the dyno graph starting at 5200 rpm.
I would first suspect old valve springs or inproper spring set up... but something as simple as the rocker/valve train geometry not being correct would also cause it.
Will
You can see it plain as day on the dyno graph starting at 5200 rpm.
I would first suspect old valve springs or inproper spring set up... but something as simple as the rocker/valve train geometry not being correct would also cause it.
Will
We think it is fuel related.
Safety Car
Joined: Apr 2005
Posts: 3,624
Likes: 431
From: Dale City VA
On the other hand valve control issues show precisely what you have. Good power to a certain RPM then a choppy curve with power dropping dramatically as the springs cannot recover control of the valves closing event.
Will
Thread Starter
Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 79
From: Monroe OH
NCM Sinkhole Donor
I don't agree. Fuel delivery problems will show up as lean, and increasing the injector dwell time won't fix it.... power output just flatlines nice and smooth like.
On the other hand valve control issues show precisely what you have. Good power to a certain RPM then a choppy curve with power dropping dramatically as the springs cannot recover control of the valves closing event.
Will
On the other hand valve control issues show precisely what you have. Good power to a certain RPM then a choppy curve with power dropping dramatically as the springs cannot recover control of the valves closing event.
Will
Le Mans Master
Joined: Apr 2000
Posts: 5,713
Likes: 105
From: Manassas VA
FWIW when I had a stock bottom end, hotcam, reworked LT1 heads, headers, and factory exhaust, I made 362hp through a 3000 stall converter. It made power past 6000 rpm actually was still making power at 6,200 rpm when we shut it down. Also, this was all done with stock injectors and stock pump.
Looking at your dyno sheet it is really hard to see, but it appears you still have plenty of fuel, you are not going lean.
As Will said, I would check your valve train geomentry first.
Looking at your dyno sheet it is really hard to see, but it appears you still have plenty of fuel, you are not going lean.
As Will said, I would check your valve train geomentry first.
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Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 79
From: Monroe OH
NCM Sinkhole Donor
FWIW when I had a stock bottom end, hotcam, reworked LT1 heads, headers, and factory exhaust, I made 362hp through a 3000 stall converter. It made power past 6000 rpm actually was still making power at 6,200 rpm when we shut it down. Also, this was all done with stock injectors and stock pump.
Looking at your dyno sheet it is really hard to see, but it appears you still have plenty of fuel, you are not going lean.
As Will said, I would check your valve train geomentry first.
Looking at your dyno sheet it is really hard to see, but it appears you still have plenty of fuel, you are not going lean.
As Will said, I would check your valve train geomentry first.
Do you have a good example of the expectation of a similar set up LT4?
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
If so the springs in the kit are the same as the stock springs. Now, if you used the rockers, which I believe are also in the hotcam kit, they are going to be different than the stock rockers, I'm sure you know that.
Another thing to look at would be the lifters and pushrods. Although they would be pretty much the same, if the lifters are older, perhaps they're not keeping up at the top end?
But numbers wise, it seems like it's about where it should be. The Hotcam is a pretty mild cam. I would think that a 40 or so gain at the crank from the cam and the headers should be about right.
Thread Starter
Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 79
From: Monroe OH
NCM Sinkhole Donor
I'm going to go on the assumption that this is a true LT4 as opposed to LT1 w/ hotcam kit.
If so the springs in the kit are the same as the stock springs. Now, if you used the rockers, which I believe are also in the hotcam kit, they are going to be different than the stock rockers, I'm sure you know that.
Another thing to look at would be the lifters and pushrods. Although they would be pretty much the same, if the lifters are older, perhaps they're not keeping up at the top end?
But numbers wise, it seems like it's about where it should be. The Hotcam is a pretty mild cam. I would think that a 40 or so gain at the crank from the cam and the headers should be about right.
If so the springs in the kit are the same as the stock springs. Now, if you used the rockers, which I believe are also in the hotcam kit, they are going to be different than the stock rockers, I'm sure you know that.
Another thing to look at would be the lifters and pushrods. Although they would be pretty much the same, if the lifters are older, perhaps they're not keeping up at the top end?
But numbers wise, it seems like it's about where it should be. The Hotcam is a pretty mild cam. I would think that a 40 or so gain at the crank from the cam and the headers should be about right.
I am content with the gain. What surprised me actually was the torque out put. It was higher than what I thought it would be.
Safety Car
Joined: Sep 2001
Posts: 4,162
Likes: 555
From: Glenbeulah Wi
I also agree that it looks like valve float to me. The fuel pump may be fine, you need to monitor fuel pressure and if it is not dropping the pump is fine. A car will read lean when it starts to have valve float because the O2 sensor looks for oxygen in the exhaust and when the valves start to float there will be more oxygen in the exhaust. This happens combustion process is not complete and some of the fuel/air charge is ending up in the exhaust causing the sensor to read lean when it may not be lean. This is the same thing that happens when you foul a plug, the O2 reads lean but the car is not lean.
Racer
Joined: May 2013
Posts: 278
Likes: 7
From: Long Valley NJ
I used the stock 1.6 rockers that are stock with an LT4.
Yes this is a true LT4. Rebuilt due to spun bearings. Stock LT4 Heads. We used the new springs from the Hot Cam Kit and re-used the stock rockers. I sold the new Rockers in the kit to another fellow.
I am content with the gain. What surprised me actually was the torque out put. It was higher than what I thought it would be.
Yes this is a true LT4. Rebuilt due to spun bearings. Stock LT4 Heads. We used the new springs from the Hot Cam Kit and re-used the stock rockers. I sold the new Rockers in the kit to another fellow.
I am content with the gain. What surprised me actually was the torque out put. It was higher than what I thought it would be.
Drifting
Joined: May 2007
Posts: 1,552
Likes: 324
From: Mid Ohio
l98tpi, I've done some tuning & I agree with the valve control opinions. Something small like pushrod length can change the effective ratio. So it's not necessarily the springs alone.
btw, is the fuel filter new? If its old I'd change it before swapping the pump.
btw, is the fuel filter new? If its old I'd change it before swapping the pump.
Thread Starter
Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 79
From: Monroe OH
NCM Sinkhole Donor
l98tpi, I've done some tuning & I agree with the valve control opinions. Something small like pushrod length can change the effective ratio. So it's not necessarily the springs alone.
btw, is the fuel filter new? If its old I'd change it before swapping the pump.
http://www.youtube.com/watch?v=RjaosX63DkM
btw, is the fuel filter new? If its old I'd change it before swapping the pump.
http://www.youtube.com/watch?v=RjaosX63DkM