Too much cam for 6-speed?
10-05-2011, 05:05 AM
#1
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Too much cam for 6-speed? Hey guys!
I recently bought a '95 Formula Firebird with a balanced and blueprinted LT1. The guy who had it was kinda old-school (like me) and I don't know exactly what he did wrong, but it has some issues.
First of all, he used the Crane 2050 cam:
CRN-104241 --- 218@ .498/ 218@ .498 (1.5RR)--- 116 LSA --- 2800-6500
He added the Crane CRN 10308-1 dual springs and 1.6 gold R. Rockers.
There are LT4 heads on the motor. There are hooker headers & Hooker cat-back.
He HAD Accel 30# injectors in it and it was 'fat' (I don't think he had a pcm tune done), so I removed them and put the stock injectors back in it. I saw the last set of plugs he pulled out of it, and they were BLACK- assumably from fuel...
Two main problems:
The car doesn't want to run on the highway, in 6th gear. Anything under 1800-1900 rpms and it seems to be 'over-carbureated' (bucks and lurches when you give it gas.)
Is that a too "big of a cam" issue? I had hoped the stock injectors would help it, but they haven't seemed to.
The first tank of gas (with the 30# Accels) only got 13.5 mpg, on mostly highway driving. I haven't gone through a second tank (with the stockers) yet.
I plan to drive this mostly on the highway, with some visits to the track. If this is the wrong cam for this app, what do you guys recommend?
Also, the CenterForce clutch has a really weird issue going on: When I first take off, it pulls okay, as long as I don't stomp it. BUT, if you give it too much gas, it makes a 'grinding' noise (similar to NOT having it all of the way in gear) and you can feel the car bucking/shaking.
He said his son drove it to college for about a year and this is how it came back...
I am not quite ready to tear it down, but plan to soon. Any ideas as to what parts I will need to have on hand when I do?
I can't just run to the parts store and get a new clutch or pressure-plate, as nobody around here has them on the shelf...
I recently bought a '95 Formula Firebird with a balanced and blueprinted LT1. The guy who had it was kinda old-school (like me) and I don't know exactly what he did wrong, but it has some issues.
First of all, he used the Crane 2050 cam:
CRN-104241 --- 218@ .498/ 218@ .498 (1.5RR)--- 116 LSA --- 2800-6500
He added the Crane CRN 10308-1 dual springs and 1.6 gold R. Rockers.
There are LT4 heads on the motor. There are hooker headers & Hooker cat-back.
He HAD Accel 30# injectors in it and it was 'fat' (I don't think he had a pcm tune done), so I removed them and put the stock injectors back in it. I saw the last set of plugs he pulled out of it, and they were BLACK- assumably from fuel...
Two main problems:
The car doesn't want to run on the highway, in 6th gear. Anything under 1800-1900 rpms and it seems to be 'over-carbureated' (bucks and lurches when you give it gas.)
Is that a too "big of a cam" issue? I had hoped the stock injectors would help it, but they haven't seemed to.
The first tank of gas (with the 30# Accels) only got 13.5 mpg, on mostly highway driving. I haven't gone through a second tank (with the stockers) yet.
I plan to drive this mostly on the highway, with some visits to the track. If this is the wrong cam for this app, what do you guys recommend?
Also, the CenterForce clutch has a really weird issue going on: When I first take off, it pulls okay, as long as I don't stomp it. BUT, if you give it too much gas, it makes a 'grinding' noise (similar to NOT having it all of the way in gear) and you can feel the car bucking/shaking.
He said his son drove it to college for about a year and this is how it came back...
I am not quite ready to tear it down, but plan to soon. Any ideas as to what parts I will need to have on hand when I do?
I can't just run to the parts store and get a new clutch or pressure-plate, as nobody around here has them on the shelf...
10-05-2011, 05:51 AM
#3
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The first thing I would do is get rid of the of the Accel injectors. They are very hard to tune and extremely sensitive. Most good tuners hate them. That is not a large cam but you can be getting some cam surge under 2k. Get a set of SVO 30 injectors and get the car tuned by a repitable tuner and rock on.
10-05-2011, 06:49 AM
#4
The first thing I would do is get rid of the of the Accel injectors. They are very hard to tune and extremely sensitive. Most good tuners hate them. That is not a large cam but you can be getting some cam surge under 2k. Get a set of SVO 30 injectors and get the car tuned by a repitable tuner and rock on.
But.......from experience, I have to say save your money and run the stockers. They'll support as much as you'll get out of that heads/cam setup.
The cam isn't that bad. Definitely not optimum, but will be very streetable and make decent power when you get it tuned. It's definitely not too much cam for a 6 spd.
10-05-2011, 06:51 AM
#5
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That cam is nowhere close to being too aggressive.
I'd visit some mechanical avenues first. New set of plugs and thoroughly examine all plug wires. Check to make sure the waterpump is not leaking onto the opti. Not sure what the grinding issue can be. You may want to pull the trans and check to make sure your throwout bearing, input shaft and pilot bushing and/or bearing are all in harmony with each other.
I'd visit some mechanical avenues first. New set of plugs and thoroughly examine all plug wires. Check to make sure the waterpump is not leaking onto the opti. Not sure what the grinding issue can be. You may want to pull the trans and check to make sure your throwout bearing, input shaft and pilot bushing and/or bearing are all in harmony with each other.
10-05-2011, 07:39 AM
#6
that cam is extremely mild as stated above........that car should run stock with that cam........your issues are in the tune i just installed a 226/234 .600/.600 in my daily driver and after tuning its damn near stock but i started with the issues you described.....get the car tuned 
10-05-2011, 09:26 PM
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Thanks for the insights guys!
I will def get some better injectors, and try new plugs and check wires, etc. I am also headed for a good tune (pcm4less okay or should I buy some dyno time?), and I will be pulling the clutch apart, as soon as I can!
One more question: Can anyone estimate what kind of hp this engine will generate? I know that stock injectors may work fine, but I wanted to calculate the optimal lbs/hr, and need a rough idea of horse power to do that!
Thanks again guys!
I will def get some better injectors, and try new plugs and check wires, etc. I am also headed for a good tune (pcm4less okay or should I buy some dyno time?), and I will be pulling the clutch apart, as soon as I can!
One more question: Can anyone estimate what kind of hp this engine will generate? I know that stock injectors may work fine, but I wanted to calculate the optimal lbs/hr, and need a rough idea of horse power to do that!
Thanks again guys!
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10-06-2011, 04:56 AM
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That's OK!
I wasn't looking for rwhp, but at the crank... Then I can back-calculate the 85% max duty-cycle and make sure that I don't want to go a little bigger on the injectors!
IE- 375 X .07= 26.25 lb/hr. which would make the 30 lb injectors ABUNDANT, but the 24s a little shy. (At least that is what I read...)
Anyone else?
I wasn't looking for rwhp, but at the crank... Then I can back-calculate the 85% max duty-cycle and make sure that I don't want to go a little bigger on the injectors!
IE- 375 X .07= 26.25 lb/hr. which would make the 30 lb injectors ABUNDANT, but the 24s a little shy. (At least that is what I read...)
Anyone else?
10-06-2011, 07:57 AM
#11
For street and strip use, your stock injectors are fine for that cam and heads.
I know the popular calculations will tell you that you need more; I'm just speaking from experience. When I see 500 rwhp with a set of 30 lb injectors at an AFR of 12.8, the theoretical duty cycle is far beyond 100%, so I know the assumptions/calculations about how these injectors work is flawed.
You should get about 330 rwhp with your present combo when you get it tuned right. Your stock injectors are good for that. Only if you're going to be roadracing it or some other extended high rpm/WOT operation, then I'd install SVO 30's and tune it for them.
I know the popular calculations will tell you that you need more; I'm just speaking from experience. When I see 500 rwhp with a set of 30 lb injectors at an AFR of 12.8, the theoretical duty cycle is far beyond 100%, so I know the assumptions/calculations about how these injectors work is flawed.
You should get about 330 rwhp with your present combo when you get it tuned right. Your stock injectors are good for that. Only if you're going to be roadracing it or some other extended high rpm/WOT operation, then I'd install SVO 30's and tune it for them.
