Please help me choose...
06-14-2001, 04:30 AM
#1
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Car: 1992 RS
Engine: 305
Transmission: 700R-4 when it works
Please help me choose...
Hi,
I just built a 383.It has 9.7:1 (measured) compression, GMPP Vortec heads,Crane Cam-Energizer 274 w/218* duration @.050 and .450 lift with 106* lobe centers.
Intake is an Edelbrock Performaer RPM, exhaust is handled by Flowtech Afterburner headers with 3" pipe leading into 3" flowmaster 40 series mufflers.
Rear end is a 3.42, tranny has ~2500 stall convertor.
This is for my G Body.
I have tried a carter 625 CFM and it was just too small, the engine really suffered above 4500. I put on an Edelbrock 750 Manual choke but I was wondering if I should spend the time and the money to tune the Edelbrock or should I switch to a Holley Street Avenger 770 CFM, or maybe a Holley 750 DP, or...(insert suggestion here
)
Thanks for any help.
If there is not enough info. Please respond and I will add what I can.
------------------
LOBC-- SS-84
92 RS Heritage package with a 305
84 El camino
[This message has been edited by SS-84 (edited June 14, 2001).]
I just built a 383.It has 9.7:1 (measured) compression, GMPP Vortec heads,Crane Cam-Energizer 274 w/218* duration @.050 and .450 lift with 106* lobe centers.
Intake is an Edelbrock Performaer RPM, exhaust is handled by Flowtech Afterburner headers with 3" pipe leading into 3" flowmaster 40 series mufflers.
Rear end is a 3.42, tranny has ~2500 stall convertor.
This is for my G Body.
I have tried a carter 625 CFM and it was just too small, the engine really suffered above 4500. I put on an Edelbrock 750 Manual choke but I was wondering if I should spend the time and the money to tune the Edelbrock or should I switch to a Holley Street Avenger 770 CFM, or maybe a Holley 750 DP, or...(insert suggestion here
)Thanks for any help.
If there is not enough info. Please respond and I will add what I can.
------------------
LOBC-- SS-84
92 RS Heritage package with a 305
84 El camino
[This message has been edited by SS-84 (edited June 14, 2001).]
06-16-2001, 11:20 AM
#3
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Car: 4
Engine: 6
Transmission: 5
The 750 should be OK.
That's a really lame cam, I think you might find that it is holding you back more than the carb. It is a major mismatch to the rest of your intake tract. In fact, I don't think that the 625 was really the problem that made your engine run out of breath, it's the cam.
The way to pick a cam is to figure out what RPM range you want it to run best in, and choose the .050" duration on that basis; then look for one with the most lift (highest flow) and least "advertised" duration (remember that the number of degrees difference between "advertised" and .050" duration amounts to "leakage" of cylinder pressure) as possible, with lobe centers as appropriate for the induction system. In the case of a 274° "advertised" cam, look at the Comp XE274H, and compare its numbers to the one you've got. I think you'll see how poor a cam that particular Crane is. Unfortunately Comp's cam spec page seems to be broken at the moment so I can't post the numbers; but if you go to their catalog at www.compcams.com and look up the XE268H10, compare its numbers, that's a far better match for the rest of your combo.
------------------
"So many Mustangs, so little time..."
ICON Motorsports
That's a really lame cam, I think you might find that it is holding you back more than the carb. It is a major mismatch to the rest of your intake tract. In fact, I don't think that the 625 was really the problem that made your engine run out of breath, it's the cam.
The way to pick a cam is to figure out what RPM range you want it to run best in, and choose the .050" duration on that basis; then look for one with the most lift (highest flow) and least "advertised" duration (remember that the number of degrees difference between "advertised" and .050" duration amounts to "leakage" of cylinder pressure) as possible, with lobe centers as appropriate for the induction system. In the case of a 274° "advertised" cam, look at the Comp XE274H, and compare its numbers to the one you've got. I think you'll see how poor a cam that particular Crane is. Unfortunately Comp's cam spec page seems to be broken at the moment so I can't post the numbers; but if you go to their catalog at www.compcams.com and look up the XE268H10, compare its numbers, that's a far better match for the rest of your combo.
------------------
"So many Mustangs, so little time..."
ICON Motorsports
06-16-2001, 12:42 PM
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Car: 1992 RS
Engine: 305
Transmission: 700R-4 when it works
I appreciate the response.
When i switched from the Carter 625 to the edelbrock 750. I felt a major SOTP difference. The engine pulled through the rpm range a lot better, a lot faster.
With the carter installed it felt like I hit a wall at 4500 rpm. Now I can rev through 6000 rpm.
The cam was choosen to allow cylinder pressure to leak off in the low rpm range to allow running 87 octane fuel with a true 9.7:1 comp. ratio and iron heads. This was achieved. I can run 87 octane and the intial timing is set for 14*btdc.
The other objective to the cam choice was to maximize duration and stay below .450" lift. The vortec heads can only handle .470" lift (leaving .060" clearance before the retainer hit the guide and coil bind). So i decided on a .450 max so as not to strain anything or incur more machine shop bills. The vortec head flows great at low to mid lift, it really does not make sense to take a stock vortec head and spend the money to run a .500" lift cam. Is there a better cam choice that will fit the bill and give me the explosive torque of the Engergizer 274?
Back to the carbs, I am expieriencing a mojor bog off idle with the Edelbrock. I have moved the accel. pump push rod to enable a faster shot. It helped but I think I am going to have to increase the shooter size, Does this sound correct?
Also, with a calibration kit costing ~$50 and the fact that I can not find the shooters for the accel pump anywahere should I switch to the more popular Holley? If so which one?
Thanks for any help.
------------------
LOBC-- SS-84
92 RS Heritage package with a 305
84 El camino
When i switched from the Carter 625 to the edelbrock 750. I felt a major SOTP difference. The engine pulled through the rpm range a lot better, a lot faster.
With the carter installed it felt like I hit a wall at 4500 rpm. Now I can rev through 6000 rpm.
The cam was choosen to allow cylinder pressure to leak off in the low rpm range to allow running 87 octane fuel with a true 9.7:1 comp. ratio and iron heads. This was achieved. I can run 87 octane and the intial timing is set for 14*btdc.
The other objective to the cam choice was to maximize duration and stay below .450" lift. The vortec heads can only handle .470" lift (leaving .060" clearance before the retainer hit the guide and coil bind). So i decided on a .450 max so as not to strain anything or incur more machine shop bills. The vortec head flows great at low to mid lift, it really does not make sense to take a stock vortec head and spend the money to run a .500" lift cam. Is there a better cam choice that will fit the bill and give me the explosive torque of the Engergizer 274?
Back to the carbs, I am expieriencing a mojor bog off idle with the Edelbrock. I have moved the accel. pump push rod to enable a faster shot. It helped but I think I am going to have to increase the shooter size, Does this sound correct?
Also, with a calibration kit costing ~$50 and the fact that I can not find the shooters for the accel pump anywahere should I switch to the more popular Holley? If so which one?
Thanks for any help.
------------------
LOBC-- SS-84
92 RS Heritage package with a 305
84 El camino
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