GT-40p headed motor

89 Cobra LX · 06-14-2001, 10:59 AM

I recently posted here regarding a new motor that I purchased from Excessive Motorsports. The motor is an Explorer long-block with a Trick Flow stage 1 cam topped off with a Cobra intake, 24lb injectors, "stage 2" ported GT-40p heads and 1.6 roller rockers. I was extremely disappointed with the performance of the motor after a recent trip to the dyno. I made 260 (not at the wheels) peak HP at a measly 4500rpm. I have spent countless hours troubleshooting and investigating possible problems. The motor was advertised to make 325 HP with the stock rockers.

I have come to the conclusion that my problem is with the valve springs. Excessive Motorsport did not upgrade the valve springs. I'm running a high performance cam with stock Explorer valve springs. Trick Flow recommends springs with 120lbs pressure closed. The Explorer springs are probably coming in at around 90lbs pressure. I have spoken with Dennis at Central Coast Mustang and he said the Explorer valve springs are an immediate red flag (he said the Explorer barely revs to 4500rpm). My man here at HPMotorsport feels the same. I've gone through all accessories of the motor and it is bullet-proof. There is something that is not allowing me to make decent HP numbers and the valve springs seem to make the most sense.

It will be very costly for me to have the valve springs replaced at this point and was looking for some advice from some of you here. Would it make sense to change the valve springs? I'm a realistic person and don't expect to see a 65 HP gain from changing the valve springs, but does anyone have any idea what sort of power they could be costing me? Bottom line, this motor should not be making peak power at 4500rpm, it should be closer to 5400rpm.

Thanks -

------------------
Eric - 89 Mustang LX
302 - Cobra Intake - GT40p heads - Naturally Aspirated

Shawn · 06-14-2001, 11:37 AM

Sounds like the springs to me also..one rule is to always expect advertised hp numbers to be exaggerated a little bit. But in your case the valves are probably floating quite a bit, one clue is that you can sometimes hear an almost clicking/ticking sound in the higher rpm range if the springs are weak-thats the valve winging open to far and the spring slapping the valvetrain back down. Springs are cheap, anywhere from $50-200 depending on how crazy you get. And dont let anyone tell you they have to take the heads off the car to replace them-just so they can charge more $$$. I used to change springs all the time on one of my high lift cam engines, there are a few tools that easily let you change springs with the heads on, if you do it yourself just be careful to make sure the piston it 'up' in the cylinder your working on-that way you dont have to worry if a valve slides down!
good luck!

89 Cobra LX · 06-14-2001, 12:28 PM

Thanks Shawn,

HPMotorsport will change the springs without removing the heads. I can get a good set of springs and retainers for $109.

I guess my real question is if anyone has any idea what kind of power I will gain (just a ballpark figure)?

------------------
Eric - 89 Mustang LX
302 - Cobra Intake - GT40p heads - Naturally Aspirated

89 Cobra LX · 06-15-2001, 09:35 AM

Noone has any idea how much power the valve springs could be costing me?

Skankin · 06-15-2001, 02:47 PM

HP is a function of RPM, so if you can rev it higher, you'll get more power.

The torque will probably remain the same.

Unit 5302 · 06-15-2001, 06:46 PM

They could be costing you a ton of hp. If your valves are staying open, even a little bit while the cylinder is trying to compress, you'll have serious reductions in power.

06-14-2001, 10:59 AM	#1
89 Cobra LX Don Corlione Join Date: Jun 2001 Location: Omaha NE USA Posts: 491	GT-40p headed motor I recently posted here regarding a new motor that I purchased from Excessive Motorsports. The motor is an Explorer long-block with a Trick Flow stage 1 cam topped off with a Cobra intake, 24lb injectors, "stage 2" ported GT-40p heads and 1.6 roller rockers. I was extremely disappointed with the performance of the motor after a recent trip to the dyno. I made 260 (not at the wheels) peak HP at a measly 4500rpm. I have spent countless hours troubleshooting and investigating possible problems. The motor was advertised to make 325 HP with the stock rockers. I have come to the conclusion that my problem is with the valve springs. Excessive Motorsport did not upgrade the valve springs. I'm running a high performance cam with stock Explorer valve springs. Trick Flow recommends springs with 120lbs pressure closed. The Explorer springs are probably coming in at around 90lbs pressure. I have spoken with Dennis at Central Coast Mustang and he said the Explorer valve springs are an immediate red flag (he said the Explorer barely revs to 4500rpm). My man here at HPMotorsport feels the same. I've gone through all accessories of the motor and it is bullet-proof. There is something that is not allowing me to make decent HP numbers and the valve springs seem to make the most sense. It will be very costly for me to have the valve springs replaced at this point and was looking for some advice from some of you here. Would it make sense to change the valve springs? I'm a realistic person and don't expect to see a 65 HP gain from changing the valve springs, but does anyone have any idea what sort of power they could be costing me? Bottom line, this motor should not be making peak power at 4500rpm, it should be closer to 5400rpm. Thanks - ------------------ Eric - 89 Mustang LX 302 - Cobra Intake - GT40p heads - Naturally Aspirated

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06-14-2001, 11:37 AM	#2
Shawn Registered Member Join Date: Dec 1998 Location: Chicago, IL. USA Posts: 77	Sounds like the springs to me also..one rule is to always expect advertised hp numbers to be exaggerated a little bit. But in your case the valves are probably floating quite a bit, one clue is that you can sometimes hear an almost clicking/ticking sound in the higher rpm range if the springs are weak-thats the valve winging open to far and the spring slapping the valvetrain back down. Springs are cheap, anywhere from $50-200 depending on how crazy you get. And dont let anyone tell you they have to take the heads off the car to replace them-just so they can charge more $$$. I used to change springs all the time on one of my high lift cam engines, there are a few tools that easily let you change springs with the heads on, if you do it yourself just be careful to make sure the piston it 'up' in the cylinder your working on-that way you dont have to worry if a valve slides down! good luck!

06-14-2001, 12:28 PM	#3
89 Cobra LX Don Corlione Join Date: Jun 2001 Location: Omaha NE USA Posts: 491	Thanks Shawn, HPMotorsport will change the springs without removing the heads. I can get a good set of springs and retainers for $109. I guess my real question is if anyone has any idea what kind of power I will gain (just a ballpark figure)? ------------------ Eric - 89 Mustang LX 302 - Cobra Intake - GT40p heads - Naturally Aspirated

06-15-2001, 09:35 AM	#4
89 Cobra LX Don Corlione Join Date: Jun 2001 Location: Omaha NE USA Posts: 491	Noone has any idea how much power the valve springs could be costing me?

06-15-2001, 02:47 PM	#5
Skankin Registered Member Join Date: Dec 1998 Location: London, Ontario, Canada Posts: 1,349	HP is a function of RPM, so if you can rev it higher, you'll get more power. The torque will probably remain the same.

06-15-2001, 06:46 PM	#6
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	They could be costing you a ton of hp. If your valves are staying open, even a little bit while the cylinder is trying to compress, you'll have serious reductions in power.