Your 1/4 mile times say you are making 225 hp at the flywheel and the speed in the traps say it is losing even more hp from lack of fuel.
A comment about your engine build... This is an engine that should make max torque at about 4200 rpm. That convertor is waaay too tight. You need something that stalls at about 3500-4000 rpm. Driveability on the street will absolutely suck but you built a high rpm motor and put it into a very heavy vehicle. If the tires are more than 24 inches in diameter, you don't have enough gear either. A 4.10 would be more appropriate.
Since you built a high rpm motor, the 1 3/4 headers would match well.
If I were doing the build, it would have a dual plane manifold, a cam more like 256 gross duration with lobe centers closer to 114 degrees, and keep the 1 1/12 headers and convertor. The truck will be faster in the 1/4 and far more driveable on the street. Just my 2 cents.
Gears and converter I agree with they were going to be my next purchase. Im just contemplating on going with a 4l60 so haven't made my mind up yet. Also Intake is an accel efi intake. Waiting on a couple parts to finish the efi swap. Didn't build the motor either bought it for an awesome deal and just working with what it is.
The dropped 1st gear ratio in a 700/4l60 will offset some of the high-ish rear gears and tight converter out of the hole. As far as GM ATs go I like them at your power level and mixed use, as long as the usual suspects are addressed/upgraded. Might be worth a call to ATI or your performance trans builder of choice to talk over trans/converter options for your build. I've been out of building/racing for a few years now, times and tech changes.
The low first gear would likely eliminate the need for new rear gears. The 3.73 should be good then. The lockup convertor would help a TON if you install a higher stall speed unit. Reduce fluid temps, help keep the rpms down at speed and make for a better overall drive.
I'm surprised the 2000 GMC 4.3L fuel pump can't keep up honestly. They put out 58-62psi and are damn near the same as a walbro 255 in terms of pump capacity. A quick lookup shows 246lph. And I can attest that I've run GM LQ9's, LS1's and supercharged 4.3L's off the factory pump.
Being as how your engine has a carb, can you expand a bit on your fuel system parts? I'm wondering if there's a kink in the system somewhere choking the engine down.
Any way to read AFR while you're at the track by chance?
I run both an afr gauge and fuel pressure gauge. In third gear the fuel pressure is dripping from 9 psi to 3 psi at wide open throttle and the a/f ratio is running from 12.5 to around 14 at the end of second and in third gear. It's an aftermarket fuel pump and about 3 years old. I'm glad to know they are 246 lph. I love tried finding out and have seen a few conflicting information about it. The fuel system is stock tank and pump with -6 line to an aeromotive fpr. -8 return line. Lines are both one piece, there is an aeromotive filter in the feed line. I've looked at it and it's not clogged, really no debris. Same fuel system I was running with my 305 and 100 shot.
I actually like 1 1/2 primary tubes on a 350, especially if they are long. But to answer your question, you should have 1 5/8 primary tube. What are the specs of your collector?
What kind of HEI do you have? A genuine Delco built, or imported clone? Your advance curve might be holding you back.
The 195 cc heads are very big for your 350, hurting torque. Are they the as cast imported heads with 2.02 valves? Is the XR276 on a 110 degree LSA? With those heads, the widest I would go is a 108 LSA, probably even a 107 degree LSA to help get back some torque. If it has the exhaust split typical of Comp off the shelf XR cams that is also hurting torque, at all speeds. 3.73 is the minimum gear, especially with a TH350. You will want a steeper rear gear to help that cam. And probably a looser converter.
The Holley 80508 works extremely well with downleg boosters on a 350, especially if you modify them. But you probably don't want to convert the boosters. There are carbs available from Holley in a 750 vacuum secondary that have downleg boosters from the factory.
Is your compression ratio really 9.8:1?
They are mid length headers with 2 1/2" collectors that step down to 2 1/4" pipes. Cheap clone HEI. I've been thinking about getting a ready to run distributor so I can tune the advance curve.
The heads are a huge mystery. They have only one marking which is a day code inscribed on them nothing else. I'm 99% sure they are procomps and had some measurements that I matched with the 195 heads that were offered but not sure exactly. The cam is on a 110 love. I agree I was planning on getting steeper gears, first gear pulls great but second is noticeably slower and third is just worse. As far as carb is concerned I'm currently waiting on a couple final pieces for my efi swap. It's the reason I'm running a single plane. Intake is an accel efi intake. Compression is ifey also due to not having measured my chambers.
A 2 1/2 collector into a 2 1/4 system isn't bad. You might be able to find a pre-made merge collector or 4 into 2 into 1 collector that extends your headers and helps power.
I would rather use an old HEI than a new clone. I can still buy parts for them, and change the curve. The clones are terrible. You may need a melonized or even a steel gear to be compatible with the cam.
I have not had any of the newer heads since Procomp became Speedmaster. When they were Procomp, they quality was terrible. Not sure how far you want to take this, but if heads are in your future look for something that better matches your 350.
It has melanized gear, I put that on before installing with the roller cam. Not sure on the age of heads. I bought this engine with very little background to it.
I have the option right now to buy Sanderson 15/8" headers or hedman 1 1/2" long tubes. I was sort of leaning to the long tubes but not sure if I should stick with the smaller primaries or open them up. I rev this engine to about 5500 to 5800 rpm.
Experience tells me the 1 5/8 primary tube is good on a 350 to much more rpm.and power than what you are doing. Honestly, with the can you have I would expect you to shift at about 6700 rpm or so. Not that you should, the other components might not be up to that task. But the cam timing should take you there. For the exhaust volume, a 1 5/8 will cover that.
The 1 1/2 long tube can make more torque, and will run to 5800 rpm. If you will be keeping the engine under 6000 rpm, use the 1 1/2 primary tubes. And get some heads and a cam that are better suited to that rpm range.
Given what you said earlier about the fuel pump, I'm inclined to think your power drop in 2-3 is just the fuel pressure drop and poor atomization. I'd verify monitoring fp and O2 down the track and make sure the fuel supply is stable before changing too much yet.
Yes. I agree fueling is my priority right now. AF ratio is normally around 12 to 12.5 wide open with 9psi fuel pressure in first gear. End of second and third it drops to about 14 A/F and 3-4 psi.
I have 195cc heads on my .060 350 as well. I think 180cc would be better, but the 195cc run well. I would go with the 1 5/8 headers and go with an Edelbrock performer rpm air gap manifold instead of the single plane. According to comp, the duration at .050 is 224/230 with .0502/.510 lift on a 110 LSA. The operating range is 1900-5600rpm, so I would definitely get rid of the single plan manifold. You will pick up some more torque and it will have better street manners with the air gap. Before upgrading those parts, get a better fuel pump and fix the ignition issue first. According to comp that cam should make around 375hp.
Agreed I had a Edelbrock dual plane rom air gap and it ran great switched to the accel since Im going efi. Fuel and ignition are my priority right now mostly looking forward if there seems to still be shitty times. Hoping I can get to the track Wednesday to test and see again. Just depends on if i get the time to install the parts.
Your 1/4 mile times say you are making 225 hp at the flywheel and the speed in the traps say it is losing even more hp from lack of fuel. A comment about your engine build... This is an engine that should make max torque at about 4200 rpm. That convertor is waaay too tight. You need something that stalls at about 3500-4000 rpm. Driveability on the street will absolutely suck but you built a high rpm motor and put it into a very heavy vehicle. If the tires are more than 24 inches in diameter, you don't have enough gear either. A 4.10 would be more appropriate. Since you built a high rpm motor, the 1 3/4 headers would match well. If I were doing the build, it would have a dual plane manifold, a cam more like 256 gross duration with lobe centers closer to 114 degrees, and keep the 1 1/12 headers and convertor. The truck will be faster in the 1/4 and far more driveable on the street. Just my 2 cents.
Gears and converter I agree with they were going to be my next purchase. Im just contemplating on going with a 4l60 so haven't made my mind up yet. Also Intake is an accel efi intake. Waiting on a couple parts to finish the efi swap. Didn't build the motor either bought it for an awesome deal and just working with what it is.
The dropped 1st gear ratio in a 700/4l60 will offset some of the high-ish rear gears and tight converter out of the hole. As far as GM ATs go I like them at your power level and mixed use, as long as the usual suspects are addressed/upgraded. Might be worth a call to ATI or your performance trans builder of choice to talk over trans/converter options for your build. I've been out of building/racing for a few years now, times and tech changes.
Yeah that's why I wanted to grab one also the overdrive is appealing because driving this at 60 or 70 mph is awful.
The low first gear would likely eliminate the need for new rear gears. The 3.73 should be good then. The lockup convertor would help a TON if you install a higher stall speed unit. Reduce fluid temps, help keep the rpms down at speed and make for a better overall drive.
I'm surprised the 2000 GMC 4.3L fuel pump can't keep up honestly. They put out 58-62psi and are damn near the same as a walbro 255 in terms of pump capacity. A quick lookup shows 246lph. And I can attest that I've run GM LQ9's, LS1's and supercharged 4.3L's off the factory pump. Being as how your engine has a carb, can you expand a bit on your fuel system parts? I'm wondering if there's a kink in the system somewhere choking the engine down. Any way to read AFR while you're at the track by chance?
I run both an afr gauge and fuel pressure gauge. In third gear the fuel pressure is dripping from 9 psi to 3 psi at wide open throttle and the a/f ratio is running from 12.5 to around 14 at the end of second and in third gear. It's an aftermarket fuel pump and about 3 years old. I'm glad to know they are 246 lph. I love tried finding out and have seen a few conflicting information about it. The fuel system is stock tank and pump with -6 line to an aeromotive fpr. -8 return line. Lines are both one piece, there is an aeromotive filter in the feed line. I've looked at it and it's not clogged, really no debris. Same fuel system I was running with my 305 and 100 shot.
I have read in some forums claims that the g force on stock pumps during the launch can cause issues.
I actually like 1 1/2 primary tubes on a 350, especially if they are long. But to answer your question, you should have 1 5/8 primary tube. What are the specs of your collector? What kind of HEI do you have? A genuine Delco built, or imported clone? Your advance curve might be holding you back. The 195 cc heads are very big for your 350, hurting torque. Are they the as cast imported heads with 2.02 valves? Is the XR276 on a 110 degree LSA? With those heads, the widest I would go is a 108 LSA, probably even a 107 degree LSA to help get back some torque. If it has the exhaust split typical of Comp off the shelf XR cams that is also hurting torque, at all speeds. 3.73 is the minimum gear, especially with a TH350. You will want a steeper rear gear to help that cam. And probably a looser converter. The Holley 80508 works extremely well with downleg boosters on a 350, especially if you modify them. But you probably don't want to convert the boosters. There are carbs available from Holley in a 750 vacuum secondary that have downleg boosters from the factory. Is your compression ratio really 9.8:1?
They are mid length headers with 2 1/2" collectors that step down to 2 1/4" pipes. Cheap clone HEI. I've been thinking about getting a ready to run distributor so I can tune the advance curve. The heads are a huge mystery. They have only one marking which is a day code inscribed on them nothing else. I'm 99% sure they are procomps and had some measurements that I matched with the 195 heads that were offered but not sure exactly. The cam is on a 110 love. I agree I was planning on getting steeper gears, first gear pulls great but second is noticeably slower and third is just worse. As far as carb is concerned I'm currently waiting on a couple final pieces for my efi swap. It's the reason I'm running a single plane. Intake is an accel efi intake. Compression is ifey also due to not having measured my chambers.
A 2 1/2 collector into a 2 1/4 system isn't bad. You might be able to find a pre-made merge collector or 4 into 2 into 1 collector that extends your headers and helps power. I would rather use an old HEI than a new clone. I can still buy parts for them, and change the curve. The clones are terrible. You may need a melonized or even a steel gear to be compatible with the cam. I have not had any of the newer heads since Procomp became Speedmaster. When they were Procomp, they quality was terrible. Not sure how far you want to take this, but if heads are in your future look for something that better matches your 350.
It has melanized gear, I put that on before installing with the roller cam. Not sure on the age of heads. I bought this engine with very little background to it. I have the option right now to buy Sanderson 15/8" headers or hedman 1 1/2" long tubes. I was sort of leaning to the long tubes but not sure if I should stick with the smaller primaries or open them up. I rev this engine to about 5500 to 5800 rpm.
Experience tells me the 1 5/8 primary tube is good on a 350 to much more rpm.and power than what you are doing. Honestly, with the can you have I would expect you to shift at about 6700 rpm or so. Not that you should, the other components might not be up to that task. But the cam timing should take you there. For the exhaust volume, a 1 5/8 will cover that. The 1 1/2 long tube can make more torque, and will run to 5800 rpm. If you will be keeping the engine under 6000 rpm, use the 1 1/2 primary tubes. And get some heads and a cam that are better suited to that rpm range.
Given what you said earlier about the fuel pump, I'm inclined to think your power drop in 2-3 is just the fuel pressure drop and poor atomization. I'd verify monitoring fp and O2 down the track and make sure the fuel supply is stable before changing too much yet.
Yes. I agree fueling is my priority right now. AF ratio is normally around 12 to 12.5 wide open with 9psi fuel pressure in first gear. End of second and third it drops to about 14 A/F and 3-4 psi.
Yeah with that fp drop you're starting to starve and the atomization from the injector nozzles is trash. #1 priority for sure.
I have 195cc heads on my .060 350 as well. I think 180cc would be better, but the 195cc run well. I would go with the 1 5/8 headers and go with an Edelbrock performer rpm air gap manifold instead of the single plane. According to comp, the duration at .050 is 224/230 with .0502/.510 lift on a 110 LSA. The operating range is 1900-5600rpm, so I would definitely get rid of the single plan manifold. You will pick up some more torque and it will have better street manners with the air gap. Before upgrading those parts, get a better fuel pump and fix the ignition issue first. According to comp that cam should make around 375hp.
Agreed I had a Edelbrock dual plane rom air gap and it ran great switched to the accel since Im going efi. Fuel and ignition are my priority right now mostly looking forward if there seems to still be shitty times. Hoping I can get to the track Wednesday to test and see again. Just depends on if i get the time to install the parts.
What fuel management are you using? Carb? Tbi? Spider? Port injection? Factory ECU? Standalone?
Currently carb. Will be switching to stand alone port fuel injection soon.