Help me out here. I have a 93 mustang lx. Rebuilt 351w,gt40 3 bar heads, lunati 280/290 with 472/496 lift camshaft, edlebrock performer, summit 600cfm carb, t5 trans out of 99 v6 stang. 3.73 gears in the rear. I built this car to be a reliable street car that could still kick some import ass if needed. I was bored so I took the car to atco raceway 1/4 mile to play around. Problem I have is when I hit about 1/8 mile my car starts to fall flat. My car is reved out in 4th gear and I need to switch to 5th which really slows my momentum. I was racing an 01 gt and i was 5 car lengths on him but we finished both with the same exact mph which tells me I'm really falling off towards the end. Is my setup not right?? I know t5 trans is not exactly a drag racing trans but is it the trans gear ratio that's killing me?
1/4 Mile Issues
- Thread starter sharp2377
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mikestang63
SN Certified Technician
IMO that cam is way to small. The lift is about what a stock 5.0 is and you have 50 more cubes. The GT40 heads are not the best choice and I also think your carb is too small. That setup would work better on a 302. If you want to keep those heads you need way more cam.
What are your shift rpms?
What are your shift rpms?
Everyone kept warning me not to put in too big of cam so I thought the cam I picked was going to be perfect with that setup since the bottom end was stock. This was my first complete build I did myself so I was trying to play it safe. Do you recommend a better size cam for my setup? Right now I'm shifting at 4500 rpm maybe 5000. I'm at 4500 rpm in 4th gear with 100 yds to go.I know the gt40 heads aren't ideal but I did port them. With 3 kids and a mortgage I had to make do with what was available lol
You're shifting to early also. You should be able to pull till at least 5200-5500rpm. You shouldn't have to shift to 5th gear with 3.73 gears. I'd run a 650-750 carb. Keep raising your shift point rpms until you start slowing down or valve float etc. the heads and cam are to small but at that track I'd think you should be in the 12s at least
mikestang63
SN Certified Technician
.Is yours a pre 94 block? Then it's a non roller cam and that will limit your choices unless you want to install a retrofit kit. If its a F4TE block you can use roller lifters, cam, dogbone.
Here are some cam options
These will work with pedestal rockers.
Hyd. Hyd. 1500 to 5600 35-552-8 NX264HR 264 276 212 224 .512 .512 114°
Hyd. Hyd. 1800 to 5800 35-351-8 XE270HR 270 276 218 224 .512 .512 114°
These are listed for 1.7 rockers.
Hyd. Hyd. 1500 to 5500 35-320-8 XE264HR 264 270 212 218 .544 .544 112°
Hyd. Hyd. 1800 to 5800 35-324-8 XE270HR 270 276 218 224 .544 .544 112°
Your T5 is actually one of the stronger factory 5 speeds and is fine. It's the same gears as other T5's if I remember correct.
Here are some cam options
These will work with pedestal rockers.
Hyd. Hyd. 1500 to 5600 35-552-8 NX264HR 264 276 212 224 .512 .512 114°
Hyd. Hyd. 1800 to 5800 35-351-8 XE270HR 270 276 218 224 .512 .512 114°
These are listed for 1.7 rockers.
Hyd. Hyd. 1500 to 5500 35-320-8 XE264HR 264 270 212 218 .544 .544 112°
Hyd. Hyd. 1800 to 5800 35-324-8 XE270HR 270 276 218 224 .544 .544 112°
Your T5 is actually one of the stronger factory 5 speeds and is fine. It's the same gears as other T5's if I remember correct.
Most naturally aspirated V8 engines operate basically the same with regard to air consumption. I've had moderately cammed 350 Chevy's with 600 carbs pull hard to 6k rpm no problem. With carb sizing, it's basically cubic inches and rpm that set the required amount of air needed.
Are you guys sure the 600 is too small for a 351? Shoot, I had a modded 455 olds getting to 55oo without falling flat on a 650. To suggest a 351 needs a 750 is overkill in my opinion. Furthermore, the larger carbs will reduce incoming air velocity and result kin a net negative.
If its a vac sec carb, maybe the secondaries are not coming in all the way. Maybe he's running out of fuel or has a ignition timing or cam timing issue.
I agree that he should be taking the r's to at least 5500.
Are you guys sure the 600 is too small for a 351? Shoot, I had a modded 455 olds getting to 55oo without falling flat on a 650. To suggest a 351 needs a 750 is overkill in my opinion. Furthermore, the larger carbs will reduce incoming air velocity and result kin a net negative.
If its a vac sec carb, maybe the secondaries are not coming in all the way. Maybe he's running out of fuel or has a ignition timing or cam timing issue.
I agree that he should be taking the r's to at least 5500.
Try this calc >>> http://www.carburetion.com/calc.asp
600 CFM is enough for a mildly built 351 and would get it to 6000 rpm.
600 CFM is enough for a mildly built 351 and would get it to 6000 rpm.
I feel like I'm screaming at 5k rpm and falling off. I am running a 84 351w so its flat tappet. The best way I could describe the feeling would be like drag racing a 2 stroke dirt bike. Sure, it takes off like a bat out of hell but you run out of gears very quickly.
There is nothing limiting me, I'm actually using a msd 6a so it doesn't have the rev limiter. I need to run it again, maybe I'm just getting scared listening to my engine scream after all that hard work and afraid I'm going to blow it up. Thank you everyone for not being judgemental though. I already know gt40 heads aren't ideal but they are better than stock 84 heads and they were free lol. I had them hot tanked, magnafluxed, and surfaced. Installed trick flow springs, retainers, felpro seals , and lapped the valves.
Your shortblock should be able to pull 6000 rpm no prob without self destructing. As long as you're tuned right ie no detonation etc. As far as carb is concerned I ran a 650 mech sec on a bunch of Chevy small blocks and a 750 vac sec carb on a 351w truck that had stock heads. I do agree that you should check and make sure the secondaries are opening all the way and the ign/fuel system are working properly. With those springs and a proper tuneup I wouldn't be afraid to start shifting at 5500 and maybe eventually shift closer to 6k
Racing a T5 in 5th gear is a sure fire way to blow it up. 5th gear in a T5 is mounted outside of the main case and structured completely different than the other gears. It is not intended to be an acceleration gear and is much weaker.
Anything you can do to help that engine breathe is going to produce gains. If a cam swap is what you're after, your best bet is talking to a pro cam guy.
Anything you can do to help that engine breathe is going to produce gains. If a cam swap is what you're after, your best bet is talking to a pro cam guy.
The air cleaner setup can limit top end. If you're using a short filter or a recessed base to make room for hood clearance it can close the gap between the air cleaner lid and carb airhorn resulting in restricted airflow. Try a run with the filter removed to see if you notice a difference.
Also, what kind of distributor are you running? Does it have electronic or mechanical advance? Many people focus on initial timing settings while neglecting to set up the distributor to limit the full advance. Full advance should be 34-36 degrees BTDC and it should all be in by 2500 rpm. Excessive full advance will hurt top end.
Put timing tape on the harmonic balancer and set full advance 34-36 degrees max, all in not later than 2500 rpm.
Also, what kind of distributor are you running? Does it have electronic or mechanical advance? Many people focus on initial timing settings while neglecting to set up the distributor to limit the full advance. Full advance should be 34-36 degrees BTDC and it should all be in by 2500 rpm. Excessive full advance will hurt top end.
Put timing tape on the harmonic balancer and set full advance 34-36 degrees max, all in not later than 2500 rpm.
I would simply like to see you rev this thing out a little farther and see how things go. Also I could recommend you to a shop local to atco that has reasonable rates for their dyno and you could get an Idea of where your peak tq and hp numbers really are to tell you where you should be shifting. Rates at the shop I deal with are very reasonable and the guys there are great. I think 3 dyno pulls with a/f is only 125$ and tuning on a carbed car should be relatively cheap if you decide to go that way as well. PM me if you want some more details I'll be more than willing to help anyway I can.
Update,
apparently it WAS the secondaries. Thank you to everyone who helped. I got it figured out, and took it back to atco raceway. I bit the bullet and set my shift light to 5800 and launched at 2500 rpm on BF drags and turned a 12.86 and never felt I needed to shift to 5th gear. That was exactly the target time I was looking for when I built this car. Of course, like any other mustang owner,I want to get my time even lower in the future lol.
apparently it WAS the secondaries. Thank you to everyone who helped. I got it figured out, and took it back to atco raceway. I bit the bullet and set my shift light to 5800 and launched at 2500 rpm on BF drags and turned a 12.86 and never felt I needed to shift to 5th gear. That was exactly the target time I was looking for when I built this car. Of course, like any other mustang owner,I want to get my time even lower in the future lol.
Good to hear. What exactly did you do to the secondaries to get them behaving better?
its all about booster signal. that combo would probably run fine with a dominator, it has so much signal its crazy. if it were mine I would put a vic jr and a good 750 4150 like a quickfuel or AED and watch it go 11s. we had issues with three holley 4150s with a 10:1 358" Cleveland headed Windsor with a decent restrictor intake and a decent sized flat tappet cam. it wouldn't even run right with a new 650HP. the 650HP, a good known 750 HP, and an 830 that ran good on a 347 with small heads all had a stumble out of the hole on the secondary side. all these carbs went 7.30s@95 in the 1/8th. then we unhooked the secondaries on the 830 and the stumble went away. the car went 7.20s@93 like that. then we bolted on my AED 750 HO modified, adjusted the idle and made sure everything was adjusted correctly. the car went a 6.88@98mph with it setup the same as it came out of the box from summit. so there is a little more to carbs than just having the 'right' cfm rating.
http://www.aedperformance.com/tuning-tips.html
im gonna have to disagree with ya. its about finding the right size based on displacement, induction cross section, compression, camshaft, vehicle weight, gearing, and converter.
http://www.aedperformance.com/tuning-tips.html
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