Road Race Track/AutoCross 351w

[GimpyHSHS]

Hello folks, I am new to the boards, but I'm no stranger to reading a lot from the bright minds of racing here.

Here's the story: I bought a used engine I found on Racing Junk. I got a good enough price that the sum of the parts made sense to buy it. I've listed the full specs that I know below. I didn't put it together and I've never had it completely apart, so I don't know everything. I had a carb on it for a little while before deciding to convert to EFI. I went with a Holley Sniper throttle body injection system.

The car is a 3100lb 1995 Mustang GT. I use it for track days and autocross only pretty much, but I do occasionally take her for a leg stretch on the street. Fairly extensive braking, tire, and suspension changes. Has a Tremec TR3550, aluminum driveshaft, 3.73 gears, things like that.

My only real complaint about the car now that I've got the suspension mostly dialed in is the engine and tune. I know that the cam is fairly large for what I'm doing. It idles at around 6 in/hg. Autocross events are nearly entirely run in 2nd gear. I may get up to 70mph on one part of the course, then go down to 30, then back up to 50, etc. The car pulls...ok? but struggles coming out of the slow parts of the course. I always felt like it had decent power, but my cousin with much more experience behind different wheels has said he doesn't think the engine is "explosive" enough, at least not like the ones he's driven before. Recently I rode shotgun in my buddy's 3.08 gear 1995 Cobra with a B Cam and the MAF unplugged (his idea of a tune). His car felt like it pulled harder than mine!

Here's a video of mine: https://www.youtube.com/watch?v=3t2E1_EpKd4

Toward the end, you can hear the engine struggle to go from slowing down to accelerating again.

I've been of the opinion that the cam was the problem. Too big to work down low with my gearing. But now I'm wondering if the problem lies in my tune. I've read that bigger cams need more timing at low RPMs and cruise, something I didn't realize. I figured it would be the opposite. I've been running 20*(ish) at idle, 35* cruising, and right around 34* at WOT. Since the engine is 11:1 and I'm running 93 pump, I figured that was a safe tune. My cousin was against having much "vacuum advance" (it's all electronic, obviously, with the Holley EFI, but you get my drift).

I'm curious to hear people's suggestions on where I should start the timing out. I've made some changes to the tune to try out. But in general, will a little more idle timing down low help with low end power (2000-3500) where it feels a really weak?

I'm kind of at a crossroads now, I have time after the autocross event this weekend to try out a custom cam or off-the-shelf cam that would better fit my application. I just don't want to do that if the cam I have should work for the application and the problem lies elsewhere. My cousin has suggested that he thinks the problem is in the engine, a valve hanging or a piston ring not sealing, but the leakdown test showed 90%+ across all cylinders. He has also opined that I might need a lighter flywheel (something that probably would help with the quick speeding up and slowing down we do in AutoX, but I'm not sure that's actually the issue).

Anyway, I welcome any input you folks have. I'm young and dumb, like everyone else out there was one day. If you have any questions, please just ask and I will try to clear it up. My little ADHD brain bounces around writing these posts

Specs on the engine:
351W + .030” overbore = 357 cu in.
11:1 compression
Aluminum Windsor Sr Heads. 200cc intake runners. 2.02/1.6 valves.
Crower 1.6 ratio roller rockers on exhaust
Crane 1.7 ratio roller rockers on intake.
Victor Jr. single plane intake.
BBK 1-¾” Long Tubes
BBK X Pipe
Flowmasters, Dumped
Holley Sniper EFI
Holley Hyperspark Distributor
Holley Hyperspark Ignition Box
Holley Hyperspark Coil
Taylor Spiro-Pro 8mm Wires
Autolite 25 Plugs
AEM 10-1005 Fuel Pump
Sumped/Baffled Tank
Aeromotive 13129 Bypass Regulator
Aeromotive ORB-10 Fuel Filters

Cam profile:
Schneider Cams Solid Flat Tappet
Part Number: 13032
Grind Number: 284-92F
Intake Duration (gross): 284
Exhaust Duration (gross): 292
Intake Duration (.050”): 248
Exhaust Duration (.050”): 258
Intake Valve Lift: .600" (based on 1.7 rocker)
Exhaust Valve Lift: .584" (based on 1.6 rocker)
Lobe Separation: 106
Intake Valve Lash: .020"
Exhaust Valve Lash: .020"
RPM Range: 3000-7000


Some various other specs on the car:
Steeda Ultralite 18x9" wheels
275/35/18 Falken Azenis RT615K+
Maximum Motorsports Race RA-2 Gen 3 Coilover Struts
Hypercoil 10"/425 lb/in Front Coilover Springs
Maximum Motorsports Race RA-2 Gen 3 Coilover Shocks w/Spherical Lower Bearing
Hypercoil 275 lb/in Rear Coilover Springs
Stiffler's FIT Chassis System (Subframe Connectors, Jacking Rails, Web Bracing)
SR Performance Strut Bar (Modified to Clear 351w)
Maximum Motorsports Caster/Camber Plates
Maximum Motorsports Torque Arm
Fays2 Watts Link
MM Rear Shock Mounts
Steeda Front and Rear Swaybars
Steeda Aluminum Radiator
Steeda Rear Lower Control Arms
Steeda Front Offset A-Arm Bushings
Steeda Battery Relocation Kit
2000 Cobra R Brembo Brakes
Raybestos ST47 Pads (Front)
Raybestos ST43 Pads (Rear)
Wilwood 570 Brake Fluid
Stainless Front Brake Lines
Russell Speed Bleeders
Tremec TR-3550 Standard Ratio Transmission
Aluminum FRPP Driveshaft and Loop
3.73 Rear Gears
Steeda Tri-Ax Shifter w/Hurst Ball
Steeda Adjustable Clutch Cable, Quadrant, and Firewall Adjuster

[dannobee]

You could try borrowing or changing the rockers to 1.5's before changing the cam to see if that helps.

[GimpyHSHS]

You could try borrowing or changing the rockers to 1.5's before changing the cam to see if that helps.

That would be an option. I just realized I didn't even post the cam specs like I meant to. It's a 248/258 duration @.050". Not sure if that makes a difference. I know that a lower ratio rocker would reduce the lift, but would it have that much effect on the duration? And it's a 106 LSA, too, fairly tight.

[Bryan Maloney]

I would try a Performer Rpm manifold, small venturi merge collectors, and confirm existing cam was advanced 4 degrees.

[rustbucket79]

Have you tried shifting more? I’ve only autocrossed a couple of times in sh*tboxes, so perhaps it’s too busy adding shifting along with the steering and braking.

If you’re racing it at 34 and not showing detonation on the plugs, I would have no issue running 42 to 45 degrees with vacuum (cruise) since the engine’s volumetric efficiency is very low in a cruise situation, which also helps to reduce exhaust temperature. It also might benefit with a slightly more aggressive advance curve.

What are you setting your cruise and WOT AFR’s to on your Sniper?

[GimpyHSHS]

Have you tried shifting more? I’ve only autocrossed a couple of times in sh*tboxes, so perhaps it’s too busy adding shifting along with the steering and braking.

That would be an option, but you do lose time trying to shift. About half a second shifting, which is a lot in AutoX. And these Tremecs are nearly impossible to downshift to 1st gear...that'd be very interesting. I have a 3.73 rear gear, so I can run out to 70mph in 2nd, which is about perfect if you talk to the fast AutoX guys. Saving time not having to shift makes a big difference.

If you’re racing it at 34 and not showing detonation on the plugs, I would have no issue running 42 to 45 degrees with vacuum (cruise) since the engine’s volumetric efficiency is very low in a cruise situation, which also helps to reduce exhaust temperature. It also might benefit with a slightly more aggressive advance curve.

What are you setting your cruise and WOT AFR’s to on your Sniper?

Here are my old Target AFRs.

Target AFRs old.JPG

Here are my new Target AFRs. The white box is where I idle, the line coming off of it is about where I cruise, and the line at the top is at WOT. (It's hard to see with the blurriness, but the idle and cruise I have set to around 14.xx).

target AFRs new edited.jpg

I tweaked them tonight, because the tune my tuning guy had me running was about 13.7 AFR at idle. He had had it even richer than that before, I had tweaked it up a little before even.

Here's the timing table. I was actually wrong, my tuning guy had me at a whole 31-32 degress at WOT. I can't imagine that's the optimal...

Base Spark old.JPG

Changed it up to around 22-23* at idle, up to around 40* at cruise in the 2000-3000 RPM range, and 35* at WOT. I can always give that a shot tomorrow and see if the power picks up. I do need to do a WOT pull after and datalog it. I can always revert back if it doesn't work.

Base Spark new.JPG

Edit: just realized I probably overdid the lower RPM cruising area...probably don't want to jump to 30 degrees at around 2000. I'll blend that tomorrow before I try it.

[mt-engines]

what does your datalog show for AFR and Spark during that spot?

You may need more fuel.

[Caprimaniac]

As other have said, more rpm. That cam works well above 4000 up to 7000 rpm.

I am autoX-ing a 302 and cam specs are very close to ehat you have. Two different at 0.603 and 0.638 lift.

I start off in 1. and throw it into 2. and it stay ther. Our track has tighter bends than yours, and speed is almost 0. I have to use the clutch, rev it up and slowly engaging the clutch out of the turnm. We also have a 360 turn around a dime, and there I make a donut. Handbrake would be quicker...

Ignition- wise 40 degrees, static at around 3500.

I have ran hiram efi and weber idf’s, both ran great, but the carbs could not be trusted; linkage doing things...

T5 trans, 3.75 rear 225/45-16 tires and light car.

More rpm, more ignition and maybe rear gear change are what I’d suggesr.

Maybe a drysump- system if you drive it hard....

[barnym17]

what is the lowest rpm it sees during the run coming out of a corner? It needs to be geared so that at your slowest corner exit you are not below the rpm range of the cam.

[Walter R. Malik]

What first must be determined is in what RPM range and the peak RPM encountered will the combination be run ...

[rustbucket79]

Tuning will likely find you some time, car setup and overall driving skill/smoothness will gain you a bunch.

Watching the video, you spend a BUNCH of time in the midrange accelerating, a fair amount lower down, and not much at peak.

If you dissect the course into sections, and consider that time can be gained at a greater rate by coming out of a corner more efficiently quicker rather than at the end of a straight, and you have several corners to gain from, I would consider a set of 4.10's, and accept you might need to shift to third once during the course.

(say gain a tenth for every corner exit for the lower gear)

My other recollection of autocross, is everyone finds out their rev limiter, didn't hear that in your video.

[frnkeore]

The first thing you must do, is figure out your max speed and gear for that.

If there is enough of a speed differential, that you need to shift, don't ever gear, to use 1st gear. 2nd and third or better 3rd and 4th. There is to much rpm drop using 1st for all transmissions, used in production cars.

I think the cam is ok, if you can keep in it's rpm band with gearing. A little wider LSA might be helpful though, like 108.

After the power band is figured out, the next thing will be balance and if you don't already have them, scales are very helpful. For me, a very necessary part of the setup.

[GimpyHSHS]

Tuning will likely find you some time, car setup and overall driving skill/smoothness will gain you a bunch.

Watching the video, you spend a BUNCH of time in the midrange accelerating, a fair amount lower down, and not much at peak.

If you dissect the course into sections, and consider that time can be gained at a greater rate by coming out of a corner more efficiently quicker rather than at the end of a straight, and you have several corners to gain from, I would consider a set of 4.10's, and accept you might need to shift to third once during the course.

(say gain a tenth for every corner exit for the lower gear)

My other recollection of autocross, is everyone finds out their rev limiter, didn't hear that in your video.

That's why a different cam has come into the consideration. We do spend a lot of time in the mid-RPMs, where I know this cam isn't really designed to operate best. Then again, my intake and things probably aren't the best at AutoX either.

I've made some suspension changes here recently that may help us take the entire course faster, so that may help us stay in the powerband better. The old suspension had worn out front struts, stiff poly bushings in all the rear control arms, very mild aftermarket springs, etc.

We've only had a couple fast courses where we have found the rev limiter. Mine was set to 7200rpm, about 74mph in 2nd gear. My cousin usually short shifts 1st, I let it wind out a bit because the engine sounds pretty good lol. SCCA rules typically limit courses to 70mph, so that allows me to stay in 2nd on faster courses. Drawback, of course, being that we lose some help down low. I need to start datalogging every run so I can see what RPMs we're getting and staying in. 4.10s/4.30s are not out of the consideration, especially if we aren't getting anywhere near the rev limiter on MOST courses.

[GimpyHSHS]

The first thing you must do, is figure out your max speed and gear for that.

If there is enough of a speed differential, that you need to shift, don't ever gear, to use 1st gear. 2nd and third or better 3rd and 4th. There is to much rpm drop using 1st for all transmissions, used in production cars.

I think the cam is ok, if you can keep in it's rpm band with gearing. A little wider LSA might be helpful though, like 108.

After the power band is figured out, the next thing will be balance and if you don't already have them, scales are very helpful. For me, a very necessary part of the setup.

Yeah, we've found some times where we got into the rev limiter (74mph at 7200rpm in 2nd). Only a couple courses. I need to start datalogging so I can see where I spend most of the time RPM-wise.

Yeah, I just recently got the parts to be able to better balance the car out. Coilovers, stiffer springs, torque arm, watts link, all that stuff should help, but I haven't invested time and energy into balancing the car since I was adding and removing hard parts. One of my next goals is to remove weight off the nose: lighter bumper bar, remove the AC compressor, delete the ABS module, lighter K member and control arms, aluminum flywheel, things like that.

The 351w added some weight over the 302, but I'm hoping to move it back about an inch and move the front wheels forward 1.5". I have them forward 3/4" right now. Little more caster, little less weight over the front, etc.

[BILL-C]

I would give it more rear gear first off. Use the full rpm capabilities of the valvetrain. 2nd upgrade would be light weight flywheel and clutch .