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John_in_SC 05-07-2019 09:59 PM

Help me find 20+ HP
4 Attachment(s)
Hi Team VMF -

Car Specs:
302 with .030 over bore
Stock crankshaft/rods/pistons /rocker arms
Comp Cam 31-414-3
Edelbrock Perfomer RPM Heads and Intake
T5Z conversion w/3.55 gears/trac-loc
Quick Fuel Street Q 750 Carb
New 3'' driveshaft/electric fan
MSD ignition w/6AL box
Windows for AC and power assist steering
17x8 wheels with 245x45 on back/235x45 on front

Car sat for 2+ years in the garage. Got the bug again and pulled it out, got it tuned, added the Carb, new radiator, driveshaft, electric fan, Caltracs in addition to replacing misc items due to wear and rot as well as fixing some small misc leaks. Car is running great and pulling hard. Love the Caltracs BTW.

Got it dyno'd today. 4 pulls. Pull 1 was terrible due to recovering from flooded carb. Once it worked itself out pulls 2-4 were good with pull 4 yielding 282HP/301TQ (see attached dyno sheet).

I want to cross the 300 threshold using my SB. Looking for suggestions on where to find 20+ HP gains without breaking the bank and without tearing down engine. Suggestions?

Also - looking to put some softer tires on the back. After I get my 20 HP - want to give it a run on the track. Never done that before and it seems like fun. Suggestions based my rim size? Car not tubbed.

Looking forward to the feedback.

John_in_SC 05-07-2019 10:34 PM

Looking for 20+ More HP
4 Attachment(s)
Good evening VMF

Apologize if this is a duplicate posting. Not sure if my original made it or not. Anyhow: Backstory and build below

Backstory: Car has been dormant for 2+ years in garage due to a trip to the middle east and then catching up on life afterwards. Got the itch and found some funding so took it my my guy for a tune and some modifications that I've been wanting to do.

302 bored .030 over w/stock pistons/rocker arms/crank
Edelbrock Performer RPM Heads and Intake
COMP CAM 31-414-3
MSD ignition w/6AL box
Quick Fuel Q-750 CARB
T5Z conversion with trac-loc and 3.55 gearing
New electric fan/new 3' driveshaft/new radiator

Car runs great and pulls hard. Had some wheel hop issues but Caltracs fixed that up quickly. Took it to dyno today. 4 pulls. 1st pull was a dud due to flooded carb. Pulls 2-4 were solid. Final pull resulted in 282HP/301TQ. Net gain of 15+HP from my last dyno 9 years ago.

Looking for suggestions to get me 20+ more HP to crack the 300 mark. I'm not to keen on a tear down/stroke etc at this time. Also looking for suggestions/recommendations on soft street/slick tires. Current wheels are 17x8 with 245x45 for rear tires and 235x45 for fronts. Car not tubbed.

Looking forward to hearing from you all.


awhtx 05-07-2019 11:47 PM


bbmach 05-07-2019 11:51 PM

What are you running for an exhaust system?

NEFaurora 05-07-2019 11:53 PM

Easy... Headers and a straight exhaust.... Done.


Tony K.

2nd 66 05-08-2019 12:39 AM

ditch the power steering and a add phenolic carb spacer and a Filter top :shrug:
By track I assume you mean drag strip? Probably most any DOT drag radial will work , If you want it to handle with sticky tires look for a 200 treadwear autox tire
Welcome and good looking 66 BTW

rkite 05-08-2019 12:47 AM

What is going on starting at 5250 rpm? It looks a bit jittery. Something is holding you back at higher rpm. That head, intake and cam combo should pull past 6000 rpm. Make sure your ignition and valve springs are up to snuff. I'm not sure if that's valve float or not. Yes like already stated some sort of header even 1 5/8" shorties and a 2.5" dual exhaust assuming you don't already have that.

Tom65 05-08-2019 01:17 AM

seems like a lot of carburetor for that setup. May make it difficult to dial in. I would get that sorted first. 600cfm will do the trick.

Grimbrand 05-08-2019 03:57 AM

You are a bit overcarbed, but honestly, unless you're really hurting off the line, it's doing its job, looks like. It's not going to cost you performance so much as economy and driveability. Part throttle would suffer more than anything.

Going to an Air-Gap might get you some, but if you just want that magical 'peak horsepower' long-tube headers should provide more top end charge starting around 5k or so. Not sure what your exhaust system is like. Stay conservative; don't shoot for stovepipes. I'd recommend 2.5" for you, to improve scavenging.

Shorties give you nothing except a way to get the burnt fuel out of your engine. Tri-Y headers give you a modest midrange AND top end charge, because they offer harmonics that improve scavenging at both those RPM ranges. Long tubes give you nothing at the low to mid, but REALLY pull on the top, which is why most drag racers use 'em.

gordonr 05-08-2019 06:42 AM

It would be real helpful to see an AFR graph on the same page as the Hp and torque info. Also what info the tuner discovered with timing changes.

j persons 05-08-2019 07:13 AM

Did the dyno operator make any changes to the carb or timing between runs? My old 331 picked up 23 HP with just a main jet change. Another thing you can do is reduce the cars's weight. Remove the spare, back seat and anything else that isn't welded on. It won't create anymore HP but it will reduce your run times.

John_in_SC 05-08-2019 07:44 AM


Will do my best to provide information on all the good observations:

- NOS is not really an option for this build right now

- Car has long tubes and a 2.5" straight back to a pair of Dynamax turbos. Should have mentioned that in the original post.

- Regarding the CARB. I pulled an Edelbrock 600 off and replaced with the 750. My first impression was the same as some, too much carb but I went with it and it seems to be performing substantially better than previous CARB

- No carb adjustment or tune was done on the dyno - just 4 pulls for a baseline on where the car is

- Will ask to see if the operator has an AFR for the pulls: didn't think to ask. =(

Good call out on that strangeness at 5200 RPM - I was thinking about replacing the 6AL spark box - a few times it has behaved strangely enough to make me say hmmmm. Springs are stock so that has crossed my mind as well. Thoughts on a 6AL refresh and a look at some non-stock springs and new rockers?

I was sniffing around Tire Rack last night and the Firehawk Indy 500's caught me eye due to price point and reviews. With the wheel wells as stock and standard drums, does anyone see any issues with going to 255/40s and the back and 245/40s up front. 17x8 with 4.5" backspacing is the current setup. Nothing done on front suspension.


bbmach 05-08-2019 07:54 AM

Iíd start with getting the afr data. Then a crossover (H or X) in the exhaust system... straight through mufflers instead of the turbo style will help too.

Whatís your compression ratio?

I know you said you didnít want to open the engine, but youíre leaving a lot on the table with that cam. A properly ground hydraulic roller will get you there and then some.

Dan Babb 05-08-2019 09:33 AM

You really do need to get the AFR graph to see if the carb needs any adjustments. If you're running rich anywhere, that will help you pick up the power you're looking for right there. Without that key info, the other lines on the graph don't really help.

Wonder if the bouncing around at the higher RPM is ignition related. It's a long shot, but trimming the plug wires and routing them so they don't cross over each other at all couldn't hurt. Make the coil wire as short as possible and same with the plug wires. I had an issue with another car I owned that was bouncing around at higher RPMs and cleaning up the plugs wires actually did take care of it.

BlakeTX 05-08-2019 09:35 AM

I'm willing to bet you have that much power hiding behind the carb and timing tune. I agree that 750 is too much carb. You can tune it to compensate, but box stock, you can't expect that it's performing it's best. AFR would definitely help inform this.

I would certainly focus on dialing in the carb before throwing money at parts like the 6AL box. From my understanding, they usually work until they don't, as opposed to intermittent failures.

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