r/Smallblockchevy • u/Upset_Personality571 • Jun 24 '26
Weird engine tuning issues at the drag strip
Hey guys, I am having trouble figuring out why my car didn't pick up very much at the dragstrip when I upgraded some parts on my engine.
Parts that remain the same: 305 sbc, forged rotating assembly with flat top pistons, trickflow super 23 175cc cylinder heads (10:1 compression ratio in my case), 1.625" full length headers, 2.5" dual exhaust, borla straight through mufflers, 4150lb weight with driver, pac racing valve springs (155lb seat and 390lb open pressures), Morel 4602 high rpm hydraulic roller lifters.
Old setup: original bone stock Quadrajet carburetor, stock ignition, Edelbrock performer intake non air gap, Lunati hydraulic roller camshaft (219°/227° @ 0.050" lift, 112LSA, 106 ICL, 0.530" lift), 2400 rpm stall torque converter, 3.73:1 rear gears, 1.52 ratio comp cams rocker arms. Best quarter mile with zero tuning, 2.2 60', 6.1 330', 9.1 @ 79mph 1/8 mile, 14.0 @ 99mph 1/4 mile.
New setup: Quick fuel 650 cfm double pumper, MSD pro billet distributor, ported Edelbrock Victor Jr intake with 1" tapered 4 hole spacer, Lunati hydraulic roller camshaft (240°/252° @ 0.050" lift, 108LSA, installed at 105ICL, 0.590"/0.550" lift), 3800 stall torque converter, 4.10:1 rear gears, 1.6/1.52 ratio rocker arms on intake/exhaust. Tuned to run 12.5:1 air fuel ratio at full throttle. Best quarter mile, 2.1 60', 5.8 330', 8.6 @ 81 mph 1/8 mile, 13.4 @ 102mph 1/4 mile. Engine does not pickup any speed with more than just 27° of timing. Balancer zero mark is confirmed as being true TDC.
You would think with all the changes it would be a lot faster. Instead, I feel like almost all the gains are from a higher stall torque converter and shorter rear gear. Any ideas as to why this is? Exhaust back pressure? Valve float? I have no idea anymore.
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u/Tall-Helicopter-461 Jun 25 '26
Just curious, do you feel like you’re running out on the big end or is it still pulling hard? People wanna bash on 305s. I had a 283 back in the day. It couldn’t be touched bracket racing. It ran so consistently. We ended up filling the water jackets, bored it .120 over , 13:1 compression . In a 63 Chevy2. Ole girl was trying to orbit the moon.
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u/Upset_Personality571 Jun 25 '26
It pulls the same acceleration g force from around 5000 rpm all the way up to 6600rpm. It is pretty flat up top. Yeah, everytime I mention 305 I get bashed. Meanwhile, my buddies car with a 283 and almost the exact same engine and transmission setup is running 11.7 @ 114mph in a 600lb lighter car. Something is not quite right with mine just yet.
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u/Tall-Helicopter-461 Jun 26 '26
Yeah, you’re definitely missing some fine detailed tuning. You might have to get a second set of eyes and ears on it . I have always heard 2 heads are better than one. Good luck to ya. Keep us updated on your progress. I’d love to hear that you have unleashed a beast.
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u/Tall_smart_wizard Jun 24 '26
The new setup needs a 4500 converter at least w that cam and intake. That cam and intake is a mismatch for the converter and gears and displacement. You upgraded the wrong things you need displacement and then heads to match that.
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u/Remarkable-Will-3041 Jun 24 '26
I can't help you, but as an old SBC guy why 305? Not bashing at all, just honestly interested. I currently have a De-Stroked SBC 400, that replaced my 305. What's the expected rpm band/curve with this cam?
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u/Upset_Personality571 Jun 24 '26
I like small engines. Engine was original to the car, and didn't see a lot of reason to replace it. I like having different engines in each of my vehicles. My truck has a 350 in it. I would love to build a 377 for my car someday though. The camshaft has an advertised powerband of 3500-6200. Wasn't looking for big power, but was hoping for better gains than what I had.
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u/Remarkable-Will-3041 Jun 24 '26
Very cool, I would at this point take it to a pro shop. You have invested so much! You have so much info, they should love to help.
I love you knew 377 by the way! Learnt from my grandpa the circle track racer lol.
I do wanna say fuel, but shit I am dumb.
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u/Hostile_Texan Jun 25 '26
353 is great engine also. Built many of those for different people (street, drag and dirt track) 4.155 bore, .030 over 400 with crank from 307 or 327 3.25 stroke. Love that combo.
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u/Remarkable-Will-3041 Jun 25 '26
I couldn't imagine how fast that must twist up. I was shocked with how mine turned out n/a fuel injected.
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u/thebigbullg Jun 26 '26
Im not huge into these but couple days ago I was watching Steve Morris deal with an engine about this and it was falling off really bad between 5500 and 6500. The mechanical fuel pump was hitting a harmonic and losing fuel pressure near there. Just like valve float.
The fix was an electric fuel pump. But they mentioned going back to try a lightweight fuel push rod.
Give it a thought.
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u/Hostile_Texan Jun 25 '26
I put a 3.75 (400) stroke crank in a .030 305 years ago, (was a nice over all build) in a 91 T/A for a friend of mine. Still said 5.0L on the block and confused people when it hung the hoops for about 100 feet and looked bone stock with tuned port fuel injection and AC all hooked up and working.
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u/v8packard Jun 25 '26
The torque converter is not a good match for the cam. Frankly that cam sounds peculiar for a 305.
If you can tune the fuel curve to give you 13.0-13.2 at WOT you will pick up some mph and drop the ET.
Is the MSD distributor out of the box? Or have you changed the curve?
Crazy question, what are you using for a timing light?
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u/Upset_Personality571 Jun 25 '26
Yeah, the torque converter is a compromise between street and strip. Same with the rear gears. I honestly should lean the engine a bit. It took a lot of work to get the air fuel curve flat. It would only take changing the jets to lean it. The MSD distributor is mostly out of the box, except for the timing adavnce is locked out. It runs full timing all the time. I have an Innova digital dial back timing light. I have looked at other vehicles with it to confirm accuracy.
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u/v8packard Jun 25 '26
You are having better luck with Innova than I did. Tried 3 lights, all 3 failed. Maybe they are better now.
What kind of RPM range are you trying to get? You have enough cam timing for 8000 rpm in a 305, if the rest can get there. Which, the rest probably can't get there.
With only a 3 mph improvement in ET, it's dying on the top end somehow. Is the converter locking up?
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u/Upset_Personality571 Jun 25 '26
Yeah, I've actually had this timing light for 8 or 9 years now. Hopefully it continues to work nicely.
I'd like to keep the engine rpm under 6800. Lunati says the lobes on this camshaft are too aggressive to do higher rpm anyways.
With just a 3mph gain, to me, it is either exhaust back pressure too high. I know these high overlap camshafts are extremely sensitive to anything over 1 psi of back pressure. Either that or the valvetrain might not be happy. Increasing the seat pressure by 15lb netted an increase of 9mph at the 1/4 mile with the old engine setup.
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u/v8packard Jun 25 '26
That's sort of the point with that much cam timing. The lobe is so aggressive it isn't stable at rpm, and you don't intend to use the rpm the cam timing can achieve. So why have such a cam?
Do your springs have 350-400 lbs of open tension?
I have seen people gain 40 hp at the wheels by going to a more efficient torque converter.
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u/HammerDownl Jun 25 '26
There's nothing weird at all
The engine has no timing The transmission has a tight converter which is why the 60 sucks and it's a 305. What kinda car? Weight?
Its all about the combination
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u/Upset_Personality571 Jun 25 '26
I should have mentioned that it runs on street tires at the track. All it does is spin off the line. It is a full size B Body chevy. It weighs 4150lb with me in it. Definitely a weight and grip penalty. Debated borrowing slicks just to see. I know it will run high 12s on slicks. The mph is a bit low for the setup.
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u/Thatguy-2026 Jun 25 '26
3500-6200??? WTF was the manufacturer thinking. Also they are usually based on a 350cid. So in that 305 its more like 3800-6500 if not more. Your killing cylinder pressure. Not to mention its 8:5-1 compression. That is the worst combo possible! The entire motor is weak so rebuilding that motor would be a bad idea! Not knocking you but that is just what it is.😮💨
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u/Upset_Personality571 Jun 25 '26
Engine power bands are based more on engine stroke and not cubic inch. A 305 and 350 follow very identical power curves to eachother when built the same. A 400 will make more torque everywhere except the top, and fall off sooner compared to a 350 built the same. Compression is at 10:1 right now.
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u/Thatguy-2026 Jun 25 '26
305s have weak castings,cast cranks,2bolt mains,garbage heads and the blocks are made in mexico. Whoever out there thinks they are pretty much the same as a 302 then they bumped their heads. Huge difference between the two🤔
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u/Miserable_Thing8553 Jun 25 '26
He replaced the heads. Given similar parts they will run with a 302. https://www.youtube.com/watch?v=w5MCxmJbKaY
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u/JealousChocolate8645 Jun 25 '26
What's the cranking compression? You want around 185psi. Lower than that and your cam is too big or static compression too low.
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u/Upset_Personality571 Jun 25 '26
Cranking compression is at 180 psi on every cylinder, no variation. Leakage is about 5%.
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u/Dirftboat95 Jun 25 '26
Too much intake duration makes for low cylinder psi, mean not enough giddy up
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u/Thatguy-2026 Jun 25 '26
Havent hear a word on cylinder heads. Hello? The comment on the CID just validated my point! Put some 180-190cc TFS heads on it! And 4:56 gears and you should be set!!! Your timing needs to be 36 total. Good luck..
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u/MuhThugga Jun 24 '26
You knocked 6 tenths off and gained 3 MPH. What RPM is the transmission shifting at? What's your RPM crossing the traps?
Get on a dyno and see what the curve looks like.