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Old August 25th, 2017, 06:22 PM   #1
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Question Small block feedback

I am looking for feedback on my current setup and suggestions on how to get more from my motor. It is more of a cruiser than race car. I plan to upgrade the rear to a 3.42 posi in the near future. I am also wondering what kind of gains I can expect by changing to aluminum heads. The two links below are my engine build and dyno results.

http://fivelugs.com/2017/08/14/72-cutlass-engine-specs/


http://fivelugs.com/2017/08/14/men-l...-numbers-dont/
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Old August 25th, 2017, 08:57 PM   #2
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Just a gearing comment: 3.42 gears may be uncomfortable for you at highway speeds if you're big on road trips - my former posi 3.23-geared '72 Skylark 350/TH350 ran above 3000 rpm in the 60mph range on 245-60-r15 tires. I've since scaled back to a 3.08 posi on my '72 Cutlass with same drivetrain and tire size - much better on the RPM's and still a strong pull from idle.

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Old August 25th, 2017, 09:24 PM   #3
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Just a gearing comment: 3.42 gears may be uncomfortable for you at highway speeds if you're big on road trips - my former posi 3.23-geared '72 Skylark 350/TH350 ran above 3000 rpm in the 60mph range on 245-60-r15 tires. I've since scaled back to a 3.08 posi on my '72 Cutlass with same drivetrain and tire size - much better on the RPM's and still a strong pull from idle.
Thank you. I put 1,000 miles on the car during part of the Power Tour and the 2.73 gears were great on the highway. I would like a little more pep off the line but low RPMs are nice. How do you like the 3.08 gears?
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Old August 25th, 2017, 09:41 PM   #4
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my 3.23 gears had a bit more grunt off line from idle but really not worth the trade off for highway RPMs. I'm now at 70+ mph before I hit the 3000 rpm range - much better for most highways.


And the reality is, you can essentially build and tune the motor to compensate for any low-end performance difference between gear sets.


I built my 350 with flat top pistons, a Howards street performance cam, E-brock 2711 intake and a mid-70's electric choke Qjet. Stock heads rebuilt with new valves, rockers, springs, etc., added aluminum water pump, 2x roller chain, HEI. It hits strong from idle and the 3.08s are a great fit for it.
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Old August 26th, 2017, 07:15 AM   #5
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First the 600 carb is way too small. Needs a 750.
You could modify your current heads or get the aluminums, either way that will uncork the power.
People normally think they have more power than they really do. 300 at the wheels would be pretty good. That equates to at least 360+ or so at the crank. It's harder than you think to get there with your current crappy heads.
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Old August 26th, 2017, 07:55 AM   #6
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I've got 3:42s w 255-60-15s IIRC its 3kish rpms @ 60 ish mph

They're great if you mostly do 50 mph or less roads, but if hi way travel is a thing some might prefer a lower hi way rpm, I swapped from 2.7x gears and I agree the 3:08 seems like a nice compromise now.

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Old August 26th, 2017, 08:26 AM   #7
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Might want to lose that glass fuel filter.
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Old August 26th, 2017, 09:47 AM   #8
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Might want to lose that glass fuel filter.
X2 throw that pos as far as you can. Then don't go looking for it later.X2 on the carb being to small.
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Old August 26th, 2017, 11:01 AM   #9
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X3 on the glass filter, its a fire looking for a place to happen.
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Old August 26th, 2017, 12:03 PM   #10
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Might want to lose that glass fuel filter.
I did. It started leaking in the fall and I replaced it with a billet one.
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Old August 26th, 2017, 12:11 PM   #11
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First the 600 carb is way too small. Needs a 750.
You could modify your current heads or get the aluminums, either way that will uncork the power.
People normally think they have more power than they really do. 300 at the wheels would be pretty good. That equates to at least 360+ or so at the crank. It's harder than you think to get there with your current crappy heads.
I have said that if I replace the carb, I would go with EFI.

The heads received the normal machine work. 3 angle valve job and seals. I did not increase the sizes at that time. Sounds like heads should be moved up the list.
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Old August 26th, 2017, 02:16 PM   #12
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Figure this. Stock SB heads with the 1.88 valve flow about 180cfm. Barely enough for 400hp with first rate parts.
I'd put 2.07/1.62 valves in there and a real good bowl blending. Then add a cam with more lift and a bit more duration. Upgrade to a 750 carb and you'll be much much closer to your desired power level.
I'll be dynoing a 375sb in about 2 weeks. It has stock Procomps, 9.5:1, a small roller cam, a 735 QF Carb and the same intake as yours. I'll bet it makes 400/400+ solidly but we'll see.
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Old August 26th, 2017, 05:35 PM   #13
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Can someone take a moment and briefly explain why the OP's 600 cfm carb is too small? The OP indicated the engine is 355 cubic inches. At 5,000 rpms and 100% volumetric efficiency (VE) the naturally aspirated (NA) engine can flow 514 cfm. The carb has a cfm rating that should work up to almost 6,000 rpms (again, assuming an unlikely 100% VE).

Is it that the carb cfm ratings aren't accurate? Or the carb itself reduces the VE? I'd like to understand why a 355 NA engine would need more than a 600 cfm carb.
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Old August 26th, 2017, 06:57 PM   #14
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Simple, when you have small runner and/or small ports, then you need the extra carb size because you don't have any other volume.
If he had a single plane intake with a large plenum and runners he could get by with the 600. But with marginal runner volume you need the extra cfm of a bigger carb. Just think of those small runners as real long venturis with the big ends on either side being the carb and the cyl bore.
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Old August 26th, 2017, 10:41 PM   #15
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It looks like about 265 HP and 350 ft lbs of torque, if the calculator is accurate, not bad. As Mark said, either 2.07"/1.625" valves with the bowls opened up and transitioning. The Procomp heads would work well but would need about 14cc removed from the chambers with your current pistons to retain the current compression ratio.
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Old August 27th, 2017, 07:51 AM   #16
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Installing the 3.42's you want, and a 200-4R transmission would be a nice upgrade in performance and highway cruising, without touching the engine.

http://www.monstertransmission.com/2...l#.WaLNHyiGPIU

The 200-4R has a slightly deeper first gear than the TH350, so first gear would feel like a TH350 and 3.73 rear gears. Then in 4th gear it would cruise like a TH350 with a 2.30 gear!
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Old August 27th, 2017, 09:12 AM   #17
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I would also agree to do the 3.42's before anything else.It willbe your biggest seat of the pants performance gains you can feel.

I have 3.90's and drive my car alot and to the track and back. I got used to it but my combination needs it.

I think for your heads i would just do big valves and a little bowl work and that will improve performance. i think if you went from iron to aluminum the gains would not be worth the cost unless the whole build was tailored to maximize the use of the heads.

As for the carb being too small i call BS. from personal experience. I ran 1405 edelbrock in a pretty stout 10 to 1 350 and it ran 13.3's and i ran it on a very mild 350 9 to 1 combo that went 13.8's no issues at all. It was plenty for the street and the 13.3 combo was borderline needing more fuel and since then i went to a holley.

My current 355 combo runs 12.30's 10 to 1 compression and a pretty big cam that still very nice on the street with great manners. It needs a 750 double pumper but is a hog on fuel at best i might get 9 mpg. Its fun though lol. I built it pretty much to race but i still like to drive it on the street and its not uncommon for me to put on 120 miles in one night going from cruisenight to cruisenight.
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Old August 27th, 2017, 09:24 AM   #18
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Installing the 3.42's you want, and a 200-4R transmission would be a nice upgrade in performance and highway cruising, without touching the engine.

http://www.monstertransmission.com/2...l#.WaLNHyiGPIU

The 200-4R has a slightly deeper first gear than the TH350, so first gear would feel like a TH350 and 3.73 rear gears. Then in 4th gear it would cruise like a TH350 with a 2.30 gear!
I agree with this also. Good suggestion.
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Old August 27th, 2017, 01:55 PM   #19
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It looks like about 265 HP and 350 ft lbs of torque, if the calculator is accurate, not bad. As Mark said, either 2.07"/1.625" valves with the bowls opened up and transitioning. The Procomp heads would work well but would need about 14cc removed from the chambers with your current pistons to retain the current compression ratio.
I guess I hadn't thought about the power at the crank. Those numbers are respectable for a cruiser.
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Old August 27th, 2017, 02:15 PM   #20
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I would also agree to do the 3.42's before anything else. It will be your biggest seat of the pants performance gains you can feel.

As for the carb being too small i call BS. from personal experience. I ran 1405 edelbrock in a pretty stout 10 to 1 350 and it ran 13.3's and i ran it on a very mild 350 9 to 1 combo that went 13.8's no issues at all. It was plenty for the street and the 13.3 combo was borderline needing more fuel and since then i went to a holley.
I see no mention of you trying that exact combination with a larger carb along with an apples to apples comparison. Did you?
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Old August 27th, 2017, 02:48 PM   #21
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Installing the 3.42's you want, and a 200-4R transmission would be a nice upgrade in performance and highway cruising, without touching the engine.

http://www.monstertransmission.com/2...l#.WaLNHyiGPIU

The 200-4R has a slightly deeper first gear than the TH350, so first gear would feel like a TH350 and 3.73 rear gears. Then in 4th gear it would cruise like a TH350 with a 2.30 gear!
Good suggestion. However I am plagued by my "might as well" problem. Any changes to the transmission would result in a manual conversion. I miss shifting gears. It probably won't be as much fun in traffic on the Power Tour, but I would rather go manual than spend over $2,000 on a new automatic.
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Old August 27th, 2017, 02:52 PM   #22
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@ cutlass EFI ., I never did try a bigger carb but at that time there was no need to. based off of MPH i was in the ball park for much lower e/t's but my 60 ft. was horrible. The tq. converter was the limiting factor. a 103 mph for a 13.3 car is more than enough. there was no need. The extra fuel would have helped off the line but the MPH was a good indication that it was enough.

Now my testing on my current combo showed the difference in 60 ft. between the vac. secondaries and mechanical secondaries.

Based off of the fact he will not be racing it or hitting the cars redline i doubt he really needs a bigger carb. Now if he plans on wringing out every bit of HP then yeah go bigger but for his combo a 650 DP would be plenty.

Again thats just my first hand experience. There is guys running more carb than a 600 cfm running much slower than i was with a small block and I literally have never ever jetted a carb. All i did to my 750 DP was flipped the pump cam for more initial fuel shot.I run em straight out the box. Gonna do some jetting this fall. gonna try for a 12.0 11.99 in nov. when the weather is right.

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Old August 27th, 2017, 02:57 PM   #23
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Too many guys just put any carb on without tuning it properly.
I've had multiple Olds engines on the dyno as you know. Even mild small blocks are still pulling vacuum at the end of the pull with properly tuned 750's. What does that tell you?

Last edited by cutlassefi; August 27th, 2017 at 03:03 PM.
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Old August 27th, 2017, 03:01 PM   #24
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But doesn't the engine load change between dyno and actually in car ??? Thus changin the engine vac.
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Old August 27th, 2017, 03:26 PM   #25
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It probably won't be as much fun in traffic on the Power Tour
I have two manual trans vehicles that I switch out driving to work in heavy traffic on a daily basis. I'm sure you could manage for a short duration Power Tour.
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Old August 27th, 2017, 03:28 PM   #26
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So, at the moment I am thinking: a good set of cylinder heads, EFI, and 3.08 gears in a posi differential.
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Old August 27th, 2017, 03:35 PM   #27
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But doesn't the engine load change between dyno and actually in car ??? Thus changin the engine vac.
Yes. But I have personally witnessed a well tuned carb that was "too large" have better manners than an ill tuned carb that was "too small".
Do it right and you'll be rewarded in the end.
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Old August 27th, 2017, 03:39 PM   #28
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So, at the moment I am thinking: a good set of cylinder heads, EFI, and 3.08 gears in a posi differential.
Depending on the EFI you go with you can have that control lockup on an overdrive tranny if you so choose. Something to think about.
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Old August 27th, 2017, 04:47 PM   #29
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3.08 gears are not that much of a jump. try to find someone who has a car with 3.42 gears and see how you like it. I feel like for a good blend of cruising and power the 3.42 is great.
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Old August 27th, 2017, 05:34 PM   #30
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3.08 gears are not that much of a jump. try to find someone who has a car with 3.42 gears and see how you like it. I feel like for a good blend of cruising and power the 3.42 is great.
Right now I can ride on the highway at 70mph at only 2700rpm. I will check out a few calculators to see what is reasonable.
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Old August 27th, 2017, 05:44 PM   #31
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Im doing 80 @ 3800 with 3.90's
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Old September 1st, 2017, 10:25 PM   #32
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You can drop to about 1750 with a 2004R with 3.42 gears and stock size tires. I plan on running 3.90 gears with my 2004R. I have to temporarily go back to the TH350, my daughter ran it low on fluid, toasted it. Mine sucks even with the 2.78 gears, around that same 2500-2700 rpm. The 2004R needs a few improvements to live but has very nice gear ratios. I am adding the important hardened and billet parts to live under big torque.
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Old September 2nd, 2017, 08:00 PM   #33
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Put a 2000 stall converter in. Only a few hundred dollars and should really improve your take off.
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Old September 3rd, 2017, 08:10 AM   #34
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I miss shifting gears. It probably won't be as much fun in traffic on the Power Tour, but I would rather go manual than spend over $2,000 on a new automatic.
I understand. Every one of our cars over the last 30 years has been manual transmission. I love the gears and never notice a irritation factor in traffic.

I even converted the Vista Cruiser to manual after considering overdrive automatics. That car leaves harder than any I have owned.
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Old September 7th, 2017, 05:30 PM   #35
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I understand. Every one of our cars over the last 30 years has been manual transmission. I love the gears and never notice a irritation factor in traffic.

I even converted the Vista Cruiser to manual after considering overdrive automatics. That car leaves harder than any I have owned.
Do you have a write up on your conversion? I would like to see Olds specific information on swapping out the auto for manual.
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Old September 8th, 2017, 11:37 AM   #36
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I agree with Mark 100%. I can't tell you how much time and $ guys have wasted with carbs that were too small. Those calculators do not work in the real world. IMO, Olds engines (Buicks as well) like big carbs. I don't know if it port volume or velocity or what. I had a similar 355 to the OPs and had a 780 Holley that I had 4 jet sizes richer.

Also to guys posting build specs, as a future reference, it REALLY helps to post the cam specs and not just the part/grind #. I could not find the specs for this cam.
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Old September 8th, 2017, 12:11 PM   #37
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Different animal, but I switched from 3.73 gear in my Vette to a 3.08 and I love it. Its still plenty quick and im at about 28-29 hundred RPMS at 70 mph. I have 235-60's, I think they are 26 inches tall. A taller tire would tame that number alittle more. I have 275-60's, 28 inch tall on my Olds with a Gearvendors overdrive, final GR of 3.04. I cant rate it as I haven't driven it yet, but getting close. I think you would like a 3.08.
Good luck
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Old September 8th, 2017, 05:19 PM   #38
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Also to guys posting build specs, as a future reference, it REALLY helps to post the cam specs and not just the part/grind #. I could not find the specs for this cam.
Good call.

Erson TQ40H
110 lobe seperation
Valve lift 0.504 / 0.504
Duration 284 / 296
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Old September 24th, 2017, 08:45 PM   #39
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Pro Comp heads are available in 77cc and 64cc. I currently have 64cc heads on my car. 64cc keeps my CR the same. Do the 77cc flow better than the 64cc or is it a matter of compression?
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Old September 24th, 2017, 09:52 PM   #40
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cc's are chamber volume on that figure.
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