Hello. I currently have a 355 cubic inch SBO with 5.8 cc pistons and Erson TQ40H cam. My engine runs good, but I am thinking about pulling the heads to have larger valves put in. I had the heads refreshed about 2 years ago, but I didn’t know then what I know now. Should I:

A) Have the existing 7A heads refreshed with larger valves.
B) Buy a set of iron heads and have them worked with larger valves.
C) Go with aluminum heads and why.

Thanks in advance for the responses.

 

With those pistons, get your current heads cut for larger valves with the bowls opened under them with a cutter with either 2"/1.625" or 2.07"/1.625" valves. The Procomp heads are better with quality valves added but interfere with the early power steering return line. Add in they also need a .060" minimum cut due to the 77cc chambers. Another reason to stick with your current heads are, the guides and springs, assuming they match the cam, should be good to go or need minimal attention.

 

Thanks for the response. Yes, the springs were matched to the cam. I didn’t realize the Pro Comps interfered with the power steering line. I currently have a mechanical fuel pump, so that is another concern.

 

Here is a reality. Why change it ??? The cost vs. performance gain in my opinion wont be worth it. Have you taken the car to the track to see how it runs ?? I would try to find more power from the combination you have now. You would be amazed what you will find. The same engine has been in my car for over 4 years now and it started out running 13.0's and now currently 12.20's. No internal engine mods or changes where done besides the full roller rocker arms. I made the car a little lighter , did suspension work, carb change , ignition curve change , little stuff like that. Just a thought.

 

I am guesstimating 20-30hp from better heads and carb improvement. Not sure where else to find power in my current setup. The heads seem to be the bottle neck based on having Edelbrock Performer RPM intake and long tube headers.

I have not had this car on the drag strip. That may be a thought.

 

Whats your entire combo consist of. Engine trans diff weight power accessories ??? I guess my point is not make maybe a little more HP but maximizing whats there and using as much power as you can.

 

Small Block Oldsmobile “Rocket 350” bored 0.30 over to 355 cubic inches
5.8 cc dish forged Speed Pro pistons (2264P)
Crank shortened 0.10/0.10
Erson TQ40H Camshaft 220/228 on 110 with .504/.504
64 cc combustion chamber
3 angle valve job
9.5:1 compression ratio
Edelbrock Performer RPM intake manifold
Holley 600 vacuum secondary carburetor
Melling Oil Pump
Cloyes Timing Set
HEI Distributor
Pro-Tork Mini Starter
Long Tube Headers
Magnaflow Dual Exhaust
Open differential with 2.73 gear
Jegs brand 2000-2300 rpm stall converter
Trans Go Stage 1-2 shift kit in TH350

 

Id invest in atleast 3.42 gear and a 2500 stall converter. That's a much better investment that you will feel and literally make you car day and night. Once you do all that do a 750 vac. secondary carb. make that timing come in fast and you will have a real screamer. I run a light and medium spring on my distributor. My curiser as 2 light springs made a world of difference since that one is a heavier car. An X pipe helps too.

I bought one of those ebay 2600 to 2800 stall converter. Awesome for the price and it worked great then I decided to do a 3500 stall. You will have into a gear and converter what doing the heads would cost.

 

I understand the 2.73 is nice for the highway, I am leaving my 2.78 for that reason. Stock torque converter? 2000 plus stall would be better. What carb are you planning on? I say either a custom 800 cfm Qjet or a Street Demon 750, if mileage is important or the QF Slayer 750, assuming all are tuned to your motor.

 

idk the 3.08 in the cruiser is great and I run it with a short tire so its more like a 3.23 and its very nice.

now my 72 the 3.90's and mufflers dumping at the axle will drive you a bit nuts after 150 miles or so. if I had a quieter exhaust it would be so much better and I plan on making it quiet. The rpms are not even an issue. the small block runs like a sewing machine at 3800 rpm.

 

Sorry, the transmission information was left out. I have a Jegs brand 2000-2300 rpm stall converter with a Trans Go Stage 1-2 shift kit in my TH350. Tires are stock height at 245/45/18.

I am planning on Quick Fuel Slayer 750.

 

Just curious, where does that converter flash stall, it is rated very well on Jegs and is very affordable. The Quickfuel Slayer 750 should help a bunch once tuned for your motor.

 

IIRC, flash is right about 2,000 rpm. I spoke to the machine shop this afternoon. It would be about $800 and in his opinion, he wouldn’t spend that on a street car. Sounds like new QF Slayer 750 is next on my list.

 

Cleaning up the bowls, installing bigger valves and doing crossover work will make a noticeable difference, a minimum of 20hp. That with the jump from a 600 to a 750 would be very noticeable. But I understand, it’s your money.
Conversely if you’re not spending the $800 then buy a wideband and tune the carb correctly. You’ll be glad you did.

 

Mark,

Is there a better way to go about doing this? How much more work is involved in getting aluminum heads fitted to my setup? If aluminum is it best to start with a bare set or buy a complete set. I am thinking Pro Comp. Edelbrock is not in my budget.

 

You just need to address the items listed, fuel pump, power steering etc.
But if you buy the Procomps from anyone other than me or Bernard, have them checked. They won't be what you expect.

 

You're looking at aluminum heads when you have a 2.73 open rear? Spend some money on that, as said get a 3.42 or better gear and a limited slip diff. It will feel like you added engine power by doing that.

 

I have been hesitant to upgrade the gear. I understand that it needs to be addressed but I don’t want to get it wrong. I like to drive my car. Last year I put over 1,000 miles on it during a weekend of Power Tour. It is nice not turning high rpm’s on the highway. I need to figure out the right gear and get the posi differential installed as well.

 

Honestly the 3.23 will be your best bet or even a 3.42 depending on tire height . You will love it and wont mind the RPMs at all. I got used to the RPMs with my 3.90's only problem is the exhaust is loud lol. At highway speeds and higher rpms the sbo just hums and isn't even working.

 

Right now I am at 2400 RPM at 60 mph with my 2.78 gears and a 26.6" tall tire. I am going TH350C which will lower it to 2100 RPM. This calculator is accurate just add 300 RPM for your non lock up converter. Just change the transmission ratio to 1:1. Basically a 3.42 gears adds 500 RPM at 60 mph.
http://tech.oldsgmail.com/ch_axle.php

 

I run a 26.7 inch tire, so my numbers are basically identical to what you are seeing. My original plan was 3.42 gear. I just want to be sure that 2900-3000rpm is safe for hours at a time on road trips.

 

You wont hurt it. I drive 1 hr to the race track at highway speeds , race then drive back. And then i do alot of crusing on weekends.

 

Thanks again everyone for the responses. When I originally established my setup, Mark told me my cam would be best with the 3.42 gears. It has been in the list since then, but it sounds like it should be next. Limited slip differential with 3.42 gears and QF Slayer 750 carb. Probably enough upgrades for this year.

 

You should be right around 2900 RPM at 60 mph. What radiator are you using? It may need upgrading.

 

I have a 3 core radiator that was on the car when I bought it in 2011. Engine temperatures are usually at 190* with factory fan setup.

 

It may be marginal with the extra rpm, what thermostat temp? I run that temp with a 160 thermostat, actually only at idle with a recored 2 core rad.

 

I am pretty sure I have a 180* thermostat. It holds there even while cruising. While running 70mph last summer for about 30-45 minutes it crept up to the 205 range.

 

I have the smaller GM A body radiator. So I wanna say 26 inches wide ? Its a big 2 core . I use 2 14 inch electric fans from the fan assembly of a 9c1 caprice. For the water pump I run an moroso water pump drive kit with an old servo motor. ON really hot days I might hit 210 usually 180 is the sweet spot with no thermostat.

One particular summer day after a long day of racing ( about 12 runs ) on the way home it stayed at 210 the whole drive home 60 miles but it was 94 degrees and humidity was through the roof. This is with 3.90's

 

That 205 temp is passable for our old cars, can you live with maybe 220 temps?

 

I would probably make other changes to keep the temperature down. It seems like Good Guys and Power Tour always include 90+ degree days.

 

Get a large two core aluminum rad at the same time as the gear swap.