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Awesome, believe it or not you already reduced your cars elapsed time if you ran a 1/4 mile by 1 full second.
The 4BBL alone, drops you another full second.
Now your in icing on the cake territory.
For reference here are Automobile Catalogs simulations for your car and the like with factory mods.
1968 350 2BBL 2SP = 17.4 in the 1/4 mile
1969 350 2BBL 3SP = 16.4 in the 1/4 mile
1969 350 4BBL 3SP = 15.4 in the 1/4 mile (i personally ran a 15.5 with my 120,000 mile 69 weighing 125 LBS more than Auto Cats version, the weight difference alone makes us dead even so these numbers are absolutely attainable)
All above are with standard 2.78 rear... You are missing the 4BBLs compression (-10 HP gross or about - 7 HP net) but you can make that up in other ways. Performance mufflers and a balance tube may do it. Performance mufflers and a X pipe should do it.
Headers, better converter, 3.42s maybe you see a 14.4
This is all very encouraging! Frankly, anything in the 14.5 to 15.5 range will probably satisfy the "fun to drive" target.
Back in the 80s, when I bought my '66 4-4-2 convertible, it had a stock '68 350 4bbl in it, and even with my 2 speed Jetaway and 3.23 posi, it was plenty of fun once you got off the line. After I installed a rebuilt 425 out of a '66 Starfire, I could go 0-60 in under 5 seconds and 0-100 in about 10 seconds. I was never able to time it at the drag strip since they required roll cages on any convertible that could run faster than a 15 second quarter mile, but on the streets I beat my friend's Nova that consistently ran 13.8s. I have no desire to make my '68 Cutlass this quick or this fast, but I think somewhere around 15s in the 1/4 would be fine.
Maybe someday I will buy a 64-67 hardtop and try to build a proper drag car.
I went from 2.56 to 3.42 and gained .6 in the 1/8 mile. A mild cam swap will work well since you are close to 9 to1 compression, probably need a timing chain anyways. A 2000+ stall with also help a lot. I had your basic motor, a 76 350 with slightly milled #6 heads with a bigger intake valve and the bowls opened, 214/214 cam, Sanderson shorties and 2.5" dual exhaust, 2300 flash stall and 2.78 open rear. I could do a 1/4 block burn out. The day before I took it to the 1/8 mile my Daughter fried the trans. I should have took it with just first and second gear in the 2004R. It probably would have ran mid 9's in the 1/8, not fast but a definite improvement over stock.
I am going to use my borescope to examine the timing chain when I change the fuel pump. If it appears it still has the nylon timing gear, I will probably go ahead and replace it. I could change the cam at the same time, but I am not sure if the cam I would want to use after a full rebuild to boost the compression of the engine would work that well with the lower compression. The stock compression is 9:1, but since the engine appears to have been rebuilt, it could be lower. I only intend to go to around 9.5 compression, so maybe the existing compression and future compression are close enough for a 1000-5000 rpm operating range cam to work well both now and later.
I went from 2.56 to 3.42 and gained .6 in the 1/8 mile.
Tremendous improvement. If your ride weighed around 3800 LBS the gear swap showed the equivalent of a 35 HP gain...
Originally Posted by NTXOlds
This is all very encouraging! Frankly, anything in the 14.5 to 15.5 range will probably satisfy the "fun to drive" target.
I'm barely in that range and I find my ride very fun to drive. The torque goes a long way in that department.
Originally Posted by NTXOlds
Back in the 80s, when I bought my '66 4-4-2 convertible, it had a stock '68 350 4bbl in it, and even with my 2 speed Jetaway and 3.23 posi, it was plenty of fun once you got off the line. After I installed a rebuilt 425 out of a '66 Starfire,
I beat my friend's Nova that consistently ran 13.8s.
I believe it. 425s are incredible engines well deserving of there Super Rocket nickname. 1966 Starfires came with 425s rated at 375 HP and 470 LB FT those numbers are higher than the ratings on the 1966 W30. Knew of someone who had a stock 1985-1987 442. He swapped in a stock good running 425 and ran 13s.
Yes, the 88 Cutlass weighs 3750 pounds. I can hardly wait to put in a 3.90 posi in the 70S. With a 2004R and lock up converter, 1900 rpm at 60 mph. It doesn't have the flimsy 7.5" in it like the 88. I blew up Spider gears taking out the pinion and broke the pins on a no slip.
Last edited by olds 307 and 403; January 5th, 2021 at 06:09 AM.
My goal for the holidays was to switch the 2bbl intake to an Edelbrock Performer with a new Holley Street Warrior. The disassembly is done, and I was pleasantly surprised at how good the top side of the engine looks. This certainly makes me think that there is not a lot of mileage on the engine since it was at least partially rebuilt even though the outside of the engine is very dirty.
Now I am thinking that maybe I should just go ahead and pull the engine at this point and drop in a new cam while I have already disconnected almost everything. Decisions, decisions, decisions...
I completed my goal to switch out the 2bbl intake and carb to a 4bbl. I installed an Edelbrock Performer intake and Holley Street Warrior carb. I still have a couple of loose ends to fix like rewiring the electric choke to the fuse box since Holley includes a very short wire for it, and I want to reroute the fuel line a little bit.
Anyway, I could not be happier with the results. The car is so much more responsive now, so it passes the seat of the pants dyno tests for sure. Throttle response is instantaneous, and it is so much fun. I don't think that I am seeing a huge performance increase in overall power (I was not expecting much since it still has low compression and the factory cam), but the fun to drive factor is much higher. The throttle kick down works perfectly, too, so passing is effortless.
If I had any complaint at all, it is that there seems to be a bit of a lazy spot in the acceleration at WOT in low to mid-RPMs. I do not have a tach, so I cannot say exactly the range, but when taking off at WOT the engine pulls very hard at first then eases up a bit until the secondaries start to open (I can hear them) at which point it starts pulling really strongly again.
I am thinking that it needs lighter springs in the distributor for the mechanical advance. I set the initial timing to about 10 degrees before TDC, but I do not have a timing light that you can adjust to see the final timing advance.
Also, at idle it seems like the timing jumps around more than I expect. The timing seems to jump between 5 to 13 degrees before TDC, although most of the time it is right around 10. Is this within normal tolerances? I have changed the cap, rotor, plugs and wires, but I probably need to change the points and condenser, too.
The unstable timing could be a loose timing chain. If its never been changed the original gear was covered w nylon teeth that break off over time, this results in a loose chain and a bunch of debris in your oil pickup. The timing chain and gears can be changed w the engine in the car, but IMO its better to pull the engine and clean out the oil pan and pickup and do the chain at the same time
The unstable timing could be a loose timing chain. If its never been changed the original gear was covered w nylon teeth that break off over time, this results in a loose chain and a bunch of debris in your oil pickup. The timing chain and gears can be changed w the engine in the car, but IMO its better to pull the engine and clean out the oil pan and pickup and do the chain at the same time
I am concerned that this could be the case, but since the engine was rebuilt sometime in the past, I’m hoping the timing chain and gear were replaced. I didn’t change the fuel pump, but if I do, I’ll use my bore scope to see if the gear was changed.
If that turns out to be the issue, I’ll wait to change it out when I do a full rebuild.
At one point in my life I had a Holley 600 on my car and I had to get the spring kit to tune the vacuum secondary opening. I found the secondaries opened a bit too late with the original spring.
If the idle is not completely smooth, the timing will bounce as the RPM changes. Try a full tune-up before changing anything to see if that helps stabilize things. You may need to adjust the idle air/fuel mix on the carb, too.
Last edited by Fun71; December 30th, 2020 at 08:47 AM.
At one point in my life I had a Holley 600 on my car and I had to get the spring kit to tune the vacuum secondary opening. I found the secondaries opened a bit too late with the original spring.
If the idle is not completely smooth, the timing will bounce as the RPM changes. Try a full tune-up before changing anything to see if that helps stabilize things. You may need to adjust the idle air/fuel mix on the carb, too.
The spring kit is a good idea. I had not considered that. Thanks!
The idle is a little choppy while it is warming up, but it seems really smooth once it is warm. If I didn’t see the timing variations with the timing light, I would have never guessed that it wasn’t spot on every time. Maybe I’m overthinking it.
At one point in my life I had a Holley 600 on my car and I had to get the spring kit to tune the vacuum secondary opening. I found the secondaries opened a bit too late with the original spring.
Good call on the spring, Kenneth. According to Holley, it appears that the out of the box spring starts opening around 2240 RPM and does not fully open until 8160, which is well past my redline.
I ordered the spring kit and will switch to a lighter spring, probably an Orange (1620 - 5680 RPM range) and try it out once it stops raining.
Good call on the spring, Kenneth. According to Holley, it appears that the out of the box spring starts opening around 2240 RPM and does not fully open until 8160, which is well past my redline.
I ordered the spring kit and will switch to a lighter spring, probably an Orange (1620 - 5680 RPM range) and try it out once it stops raining.
Thanks!
Fun71 is the man, I've been reading and appreciating his posts for years. Tons of life experience with our engines and setups.
NTXOlds just keep on tinkering you are now a one man car company. Trial and error is on you now that your car has been modified. She should feel just like mine. My car will make the tire scream on a dead punch straight through an intersection. And chirp the tire at a 15 MPH roll when you tap the gas pedal. The compression difference just isn't that big a deal IMHO. Fine tune it advance your timing run premium gas and let it rip !
The compression difference just isn't that big a deal IMHO.
Yeah, it's hard to imagine a 1.75-2 point increase in compression creating a huge increase in horsepower, since just about everything else in the engines was the same.
Back in high school I had a 1970 Supreme 350-4bbl, 2.56 rearend and a friend had a 1971 Supreme, 350-4bbl, 2.56 rearend. On paper my car would destroy his in a race, with my awesome high compression 310 HP car against his puny low compression 200 HP car. But in reality the cars were fairly even until the very top end of 1st gear, where I started pulling ahead of him. This was a severe blow to my young ego.
Yeah, it's hard to imagine a 1.75-2 point increase in compression creating a huge increase in horsepower, since just about everything else in the engines was the same.
Back in high school I had a 1970 Supreme 350-4bbl, 2.56 rearend and a friend had a 1971 Supreme, 350-4bbl, 2.56 rearend. On paper my car would destroy his in a race, with my awesome high compression 310 HP car against his puny low compression 200 HP car. But in reality the cars were fairly even until the very top end of 1st gear, where I started pulling ahead of him. This was a severe blow to my young ego.
That is a great comparison, other than pistons, the same car, definitely apple's to apple's. I got blasted comparing my Olds 350 powered 94 Z1 to mid 2000's LS 5.3 trucks, my 307 headed 350 felt way faster idle to 4500 rpm on another forum. On paper, the LS had 100 hp and TQ, felt like less torque and the hp over 4000 rpm was where the LS came alive. Same trans, gearing and I actually had taller tires, apple's to apple's IMHO. A 73 and later also would not work for direct comparison, restriction under the exhaust valve and heavier car. You can go with a small cam but a 2000+ stall will be needed or you will gain nothing in the acceleration department, the stock 1600 stall sucks. I went from a 2350 stall 2004R to a 1600 stall TH350, it was so much less fun. From 1/4 block burnouts to barely being able to spin tires.
Yeah, it's hard to imagine a 1.75-2 point increase in compression creating a huge increase in horsepower, since just about everything else in the engines was the same.
It is hard to say how much horsepower is lost in due to the lower compression. My understanding was that the 250 HP 2bbl and 310 HP 4bbl had the same cam and the same heads. The HP difference would be due to the 4bbl intake and carb, higher compression, and (I assume) dual exhaust.
I have done all of the things that I can do to make it similar to the 310 HP version (dual exhaust, 4bbl) except for rebuilding the engine to increase the compression. At that point, I will go with a hotter cam, too.
The good news is that the engine is very responsive, feels very strong and doesn't burn any oil. Since I intend to rebuild it at some point, it feels like I am playing with house money - I can drive it like I stole it as long as I maintain it regularly and listen for any odd noises.
It is hard to say how much horsepower is lost in due to the lower compression.
I agree, but I think it was fairly small based on my side-by-side racing experiences.
I did not know back in school that the ratings method changed from 1970 to 1971. The older rating method was SAE GROSS which means a bare engine with no accessories and free flowing exhaust, whereas the 1971-up method was SAE NET which means the engine as-installed in the vehicle, with all of the accessories, air cleaner, full exhaust system, etc.
The 1971 Owners Manual lists the engine ratings for both methods, which gives you an idea of how much different those rating methods actually are:
1971 350-4bbl engine with dual exhaust:
GROSS = 260 HP @ 4600 RPM, 360 Ft-Lbs @ 3200 RPM
NET = 200 HP @ 4400 RPM, 300 Ft-Lbs @ 3200 RPM
So comparing the 1970 350 to the 1971 350 using the SAE GROSS ratings:
So does anyone really believe there was a 50 horsepower drop due to 2 points of compression alone? That seems unreasonable to me. It has been said many times that the GROSS ratings were not based in reality, and I think this confirms it.
Last edited by Fun71; January 1st, 2021 at 08:51 AM.
So does anyone really believe there was a 50 horsepower drop due to 2 points of compression alone? That seems unreasonable to me. It has been said many times that the GROSS ratings were not based in reality, and I think this confirms it.
The 1970 to 1971 comparison is very interesting. Does anyone know if there were any other significant differences between the two engines? The difference is almost the same as the difference between the 68 4bbl high compression 350 and the 68 2bbl low compression 350 which was 310 HP to 250 HP.
Only difference I am aware of is one had a 6cc dish and the other had a 24cc dish piston, same cam in automatic cars. The 6 and 7 heads are so close to each other it doesn't matter.
Back in high school I had a 1970 Supreme 350-4bbl, 2.56 rearend and a friend had a 1971 Supreme, 350-4bbl, 2.56 rearend. On paper my car would destroy his in a race, with my awesome high compression 310 HP car against his puny low compression 200 HP car. But in reality the cars were fairly even until the very top end of 1st gear, where I started pulling ahead of him.This was a severe blow to my young ego.
Would've bothered me also. On the surface doesnt make much sense. Digging into it is the only way to understand. Besides gauging the difference in power rating methods. Track time and the 1/4 mile passes is what helped me see the light to further understanding HP and torque vs gearing.
The torque was sufficient enough to get both of you off the line in just about even fashion. The fact that you both had the same rear gear kept it there, till the difference in HP started to rear its head.
A 2.56 gear will never let you see the true HP of the 310 HP 350 and its also holding back a 71 260 HP 350 but to a lesser extent. 3.42s for both of you and you'd smoke him on both ends all else the same.
1970 Supreme 2.78 auto 310 HP gross = 15.5 @ 91 MPH
1970 Supreme 2.56 auto 310 HP gross = 15.6 (estimated)
1971 SX ---- 2.56 auto 250 HP net-- = 15.7 @ 90 MPH
1971 Supreme 3.42 man3 200 HP net-- = 16.1 @ 87 MPH
1971 Supreme 2.56 auto 200 HP net-- = 16.7 @ 85 MPH
1974 Z28 --- 3.73 auto 245 HP net-- = 15.9 @ 89 MPH
All above are simulation... Automobile Catalog
1974 Z28 --- 3.73 auto 245 HP net-- = 15.31 at 91.46 mph.
Just above is actual road test of Z28 for Car Craft 1974, car ran with 1/4 tank of gas and no air filter element.
Plenty to take in there, how torque can compensate for a lousy gear, etc. But as you can see even the stick shift 71 350 cant touch your 70, even with a 3.42.
It is hard to say how much horsepower is lost in due to the lower compression.
On paper with no further details Olds pegged it at 10 gross HP for 2BBL big blocks 1968 and back and 2BBL and 4BBL small blocks 1967 and back.
Originally Posted by NTXOlds
My understanding was that the 250 HP 2bbl and 310 HP 4bbl had the same cam and the same heads. The HP difference would be due to the 4bbl intake and carb, higher compression, and (I assume) dual exhaust.
I believe its a a combination of all the above along with how well the factory got them to blend (timing, carb adjustments, etc). Factory dual exhaust on the 310 HP was only in play on the Rallye 350. Otherwise it was an option request.
Originally Posted by NTXOlds
I have done all of the things that I can do to make it similar to the 310 HP version (dual exhaust, 4bbl) except for rebuilding the engine to increase the compression. At that point, I will go with a hotter cam, too.
Rallye stick cam is a nice option IMHO.
Originally Posted by NTXOlds
The good news is that the engine is very responsive, feels very strong and doesn't burn any oil. Since I intend to rebuild it at some point, it feels like I am playing with house money - I can drive it like I stole it as long as I maintain it regularly and listen for any odd noises.
So does anyone really believe there was a 50 horsepower drop due to 2 points of compression alone? That seems unreasonable to me. It has been said many times that the GROSS ratings were not based in reality, and I think this confirms it.
I've been trying to prove the truth for quite some time now. The 310 HP looks to definitely make more than 10 HP over a 260 HP version. Auto vs auto net to net my 69 has shown 217 HP twice. Once in full stock configuration plus dual exhaust. As well as almost bare bones... plus dual exhaust. VS a 200 net HP dual exhaust 71 350.
The comment about the 1.75 to 2 points of compression not making a difference caught my attention. Cylinder pressure is everything. Specially when talking in the range of 9 to 1 to 12 to 1 you will see the biggest effects . Hot rod did a comparison sometime back by just swapping heads on a 6.0 ls going from a 70 cc head to a 65 cc head the change in compression was good for 15 HP. That's huge imo. Clearly you don't want to run so much compression that it wont run properly . But you want to maintain as much cylinder pressure as you can to make power. Any who just my 2 cents.
Also an other variable to toss into the factor HP ratings is they probably where never dead on due to manufacturing inconsistencies .
I have decided to go ahead and upgrade the ignition to see if I get better stability in the idle timing (the issue mentioned above with the bouncing around) if it happens to be related to worn gears. If it is due to the cam gear or slop in the timing chain, it will require more significant work. Either way, I get new ignition out of it.
I chose the MSD Ready to Run distributor, and I am trying to settle on the timing curve for the first setup. I can always change it if it doesn't meet expectations. Mind you, the engine is a stock '68 Cutlass 9:1 compression ratio 350 with an Edelbrock Performer intake and Holley 600 CFM carb, dual exhaust and factory exhaust manifolds.
I am running about 10-12 initial timing, I am planning to leave it around 12. Here is what I am thinking:
12 degrees BTDC initial timing
1 Sliver (Light) & 1 Blue (Light) spring to bring all of the advance in by around 3000 RPM
Green Bushing for 22 mechanical advance for 34 degrees total
Limit the vacuum advance to 10 degrees
More initial will idle smoother, if that is what you want. Don't be scared to run a couple more degrees total without vacuum advance. I ran 22 base and about 15 mechanical advance with 30 degrees vacuum advance with a 214/214 cam on a 9 to 1 350. This was on 87 with ethanol. I experienced minor bucking at stop lights, a 20 degree vacuum advance can fixed it. I currently have 22 initial, 18 mechanical, all in by 2600 and 11 vacuum advance. I will probably drop it by 2 degrees for the current temporary 9 to 1 Olds 350.
More initial will idle smoother, if that is what you want. Don't be scared to run a couple more degrees total without vacuum advance. I ran 22 base and about 15 mechanical advance with 30 degrees vacuum advance with a 214/214 cam on a 9 to 1 350. This was on 87 with ethanol. I experienced minor bucking at stop lights, a 20 degree vacuum advance can fixed it. I currently have 22 initial, 18 mechanical, all in by 2600 and 11 vacuum advance. I will probably drop it by 2 degrees for the current temporary 9 to 1 Olds 350.
December 16th, 2020, 06:59 AM
