jensenracing77

i am full of questions tonight, does anyone know about these manifolds for the SBO? i am using the stock exhaust manifolds on my Rallye 350. when i built the engine i told Joe Mondello that i was going to use the stock manifolds. he told me to have the outlet bored to help with the cam i used since i wasn't going with headers. i see these Thornton manifolds are bigger outlets, i am just wondering if they would be worth the money. i want to keep it looking stock so i thought they would be great.

http://thorntonmusclecars.com/produc...aust-manifolds

GreekDog

they are cheap compared to a good pair of headers. I dont know anyone using those but it could turn out to be a good investment.

Hurstolds1973

I bought the BB units for my car. I really like them on my cars and like GreekDog said they are cheap compared to most headers. IMO

joe_padavano

This comes up regularly. See these two threads. And yes, I have held them in my hands (well, the ones sold by Ram Air Restorations - I can't believe that there is more than one set of molds for these manifolds).

https://classicoldsmobile.com/forums...manifolds.html

https://classicoldsmobile.com/forums...manifolds.html

jag1886

I put a set on my 330 last fall, they are very well made and eliminate the mix master on the PS and is cast like a BB manifold. I laid the new manifolds and the old manifolds next to each other and the Thorntons do have a larger internal volume (some say they don't but they sure looked bigger to me) the DS has a 2 1/4 outlet where the stock manifold has a 2" outlet. I think they where well worth the money and I'm glad I don't have to listen to header noise.

joe_padavano

Thornton makes good products, but my whole point is that one should make an informed decision. Despite marketing hype, these manifolds are NOT based on the individual runner BBO W/Z manifolds. There simply isn't enough room to run full individual runners on an SBO due to the lower deck height. The aftermarket manifolds have a divider between the center two ports that's maybe 1" deep. Beyond that, the internal shape is nearly identical to that of stock SBO manifolds. The ribs and styling on the outside that make these look like W/Z manifolds is irrelevant as far as flow is concerned.

More to the point, internal volume is NOT a measure of flow rate. Subsonic flow is not intuitive and something that appears to improve flow often does not. Witness the E-brock heads that flow better than stock despite having smaller exhaust ports. Shape is more important than volume.

Yes, these manifolds have larger outlets than stock. If that feature and the lack of a cap on the crossover port is worth $300 to you, go for it. Personally I'd put the money into a set of headers or keep the stockers. Anyone contemplating these manifolds should do their own research and make their own decision.

jensenracing77

thanks guys. i done a search for other threads before i posted this but i must not have done it right cause i didn't find anything. the only reason i was thinking about it was that they had the bigger outlet. Joe Mondello and also Jack Merkel both said i should bore my outlet on the stock manifolds if that was what i was going to use. i found a guy that would bore them but wanted $80 for each one. i thought at that price i would consider these. i think i may just have them bore mine. i did call Thornton and they told me to use the stock heat shroud, i would have to grind off the ribs of there manifold on the passenger side.

joe_padavano

For well under $160 you could buy a die grinder, carbide bit, and a can of machinist's blue dye and port them yourself.

jensenracing77

i thought about doing that also. i don't have any experience doing that but i don't guess it would matter that much. i don't know how much it would really help anyway.

jag1886

I don't understand why people are so negative about a better iron manifold. Just seems to me that if it is not a noise old set of headers it must be crap in a lot of peoples eyes.
Shape is better, that's why I always try and point out the the PS get's rid of the stock OLDS Mix-Master that the stock manifold has and they are larger inside, this is a stock type iron manifold not a set of E-heads and I have never come across anything that says a Mix-Master 2" exhaust exhaust system is better than a slightly larger system that is 2 1/2" .
These made a felt difference after installation and after I added a new 2 1/2 exhaust system behind them there was a still larger felt difference.
I know alot of people can only speak in overall HP figures and I know these are not going to make those #'s but they did help and we don't all want the noise or the hassle of a set of headers.

joe_padavano

First, I was not negative on the product, just presenting the facts. As I pointed out, make an informed decision. The fact that the outlet is larger is not proof that these manifolds flow better or worse than stockers. Unless your butt-dyno has been recently calibrated, however, I don't believe any "felt" improvements. Someone who has just spent $300 on parts will ALWAYS feel an improvement. Only the timers at the track know for sure, however.

jensenracing77

i have a friend that said he was going to order a set for his 403 in his trans am. if he does i will get close up pictures. he said on the driver side he would fill it and the stock one with water and see who much difference there will be. i don't think i will get a set. i have several sets of stockers so i will just try to grind out the outlet like Joe stated. i am still not convinced it will help and i won't know even if it does help. i will be getting my carb back from sparky, adding a pertronix, doing some exhaust work, and going from a 4 speed to an automatic all at the same time.

jag1886

I've been around the block more than once and my BUTT-DYNO works just fine. Just so you know I have installed $10'000's of parts on my Harley's and if a part is a piece of crap I tell people it's a piece of crap and take it off and throw it in the crap pile with all the other crap Harley parts. If these where junk I'd say they are junk and they'd be in the crap pile beside all the crap Harley parts.
You are entitled to an opinion but in this case it is just an opinion as it sounds like you have never actually used a set of these. I don't see the you have any facts just hypotheses.

Big Blue 72

C'mon gentlemen, it isn't a pissing competition

Allan R

Gotta say, I'm a little confused after reading all the interesting 'discussion' re: Thornton SBO E Man. When the product first came out, there did not appear to be a lot of acceptance for whatever reasons. I didn't buy them for the aesthetics. I don't want my exhausts (even if they are a more correct looking set) to say THORNTONS on them. Don't know why they did this, since they cast factory numbers on the BB ones. I'm sure there is a factory number for true SB exhausts. GM couldn't have overlooked that market.

I originally thought of changing the exhaust flow by installing headers (still new in the box) but decided not to. Only for issues of exhaust height clearances. BTW, I have not had any noise issues from headers installed and maintained properly. And most exhaust noise is usually determined by the type of exhaust pipe and muffling system used.

I read that you decided to stay stocker on the exhausts. So did I with my 350, only I didn't modify their clearances as suggested to you by Joe M (RIP) . I had the crossover pipe welded shut and went dual. From everything I've read, this is quite a common way to convert single to dual exhaust. I also know that the exhaust parts/sound/performance/provenance etc is a real personal thing; and that others input does help make an informed decsion. I guess that since my car is not a strip car, or daily driver and I'm not a leadfoot there is no real downside to my decision and application.

When I finish building my 455 and drop it into the car, yes I will look at the W/Z exhausts. For my power rating and performance expectations (not to mention noise and appearance) they will do the job just fine. If they come from the web market as OEM or aftermarket (likely Thornton) it won't matter as long as they do what they are supposed to.


Joe P?
I'm not a gearhead, so in simple terms can you explain what means? I'm guessing that subsonic is the sounds you don't hear such as the detonations in the engine or valve actions used to clear the exhaust. Why would something that appears to improve flow be a 'misnomer' in terms of improving flow? I though improved flow increased performance, or am I just reading too much into this?

joe_padavano

Nope. Even the W-31 used the cap on the passenger side manifold

Subsonic simply means below the speed of sound. Air (and all other gasses) are compressible, so as soon as you get a shock wave when passing through the speed of sound, the aerodynamics analysis changes.

Getting back to my original comment, everyone seems fixated on whether or not these manifolds are larger than stock. Who cares? That is NOT a measurement of whether or not they flow better. Again, back to my example. The exhaust ports on the Edelbrock heads are SMALLER than on stock Olds heads, yet they flow better. The flow in the ports is subsonic and thus shape of the port (and the exhaust manifold) is MUCH more important than the volume.

Again, I'm not ragging on the aftermarket manifolds, just telling people to make an informed decision before spending $300. I'm still waiting for real, back-to-back test data with numbers properly corrected for weather. The butt-dyno is notoriously incorrect when it comes to HP numbers.

Allan R

Joe,
Ok, I think I get it. Functionality driven by form design of the exhaust creates less restriction. So in this case size doesn't matter, shape and ?smoothness? does.

BTW, I didn't read your post as being negative, and I don't believe that you're ragging on Thorntons. Your comments appear to be very objective, and I've learned some great information from this thread.

Given that:
1. My exhaust is 'plugged' the same way a W30 dual may have been on the PS
2. My car is not a strip racer, or ever will be
3. I'm happy with the existing performance
4. Spending $300.00 + shipping for something that I don't believe will create any obvious benefit

I'll just leave my Rocket with it's OEM exhaust and be happy

jensenracing77

now on the other hand, i think there new hood they are about to release will be a perfect example of the original. most likely be better as far as consistency and fit. i have seen oem hoods that fit like crap.

Allan R

According to Troy, they will be even better than the ones they had before since the new molds will be better. I agree the hood will likely be as close to being a GM OEM hood as you can get. But, I still shudder everytime I look at the price. Remember when (2005/2006) Fusicks was Thorntons almost sole source supplier of OAI hoods? Price back then? 1250.00 I only wish it was that much today.

You're right about some OEM fitting like crap. Not sure if that was a production flaw or sloppy workmanship. I do remember that in the 70's the fit and alignment of the metal panels had some incredibly outrageous gaps compared to todays exacting standards. In many ways, we have the import market to thank for improved fit/finish/reliability and overall quality.

1965cutlassragtop

i am looking to get a set of these manifolds ASAP. i can't stand having the crossover inlet capped, and i always have a leak on the driver side 2" outlet. we had to use a donut to match it up to my downpipe, it never stays sealed for long. just having that taken care of is worth the $300 to me. plus, my stock manifolds are the only thing under the hood that are all rusted and pitted, it aggrivates me cuz it looks terrible. i think these horton manifolds are well worth the money considering the battles i've fought trying to find headers, and it will be great to not hear that leak anymore where the donut is. these are literally my next purchase!!

Allan R

Horton hears a who, not an exhaust leak? Obviously Dr. Seuss needs to meet Dr. Olds!!



Just havin some fun with the typo. (I know, I'll probably get one of these too sometime when I make the same oops posting) Best of luck with your purchase and install. Let us know how it works out.

jensenracing77

you may be able to find someone here that has a super nice set of stockers for much less. it will still have the cap but if they are good manifolds they shouldn't leak. just a thought.

1965cutlassragtop

hahahaha.....my mistake!!! u all know what i meant. @ jensenracing....my leak is at the donut used on the 2" side, when i try tightening the flange bolts, the donut never stays right where it should. it always gets tweaked a little and leaks a bit. although, it doesn't bother me as much anymore since i switched to the Jones Full Boar mufflers, those things rumble something fierce!!! i can barely hear the leak over those things :-) when i had the Dynomax Super Turbo's, you could hear the leak over the exhaust clearly. i'm just saying i would feel much better with both sides matiching up to my exhaust downpipes, not having the inlet capped, and improve the look under the hood.

joe_padavano

Most Olds manifolds don't use donuts. The metal flare on the pipe seals to the metal taper on the manifold. The only ones I've seen with replaceable donuts are the driver's side 307 manifolds with the EFE flapper.

1965cutlassragtop

i am not talking about a factory donut.....this is a donut that i had to use to make the 2" outlet on the driver's side match up to my downpipe, which has a 2.25" diameter. it sounds even worse without it, i tried.....i can't see how to make a 2" match up to a 2.25" pipe without using some sort of sealing device/mechanism.

joe_padavano

You match the 2" flare by using a necked-down section that mates to the flare properly. A cobbled donut isn't going to seal properly.

1965cutlassragtop

thanks, i'll give that a shot....i can buy that piece at any parts store pretty much???

TripDeuces

What's a Mix-Master on a small block? Is that the passenger side manifold with the crossover? Just curious.

jag1886

You got it! With or without the cross over hooked up that's a pitiful design.

Toms cutlass

There are several old threads regarding the Thornton 350 dual exhaust manifolds, and I don't intend to resurrect that debate. Thornton is now offering a short custom 350 header, and I wondered if anyone has any experience with it?

https://www.ebay.com/itm/1970-1971-O...-/183102807998

olds 307 and 403

Check out page 4 on this link.

https://gbodyforum.com/threads/cutla...s.66156/unread

fasteddy

Question regarding these manifolds: My Rallye 350 had a 455 in it and has a nice aftermarket stainless exhaust system. The original numbers matching engine will be going back in. I was thinking about keeping this exhaust and am speculating that the Thornton 350 manifolds might work with that exhaust?

If it is going to be way off I will probably just pick up some OEM factory manifolds and figure I need to refit the exhaust at the manifolds.

Any input is appreciated!

Thanks

Pat

olds 307 and 403

If it is stock manifolds, it should be close.

zeeke

Ie chewowowa! What do you get when you cross a monkey with a hammer? This is why I try to do all my own work. This definitely needs to make the wall of shame post. Hope I can find it.

Allan R

WTH is that???! No flow exhaust at its finest.

Ikesgotav8

oldsmobuser

I bought a set of 350 JR exhaust manifolds for my new engine. The drivers side has a raised section that just touches the oil dipstick tube. Also the outlet comes VERY close to the starter solenoid, about 1/4" away,. I'm afraid it will melt my purple crank wire on my solenoid. It is a brand new harness and I really don't want to take the chance. I am going to remove the manifold and contact Thornton's about the issue. The manifolds are progressively thicker from front to back which will slightly increase flow. The outlets are 2 1/4", which I do plan on installing a 2 1/4" dual exhaust system from inline tube which includes the hangars. I also used the copper Thornton exhaust manifold gaskets. The pass. side manifold had no issues. I think the manifold could be cast differently to move the outlet further away from the starter. Other than that the manifolds are solid.

Warren Seale

I just installed these maifolds on my 79 Trans Am with 403. This engine has a heat shield between the starter and manifold that I kept in place to isolate the manifold from the starter solenoid and wiring. The exhaust pipe flange plate had to be ground flat where it is up against the heat shield. I moved my dip stick tube by bending it slightly so that it fits between the manifold and head. There is a recessed area in the manifold where the dip stick tube can sit.

I had big problems on the passenger side. The 403 has raised numerals that are cast into the block to indicate it is a 403. They stick out enough to keep the manifold from seating against the head when using 1 Felpro gasket. It was only about a 1mm gap, but any gap is bad. I had to use 3 Felpro gaskets to move the manifold away enough from the block to prevent the manifold from interfering with the 403 numerals. These are the only issues I ran into.

olds 307 and 403

You guys are seeing why Olds didn't bother with HO manifolds on the W31. I imagine the larger outlet near the starter was flow and using available aftermarket down pipes. Really the 403 X hits the manifold, just shows they are larger.