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I have a 1986 Cutlass with a late 70s 350 engine in it. It has long tube headers on it and has cooked the starter a couple times. I want to go back to factory exhaust cast manifolds for reliability, and was wondering if there was a better flowing cast iron exh manifold for these g body cutlass s.. Ive read 1985 and newer exhaust may flow worse .
Thanks for your input!!
All SBO manifold suck (or more correctly, don't), but the 1985-90 tubular manifolds are the worst. My feelings on the Thornton manifolds have been published here many times - not a fan of those either due to the minimal difference over stock for the price. Sorry, but there's no good answer here.
All SBO manifold suck (or more correctly, don't), but the 1985-90 tubular manifolds are the worst. My feelings on the Thornton manifolds have been published here many times - not a fan of those either due to the minimal difference over stock for the price. Sorry, but there's no good answer here.
Have you considered upgrading to a compact starter? You could wrap your headers in some insulating wrap, and the compact starter should create a larger air gap between them to keep the starter from overheating.
A mini starter is much more compact and more than enough to turn your motor over. I ground the body of my Ebay special mini starter. Very compact but hit the block slightly in the most compact, straight up position. The Thornton manifolds give up 30 hp, regular manifolds are no doubt worse. Cutlassefi hopefully will test the new Sanderson shorties I sent to him to dyno test. I predict between Thorton manifolds and full length headers. They are very compact and fit your G body. They fit my 88 just fine.
Last edited by olds 307 and 403; February 9th, 2021 at 11:59 AM.
Thanks guys!
Joe and Cutlassefi, that's what i figured.
NTX and olds 307 i have thought about the mini starter, but instead of trying to make the headers work, I really want a quiet and reliable exhaust with using cast manifolds. I was hoping there was a decent solution for cast manifolds.
The exhaust i have on it now, I put on 20 years ago when I wanted a hot rod. It was the cheapest headers i could find out of the PAW catalog with some purple hornies bolted to them. I now want to make a cruiser/daily driver out of it. Its been sitting for 15 + years and want to do something with it.
olds 307- you say 30+ hp decrease going to manifolds, but do you really think I gained 30 hp going to full length headers with a stock 79 motor with 3a heads. It has performer 350 intake, slightly bigger cam, and carter afb 750 (going to replace with edelbrock 500cfm most likely) all from the PAW catalog from around 2001.
Also i heard bad things about wrapping cheap headers and them warping.
Im really thinking about a single 3" exhaust system. It will flow a little better than dual 2inch and not as god as a dual 2.25" if my math is correct.?.. And only have to buy one muffler. i dont know!
also the car has a th-350 and will have a 2:41 rear end (replacing a 3:23) I know, I know, but its going to be a daily driver. You ll get me at the stop light but im getting on the hwy real quick.
A ceramic coating is much better than wrapping headers. It may be not be quite that much on a mild motor. Cutlassefi did a dyno comparison with Thorton manifolds which are slightly larger inside and have larger outlets, 2 1/8" vs 2" on factory manifolds. Those Thornton manifolds were a 30 hp loss and similar torque on a 9.5 to 1 350 with ported heads and a TQ40 Erson cam, I believe. The stock manifolds will flow less, hard to say how much. I would go the Thornton Jr route, if you are dead set against headers. The pic of a set I saw were much better than some of the early castings. You should be able open the outlets to 2.25". Good part is both Pypes and Ram Air Restorations make direct fit down pipes for the early or Thornton manifolds. Then add large body Dynomax Super Turbo mufflers with 2.5" pipe. It will be nearly stock quiet in comparison to your current exhaust.
Last edited by olds 307 and 403; February 10th, 2021 at 10:55 AM.
Thanks olds307- There is actual proof of the loss in hp and tq... wow! But I cant spend the dough for the Thorton manifolds. Its been well over ten years since i drove the car on the street, so I guess I wont miss the power decrease.
Will all years of stock olds manifolds fit my 86 g body or will only 1978 + fit it? I pretty set on the stockers, with the 2;41 gears its sure to be a dog, but maybe 20mpg. Thats what my s10 4x4 blazer gets. Rather drive the cutlass.
Any input is appreciated, even if you want to call me a stupid dummy.
Bryan
The driver's side is basically the same. The passenger side angles back and has a two bolt flange on early manifolds. On late manifolds, it points straight down and has a 3 bolt flange. I believe both will work on your G body. Are you planning on the awful and restrictive factory 2" crossover between the manifolds or an actual Y pipe with the single 3" pipe from the manifold?
Olds 307- I really dont know about that. I honestly thought I would install the manifolds and take it to an exhaust shop, and see what they could do for my budget. Even at 16/17 years old(20 + years ago), knowing very little about cars, I remember thinking how ridiculously small the cross pipes were before the catalytic converter as I ripped it all out.
Anyways, in Missouri you cant mess with the exhaust before the cat, so my plan is to find someone who will build an exhaust system and hopefully inspect it also.
I also DONT have a double hump trans crossmember. That is also why I was thinking about a single 3" exhaust.
But I did get some clearance in the crossmember for the purple hornies with a torch and hammer, but no where near the clearance on oem dual exh or aftermarket trans crossmembers.
Yeah, the single hump crossmember is an issue on the G body. I used from the Y back a Hooker 2.5" cat back exhaust to run under the single hump. I got custom head pipes from my Sanderson shorties into a compact X pipe then into the Hooker cat back system, it sounded amazing under my G body, just a hair loud. It ran under the passenger side hump. If you do get a custom bent single 3", have it exit behind the rear tire, looks a lot better. For the Y pipe, the factory used 2.25" head pipes on dual exhaust. They could do 2.25" just at the manifolds into 2.5". Pypers down pipes for manifolds are exactly that. Then into a 2.5" to 3" Y pipe. Here is my system off the car, it is going onto my 70 Cutlass S since my G body will be gone.
Thanks olds307- There is actual proof of the loss in hp and tq... wow! But I cant spend the dough for the Thorton manifolds. Its been well over ten years since i drove the car on the street, so I guess I wont miss the power decrease.
Will all years of stock olds manifolds fit my 86 g body or will only 1978 + fit it? I pretty set on the stockers, with the 2;41 gears its sure to be a dog, but maybe 20mpg. Thats what my s10 4x4 blazer gets. Rather drive the cutlass.
Any input is appreciated, even if you want to call me a stupid dummy.
Bryan
I won't call anyone a dummy. It is your car, and you can do whatever you want to with it. My suggestion of installing a compact starter was really about finding the easiest solution to your problem.
It also seems like you are implying that putting on the stock exhaust manifolds is a part of your strategy to get 20mpg. My apologies if I am putting words into your mouth, but I want to address this point. My point of view is that removing the headers may lead to worse gas mileage. This may be an oversimplification, but headers help to make your engine more efficient by making your engine work less to get rid of exhaust gases. In the end you get more power and better gas mileage as long as the extra power doesn't tempt you to stomp on the gas at every opportunity.
I got 24 mpg Imperial with Sanderson shorties and the 2.5" X pipe exhaust in the pictures. Talking a stock cam 73 350, TH2004R and 3.42 gears with a 225/70R14 tire. I am running a mini starter due to the custom front pipes but a stock starter will work Sanderson shorties, the pipe just needs to go straight back.
olds 307- Thank you so much for those photos, I really like that setup. I like the idea of using parts of a pre built system. I would love to get those Sanderson shorties but I just cant afford them, even at half price i couldn't do it. but if I do a dual exhaust, ill have to do a x or even a "H" pipe.
NTX- I thank you for suggestion, but these are very cheap headers and I dont want to keep changing things, like installing a remote oil filter and the mini starter, and then a year or two later have constant exhaust leaks. Where the cast manifolds might be more reliable.
I would love to keep the full length headers but i am looking for reliability over power.
Fifteen years of use is what happened😁. I should have paid a couple of grand less or passed on it, I payed about 2 grand too much for a basic Cutlass. I thought they were going to go up in value🤣. I wanted a 84 Hurst/Olds, I should have spent the extra dollars right off the bat. Honestly the paint was never great and rear frame rails are starting to get thin. Unfortunately, with a few exceptions, G bodies are like the mid 70's Cutlass, they have very little $$$ value and may never have any value. I bought a 76 Cutlass for $50 around 15 years ago with a really nice interior. Again, nice ones sit forever over a couple of grand. I picked up a rough 1970 Oldsmobile Cutlass S for $1500 with an Olds 260. I spend 10 grand to make it nice, I would have a hope in hell of getting that. Already had multiple people want to buy it. Trying to fix up and keep two old cars on the road is tough. I have 3 other vehicles I do everything on as well. Already the 70 is going to be much better, complete car. They take way too many of the same parts. Yes, manifolds last forever and get some estimates to see what you can fit in your budget for an exhaust system. Loud gets old really fast driving any distance, I have been there before.
olds 307- Hopefully it was a good 15 years of use. Its funny with value on these g bodies, if you have the right car (ie a monte ss, 442, hurst, grand national) you can expect 10k or more for a nice car, but the guy who has a rusty stock 307 cutlass or a ls monte wants 5 grand, makes no sense.
I clicked on your profile and saw you had pictures! The 70 is getting nice! Did you do the green paint? I can tell its a 2 foot paint job but way nicer than the black, like you bought it like(same car, right?). I love green cars and with white interior, it looks great. No way could you get a car like that here in the kansas city area anywhere close to 1500 bucks.
alright I got questions-
you said you got 24 mpg Imperial (around 20mpg)with stock 350, what carburetor were you using?
in your bio, it say forced air, is that turbo or super charged, of something else??
What is Dr Olds Mileage Machine??
Thanks for your insight. And for everybody's thoughts!
This forum seems great. Looking forward to learning from you all!
Bryan
The carb is 78 403 800 cfm Qjet custom tuned by Everyday Performance. I added a thread in plug and notched the Adjustable Part Throttle(APT). I can change from tire smoking to good mileage in about 2 minutes with a little flat screwdriver. Forced air, or maybe I should say Outside Air Induction. My 88 had an aftermarket cover on the torque converter, it rubbed and sounded like boost😁. I had a hood scoop and used an air flow top on the stock air cleaner. The 70, I cut holes in the plastic inner fenders and now have 4" stainless heating exhaust pipe that I attach hoses to my homemade dual snorkel air cleaner. Dr Olds Mileage machine was my 88 Cutlass Supreme Classic Brougham in an attempt to use an Olds 260 to see what mileage I could get, 26 mpg Imperial was the best. Problem was, someone abused the poor little 260. Compression was even, if not slightly low at 100 to 110 psi. The real issue was oil pressure, I needed 20W50 to get any decent oil pressure. Either way, a good running 260 might have eeked out a couple more mpg. Having headers, dual exhaust, a 2004R and 3.42 gears made it acceptable to drive. For 2 mpg, it wasn't really worth it. Remember my car was around 3750 pounds on a certified truck scale, converted from Metric of course. Those were some tight years money wise, a lot of extra expenses. I am in a much better place financially now but two cars just stretch the budget too much. It was hard to let it go. Being an 88, 87 ins the cut off, no Classic insurance. I am not paying $90+ a month for a car they would me a grand if wrote off. I may in the future get a 79, 83 or 8r Hurst Olds or a 80, or 85 or most probably a 87 442, I like the Euro front end. I am kicking myself for not buying a nice 87 442 for 5 grand. Some ******* drove it a few Winters and was asking 4 grand. I almost went and bought it again but the rust holes in the fenders brought me to my senses. I love Oldsmobile cars, if you don't, why are you here? Our 75 Cutlass was one of our best cars, mainly due to the Olds 350 but everything made were awful cars during that time, still Oldsmobile were the best of the worst😁. Our 81 Delta 88 was even better, probably the best car my parents, then I owned. We had all the bills since it was purchased new in 82 by the previous owner, no major repairs.
Last edited by olds 307 and 403; February 13th, 2021 at 06:39 AM.
Thats funny about the cover rubbing sounds like a turbo.
Most people see the small v8 useless but the 3.8 and 4.3 v6 run quite rough. i think to the offset rod journals. I bet a 260 v8 is much smoother than a 3.8... I never thought about that.
I never thought bout insurance, I got to look into that.
It sounds like you know what you want if you get a g body, but focus on that 70 S. Its super nice!
1987 cutlass 350 SBO ceramic coating, powermaster mini starter With Thermo-Tec Starter Heat Shield.
. Run my car on highway for long trips. Starter still going after 14+ years. https://www.summitracing.com/parts/t...xoCyyUQAvD_BwE
All SBO manifold suck (or more correctly, don't), but the 1985-90 tubular manifolds are the worst. My feelings on the Thornton manifolds have been published here many times - not a fan of those either due to the minimal difference over stock for the price. Sorry, but there's no good answer here.
Joe, Did you have clearance issues with the driver's side Thornton exhaust manifold being too close to the starter solenoid? Mine has about 1/8" clearance. The outlet flange is too close to my purple crank wire on my new harness. I would like to run the stock starter but I may have to get a mini starter. I have 5 stock starters and if I get a mini starter then I can't use any of them which is something I don't want to do. What was your experience with the Thornton manifolds? I have the 350 JR ones. Thanks and take care.
Joe, Did you have clearance issues with the driver's side Thornton exhaust manifold being too close to the starter solenoid? Mine has about 1/8" clearance. The outlet flange is too close to my purple crank wire on my new harness. I would like to run the stock starter but I may have to get a mini starter. I have 5 stock starters and if I get a mini starter then I can't use any of them which is something I don't want to do. What was your experience with the Thornton manifolds? I have the 350 JR ones. Thanks and take care.
The 3:23 rear was put together with hopes and wishes. No crush sleeve and super slop in the carrier side to side. Going to replace with un molested 2:41 rear for reliability. Maybe some day have lsd 2:70 or 2:90 but for now this is what i got.
Is the diff noisy? Was a solid spacer used? When I assembled the 3.42 gears in my 88, I used a solid pinion spacer and shims. It supposedly helps add strength to the flimsy 7.5" rear. I set the pinion depth the same as the factory 2.56 gears. I bought the aftermarket carrier shims, some are very thin, so fine tuning can be done. I first broke the pins off a Powertrax No Slip at the track with slicks. It became a spool, parking was a violent affair. After the stock soft spider gears exploded, horsing around on the street, that took out the ring and pinion. I realized my carrier, I set on the loose side. I shimmed it tighter and added Yukon spider gears which are much harder and survived quite a few passes with slicks at the track with no signs of wear when opened up.
Im really thinking about a single 3" exhaust system. It will flow a little better than dual 2inch and not as god as a dual 2.25" if my math is correct.
Hi Bryan.
When you compare restriction in an exhaust system, you want to calculate the friction loss (back-pressure) of the pipe, not the cross-sectional area of the pipe.
Using the back-pressure metric:
a single 3" exhaust has 51% lower back pressure than a dual 2"
a single 3" exhaust has 12% lower back pressure than a dual 2 1/4"
Gary
Hi Bryan.
When you compare restriction in an exhaust system, you want to calculate the friction loss (back-pressure) of the pipe, not the cross-sectional area of the pipe.
Using the back-pressure metric:
a single 3" exhaust has 51% lower back pressure than a dual 2"
a single 3" exhaust has 12% lower back pressure than a dual 2 1/4"
Gary
^^^THIS!
Area doesn't tell the story. The problem is that you get boundary layer drag along the inner wall of the pipe, which reduces flow and increases backpressure. Two smaller pipes with the same cross sectional area as a single larger pipe have more wall area and thus more boundary layer drag, which is why they have more backpressure. Bends just make it worse.
February 8th, 2021, 09:52 PM
