427 BBC CHEVY EXHAUST TEST-STOCK L72 VETTE MANIFOLDS VS LONG TUBE HEADERS. BONUS TEST-600-HP 427!!!

427 Chevy long tube headers versus stock exhaust manifolds who wants to see the shootout well let's put one together put it on the dyno and find out what happens but what happens if you want something even more powerful we also have that hello everybody I'm Richard holdner and as always welcome to the channel where are my big block Chevy fans specifically the 427 big block that's right I'm not talking about the 454 or even the 396 which also I'm working on we're talking about the 427 and specifically to start off with we're talking about the l72 425 horse 427 let's imagine you were lucky enough to have one of those what if you wanted that but you also want to drive a little bit better what kind of accommodation would you put together we wanted to look like the 427 originally did but drive a lot better than the high compression big cam deal so we have that combination we're going to take a look at I even did a comparison long tube headers versus the stock exhaust manifolds I'm a big buck Chevy how much are they worth but what if you wanted a second combination you still wanted 427 but you wanted a lot more power and maybe just a little bit of drivability we also have that so check it out okay guys let's take a look at a 427 build up this particular one was going in a late 60s Corvette we can take a look and see this one the 427 was actually built as a driver so rather than doing a complete you know reproduction of a l-72 425 horsepower 27 Corvette what they wanted was something that made that kind of power but was more drivable so they chose to lower the compression and change the camshaft but otherwise it uses a lot of factory Parts including a factory 427 block a stock 427 steel crank Factory rods and then they use an aftermarket piston because this was a 30 over bore and the combination of the Dome design and then using the 119 to 120 CC Rec Port you know performance iron cylinder head that combination produced just under 10 to 1 static compression so let's take a look at what's going on with this test motor so we get a better understanding this thing as as I said Iron Block iron Factory recport heads a little under 10 to 1 compression they did do a retrofit hydraulic roller cam rather than going with a flat Tapper cam you could get good power with a flat type of Cam either a solid or a hydraulic version but they went with the retrofit hydraulic roller this was a 510 lift 224 230 degree duration and 110 degree load separation angle they use retrofit link part hydraulic roller lifters this thing had a factory GM dual plan I'm going to show you a picture up here this thing was run with a 750 Mighty Demon carburetor on the dyno they also at the end ran it with the 780 vacuum secondary it made slightly less power although not very much and that ultimately was the one that went in the car because it kind of wanted the motor to look like it was a you know a factory original one on the engine Dyno it started out with two inch chassis style Hooker Headers with 18 inch collector extensions actually I think they're a little bit longer than that and then they ran straight through performance mufflers this was a good combination and the cool thing is they ran a few tests while they were on the dyno rather than just taking the 427 and putting it up and saying hey it made this much power which is kind of cool so this thing started off with 33 degrees of total timing and run in this manner the 427 produced 443 horsepower and you can see it's hard to determine Peak torque here because they didn't load this thing low enough to figure out exactly where Peak torque was but let's say it's in the 470 to 480 foot-pounds of torque so the first thing that they did when they're running this thing on the engine Dyno is you start trying to play with timing and Airfield so that means jetting on the carburetor and then simply turning the distributor in this case this was an MSD here's what happened when they first tried timing so they went from 33 degrees to 36 degrees and 37 and 38 didn't seem to show any extra power in fact they win it but one degree increments I'm just showing you where they got to ultimately by changing the timing so the peak power jumped up to 449 horsepower and the peak torque didn't change dramatically because all of the gains really came uh past 46 or 4700 RPM and we were already well past the torque beat so they made one more chain and that was actually they wanted to find out what would happen if you know we made big changes to the timing and this thing was running around 203 I'm going to go ahead and put up after I show you the power changes I'm gonna go ahead and put up a an air Fuel Curve and you guys can kind of see what happened here but here's what happened when they changed the timing or change the air fuel so they actually ran this thing richer this motor wanted to run richer so you could see um after changing the jetting and running this thing down in the 11s basically 454 horsepower and again Peak torque was not changed but the power change from about 4 900 all the way out I'll go ahead and show you here here is a here's what the change in Airfield did with the change in jetting and as we normally see jetting made a big change kind of everywhere all all the way through the curve they did primary and secondary jet changes and they changed the air fuel quite a bit as you can see but at least at the top this thing like being richer than 12 the one it actually liked being in 11. so now let's take a look and see what happened when we compared the factory Corvette exhaust manifolds to long tube headers okay taking a look and see what happens when we run a 427 up on the dyno iron headed hydraulic roller cam and then we tried a couple things as far as tuning timing and air fuel and you guys saw what the changes were but one of the cool tests that these guys ran at West Tech was to find out hey what's going to happen this is the way that we run it on the dyno with long tube headers in this case I think that these were um Chevelle chassis headers so they were two inch in into a three inch collector extension and then we ran basically three inch straight pipes with a with high flow like straight flow straight through Mufflers but what happens when you have to run this thing in a car with a stock exhaust manifold because this is often a point of contention hey look these Big Blocks made good power but not when you saddle them with stock exhaust manifold so what actually happens and this was a cool test so what they did I'll go ahead and show you a photo is they replaced the headers that we ran on the engine Dyno with stock exhaust manifolds to find out what it was going to do once this thing actually went in the car because it was going to go in the Corvette with Corvette exhaust manifold so that it had the right look but they wanted to know what hey how much is this going to hurt us and as it turns out it hurts the power output quite a bit so the stock exhaust manifolds were also run with two and a half inch exhaust and exiting the exhaust manifolds and then run into they had two and a half inch um I think that they were MagnaFlow again straight through Mufflers so no restriction in the Mufflers I know because I've tested these Mufflers um on my engine Masters motor and they worked good but here is what happened when they ran the stock exhaust manifold as you can see it's a dramatic change in power and it's a dramatic change not just in Peak power where a lot of guys think oh well these manifolds don't flow as well as the stock ones or as well as headers but the reality is that we see big Power gains down low from the headers and that's because we have a Scavenging effect from the long tube so it's a tube length and it's not just ultimate flow but the peak power dropped from 454 horsepower down to 406 horsepower and then you can see big jumps in torque we can't really talk about Peak torque but we can talk about differences of you know 45 to 50 foot-pounds of torque so this is a dramatic change in torque production from the stock exhaust manifolds and this is not unusual we see this and more so on Big Blocks than other combinations so if you want to run your stock exhaust manifolds even the good Corvette ones on your big block this is what happens and this is why people when they put together Big Blocks and they're actually going to go to the track and race it headers obviously are a good idea so now let's take a look at one more 427 combination that actually ended up going in a 57 Chevy um and this one was more it was still a street motor but something a little hotter all the testing on the near stock 427 it had a hydraulic roller cam in it but we would have made comparable power even with like a factory flat tappet you know a solid Cam that came in the l72 but those kinds of builds are very very cool you know stock heads and stuff and sock and Dick manifold and that's very very cool and you're putting in a car you want to look stock and you wanted to drive around so that's good but what happens if you want something a lot more sporty and the 427 has no problem making a lot more power so let's take a look at another combination that was put together to run again as a street motor but this one went in a 57 Chevy behind a Doug Nash 5-speed so you know something that you could row through the gears with and make some decent power and the key to that is again they kept compression down for you know pump gas friendly kind of deal but they went up in a couple of things obviously more camshaft much more cylinder head flow a better combination and the intake manifold was a single plane rather than a dual plane bigger carburetor you know all the stuff that you change to make more power so let's take a look this was a 427 compression was down actually in the nines slightly lower than the previous combination but the way that they ended up making power was you know heads Cam and intake manifold So speaking of cylinder heads rather than run the iron recport Factory head this thing was equipped with very very good heads airflow research 315 CNC ported heads so certainly enough to support way over this power level but they worked very well on this combination of displacement and like intended power output but to take advantage of those heads they put in a crane hydraulic roller camshaft which is good good thing for driving around this one had 595 lift again getting up near 600 so able to take advantage of the extra airflow offered by the airflow research heads a 244 256 degree duration split and 112 degree lobe separation angle topping all that off and it'll Rock Victor Jr intake manifold while the Dual plane good for a milder combination in you know a different RPM range the Victor Junior allowed this thing with the head and the camshaft to rev out and I actually make power they ran a one 850 Street HP carburetor this thing was run with two and a quarter inch Dyno headers because this thing was going in the 55 Chevy and they could actually run long tube headers in that combination they weren't restricted to stock exhaust manifolds it had an MSD distributor and then actually they did timing and jetting it had a good oil pan on it because the last thing you want to do is run into windage problems and or like oil starvation problems neither one of them are good and here's what happened after they put this combination and brulee through the tune up this thing this thing made right at 600 599.7 you could see a nice flat broad torque curve peaking at 517 foot-pounds of torque so as you might imagine with you know running out to 6500 RPM this is a good combination it's certainly going to be plenty of fun in a 57 Chevy with a Doug Nash five-speed you know kind of going old school which is very very cool let's see how this thing Compares for those of the guys that are interested we'll see how this compares to the previous Milder build and you can see the milder build actually probably is a little bit better down below 3600 or so RPM not surprising but once we get past their you know heads cam intake really kind of come into their own and allow this thing to take off and not only make more power but more RPM and obviously more fun our Geralds or please make sure to like share subscribe ring the bell do all that stuff and I'll keep testing

Channel: Richard Holdener

Views: 28,274

Keywords: 427 CHEVY, L72, L36 427, 425-HP 427, STOCK MANIFOLDS, AFR 315 HEADS

Id: BX98dHkrWUo

Length: 12min 44sec (764 seconds)

Published: Fri Aug 18 2023