exhaust flow impact on cam specs
Thread Starter
Joined: Jun 2005
Posts: 2,265
Likes: 671
From: Oskaloosa, Iowa
exhaust flow impact on cam specs I know everything matters when spec'ing a cam. I'm curious how much exhaust flow can be compensated by with cam specs on very high horsepower combinations.
I want to stay quiet for street driving without getting too much attention. I have 1 3/4" primary, 3" collector long tube headers, off road pipes and a 2.5 magnaflow catback with their quieter mufflers.
I'm also making around 4 digit power estimated at the crank shaft. It doesn't seem like most dyno comparisons show a huge difference in power by going to larger headers or exhaust. Looking ahead to even more power on a new engine combo how much can I compensate with cam specs for the restrictive exhaust at over 1000 rwhp?
I want to stay quiet for street driving without getting too much attention. I have 1 3/4" primary, 3" collector long tube headers, off road pipes and a 2.5 magnaflow catback with their quieter mufflers.
I'm also making around 4 digit power estimated at the crank shaft. It doesn't seem like most dyno comparisons show a huge difference in power by going to larger headers or exhaust. Looking ahead to even more power on a new engine combo how much can I compensate with cam specs for the restrictive exhaust at over 1000 rwhp?
TECH Addict
Joined: Dec 2017
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Likes: 977
More duration; narrower LSA (i.e. leave the exh open later, let the boost in the intake push more out during the e/i overlap period); asymmetrical lobe (steeper opening ramp than closing); lots of spring seat pressure so that it stays closed when it's supposed to. High lift won't help as much because the valve opening isn't The Bottleneck, therefore opening it up won't increase the flow.
I once had a combo that ran far better than expected. The cam was a 230/244. I ended up breaking the crank in that engine and decided to try a "bigger" cam as recommended by compcams. same size engine. 242/248 cam. it was noticeably slower and would not turn but 6500rpm vs the 7800rpm it did previously. I had the same 1 5/8 headers on both combos. (383 sbc, 3rd gen camaro. 3400lbs, circa 1997ish... ran 11.4 @ 122 with old motor.) I feel like that cam just helped it breathe far better. the new combo even had far better heads on it. The first combo was GM fastburns, second combo was trick flow R heads that flowed 300cfm on the intake and 227 on the exhaust. the fastburns flowed around 280/190 iirc. new combo trapped 3mph slower. After that I always favored a large intake/exhaust split. Its worked well for me. This was by no means a well tuned combo nor optimized. I believe it had far more potential. The 700r4 was slipping in 3rd, I had drag radials with cords showing, 1.9-2.0 60ft. Spun through first and still managed numerous 11.4 slips.
Thread Starter
Joined: Jun 2005
Posts: 2,265
Likes: 671
From: Oskaloosa, Iowa
I don’t have any trouble turning rpm. The Procharger with the btr equalizer intake loves rpm. I just went from 6.68 to 6.53 to 6.45 to 6.30 in the 1/8th only adding 150 rpm to the shift points between each run and half a degree of timing. This was leaving off idle and just rolling into the throttle trying to make clean runs for tuning purposes. I still have more room to go looking at plugs. I went 5.9x with the smaller blower but I was way over spinning it then got kicked out for no cage. After a couple years off and a bigger blower I’m just creeping up on the tune. I’m thinking ahead to my next combo and researching for that now that’s what made me think about what I can do to make more power but keep the sleeper exhaust.
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I don’t have any trouble turning rpm. The Procharger with the btr equalizer intake loves rpm. I just went from 6.68 to 6.53 to 6.45 to 6.30 in the 1/8th only adding 150 rpm to the shift points between each run and half a degree of timing. This was leaving off idle and just rolling into the throttle trying to make clean runs for tuning purposes. I still have more room to go looking at plugs. I went 5.9x with the smaller blower but I was way over spinning it then got kicked out for no cage. After a couple years off and a bigger blower I’m just creeping up on the tune. I’m thinking ahead to my next combo and researching for that now that’s what made me think about what I can do to make more power but keep the sleeper exhaust.
Last edited by Kfxguy; May 21, 2024 at 01:31 PM.
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Verdad Gallardo Recent run at the track just leaving off idle and rolling into it.
https://m.youtube.com/watch?v=_LIJTbAa4K8
https://m.youtube.com/watch?v=_LIJTbAa4K8
are you wanting an answer to your question, or are you just showing off your car? just wondering because this looks like its taking a turn.....lol
Thread Starter
Joined: Jun 2005
Posts: 2,265
Likes: 671
From: Oskaloosa, Iowa
My apologies I didn’t want to offend anyone. I’m very sorry the example you gave wasn’t relevant to my current or planned combo.
I already have a 232/248 custom cam for my current combo. I’m not a smart man so I should have explained better.
I’m considering building a 388 putting more of my budget into the bottom end with an aftermarket aluminum block while running cheaper heads and my current exhaust. I would also be going with an F1x over my current f1a-94.
Basically with this exhaust and less than ideal heads initially shooting for 1200 plus rwhp is it possible to compensate for those factors with cam specs and how much would I really be giving up on a combo like that.
Compression would be 10.5 ish to 1 static and fuel is e85 plus meth injection.
I already have a 232/248 custom cam for my current combo. I’m not a smart man so I should have explained better.
I’m considering building a 388 putting more of my budget into the bottom end with an aftermarket aluminum block while running cheaper heads and my current exhaust. I would also be going with an F1x over my current f1a-94.
Basically with this exhaust and less than ideal heads initially shooting for 1200 plus rwhp is it possible to compensate for those factors with cam specs and how much would I really be giving up on a combo like that.
Compression would be 10.5 ish to 1 static and fuel is e85 plus meth injection.
My apologies I didn’t want to offend anyone. I’m very sorry the example you gave wasn’t relevant to my current or planned combo.
I already have a 232/248 custom cam for my current combo. I’m not a smart man so I should have explained better.
I’m considering building a 388 putting more of my budget into the bottom end with an aftermarket aluminum block while running cheaper heads and my current exhaust. I would also be going with an F1x over my current f1a-94.
Basically with this exhaust and less than ideal heads initially shooting for 1200 plus rwhp is it possible to compensate for those factors with cam specs and how much would I really be giving up on a combo like that.
Compression would be 10.5 ish to 1 static and fuel is e85 plus meth injection.
I already have a 232/248 custom cam for my current combo. I’m not a smart man so I should have explained better.
I’m considering building a 388 putting more of my budget into the bottom end with an aftermarket aluminum block while running cheaper heads and my current exhaust. I would also be going with an F1x over my current f1a-94.
Basically with this exhaust and less than ideal heads initially shooting for 1200 plus rwhp is it possible to compensate for those factors with cam specs and how much would I really be giving up on a combo like that.
Compression would be 10.5 ish to 1 static and fuel is e85 plus meth injection.
man come on. You ain’t no dummy so don’t say you aren’t smart lol.
I felt like my example was relevant. The first combo ran far better with a large split on the exhaust. Thinking going to a larger cam but a closer split with better heads should have made the car faster but it didn’t. That big motor with the small exhaust really liked the large duration split. If I had a supercharged motor I’d be running large split like that. The cam you have now seems pretty ideal on the split. I think in your situation you should be looking at doing really quiet exhaust setup with some cutouts or bypass mufflers for racing. That’s why I built my whole exhaust and fabricated my muffler. Quiet for driving and bypass the muffler when I want to. It makes 2-3 more psi boost when the bypass is open.