When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Cam is too small and does not match the heads at all
Btr recommended this cam for the setup they had a dyno sheet with the same heads ls7 and same cam thst hit 692 on a engine dyno makes me. Wonder what's wrong with mine lol
Check your cranking compression. I am willing to bet it is much higher than it should be, and will indicate the cam being advanced a full tooth on the gear instead of dot to dot. Or not, who knows?
If the exhaust is restrictive, then the BTR camshaft has too late an exhaust valve closing. Which explains why it peaks at an early 6k, but still carries out to 6700rpm.
Recommend switching to a Summit Big Gun 2: SUM-8730R1 is a 11 I/O, 51 I/C, 67 E/O, 4 E/C for 15 degrees of overlap. (242/251 116 + 6, .625/.605).
Willing to bet the exhaust, and intake setup are affecting you. There's better intakes for the LS7 heads than a FAST 102. Be better off with an MSD. True Duals would also help besides cut outs.
If that combo is peaking below 6000rpm you have some form of restriction as it basically flatlines and makes no more power beyond that RPM being choked up. Maybe post a picture of your intake system going into the TB also. That cam is really quite small for a 427 and 11:1 isn't a ton of compression. What is the intended use for this combo? Street/Race %?
We made 595rwhp on a 440ci LS with TFS235 heads, FAST 90/90, long tubes, dual 3" into a single 3.5" which was around 11.5:1 compression and bigger cam. That was 15 years ago on a Dynojet with T56. Of note it did have a 4" intake setup with a bellmouth at the bottom going into a 6" opening filter and cold air out of the engine bay. That alone gained 25rwhp+ over the previous combo that was 3.5" and no bellmouth getting hair air in the engine bay. Plus if memory serves me right a GZ Motorsports vacuum pump. Wet sump engine with factory 4th gen Fbody pan.
You have some very nice heads and while the FAST 102 isn't the rockstar choice it isn't too bad. A vacuum pump would probably gain another 10-15rwhp if you wanted every ounce out of it.... but definitely redo that exhaust. https://www.yellowbullet.com/threads...mp-ls.1188282/
Last question: Is that dyno considered a "heartbreaker" dyno? What have other similar engines made on it?
Chassis dynos are notorious for being inconsistent and often depressing, but you have to remember what they are measuring. The program only measures the rate at which you are speeding up the roller, and it cant load and drag down your engine before the start. Usually 500HP on a chassis dyno through the tires and a manual transmission is about 670 at the flywheel. 700 or more if you have a big, soft tire.
The big thing to pay attention to is Air/Fuel ratio, temperatures, and the rest. You may get a few horsepowers from a change to exhaust, but that engine is no slouch.
Chassis dynos are notorious for being inconsistent and often depressing, but you have to remember what they are measuring. The program only measures the rate at which you are speeding up the roller, and it cant load and drag down your engine before the start. Usually 500HP on a chassis dyno through the tires and a manual transmission is about 670 at the flywheel. 700 or more if you have a big, soft tire.
The big thing to pay attention to is Air/Fuel ratio, temperatures, and the rest. You may get a few horsepowers from a change to exhaust, but that engine is no slouch.
No slouch, but look at the phone screenshot where HP peaked @ only 6k. It held it nearly flat after that, well up to 6700rpm; but it should've continued climbing (likely peak around 6500-6700). It's being held back big time. There's a nice area under the curve missing from 6000rpm+, maybe even some below that. He either needs to change the camshaft to match the exhaust, or the exhaust to match the camshaft.
Last edited by 68Formula; Feb 17, 2025 at 07:32 PM.
What is the altitude?
what kind of dyno
Aee you sure all the cylinders are firing?
what does is run mph wise in the 1/4 or 1/8
LS7 heads would give a higher peak.
do you want a dyno queen or a fast street car?
The smaller GENX 235s are only 20cfm less than factory CNC ported LS7s (on intake, exhaust flows side flows more). So the larger GENX245s OP is running should be nearly, if not equal, to factory LS7 heads and their runner volume is more than sufficient to support a 427 up to 7k if everything else is properly matched.
The cam, while being somewhat small for the displacement, should also still gain power past 6k. (If the exhaust system was free flowing, the 18.5* overlap would allow the exhaust pulse to draw more intake charge at high rpm despite the intake duration).
Dyno type and altitude aren't going to cause the curve to peak and prematurely drop off after 6k.
Either there's:
A mechanical/electrical problem above 6k e.g. cam off a tooth, valve float, ignition, incorrect a/f, etc . (Although with ignition or valve float I would expect the curve to look jagged). Or
The intake manifold or exhaust setup is restricting it
If it's the setup, bets are the exhaust side as the problem (does look like a single 3" intermediate). Which means either it needs to go, or the camshaft events need to change to compensate with the exhaust he's running on the street. Running open collectors with extensions on that chassis dyno, would confirm it really quick.
Have seen cases where insufficient runner volume, insufficient head flow or too small a camshaft for displacement has caused the rpm to peak early, but for this setup, it's not the cause. If this was on just an engine dyno with the typical setup, peak hp rpm point would be way higher.
Last edited by 68Formula; Feb 18, 2025 at 08:15 PM.
Interesting find:
Here's an engine dyno test of the camshaft in question. Note the curve of the label for the cam: "LS7-BTR 400NA....TFS245 Heads Final." Seems like they ran the same heads with that camshaft on a LS7 and it's peaking around 7k and carrying past. We don't know what intake manifold was used, but the exhaust was probably headers with collectors exhausted straight out the dyno chamber tubes.
Last edited by 68Formula; Feb 19, 2025 at 04:49 PM.
If that combo is peaking below 6000rpm you have some form of restriction as it basically flatlines and makes no more power beyond that RPM being choked up. Maybe post a picture of your intake system going into the TB also. That cam is really quite small for a 427 and 11:1 isn't a ton of compression. What is the intended use for this combo? Street/Race %?
We made 595rwhp on a 440ci LS with TFS235 heads, FAST 90/90, long tubes, dual 3" into a single 3.5" which was around 11.5:1 compression and bigger cam. That was 15 years ago on a Dynojet with T56. Of note it did have a 4" intake setup with a bellmouth at the bottom going into a 6" opening filter and cold air out of the engine bay. That alone gained 25rwhp+ over the previous combo that was 3.5" and no bellmouth getting hair air in the engine bay. Plus if memory serves me right a GZ Motorsports vacuum pump. Wet sump engine with factory 4th gen Fbody pan.
You have some very nice heads and while the FAST 102 isn't the rockstar choice it isn't too bad. A vacuum pump would probably gain another 10-15rwhp if you wanted every ounce out of it.... but definitely redo that exhaust. https://www.yellowbullet.com/threads...mp-ls.1188282/
Last question: Is that dyno considered a "heartbreaker" dyno? What have other similar engines made on it?
That link about exhaust size is great. I was still under the assumption that you needed a bunch of power to need anything over a 2.5" single. I guess this was ignorant considering I think my 6.2 Escalade comes with 3 or 3.5" and makes 400hp. Perhaps my single 2.5 is holding back my cammed lm7 with flat tops after all.
