HP estimate

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Pentastarnut

Pentastarnut

67' Barracuda
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I'm putting together a magnum 408 and wondering what power output it may have with what i've planned. what's your thoughts and opinions ?
Mopar crank, eagle rods, diamond pistons ( no part number , i was told it should be 9.5 cr with magnum heads, i bought the fresh short block already assembled ). i plan on bolt on EQ heads drilled for an LA Air Gap intake, FItech go efi 4 power adder ( if i ever want to upgrade ) tti headers ( maybe full exhaust ) and a Pertronix 3 ignition. i have two cams in mind, Comp xr286hr-10 and Comp 291thr7.
not that it matters, melling hv oil pump and cloyes timing set. trans will be a 5 speed, 3.91 or 4.10 rear, 26" tire height. should be a nice driver and fun track car.
what's your guess/opinion ? go...
 
More than a Briggs and Stratton single cylinder and less than the space shuttle.
 
Simply stated, you've got a pretty good combo of parts lined up for a fun ride, but actual hp numbers are going to be dependant on how well your rings seal,quality of valve job,carb&ignition tuning etc. Pay attention to the fundamentals and you'll have a strong engine that lasts.
 
MichaelB. said:
525-550. Go get 'em
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Good lord, not even close. 9.5 CR...EQ heads? On an engine dyno with the bigger cam, my guess is 390 HP. I can't believe how people just throw out that 500 number without spending some time on a dyno.

All that being said, it should be a great motor....Oh yeah. Ditch the HV oil pump. No need.
 
When it was a Chevy it would be 500, period. With the unported EQ heads it will be a tad above 400, my guess.
 
You might want to think about the pistons again. Get something that will get it up to the 10.5 to 1 area with the closed chamber heads. The heads should have 2.02 intakes and as big an exhaust valve as you can get. A little porting and the heads are good to go. The cam should have enough overlap to bleed off some pressure and you are good to go, I had a 367 that was similar to your build except with iron heads and a comp 268H cam that produced a little over 400hp so your 408 with a little bigger cam should get close to 500hp. Make sure you do not under fuel it, it will like a lot. The timing on my 360 was 16 initial and 34 total and I ran 91 octane. It could run as low as 87 but it didn't really like it.

Jack
 
Hi, ran a pretty similar combo (408 with RHS X-Heads) with the XR286HR cam, think it was around 450 HP / 450 TQ. Best ET was 11.40 @ 117 mph, 1.57 60ft. To get more out of it the heads and cam should be replaced....what i´m doing at the moment ;-)

It idled ok with the XR-cam around 900 rpm, i´d stay away from the thumpr cam (too much overlap in my opinion due to the low LSA).

Michael
 
360duster said:
Hi, ran a pretty similar combo (408 with RHS X-Heads) with the XR286HR cam, think it was around 450 HP / 450 TQ. Best ET was 11.40 @ 117 mph, 1.57 60ft. To get more out of it the heads and cam should be replaced....what i´m doing at the moment ;-)

It idled ok with the XR-cam around 900 rpm, i´d stay away from the thumpr cam (too much overlap in my opinion due to the low LSA).

Michael
Click to expand...

This is a pretty realistic guesstimation ^^^^^^^^. The heads flow an honest 230-237 cfm OOTB and they will easily support 450-470 HP with 470-490 TQ on your combo. Have fun. J.Rob
 
i was thinking about 425. upgrading the heads to the 2.02's and working them some i KNOW it will love the increased flow, but is it worth the extra $ spent for a street car that will see 3 or 4 track days per season ? after the cost of that it's close to price of bolt on eddy's too. i know it's a question only i can answer, i'm thinking out loud. i'm liking the xr286hr, i've read the factory stock lifters are more than adequate. then i'll need some roller rockers. why do most people bash Hughes ?
...grabs popcorn
 
Are you certain those heads can be set up for the springs either of those cams will need? Seems like a LOT of cam for the springs that fit...
Anyway assuming you can get them to work - I'd say mid 420-440 is close. Those are good heads. They are not "great" heads and are lift-limited. So you will probably be airflow limited no matter what cam you choose.
 
moper said:
Are you certain those heads can be set up for the springs either of those cams will need? Seems like a LOT of cam for the springs that fit...
Anyway assuming you can get them to work - I'd say mid 420-440 is close. Those are good heads. They are not "great" heads and are lift-limited. So you will probably be airflow limited no matter what cam you choose.
Click to expand...
bolt on eddy's will prob be a better choice, let me find more $
 
Personally I prefer using the LA-based heads and have run a lot of the RPMs, but there are others that are pretty good with minimal clean up besides RPMs. So if this is still in the "design" stage, get a budget figure, then shop for heads.
 
If you don't have heads already get aluminium, at one time you could get magnum heads in aluminium not sure whats out there these days. The weight reduction off the front end alone is worth it on any car.
 
Except when aluminum make 30+ hp less, then the weight reduction benefit goes out the window. :)

Not to mention the required porting to get them to the same power level as other iron heads.

Plenty of decent heads out there. Pick your parts, pay your money!
 
The seats could be cut and longer valves used if needed also, and since they would basically be Chevy parts going on back on it, it wouldn't be too expensive for the different parts.
 
That s
Pentastarnut said:
I'm putting together a magnum 408 and wondering what power output it may have with what i've planned. what's your thoughts and opinions ?
Mopar crank, eagle rods, diamond pistons ( no part number , i was told it should be 9.5 cr with magnum heads, i bought the fresh short block already assembled ). i plan on bolt on EQ heads drilled for an LA Air Gap intake, FItech go efi 4 power adder ( if i ever want to upgrade ) tti headers ( maybe full exhaust ) and a Pertronix 3 ignition. i have two cams in mind, Comp xr286hr-10 and Comp 291thr7.
not that it matters, melling hv oil pump and cloyes timing set. trans will be a 5 speed, 3.91 or 4.10 rear, 26" tire height. should be a nice driver and fun track car.
what's your guess/opinion ? go...
Click to expand...

sounds like a good motor solid 400 hp at the least. but heads flowing 230 plus id guess around 420 hp give or take.. the 5 speed and 391 gears is going to be fun on the high way!
 
I think i'll spend the $ and go with eddy 61775's with an air gap, Hughes SER3438ALN-10 cam and the SS roller rockers for the eddy's from Hughes. i'll have to sell some stuff to recoup for the overspending of my budget but it'll be worth it. anyone need an E Body four speed set up ?
 
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