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I finally finished my 434 impala and took it to a dyno, It was so disappointing to see 375rwhp I was really expecting 500-550rwhp. Not sure what I did wrong. My buddy swears it’s the heads. 10.5:1 victor jr heads, forged rotating assembly, 1.5/1.6 rockers, solid roller cam, fitech 1200 efi, 1-7/8 headers, 3” exhaust... msd, I’m really bummed out...not sure where to start looking...
 

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EFI/N2O JUNKIE
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I finally finished my 434 impala and took it to a dyno, It was so disappointing to see 375rwhp I was really expecting 500-550rwhp. Not sure what I did wrong. My buddy swears it’s the heads. 10.5:1 victor jr heads, forged rotating assembly, 1.5/1.6 rockers, solid roller cam, fitech 1200 efi, 1-7/8 headers, 3” exhaust... msd, I’m really bummed out...not sure where to start looking...
You built a street engine and got the results I would expect..........

You don't have any compression, a nothing special head, no mention of the cam, and only a 1200cfm TB isn't going to help you any.

I am no LS fanboy, but those engines make power for a reason, the heads! Can't compare most 23* stuff to a stock 15* LS head. AFR 227's would do wonders for you on that engine, plus a decent cam.
 

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I had the heads from an old 406 build I had... but I contacted afr and they recommended the 220comp series head.. I looked at flow numbers and they weren’t too far apart... but I guess I better get them.. and I got rid of a 950 race series quick fuel for the gas smell.. it was horrible.. no shops are really able to tune in using carb so I opted for fitech...
 

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What are the cam specs?

What transmission and converter stall if automatic?

What kind of tire?

Friends 406 afr 210 248 deg solid roller made 372 whp thru a th3500 with 4500 stall and ran 10.80’s at 125 mph at 3300-3400 ish lbs. my 383 on street radial with a lockup 700r4 trans dyno’d 392whp and ran 11.4 at 119 mph at 3400-3450. they dont always dyno well
 

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That's about right to me. Put the biggest head you can afford on it.
 

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Any recommendations? Most I get is afr 220 or 227, dart 227, and Brodie dragonslayer, which do you recommend? I can afford any of them.. and I’ll match with correct cam...
 

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Discussion Starter #8
Friends 406 afr 210 248 deg solid roller made 372 whp thru a th3500 with 4500 stall and ran 10.80’s at 125 mph at 3300-3400 ish lbs. my 383 on street radial with a lockup 700r4 trans dyno’d 392whp and ran 11.4 at 119 mph at 3400-3450. they dont always dyno well

My specs
Lunati 243 @ .50 and .578 valve lift solid roller, th400 w/ gearvendor, 4:10 gears, 10” 3000 B&M stall, 31” tires (26” rims)
 

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I'd go 245 being your going to have to do valvetrain with either the 235 or 45. I have 220 Darts on my 434 and it was done about 6400. Took a new intake (ported and polished inside) and had Larry Morgan's guy do some head work to get it to shift at 6800 now on the same cam. 245 heads would crush either of the 2 things I did.
 

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That th440 and GV overdrive are soaking up some power. I lose well over 100 hp to the tires through my C6 and GV overdrive .
 

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also that converter & gearing is on the small side if you want to step up the heads & camshaft. yes it will work. no it won't be ideal at all
 

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I am a sucker for Dart heads myself so I would do their PRO1 245 CNC or a custom set from Chad. But the 434 really need to breath and your heads just ain't cutting it. Will need a good intake to match as well and something better than the FI tech TB.
 

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I am a sucker for Dart heads myself so I would do their PRO1 245 CNC or a custom set from Chad. But the 434 really need to breath and your heads just ain't cutting it. Will need a good intake to match as well and something better than the FI tech TB.
Induction restricted! No tuneing in the world will help.Bill C.
Ain't that the truth! I have a 1200cfm TB on our slow car with a 383SBC and it pulls 2" of vacuum at higher rpms going down the track, and it only goes 10.80's at 3500lbs. I don't care since we slow it down for 11.50 Index Racing anyway. I would never use anything but port EFI, it is the right way to do it.
 

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Ain't that the truth! I have a 1200cfm TB on our slow car with a 383SBC and it pulls 2" of vacuum at higher rpms going down the track, and it only goes 10.80's at 3500lbs. I don't care since we slow it down for 11.50 Index Racing anyway. I would never use anything but port EFI, it is the right way to do it.
why does it show that much vac on such a build? a 1200cfm carb wouldn't.
 

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The smallest head GM put on a 427 was 253cc....doesn't matter if Small or Big is infront of block when talking CID. 434CID is 434CID. Depending on where you want to make power will determine head. I do a package that uses the AFR220, hyd roller that is .612/570 on a 109 used with a Victor Jr and a set of 1 7/*'s headers and it makes 507RWHP at 6200 rpm.
 

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The smallest head GM put on a 427 was 253cc....doesn't matter if Small or Big is infront of block when talking CID. 434CID is 434CID. Depending on where you want to make power will determine head. I do a package that uses the AFR220, hyd roller that is .612/570 on a 109 used with a Victor Jr and a set of 1 7/*'s headers and it makes 507RWHP at 6200 rpm.
Cc is function of port length so big or small block does matter if comparing volumes. Whats the csa and valve sizes is what i’d compare, and you know that too :wink

I was gonna say afr 220 or similar size is a great street head
 

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why does it show that much vac on such a build? a 1200cfm carb wouldn't.
Good question! I don't know the answer.

When I run a restrictor plate on my car the vacuum trace for the manifold vacuum looks funny too. It starts low, then increases through low gear, then drops down a step, and continues to increase through high gear. I think it pulls 4" through the traps. I run a 1550cfm TB on my engine, it is almost large enough, still needs a bit larger for full-throttle blasts, but don't need every bit of power.

I did have a 2000cfm TB on there which makes 10hp more to the rear tires, but was pretty worn-out and the Kinsler 1550cfm TB is a piece of art compared to my old one!
 
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