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Old 02-17-2013, 12:02 AM
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350 weak link?

Hey y'all. I've been lurking in the forums for a while now and just recently decided to ask my first question.

I have a 350 4 bolt block bored .060 over with cast crank and rods but with speed pro forged flat top pistons. Specs are the ff;

Double hump heads ported and polished with the big 2.02 valves
Weiand 1985 tunnel ram aluminum intake that's been port matched
Twin Holley 450 cfm carubretors
1.6 ratio rockers
MSD 6a box
Forgot the brand of the distributor but it has a magnetic pick up hooked up to a coil
Stainless steel headers
Summit Racing Camshaft, Hydraulic Flat Tappet, Advertised Duration 313/328, Lift .508/.533

This engine is in a 68 Chevy Camaro equipped with a Muncie 4 speed that I run on the street and race in the strip and a couple buddies of mine are telling me to get rid of the tunnel ram and replace it with a good single plane intake.

I shift at 6k rpm but I feel I still have some leeway to shift at 6.5k rpm. What do you guys think? Ditch the tunnel ram and go for a single plane intake or keep it? Do you guys see anything that's potentially killing my performance or is there a mismatch with my parts somewhere?

I'm doing 13.7 on the quarter with soft compound tires with no track bite.

Thanks.

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Old 02-17-2013, 07:09 AM
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I'm sure you could shift it at 6500.

How much ignition timing are you using (initial, total)?

Heads aren't the best, and compression could be higher.

What is the trap speed at the end of the 1/4 mile?

What gear ratio?
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Old 02-17-2013, 07:47 AM
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Race car or street car? For the purpose of this question, a "race car" NEVER sees the street. Street engines have a whole different set of problems to "deal with".

A practical street engine will run well on "pump gas" (87-93 octane). With flat top pistons, that engine is making too much compression for 93. All the 327 heads ("double hump") are 64 CCs or smaller chamber size. They make a decent "street" head when ported and pistons "dished" to reduce static compression to 9.5:1 or less. Speed Pro has a nice forging that matches the factory "dished" piston.

The dual quads LOOK cool, but a good intake (Performer RPM comes to mind for the street) and a well done 650 Holley will make more usable power. This is especially true with a hydraulic flat tappet cam (limited RPM capability).

If you want to use the dual quads to their fullest, consider both a head and cam change.

If this is a race car, there's a whole different approach.

Jim
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Old 02-17-2013, 12:59 PM
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You said it yourself you have no bite!

For the strip with your combo the tunnel ram is a much better choice but your carbs are way too small! the ram effect of the intake drastically increases cfm demand of the engine! 650 double pumpers would be better Or even larger! But for street manors and low rpm performance a single carb intake would be better 180 plenum a little better on the street then a 360 plenum! You can use the 450s for street on the tunnel ram when tuned right, and have a set of matched larger carbs for the track! But you would have to tune the engine for the change from street to track. The real problem is you have to be able to get your power to the ground. Bias belted soft compound slicks should help a lot! And ladder (lift) bars if your not running them now, retarding the cam will help bottom end bite but bring your power in at mid to top end and you can make up time at top end Speed! It's Hell doing the catch up but its great to pull ahead half way down the track!

Street and strip is a compromise!! You lose at both ends Drive-ability on the street end and speed and torque at the strip end!! You cant be best at both with the same tune and components!!!!

There are much better heads available but those should produce very good power, If you run open headers at the strip add about an 18" collector at the header flanges! You may have to stagger jet the tunnel ram carbs and block the power valves at the strip to tune! that why 2 sets of carbs come in real handy for the change from street to drag!

Jester
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Old 02-17-2013, 08:48 PM
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13.7 is a long ways from where we can get that car to.A 68 Camaro hooks well and doesnt cost much to go fast.I went low 12,s with Camel bump heads in a 67 Camaro.
Do you have lake wood traction bars? are the subframes tied yet?would you be offended if I told you to ditch the hydraulic flat tappet cam?
the muncie will need upgrading too. When paintedjester explains how to tune that dual 4 system,and you tune the traction bars you should be in the mid 12s in the next few upgrades
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Old 02-17-2013, 09:46 PM
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Thanks for all the replies guys. Great info!

My rear end has a 4.11 in it. Total timing is 34 degrees, I think but the distributor doesn't have any form of advance. It's one of those race distributors, I just forget the brand and model and I'm not anywhere near my car right now. I have about 10 to 1 static compression right now, but where I live 100 octane gasoline can be found anywhere and a buddy of mine has a steady supply of methanol but I won't be going there. Yet. Hahaha.

Jester, also not sure if I wanna keep 4 carburetors. Lol. Those two on it right now are trouble enough as it is! I had an incident a few weeks ago where the back carb sprang a leak and burst into flames. I used to run a couple of 600 cfm Holleys there but fouled plugs became my constant headache. I was thinking of just switching to smaller jets but a friend of mine had a couple of 450s on a shelf and I traded those. But that's sound advice. Thanks.

I just have the old school slapper bars on it right now, and I've been thinking of upgrading to the newer Caltracs just to get better launch at the line and getting a set of slicks for better grip. I also run with open headers during race days and ditch the air cleaners for best breathing.

My trap speed averages 100mph.

Vinnie, I wouldn't be offended if you told me that but do you have a better cam in mind? I also haven't welded in subframe connectors yet. Lots of work to be done to my car, so I'm really wanting to hear from the experts here.

Thanks all of you!
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Old 02-17-2013, 10:16 PM
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Untill the experts come,I will help you.
If the slapper bars are mounted to the spring perches then all we do is dial them in.Right side snubber needs just enough preload on the "J" bolts to have the snubber touch the spring. Left side needs to be preloaded with a 1/2 gap between the snubber and the spring.
Buy a set of lakewood subframe connectors and bolt them in. weld them later.
If you run 100 MPH then we can get a 13 flat out of your car or close to it.
For a cam,I would love to see a little roller or even better a little solid roller.
DO YOU??? have a scatter shield in your car>? and a drive shaft loop?
your car is going to be faster and you need these items
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Old 02-18-2013, 04:44 AM
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I would run another 5 degrees of ignition timing.

Using the trap speed, the engine is only making around 330hp at the crank. More timing will help, but a regular Performer RPM dual plane intake and a 750 holley should run better on and off the street.

And shift it at 6500.

I'm thinking 103 mph traps with just more timing and rising the shift point to 6500 rpms. Traction will effect the et. Fresh tires will help.

Open headers aren't helping much, unless the exhaust is ess than 2-1/4" and muffler is stock.

Last edited by 454C10; 02-18-2013 at 04:53 AM.
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Old 02-18-2013, 09:59 AM
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Tunnel ram at the strip:
If you stay with the 450s there is no rear accelerator pumps so Bigger shooters are needed! and accelerator pump cams with the max volume capacity. Carb main jetting and idle circuit fine tuning is a must. Did you change the power valves yet to fit the vacuum? Do you have vacuum secondary's?
The idle circuit and off idle transition circuit is critical for any kind of track performance!! Two larger double pumpers with no tuning would alleviate these problems and will only need minor tuning

A very aggressive timing curve on the distributor with a lot of initial base timing.The more initial base timing Say 12 to 15 up the better it will respond better off idle & low rpm. A higher octane fuel may be needed at these timing points (?compression unknown?) Re curve the distributor to allow this without excessive total advance ? A quick mechanical advance curve. To allow about 24 deg timing at off idle. and curve it for (38?) total at the right RPM (trial and error method Dino or track tuning) Not on the street LOL

Slapper bars are OK but a good set of tunable ladder bars are much better! At the frame contact point were the bars are attached they lift the frame pressing the rear housing down transferring weight and planting the tires! There are many stiles that work well! The weld on are best and you must use frame connectors and install a drag loop around the drive shaft (like Vinnie said)!

A cast crank is good at lower RPMs it doesn't flex but at higher RPM it will Crack A steel forged crank actually flexes and absorbers the harsh load and is better for High RPM Shifting over 6000 rpm is border line on a cast crank (my opinion is 5500 limit on cast but thats me)!


There is no well tuned single carb intake that can perform or compete with a well tuned tunnel ram for torque or RPM at the strip! But on the street its a different ball game! My opinion again!!! The 8 large venturi of the carbs, 360 plenum, long straight intake runners, and ram effect far out performs any other normally aspirated intake and carb combo!!!!! And that's not just my opinion LOL!

Pick the 1/4 mile time you want to run, Figure out your final drive ratio, tire diameter, and RPM you need to turn that time and match your engine build to to do that RPM and still put torque to the ground! If you stay in the 12s and high 11s you won't need all the expensive safety equipment! But you should still build it safe!!!!!! Scatter shield or blanket, drag loop, engine plate, etc!! And as Vinnie said a solid lifter cam would be a great choice!!

Jester
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Old 02-18-2013, 10:37 AM
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Let me help help out here.How is the money situation or how much time are you willing to wait until you have whatever it takes??.
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Old 02-18-2013, 07:03 PM
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Thanks all of you for the great advice!

Vinnie, yeah I do need to get myself a scatter shield. I've been sitting on it for a while now since I put the car together. I do really like my toes, though, so I'm going to have to get on it soon. I have a drive shaft loop, so I'm good there. Thanks for the advice on the slapper bars. My next race is in three weeks, so I'm going to have to hustle.

454, that's kinda disappointing if my car only had 330 hp at the crank. I guess I really do have a lot of work to be done if I wanna get up to 450-500. I run 1 5/8 headers that lead to a 2 1/2 collector. Roger on that shifting at 6500. I just hope my clutch doesn't disintegrate shifting at that speed. Lol I really like my toes a lot.

Jester, yeah the 450s were run on another tunnel ram before they were shelved. My buddy had them running on a 427 and we switched to #5 power valves. The 450s don't have vacuum secondaries, since they're mechanical, and they don't have a rear pump either. You're right, I do need to switch to a bigger pump since there's a small bit of hesitation when I floor it while cruising.

I'm looking to stay in the low 12s. Things get pretty expensive when you get down to the 11s here. Roll cage, built-in fire extinguisher, ANSI helmet, fire suit, fuel cell, etc.

1gary, my budget's pretty tight right about now. But in a few months I'll have enough saved to get myself a nice forged steel crank, rods, nice solid roller cam, a better distributor, ladder bar system or Caltracs, scatter shield (gotta get this one ASAP if I don't wanna walk with a limp lol) and fresh tires.

Thanks for the advice everyone!
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Old 02-18-2013, 07:22 PM
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good luck and have fun. Paintedjester is a great guy,he will get the tunnel ram dialed in for ya.
we will all help you make that first 12 second pass.slapper bars will take you a long way. The subframe ties help the car hook and flex less.
We will need better headers in the future.Lets see how fast we can make the car go without digging deep into the engine.
run what ya got,make it safe,have fun.

later ask 1gary for and old warn out 631
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Old 02-18-2013, 07:26 PM
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Caltracs VS Ladder bars

Caltracs stop axle housing roll and tighten spring wrap, Tracktion bars do the same with the added lift and weight transfer!

The main complaint with ladder bars is "Damn the front tires keep coming off the ground"


Good luck

Jester
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Old 02-18-2013, 07:39 PM
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one major complain with ladder bars(not 4 link)is if you are inexperienced racer and chop the throttle after the traps and let the engine brake for you,,,,when the suspension tries to unload,the ladder bars are bolted solid and transfer that inertia to the tires...big slicks can get a little unstable in this situation,makes for a scary ride.
Thats why you see a lot of pros put the car in neutral after the traps
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Old 02-18-2013, 08:03 PM
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The CalTrac design was developed for the NHRA Stock rules. This means they were never intended to do anything but control axle wind up on acceleration! As Vinnie said To big slicks can get a little unstable when you unload the throttle!!!

Jester
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