1970 351C Dyno Numbers (you should all be interested in this)

[70mach1]

Well, my car is still alive (1970 Mach1 351-4v Cleveland, FMX trans, 3.00 gear, Xtreme energy Comp cam 513/519 lift 218/224 duration @ .050 with 110 seperation), dual plane edelbrock, MSD 6al, Holley 670 Avenger, roller rockers, custom full length headers, electronic dist with adjustable vacuum and mechanical advances) . Here is the skinny on the dyno day results.
Read more below for a more detailed account. So view correctly you may have
to expand out this e-mail.

Description / Pre-tune / Post-Tune / Effect of change

Idle jet OD# .027 .031 Off idle stumble
eliminated (this alone was worth the $400)
Trans kickdown non-functional you betcha Kick ass speed when you
need it.
Primary Jet OD .065 .069 Lean condition/ping
remedied
Initial timing -8BTDC -12BTDC Smoother torque curve
Total advance -40 -36 Smoother torque curve
Hp @ 4500rpm 188 202 Timing and primary jet
changes +14hp to wheels

At first I was disappointed at only making 202 at the rear wheels, but then
the owner (guy tuning my car) told me #1 that the dyno they use is very
stingy (Mustang Dyno brand) and #2 that there is something preventing the engine from making
power above 4500 rpm. He said it is most likely the 3 foot long 2" H pipe
between the headers and mufflers. The exhaust is getting backed up at that
RPM and above. He said the car should make about 260hp if there was a 2.5"
X pipe instead of the 2" H pipe with the 1.5" center that is has now. So I
have an appointment at my exhaust guy to put in an X pipe and then re-dyno
the car May 1st. There is a dyno about 1/2 mile away from the exhaust shop
and it is not the same type as before and should therefore not be so stingy.
Maybe I could get to 275hp. So basically the car feels like a 260~270 hp
car up to 4500rpm and then feels like a 150hp car.

By next year the 5-speed will be in place and the parasitic loss will be
greatly reduced. The car should put 300 hp to the ground with the Tremec
5-speed installed. My FMX auto uses about 1/3 (33%) of the engine power
(the FMX is notorious for being bullet proof, heavy and soaking up power)
where the Tremec only soaks up about 1/5 (20%).

Stay tuned all!

 

[68 & 00 GT]

It may be better for your application, but that sounds like a lot of RWHP to be made due to an X pipe only

But considering your mods that number seems awful low.

 

[70mach1]

I think it is more the 2.5" diameter vs 2.0" instead of the actual X vs H. But both tuners said the X vs the H is a noticeable improvement. It can only help. A 2" diameter pipe cross sectional area is 3.14 square inches vs 4.9 square inches. That is a 56% increase ! ! That has got to tremendously help flow at high RPM. Essentially the three foot 2" section is like a big restrictor on the whole exhaust. The headers go into the 2" and then 2.5" mufflers and 2.5" tail pipes.

 

[68 & 00 GT]

Even if you ran open headers I'd be extremely surprised if you saw anywhere close to that much gain

 

[70mach1]

The 60hp should not only come from the x pipe, but the hp that is gained with increased RPM. If the engine could breath probably to 6000 rpm, then at the current rate of hp increase, the engine would have hit 250. I through in an extra 10 hp for a better design (like an x pipe). Does that make sense?? It kinda did to me.

 

[ratio411]

I think that folks are overlooking the fact that 2" pipe is tiny for a Cleveland to try and breathe through!

You are not really gaining HP that is not there, you are uncorking the engine above 4500 rpm and allowing it to reach the prime part of it's powerband. I think that your tuner is on track.

As a side note, the Mustang dynos do register low for some reason. A 300 rwhp car on any other dyno will read around 250 on a Mustang dyno from posts I have read on other forums.
Good luck
Dave

 

[351c-ya]

I have a very similar set up in my 70 mach; however all I know is what's been done externally; I just bought it about 3 months ago (in the for sale section on VMF). Setup is 351C; Edelbrock 750 and intake; MSD 6AL box and pro billet dist.; headers; larger cam but I dont know what; FMX tranny; 3.25 9" rear. Mine also has the small H Pipe. Biggest difference (from the mods I know) between the two of our is I'm running a 750 cfm carb to your 670 cfm.

Best Pull - 266 HP; 327 ft/lbs torque

I too will be going to a tremec in the next few months, and am hoping that will get me to 300 at the wheels, and should easily get me over 350 ft/lbs torque.

 

[Fomocohipo]

No power over 4500??? The 4v heads start to make power at the top end. Especially with a 670 carb. I think a hoped up cleveland should have 3" exhaust if its a high rev engine with 4v heads. Some thing is way off, but if its fixed you should make some awesome power.

 

[D.Hearne]

I think he needs a bigger carb too. At least a 750

 

[68 & 00 GT]

sorry 70mach I wasn't trying to flame or anything, and I do understand that your just trying to unleash power that's already there by (as stated above) un corking the exhaust. I just seems like a lot to be expected by doing only that. I mean to go from 202 to 260 on a Mustang dyno that's close to saying that you'll pick up more like ~80 RWHP if you consider the percentage difference of RWHP loss shown on a Mustang dyno. Your current dyno number seem really low yes, but again I'm sure the Mustang dyno doesn't help much in that area either.

BTW- where did the puney ole 2in H pipe come from ? My 302 has Hooker longtubes to 3in pipes to 2 chamber flows to 2 1/4 in tails to 3in tips. I need a crossover pipe (probably run an H for the right exhaust sound w/ flows) and better tail pipes

Good luck man I hope it works out for you - let us know what gains you end up with.

 

[70mach1]

2 notes:

#1 The new Hp I am talking about (50 to 60+ hp increase) will be seen on a Dynojet + 2.5 dia X pipe. Some of you are confused about my statements.

#2 My engine tuner says my carb in plenty big enough (670 Avenger). Infact, my trottle cable was not opening fully (about 3/4 open) when the car put out 201 hp. When the tuner adjusted the cable, the car put out the same exact horspower (202hp). Basically he said the engine is utilizing as much carb as it needs and it doesn't require the additional air yet. Perhaps after the new exhaust goes on, it will need it.


I should also mention. I am running the Long Yellow secondary spring in the carb. There is still a purple, short yellow and white that are lighter (allows secondaries to come in sooner IF NEEDED. My tuner says that as the engine gets freed up and develops more power, the engine will be able to use a liighter spring. Once you get to the white spring, the engine needs a bigger CFM carb. So I am still a little ways away from that.

A Note: The biggest spring change was when I installed the COMP CAM Xtreme energy. The engine could take 2 steps in the lighter spring direction.

 

[Fawkes]

That 2" section of pipe is what was throwing me off in our emails. An X vs. an H is only going to give about 5 hp, but the 2" to the 2.5" is going to make all the difference in the world, IMHO. With that, and the skewed numbers from the Mustang Dyno, I think that you're going to be in that 250 to 260 range. I'm hoping that you make better numbers than that though, considering your mods.

As for the carb size, you've got a good one. A little bit of engine math says that you may even be over carbed. It's all good though.

 

[351c-ya]

In reply to the ?'s you emailed me: I had them shut it down at 5300 RPM's - That was my first time to the dyno and I was getting nervous. It's a 2 1/2" exhaust with Turbo mufflers. I don't have the print-out with me, I don't know what type of dyno machine it was. My first pull was only 177 HP - the throttle got stuck and would only open about 1/2 way. 2nd pull got me up to about 255 HP; 3rd got me the 266. I'm leaving today for the weekend, but when I get back I'll check the print-out and let you know what brand the dyno was.

Lance

One more thing - my air-fuel was dead on, which is why I said you may want try a bigger carb.

 

[hindle]

Dynoing on one dyno, switching a part and then dynoing on a completely different brand of dyno will tell you NOTHING. If you really want to see whether or not it makes a difference, go dyno on the one you've already set up an appt with for before you change the exhaust. Make the change and then go back and re-dyno. Else, go back to the original place you were at.

 

[foghorn67]

I've seen cars make incredible gains (especially the bigger engines) from ditching a restrictive exhaust.

 

[rebel65]

No power over 4500??? The 4v heads start to make power at the top end. Especially with a 670 carb. I think a hoped up cleveland should have 3" exhaust if its a high rev engine with 4v heads. Some thing is way off, but if its fixed you should make some awesome power.

the 4v means 4 barrel carb not 4 valve heads....a 670 avenger is a vac secondary so its more like a 2 barrel 335 thats always open with a backup 335 that gets you going . and they open due to speed not how hard u mash the gas!! its great ;D

 

[Fawkes]

Dynoing on one dyno, switching a part and then dynoing on a completely different brand of dyno will tell you NOTHING. If you really want to see whether or not it makes a difference, go dyno on the one you've already set up an appt with for before you change the exhaust. Make the change and then go back and re-dyno.

I agree 100% with this statement.

 

[Fomocohipo]

the 4v means 4 barrel carb not 4 valve heads....a 670 avenger is a vac secondary so its more like a 2 barrel 335 thats always open with a backup 335 that gets you going . and they open due to speed not how hard u mash the gas!! its great ;D

The clevelands that came with a 4 barrel carb had completely different heads then what came on the 2 barrel carbed cleveland, thus the 4v heads and 2v heads, The heads of the 4v engine had huge ports and a small combustion chamber. So what I was trying to say is that the huge ports make better power at the top end. Ive got the 2v heads but im puting on a 4v carb.

 

[70mach1]

Reply the Hindle

Running the car on another dyno will still tell you alot. What I am interested in is where the PEEK power occurs. I would like to see this at 5500 to 6000 rpm, not 4500 RPM. Any dyno will tell you that, the hp curve will just be scaled differently. The reason I am switching dyno shops is because the muffler guy I use is 1/4 mile away from the dynojet shop. The mustang dyno I used is about 35 miles away and is not open on Saturdays. Last time I took the day off and spent 4 hours at the shop. This time I only plan on 45 minutes for 3 pulls right after the exhaust job and can do it on a Saturday.

I predict 250 easy on the dynojet.

 

[D.Hearne]

#2 My engine tuner says my carb in plenty big enough (670 Avenger). Infact, my trottle cable was not opening fully (about 3/4 open) when the car put out 201 hp. When the tuner adjusted the cable, the car put out the same exact horspower (202hp). Basically he said the engine is utilizing as much carb as it needs and it doesn't require the additional air yet. Perhaps after the new exhaust goes on, it will need it.


I should also mention. I am running the Long Yellow secondary spring in the carb. There is still a purple, short yellow and white that are lighter (allows secondaries to come in sooner IF NEEDED. My tuner says that as the engine gets freed up and develops more power, the engine will be able to use a liighter spring. Once you get to the white spring, the engine needs a bigger CFM carb. So I am still a little ways away from that.

There's not a whole lot of difference between 3/4 and full throttle in air flow. And seeing as you have a heavy secondary spring in there, I'll bet the secondaries weren't even coming open. This could also have been why your rpm's were limited and the engine wouldn't rev any higher. You should have changed sec springs while there to see if there was a difference. I'm running a mostly stock 302 roller motor with a vac sec Holley 600, and with a purple spring, it pulls the secondaries open completely. With the spring Holley put in there they wouldn't open either, till the motor got to around 5 grand. Now they come on almost as soon as you nail the pedal, and ther's a noticeable difference when they do come open. I still maintain that you motor needs more carb than that 670.