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

[RogerC62]

D.Hearne,
I was thinking the same about the carb. Once the exhaust is opened up, the 4 barrel heads are going to flow a whole lot better. The demand at the higher RPMs is going to be greater and I don't think a 670 is big enough at the top end of the power band.

It definately sounds like the engine is being severely restricted, flow-wise, by the exhaust.

 

[70mach1]

We tried the short yellow secondary springs and it created a rich spot when the secondaries hit. Meaning they came in too early. This causes the car to stumble slightly and then catch up. My tuner says that it may feel faster (like the car just had the turbos engage) but in actuality it is slower.

So we backed down one level to the purple spring and the rich spot went away.

This fact indicates that the Carb is plenty big. If the engine needed more carb, then the vacuum would open the secondaries earlier and take the extra air/fuel that it needed while requiring a lighter spring.

I am glad there is so much interest in this topic. You will all find out May 1st when I go back to the dyno, what the numbers will be.

Any guesses?

 

[Dark Knight]

what was the A/F ration like? rich spot may have just meant that the secondary jetting was to big..or the power valve was opening late...

 

[ratio411]

...I am interested in where the PEEK power occurs. I would like to see this at 5500 to 6000 rpm, not 4500 RPM...

IMO you will peek about 5500 with your current intake and a free flowing exhaust. I think you are overcammed or under intaked, depending on your point of view.
Not that your combo will run poorly, but it will not be up to potential. With a smaller cam or more aggressive intake, your power band will be both flatter and more broad. The Performer 4v is less aggressive than even the stock 4v intake, while the cam you are running should turn a 4v up to around 6500 rpm.
Just an observation. You are cutting your useable power band at least 1000 rpm short IMO.
Dave

Edit: Racer X and D.Hearne are both touching on this issue with their thoughts on carb size. I take it one step further though and say an intake change would be more benificial than a carb change.

 

[87gn2]

I agree with ratio411 on the intake but I think that's a pretty small cam as it is, especially for a 4V Cleveland.

 

[ratio411]

It is a small cam in general, but it is well beyond a Performer intake. That intake starts early, but begins to fall off after 3500. Not that it won't spin 6k, but a mild single plane intake will out horsepower it from 3-6k, that is right where those heads shine, so why bother with an intake that won't keep up?

 

[87gn2]

After I posted I figured that that's what you meant. The Performer is basically an aluminum stock replacement, right? Not much power gain? especially for a 4V cleveland...

 

[88lx5oh]

what do you need to make a 2v cleveland a 4v cleveland
heads, cam intake and carb and what are some good ones to get sorry about jacking this. but im building a 2v out of a 73 cougar. its bored .030 over and has a larger velocity sump so i mena what would you guys suggest

 

[87gn2]

Why do you want a 4v cleveland? Do you want lots of low end grunt (2v) or lots of high end hp (4v)? You might look at the aussie heads...

 

[88lx5oh]

which would be better for some street and alot of strip

 

[87gn2]

I'll leave the final verdict up to someone who really knows the 335 series but I'd say the 2V...

 

[ratio411]

After I posted I figured that that's what you meant. The Performer is basically an aluminum stock replacement, right? Not much power gain? especially for a 4V cleveland...

I did some research a few years back and found out that the Performer 4v actually has significantly smaller ports and plenum than the stock part. Edelbrock sought to increase low end power on the 4v for cars that were strictly street and suffering on the bottom end. Alot of 4vs came in heavier cars like Torino, Montego, and late 1st gen Stangs... many weren't geared well either, so I am sure there were alot of satisfied customers back when these cars were more than just weekend crusiers or street/strip warriors.
IMHO anyway...
Dave

 

[70mach1]

My engine builder says that the HUGE ports of the Cleveland 4V are too big and in fact the 2V heads actually flow better and can make more power everywhere.

I installed the INTAKE MPG port plates. My engine builder HIGHLY recommended it. He said he has dyno tuned about 12 cleveland and Boss 302 cars and everyone of them benefitted from the plates. It doesn't lower or raise the PEEK Hp, but he said it brings the torque curve up and flatens it out. He also said the mid range power is much higher.

Basically he says you want the most area under the dyno curve and the plates increase the area under the curve.

I am not sure if they plates work or not, but Craig Blood (Blood Enterprises in Aurburn WA) is very sure. His web site is www.bloodenterprises.com. He is argualby the best tuner is Western Washington.

Bottom line is if you have 2V heads, stick with them. They will do just fine and could do better in certain situations. And I am a 4V guy!!!

 

[70mach1]

The new dyno numbers are in ! Closure at last.

Here are the results of the dyno second dyno.

I compared the dyno info from 3 weeks ago to this info. The X pipe made a huge difference. Huge. So huge, that we couldn't fully re-dyno the car. That is because the air/fuel ratio became so dangerously high that the tech stop revving the engine. The air/fuel ratio should be at 12.5 the whole time.

As a baseline, when I first had the car baseline tested 3 weeks ago, the air fuel was at 13.0 to 14.0 with a slight umbrella shape to it. Blood enterprises brought the umbrella down to 12.2 to 12.9 by changing the primary jets from 65 to 69. So 4 sizes larger brought the air/fuel down by one step. The car was in good shape air/fuel wise.

Then I found out the exhaust had a huge restriction. It wasn't the h pipe (although it would have been if not for what I am about to tell you). The tail pipe that leaves the muffler and goes over the drive shaft was bent in an elliptical fashion. It was 2.25 originally but when the bastards put it in, they smashed it. So it was seriously oval on both sides. On top of that, my exhaust tips are only 2" diameter. And the h pipe didn't help either. The whole exhaust was f--up.

The x-pipe is beautiful. I had him install flanges so I can take it out when I do the trans. And he used 2.5". It looks huge compared to what was there. And the car is a little louder now.

Anyway, you will notice on "combined" tab of the EXCEL sheet (see JPG attached), that the air fuel starts out fine but then gradually gets leaner from 2100 RPM to 2600 RPM. This should be the primary jets being too small AGAIN ! I probably will make them 2 to 4 sizes larger (71 to 73). Now that the engine can move a proper amount of air, it is! And the fuel cannot keep up.

Next, the secondaries kick in and initially richen up the air/fuel from 2700 to 3000 RPM but then the air starts flowing so fast that the jets cannot keep up and the engine goes lean. By 4300 the car is dangerously lean. By 4600 engine damage could occur and the car is struggling to make power due to lack of fuel. By 4900 the car is simply giving up and trying to prevent piston oblivion. The tuner said the #68 jets in the secondary should be 75 (75, that is a huge jump), but if it were his car he would make them 80 (not sure why). He said richer is better than leaner due to piston damage vs fuel economy. I have to agree, but I don't want the car so rich that it looses power.

So I need to change primary jets up 2 to 4 or secondaries up 6 to 8 sizes. I thought that if I make the primaries up 3, then I would only have to raise the secondaries up by 5.

What do all you think? Alot of info, but that is what is fun about it.

Ryno...

Oh, the car made 235 hp. vs 202 previously and there should be another 25hp according to the tech when the jets are proper.

 

[paintballtommy]

maybe check the power valve?

 

[Fawkes]

I think that you are on the right track with the jetting size. We'll get those swapped out and get you to Pacific Raceways for some "tuning on the fly".

 

[70mach1]

Reply to paintballtommy about power valves. Good technical info

Your power valve selection should be computed as follows. Take you initial vacuum reading at idle. Let's say it is 12 like mine. Now divide by 2 and that should be your power valve reading. So you power valve should open at 6 in of vacuum.

This is straight out of the holley tuning book. Mine is factory at 6.5. A little high, but still perfectly fine. Cars with large cams and aggresive tuning with little vacuum may use 4.5 or 3.5 power valves.


No it is definetely jets.

I am going to stick in the factory jets for the holley 770 Avenger (as compared to the 670 jets). The 770 jets are 72 primary, 75 seconday. The 670 came with 65 prim 68 secondary. As I indicated earlier, my carb was changed to 69 prim 68 secondary BEFORE THE FIRST DYNO RUN. Now after the exhaust change and second dyno run, I am making an educated guess at the jet size. I will track tune it today at 72 primary with a super heavy secondary spring (to isolate the primaries) and keep adding jet until I get a little bit of black smoke, then I will back it off 1 or 2 sizes.

 

[351LX]

Holley has on their website a different way to determine which power valve you need. http://www.holley.com/HiOctn/TechServ/TechInfo/TI-222A.html That is the method I use, I hook a vacuum gauge up to my intake a drive around a bit and pick a power valve a couple inches lower than what I am seeing in normal driving.I don't know why Holley publishes both methods.

 

[10secgoal]

The idle method of picking a PV is only to get you close and doesn't generally work for High Performance vehicles. I have about 11 in and run a 8.5,not a 5.5. It fall on it's face with anything smaller. A car with a more aggressive cam will more than likely need a higher power valve. Chances are it will need that extra fuel alot sooner that at 3.5 in. It will be running lean until until vacuum drops to 3.5. Which as paintball tommy suggested, may be sovled with a different PV.

 

[70mach1]

I think you are confused. The stock PV in the Holley 670 Avenger is 6.5. That means is takes 6.5 in of vacuum to open. Not that it opens at 6.5in Hg. If you have an 8.5, then that is really stiff. Feel the spring difference between a 3.5 and an 8.5 The 8.5 will have a much higher spring rate, thus requiring more vacuum to open. Hence it will open later.

Large PV # = later opening.
Smaller PV # = earlier opening.