Zane's 71 327 Ram Horn - restrictive?

[rcazwillis]

I remember when I was a teenager, the truck was weak in the engine department. Decent low end, but would not pull any RPM. I always thought it was just the way the engine was built.

The engine we put in it has vortec heads, good springs, Edelbrock dual plane, with a quadrajet and the same exhaust from 327 ram horns to tail pipe. Timing is 12 degrees with new HEI. Should not be a factor. Tuning is on the rich side. No vacuum leaks, plenty of fuel flow. Everything was built for a future cam swap. The engine should spin up to 5500 pretty easy with good power. It won't. It runs fine, but is kinda lame. Very reminiscent of the engine when dad drove it.

Considering the only common factors are 327 ram horn manifolds, 2" exhaust, and glass packs, I wonder about the ram horns. They are 327 versions with the alternator mount on the driver side. Could they be restrictive enough to cause the problem? Could it be the glass packs? I guess the answer is yes to both, but where should I start?

I just remember the driver side manifold also has the flapper valve on the exit that helps the engine warm up. Could that be enough to choke it down. I have not verified it is actually opening up.

I checked for bananas.

Zane does not yet know the difference, but I do. Has to be fixed.

[geezer#99]

Not likely the ram’s.
I had a 10 to 1, twisted wedge headed, 235 @.050 5.40 lift cam 350 that would spin to 6 grand all the time. Had ram’s on it.
You say you’ve got 12 initial.
How much total timing and at what rpm?
Vortec’s don’t like more than 32 degrees.

And what cam do you have?

[rcazwillis]

Originally Posted by geezer#99

Not likely the ram’s.
I had a 10 to 1, twisted wedge headed, 235 @.050 5.40 lift cam 350 that would spin to 6 grand all the time. Had ram’s on it.
You say you’ve got 12 initial.
How much total timing and at what rpm?
Vortec’s don’t like more than 32 degrees.

And what cam do you have?

I fully expected it to spin to 5500 easily.

I don't know total. HEI "average" 20 advance. So went with 12 initial. Don't have the proper timing light to measure total.

Cam is bone stock that came in 2001 Chevrolet Express 2500. Roller cam. Heads are GM new with the Z06 springs and retainers. Guides and spring pockets machined to handle springs and .550+ lift. All parts are intended to go with the Comp Cam equivalent of the GM Hot Cam. Ran through all the lifter adjustments while engine running because one was clicking.

[rcazwillis]

Also don't have a tack, but calculating it is stopping at about 3500-3800 rpm based of tire size and speed. It gets there quick in 1st, but basically stops. Shift manually to 2nd and off it goes.

[geezer#99]

I always assume an hei has about 25 degrees.
Without a dial back light you could mark your balancer.
Figure out the circumference, divide it by 360 then mark the balancer.
Or use your timing tab to figure out how long 12 degrees is.

[weim55]

Mostly, it's the stock cam that isn't allowing high RPM power. It is so small it might rev to 5000 but the power curve is finished by 4500rpm.

Steve weim55 Colorado

[67ranchhand]

That camshaft is your issue. No performance there. Change it and you will see a difference. Valvetrain is most important factor in performance. Whether it be torque or horsepower.

[cornerstone]

Originally Posted by rcazwillis

I checked for bananas.

“Look man.... We’re not falling for no banana in the tailpipe!”
-Eddie Murphy
1987?

[rcazwillis]

If the consensus is the cam, then I won't spend any time on it.

I did source a timing light to check total timing. Will set it to 32 all in. What RPM should it be all in?

[Eddie H.]

I run a small block 406 with ram horn manifolds and 2 1/4 inch pipes.
No problems with restrictions there.

[geezer#99]

Originally Posted by rcazwillis

If the consensus is the cam, then I won't spend any time on it.

I did source a timing light to check total timing. Will set it to 32 all in. What RPM should it be all in?

Usually near 3000.

[rcazwillis]

Originally Posted by geezer#99

Usually near 3000.

Thanks. Planning to address this weekend along with a number of other things needing attention.

[geezer#99]

Here’s my favourite link for you on timing.

http://www.badasscars.com/index.cfm/...d=76/prd76.htm

[rcazwillis]

Originally Posted by geezer#99

Here’s my favourite link for you on timing.

http://www.badasscars.com/index.cfm/...d=76/prd76.htm

Great article. Thanks for the link.

[ManNamedJed]

You didn't mention what fan you are using. A non-clutched heavy duty fan can really restrict how an engine revs.

[rcazwillis]

Originally Posted by ManNamedJed

You didn't mention what fan you are using. A non-clutched heavy duty fan can really restrict how an engine revs.

Good thought. It is clutched factory fan. Learned that lesson way back in the 80s when I thought a flex fan solid mount to pump was cool.

[AussieinNC]

IMO...the ram horns can be checked for bloackages easily by dropping off the primary pipes at the flanges, tying the pipes up with wire and a quick test drive around the block....if the performance improves, swap out the glass packs

One thing to check is the heat valve flapper in the exhaust manifold is not stuck closed...I have seen these things freeze shut...

[rcazwillis]

Heat valve moves freely. Your suggestion is my exact plan. I know the ram horns have no obstruction as I painted them on the bench.

Truck has a funny exhaust sound at the pipe. Kind of tractor sounding. Overall, runs good so no rush to do anything with it. A 16 year old does not need "more power"....

[garyd1961]

I don't think it's the cam, I have the same motor with a stock cam and mine will rev on up there. I don't have a tach but it has to be hitting 5000. My 383 I had with a tach would hit 7000 before the rev limiter kicked in. This motor doesn't go that high but it does rev pretty high.
I do have headers with 2 1/2 duels and MSD with a 6al box. My guess would be something in the distributor is keeping it from revving up.

[burnin oil]

You may want to double check the exhaust ports alignment on the head. I had an issue where the port height was different between the head and manifold and there wasnt enough metal to port it out. It has been a few years but I want to say that the exhaust manifold was about an 1/8" lower on the manifold side.

[rcazwillis]

Originally Posted by garyd1961

I don't think it's the cam, I have the same motor with a stock cam and mine will rev on up there. I don't have a tach but it has to be hitting 5000. My 383 I had with a tach would hit 7000 before the rev limiter kicked in. This motor doesn't go that high but it does rev pretty high.
I do have headers with 2 1/2 duels and MSD with a 6al box. My guess would be something in the distributor is keeping it from revving up.

CAM did not seem like the issue to me, either. Going to make sure timing is good. Probably take the exhaust loose, test if that is even an issue.

[rcazwillis]

Originally Posted by burnin oil

You may want to double check the exhaust ports alignment on the head. I had an issue where the port height was different between the head and manifold and there wasnt enough metal to port it out. It has been a few years but I want to say that the exhaust manifold was about an 1/8" lower on the manifold side.

I will add that idea to the things to check. I did zero porting on this engine. Verified the intake line up, but never looked at exhaust.

[68Gold/white]

My guess would be something in the distributor is keeping it from revving up.[/QUOTE]

ding ding ding we have a winner!!!

[rcazwillis]

Originally Posted by 68Gold/white

My guess would be something in the distributor is keeping it from revving up.

ding ding ding we have a winner!!![/QUOTE]

So what am I looking for in the distributor? Just timing? I will verify it.

What are the targets? The article Geezer provided indicates 20 degrees initial plus 12 degrees advance. Without making modifications for this, would 32 degrees all in at 2500 rpm work? I have a spring kit and the light to make this happen.

If the distributor has 25 degrees advance and I set the initial at 7 and put springs on to get it all in around 2500, this would fix it or eliminate the distributor as the issue?

[rcazwillis]

Installed an advance kit with the softest springs. Result was 15 degrees of initial timing with 31 all in by 2500. Did not change the RPM cap. Pretty well stops at 4k rpm. Nothing past. Will eventually check the exhaust for restriction.