Anybody tried the new 4 & 7 swap cam from Comp?
09-01-2004, 02:44 AM
#1
Instructor
Thread Starter
Member Since: Jul 2001
Location: FINLAND
Posts: 119
Likes: 0
Received 0 Likes
on
0 Posts
Anybody tried the new 4 & 7 swap cam from Comp?
I see that Comp Cams has introduced a new cam line where 4 & 7 cam lobes have been swapped...that would also change the ign. order.
The only benefit of that in my mind would be the possibility to make easy 180 deg. headers....no more need to run the primaries from side to side.
Anybody thinking of trying this out?
...I'm thinking of a Street Roller at about 250deg 050 and tri-Y headers... could make a nice street screamer!
Jussi
The only benefit of that in my mind would be the possibility to make easy 180 deg. headers....no more need to run the primaries from side to side.
Anybody thinking of trying this out?
...I'm thinking of a Street Roller at about 250deg 050 and tri-Y headers... could make a nice street screamer!
Jussi
Last edited by Jussi; 09-01-2004 at 02:54 AM.
09-01-2004, 12:39 PM
#2
Race Director
Member Since: May 2000
Location: Redondo Beach USA
Posts: 12,487
Received 1,974 Likes
on
1,188 Posts
Swapping 4 and 7 won't achieve even firing interval on each bank.
18436572
18736542
The only way to achieve 180 degree firing order on each bank is to use a flat crankshaft.
Duke
18436572
18736542
The only way to achieve 180 degree firing order on each bank is to use a flat crankshaft.
Duke
09-02-2004, 02:13 AM
#4
Instructor
Thread Starter
Member Since: Jul 2001
Location: FINLAND
Posts: 119
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by SWCDuke
Swapping 4 and 7 won't achieve even firing interval on each bank.
18436572
18736542
The only way to achieve 180 degree firing order on each bank is to use a flat crankshaft.
Duke
18436572
18736542
The only way to achieve 180 degree firing order on each bank is to use a flat crankshaft.
Duke
1->7 180deg and 3->5 180deg for the driver side bank and
2->8 180deg and 6->4 180deg for the passanger side with the new ign. order...isn't that just the thing what you want if you plan to make 180 deg headers?
To come to think of it...the same would happen even with the normal ign. order???(7->1 & 3->5)....what is that I'm missing here...
Jussi
09-02-2004, 09:09 AM
#5
Instructor
Thread Starter
Member Since: Jul 2001
Location: FINLAND
Posts: 119
Likes: 0
Received 0 Likes
on
0 Posts
Hmm...it seems that I had a little too narrow view to this exhaust thing.
Propably due to the tri-y header thing in my mind...
So its about the pulse phasing AT the bank collector...
How well would that tri-y (4-2-1) system adapt to the 180 deg. header desing?
At least it would make the middle cylinder crossover a little easier to do but would it affect the good scavenging effect of the 4->1 180deg system?
Is there a way to determine the length & diameter of the primaries and secondaries of the tri-y system...or can you use the same primary & collector pipe lenght & dia as you would in 4-1 system? I know how to calculate those...
How can you determine the size and length of the secondaries?
Jussi
Propably due to the tri-y header thing in my mind...
So its about the pulse phasing AT the bank collector...
How well would that tri-y (4-2-1) system adapt to the 180 deg. header desing?
At least it would make the middle cylinder crossover a little easier to do but would it affect the good scavenging effect of the 4->1 180deg system?
Is there a way to determine the length & diameter of the primaries and secondaries of the tri-y system...or can you use the same primary & collector pipe lenght & dia as you would in 4-1 system? I know how to calculate those...
How can you determine the size and length of the secondaries?
Jussi
Last edited by Jussi; 09-02-2004 at 09:12 AM.
09-02-2004, 11:40 AM
#6
Race Director
Member Since: May 2000
Location: Redondo Beach USA
Posts: 12,487
Received 1,974 Likes
on
1,188 Posts
Any way you bake the firing order, a cruciform crank V-8 will have two cylinders on each bank that fire only 90 degrees out of phase.
Just look for two consecutive odd of even cylinder numbers in the firing sequence
Chevrolet changed the firing order on the LS smallblocks, and the reason was better idle quality, which probably has more to do with crankshaft torsional vibration than anything else.
On a carbureted engine changing the firing order will probably impact fuel distribution. On a FI engine there would be no effect.
Duke
Just look for two consecutive odd of even cylinder numbers in the firing sequence
Chevrolet changed the firing order on the LS smallblocks, and the reason was better idle quality, which probably has more to do with crankshaft torsional vibration than anything else.
On a carbureted engine changing the firing order will probably impact fuel distribution. On a FI engine there would be no effect.
Duke
09-03-2004, 02:31 AM
#7
Instructor
Thread Starter
Member Since: Jul 2001
Location: FINLAND
Posts: 119
Likes: 0
Received 0 Likes
on
0 Posts
Ok so 4 & 7 swap cams are for better fuel distribution in carburated engines...
There was talk about flat cranks...anybody used those?
That could be a little extreme part to use but I would think that some race teams might have them...
And also have anybody used 180 deg. headers?
Was the scavenging effect and the power increase noticeable?
Jussi
There was talk about flat cranks...anybody used those?
That could be a little extreme part to use but I would think that some race teams might have them...
And also have anybody used 180 deg. headers?
Was the scavenging effect and the power increase noticeable?
Jussi
09-03-2004, 10:33 AM
#8
Race Director
Member Since: May 2000
Location: Redondo Beach USA
Posts: 12,487
Received 1,974 Likes
on
1,188 Posts
Originally Posted by Jussi
Ok so 4 & 7 swap cams are for better fuel distribution in carburated engines...
Jussi
Jussi
Duke
09-03-2004, 09:00 PM
#9
Instructor
Member Since: Mar 2002
Location: Fredericksburg VA
Posts: 239
Likes: 0
Received 0 Likes
on
0 Posts
Still a typical V8 firing order
The 4-7 swap moves the 5-7 90deg separated induction from the rear of the engine to a 4-2 90deg separated induction order in the front. This is what you want for front-of-plenum fed FI manifolds like the TPI, LT1 and LS1. The LT1 style intake are notorius for starving poor #7 of air. The rear of the manifold shrouds the runner entry, and therefore ram-tune is weakened. I think there are also some benefits to the crank from the swap.
Single-plane crank? You should have bought a Ferrari. Sounds like a twin I-4 race boat, if there ever was such a thing.
Don't fixate on 180deg headers for your V8. By the time you stretch the primaries to reach the other side of the engine, the header will be too low RPM range to warrant the effort. Just use an independence 4-2-1 design, with a step in the primaries if necessary and don't oversize the secondaries (actually 4 collectors on the engine). Size the tertiary pipes for HP as is usual for tailpipes.
Single-plane crank? You should have bought a Ferrari. Sounds like a twin I-4 race boat, if there ever was such a thing.
Don't fixate on 180deg headers for your V8. By the time you stretch the primaries to reach the other side of the engine, the header will be too low RPM range to warrant the effort. Just use an independence 4-2-1 design, with a step in the primaries if necessary and don't oversize the secondaries (actually 4 collectors on the engine). Size the tertiary pipes for HP as is usual for tailpipes.
09-04-2004, 07:14 AM
#11
Instructor
Thread Starter
Member Since: Jul 2001
Location: FINLAND
Posts: 119
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by HeaderDesign.com
The 4-7 swap moves the 5-7 90deg separated induction from the rear of the engine to a 4-2 90deg separated induction order in the front. This is what you want for front-of-plenum fed FI manifolds like the TPI, LT1 and LS1. The LT1 style intake are notorius for starving poor #7 of air. The rear of the manifold shrouds the runner entry, and therefore ram-tune is weakened. I think there are also some benefits to the crank from the swap..
I had heard that LT1's (minirams etc) starve the #1 (or #2) cyl from air...something to do about the entry angle of intake ports...is this true?
Also those swap cams from Comp had so extreme durations that I doubt they were used anywhere near the LT1s or TPIs...most likely in a all out drag racers reving near 10000rpms
Originally Posted by HeaderDesign.com
Single-plane crank? You should have bought a Ferrari. Sounds like a twin I-4 race boat, if there ever was such a thing.
Don't fixate on 180deg headers for your V8. By the time you stretch the primaries to reach the other side of the engine, the header will be too low RPM range to warrant the effort. Just use an independence 4-2-1 design, with a step in the primaries if necessary and don't oversize the secondaries (actually 4 collectors on the engine). Size the tertiary pipes for HP as is usual for tailpipes.
Don't fixate on 180deg headers for your V8. By the time you stretch the primaries to reach the other side of the engine, the header will be too low RPM range to warrant the effort. Just use an independence 4-2-1 design, with a step in the primaries if necessary and don't oversize the secondaries (actually 4 collectors on the engine). Size the tertiary pipes for HP as is usual for tailpipes.
...it must be forbidden in the rules then...
Hmm....I saw one local vette club member had those 180 deg headers in a -72 vette this summer.
It made a really weird sound but rev'ed like crazy (+8000rpm).
My plan was not run the primaries across but the secondaries.
I do not know how to tune the tri-y setup though...ie are the secondaries counted as primaries when you calculate the lenght...
or??
I do remember reading that using a 0,25" larger pipes at the collector is a good guideline in tri-y system...
so 1 3/4" primaries, 2" secondaries and probably 2,5-3" final collector.
I did use the header calcularor from your web site but that's for 4-1 headers...how should I alter the numbers for the tri-y system?
My engine specs are in the home page.
Jussi
09-04-2004, 10:45 AM
#12
Instructor
Member Since: Mar 2002
Location: Fredericksburg VA
Posts: 239
Likes: 0
Received 0 Likes
on
0 Posts
The best intake designs give the cylinders an opportunity for equal performance. Both air supply and ram tune strength are important. IR systems, 1x4 single planes, and 2x4 tunnel rams are all great for this. The LS1 style is a good plenum FI manifold. LT1...hmmm.
Just because you can build a 180deg header and the engine will rev to 8000RPM doesn't mean that it was the best header design that you could have used.
Here is an example of a short primary 180deg header with its inherent drawbacks:
http://www.howeracing.com/Exhaust/Index-180Degree.htm
On V8 race applications with tailpipes I design the headers as 4-1-X-tailpipe on longer primary (lower RPM) engines, and 4-2-tailpipe on shorter primary (higher RPM) engines.
It sounds like you are trying to build interference headers with 180deg order at the 2-1 junctions. This means that your secondaries will have 180deg separated pulses. Minimum pulse separation in the secondaries is ususally 270deg. I don't do interference designs, but if I did I would design them as bank separated.
Here is some reading that might help you. NASCAR unrestricted engine headers are shown at the bottom of the first link:
http://www.camaros.net/cgi-bin/forum...4;t=007924;p=0
http://www.popularhotrodding.com/tech/0310phr_burns/
Just because you can build a 180deg header and the engine will rev to 8000RPM doesn't mean that it was the best header design that you could have used.
Here is an example of a short primary 180deg header with its inherent drawbacks:
http://www.howeracing.com/Exhaust/Index-180Degree.htm
On V8 race applications with tailpipes I design the headers as 4-1-X-tailpipe on longer primary (lower RPM) engines, and 4-2-tailpipe on shorter primary (higher RPM) engines.
It sounds like you are trying to build interference headers with 180deg order at the 2-1 junctions. This means that your secondaries will have 180deg separated pulses. Minimum pulse separation in the secondaries is ususally 270deg. I don't do interference designs, but if I did I would design them as bank separated.
Here is some reading that might help you. NASCAR unrestricted engine headers are shown at the bottom of the first link:
http://www.camaros.net/cgi-bin/forum...4;t=007924;p=0
http://www.popularhotrodding.com/tech/0310phr_burns/
