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I'm getting closer to swapping to a more aggressive cam in my BJ7, and possibly changing the exhaust header. Does anyone have info (or a reference) for expected gains by using the BJ8 cam in the BJ7 engine? Also, sources for exhaust headers and overall discussion on changes to carb settings would be helpful.
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Horsepower Gain
- Thread starter Stretch
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GregW
Yoda
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Hi Stretch,
If I remember correctly, the Anderson/ Moment restoration book gives horsepower figures. A stock BJ8 was rated at 148 HP. A couple things to consider with headers are you loose the flex part of the down tubes and the collector may be a larger diameter than the stock exhaust pipes (mine from Denis Welsh was). If you want to keep the back end of the exhaust, you probably need to add some sort of flex pipe and step down adaptor in front of the muffler. Not a lot of space to do that. My headers end past the outrigger. What I did was use 2” pipe all the way back and fabricated hangers that were less rigid than original. So when the engine flexes, the entire exhaust moves with it.(In theory)
If I remember correctly, the Anderson/ Moment restoration book gives horsepower figures. A stock BJ8 was rated at 148 HP. A couple things to consider with headers are you loose the flex part of the down tubes and the collector may be a larger diameter than the stock exhaust pipes (mine from Denis Welsh was). If you want to keep the back end of the exhaust, you probably need to add some sort of flex pipe and step down adaptor in front of the muffler. Not a lot of space to do that. My headers end past the outrigger. What I did was use 2” pipe all the way back and fabricated hangers that were less rigid than original. So when the engine flexes, the entire exhaust moves with it.(In theory)
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You might want to check Denis Welch Motorsport. I think they're generally considered the number one performance parts supplier for big Healeys, and after perusing their website you might want to give them a call. They're in the UK. I recently ordered from them for the first time, and they were very responsive (good email commo) and the part arrived very quickly. Good luck. /ubbthreads/images/graemlins/driving.gif
MotorHead67
Jedi Hopeful
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When I was building the motor for my BJ8 I did call DW and they were very helpful. One of the things they told me was that adding headers was the best bang for the buck as far as adding horsepower. I used their headers but cut the pipe back a bit and welded on a piece of the flex pipe from a Falcon (from Moss) SS down-pipe. That flex pipe and it's tail piece slip into the mufflers. I'm sure the best setup would have been to run a full DW exhaust.
Regarding the carb changes: I think if you're serious about setting up your carbs consider an air/fuel ratio meter like the one from innovatemotorsports.com.
Regarding the carb changes: I think if you're serious about setting up your carbs consider an air/fuel ratio meter like the one from innovatemotorsports.com.
John Loftus
Darth Vader
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Stretch,
Remember that the BJ7 came with 1 3/4" carbs and the BJ8 came with 2" carbs so changing the carbs/manifold along with a BJ8 cam should get you up to the stock BJ8 horsepower.
Cheers,
John
Remember that the BJ7 came with 1 3/4" carbs and the BJ8 came with 2" carbs so changing the carbs/manifold along with a BJ8 cam should get you up to the stock BJ8 horsepower.
Cheers,
John
Skip & Lynne
Jedi Warrior
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I have a great set of Chevrolet numbers that I had my cam ground to and it is really sweet. It works great with my stock carbs and exhaust. It has a nice mild chop at idle and is great in the midrange. I wanted something that was good on the street and yet had more punch than the stock cam. Skip
Bruce Bowker
Obi Wan
Offline
Denis Welch Motorsport.
I also bought from them. Spoke over the telephone and by email. Very helpful and nice items. Catalog is fun.
Bruce
I also bought from them. Spoke over the telephone and by email. Very helpful and nice items. Catalog is fun.
Bruce
GregW
Yoda
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Fun yes, but I have to lock up my credit cards when I’m on that site. /ubbthreads/images/graemlins/grin.gif
As Skip mentioned, another option that has been covered in the past is regrinding your cam. Iskenderian ground my cam and other companies do it as well. Much cheaper than buying a new cam from the usual suspects.
As Skip mentioned, another option that has been covered in the past is regrinding your cam. Iskenderian ground my cam and other companies do it as well. Much cheaper than buying a new cam from the usual suspects.
BlueRidge1
Jedi Warrior
Offline
Stretch, I had my cam reground to the chevrolet specs
Holman Automotive Charlotte NC www.holmanmoody.com
it has a nice sound and I am retaining the three su 4 carbs,not sure on the horsepower numbers and I intend to take it to a reputable shop for fine tuning the carbs and timing(still wish Dave Russel lived near by) Bob G
Holman Automotive Charlotte NC www.holmanmoody.com
it has a nice sound and I am retaining the three su 4 carbs,not sure on the horsepower numbers and I intend to take it to a reputable shop for fine tuning the carbs and timing(still wish Dave Russel lived near by) Bob G
Skip & Lynne
Jedi Warrior
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My cam was reground by Holman Automotive they used to be Holman and Moody who built engines for Nascar and Trans Am cars. My cam has .425 lift on a 108 degree lobe centerline. The intake opens as 31 before top and closes 64 after bottom. The exhaust 67 opens before bottom and closes 28 after top. Larry at Holman is a great guy and he will check the cam to be sure it is straight and everything is good before he will grind it. You use your cam not a Chevrolet cam. I wanted a good street cam that had a little more punch and I am really pleased with this cam. Tell Larry you want yours cut to HA-406-8. Be sure to get the lifters reground. Larry has a place right there in Charlotte that will regrind them for you. Skip
BlueRidge1
Jedi Warrior
Offline
I can give you the information on the cam card as follows ex closes 28
ex opens 67
int closes64
int opens 31
int lift 425 lash .018 rocker ratio 1.42
ex lift 425 lash .018 rocker ratio 1.42
lobe centers 108
cam model ha 406.8
I don't know how this all translates or what alot of it means or the duration.Maybe Dave Russell can help?
ex opens 67
int closes64
int opens 31
int lift 425 lash .018 rocker ratio 1.42
ex lift 425 lash .018 rocker ratio 1.42
lobe centers 108
cam model ha 406.8
I don't know how this all translates or what alot of it means or the duration.Maybe Dave Russell can help?
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Hi BR,
The Holman cam is rated at 275 degrees duration (valve open time in crankshaft degrees) & installed slightly advanced. The lobe center angle is 108 degrees, overlap is 57 degrees, lift is .434, intake closes at 64 degrees abdc. This cam is very similar to the Piper BP220, the DWR8, & the Kent AH2.
For reference, the later BJ8 cam is 252 degrees duration & installed slightly advanced. Overlap is 37 degrees, lift is .368, intake closes at 56 degrees abdc.
The point of intake closing probably has the greatest affect on low rpm power. Compared to the BJ8, which closes the intake at 56 degrees after bottom center, the Holman cam closes at 64 degrees after bottom center & so will build less cylinder pressure (torque) for a given rpm. The increased overlap of the Holman cam at tdc, 57 degrees vs 37 degrees for the BJ8 cam will give a rougher idle & less low rpm torque.
In general terms, the Holman would probably be considered a fast street cam.
My personal feeling is that unless you plan on turning the engine over 5000 rpm a lot, the BJ8 cam would be more suitable. If you don't mind a fast, rough idle, & turning the engine faster to obtain a given amount of torque, then go for the more radical cam. It will give a bit more power over 4500 rpm.
When any cam is reground to give more timing & lift, the cams base diameter is reduced which puts more stress on the cam lobes & followers.
Cams ground on new blanks can have the larger original base circle & still give the desired timing. Some times, old cams are built up with weld & then ground to the desired contour. This gives the desired larger base circle & works ok if the welding is good.
When using a higher lift cam, always check clearance between the open exhaust valve & the cylinder deck. If there is too much lift the cylinder block needs to be relieved to give exhaust valve clearance. Depending on the head gasket thickness this sometimes occurs around .430 valve lift & over.
By all means, have a machine shop check ALL of your followers for a hardness of RC 55 or greater. I probably don't need to say that all followers should be reground or new.
D
The Holman cam is rated at 275 degrees duration (valve open time in crankshaft degrees) & installed slightly advanced. The lobe center angle is 108 degrees, overlap is 57 degrees, lift is .434, intake closes at 64 degrees abdc. This cam is very similar to the Piper BP220, the DWR8, & the Kent AH2.
For reference, the later BJ8 cam is 252 degrees duration & installed slightly advanced. Overlap is 37 degrees, lift is .368, intake closes at 56 degrees abdc.
The point of intake closing probably has the greatest affect on low rpm power. Compared to the BJ8, which closes the intake at 56 degrees after bottom center, the Holman cam closes at 64 degrees after bottom center & so will build less cylinder pressure (torque) for a given rpm. The increased overlap of the Holman cam at tdc, 57 degrees vs 37 degrees for the BJ8 cam will give a rougher idle & less low rpm torque.
In general terms, the Holman would probably be considered a fast street cam.
My personal feeling is that unless you plan on turning the engine over 5000 rpm a lot, the BJ8 cam would be more suitable. If you don't mind a fast, rough idle, & turning the engine faster to obtain a given amount of torque, then go for the more radical cam. It will give a bit more power over 4500 rpm.
When any cam is reground to give more timing & lift, the cams base diameter is reduced which puts more stress on the cam lobes & followers.
Cams ground on new blanks can have the larger original base circle & still give the desired timing. Some times, old cams are built up with weld & then ground to the desired contour. This gives the desired larger base circle & works ok if the welding is good.
When using a higher lift cam, always check clearance between the open exhaust valve & the cylinder deck. If there is too much lift the cylinder block needs to be relieved to give exhaust valve clearance. Depending on the head gasket thickness this sometimes occurs around .430 valve lift & over.
By all means, have a machine shop check ALL of your followers for a hardness of RC 55 or greater. I probably don't need to say that all followers should be reground or new.
D
Bob Claffie
Jedi Knight
Offline
Another thing to keep in mind when going to a higher lift cam is valve spring coil bind. Probably not a problem with a "factory" BJ8 cam, but certainly check it out if using something more radical. When talking chevrolet cam specs be aware that the radicalness of a cam is in some way proportional to the size of the engine. Bob
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[ QUOTE ]
When talking chevrolet cam specs be aware that the radicalness of a cam is in some way proportional to the size of the engine. Bob
[/ QUOTE ]
Hi Bob,
You are certainly correct. The per cylinder volume of the Healey would be only something like 77% of the Chevy cylinder volume. The smaller Healey cylinder would require less cam/valve timing to give the same cylinder filling as the larger Chevy cylinder. 270 degree cam duration would be fairly mild for the Chevy, not so mild for the healey. In reality, cam timing, valve size, port size, all need to be matched to cylinder capacity & intended engine use.
I also agree on checking spring coil bind.
D
When talking chevrolet cam specs be aware that the radicalness of a cam is in some way proportional to the size of the engine. Bob
[/ QUOTE ]
Hi Bob,
You are certainly correct. The per cylinder volume of the Healey would be only something like 77% of the Chevy cylinder volume. The smaller Healey cylinder would require less cam/valve timing to give the same cylinder filling as the larger Chevy cylinder. 270 degree cam duration would be fairly mild for the Chevy, not so mild for the healey. In reality, cam timing, valve size, port size, all need to be matched to cylinder capacity & intended engine use.
I also agree on checking spring coil bind.
D
Skip & Lynne
Jedi Warrior
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Guys it was my understanding that this was a dirt track cam for a 260 cu/in Chevrolet 6 cylinder, it was supposed to make everything below 5ooo rpm. When I built my engine after it was all togther on the stand I turned it over several times with a ratchet really slowly to check for spring bind and well as valve piston contact. Mine idles really well around 500 to 700 rpm with just a little lope. In the mid range it is really strong and pulls like a tractor. I didn`t want something so radical I couldn`t enjoy a sunday drive but I wasn`t going to put the cam and lifters back without at least regrinding the faces so I had a little extra put into it and I am well pleased with it. I will most likely use the same cam on my other BT7 when I restore it too. Lynne drives this car with no problem at all and she`s a grandma. Skip
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Hi Skip,
The cam likely does make everything below 5,000 rpm on the Chevy. Since the Chevy 6 has almost 50% more displacement per cylinder than the Healey, the power curve would be moved somewhat higher in the rpm range when the same cam is used on the Healey. Glad you have a combination that you like.
D
The cam likely does make everything below 5,000 rpm on the Chevy. Since the Chevy 6 has almost 50% more displacement per cylinder than the Healey, the power curve would be moved somewhat higher in the rpm range when the same cam is used on the Healey. Glad you have a combination that you like.
D
GregW
Yoda
Offline
Well Dave, you seem to have a very good grasp on cam design, or the same engine simulation program I have. /ubbthreads/images/graemlins/grin.gif I ran some numbers and came up with what you have already said. The best results look to be a BJ8 cam with headers up to 4500 RPM. At that point the Isky cam w/headers starts making more power followed closely by the Chevy grind w/headers. The torque curves tell the same story.
