manifold choice
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,032
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From: Marlton NJ
It is critically important that you carefully match the camshaft (engine power curve) to the gear ratio. There is a range of gears that will work, for any cam, but if you get outside of that it will be lazy or a real dog.
Since you don't know your gear ratio but the car is driveable, here is a good way to calculate it: All you need to know is your rpm at 60 and tire diameter:
http://www.wallaceracing.com/calc-rgr.php
I also concur with a dual plane for the street for 90% of folks.
And you have some really big rear tires. It is going to take a well setup combination to be able to break them loose.
That's a pretty mild cam, so it should be pretty strong down low, it could be the gears/tires killing it.
Since you don't know your gear ratio but the car is driveable, here is a good way to calculate it: All you need to know is your rpm at 60 and tire diameter:
http://www.wallaceracing.com/calc-rgr.php
I also concur with a dual plane for the street for 90% of folks.
And you have some really big rear tires. It is going to take a well setup combination to be able to break them loose.
That's a pretty mild cam, so it should be pretty strong down low, it could be the gears/tires killing it.
Last edited by leigh1322; Jul 26, 2019 at 11:07 AM.
Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
Don't get me wrong, its not a dog or running like crap. It runs well and is fairly quick. Its just the off the line performance I feel could be improved a little if that's possible. I just got this build done, so I wont be tearing it apart anytime soon. The only thing I could think of that might be bogging the low end which would be a potential quick fix would be upgrading the intake and then retuning the carb/timing/ignition etc.
I have no clue about the gears, is there a way to confirm without opening up the rear end? The rear tires are 295-40-18 falken azenis RT615K which is just about as wide as a 335 tire I had mounted on another vehicle. Its a very wide and grippy tire so perhaps its doing its job.
What do you think about getting the air gap and adding a 1" phenolic spacer to it? and then having the carb, ignition, distributor re-adjusted?
I have no clue about the gears, is there a way to confirm without opening up the rear end? The rear tires are 295-40-18 falken azenis RT615K which is just about as wide as a 335 tire I had mounted on another vehicle. Its a very wide and grippy tire so perhaps its doing its job.
What do you think about getting the air gap and adding a 1" phenolic spacer to it? and then having the carb, ignition, distributor re-adjusted?
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
295/40R18 tires have a diameter of 27.3", a section width of 11.6", and a wheel diameter of 18". The circumference is 85.7" and they have 739 revolutions per mile. Generally they are approved to be mounted on 10-11.5" wide wheels.
That is another area to improve on a holley carb. If your 750 has straight leg boosters, that is the worst design. down leg booster are an improvement, but the best is replace your boosters with Annular boosters. It makes for the best of idle throttle response.
Last edited by gkull; Jul 26, 2019 at 12:09 PM.
Le Mans Master
Joined: Mar 2004
Posts: 7,465
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From: Little Rock AR
Gearing is easy to get close. put a lift jack under the diff and lift both rear tires off the ground (and safety stands). put a piece of tape on the drive line and on the side of one tire. count the number of tire rotations to get one drive line rotation. Example if the tire goes around 3 1/2 times to get one drive line rotation you have a 3.55 rear end gear. Or you can go to an online RPM/speed/tire diameter calculator.
295/40R18 tires have a diameter of 27.3", a section width of 11.6", and a wheel diameter of 18". The circumference is 85.7" and they have 739 revolutions per mile. Generally they are approved to be mounted on 10-11.5" wide wheels.
I still say out of those choices that the W-8501 is the best choice and would be usable in the future on bigger port heads. As to spacers and wanting low end grunt you have to use a spacer that adds velocity to the carb boosters. the best product is a wood 4 hole spacer the wood is the best thermal spacer and the 4 holes maintain the venture velocity. big open plenums and open spacers drop booster velocity.
That is another area to improve on a holley carb. If your 750 has straight leg boosters, that is the worst design. down leg booster are an improvement, but the best is replace your boosters with Annular boosters. It makes for the best of idle throttle response.
295/40R18 tires have a diameter of 27.3", a section width of 11.6", and a wheel diameter of 18". The circumference is 85.7" and they have 739 revolutions per mile. Generally they are approved to be mounted on 10-11.5" wide wheels.
I still say out of those choices that the W-8501 is the best choice and would be usable in the future on bigger port heads. As to spacers and wanting low end grunt you have to use a spacer that adds velocity to the carb boosters. the best product is a wood 4 hole spacer the wood is the best thermal spacer and the 4 holes maintain the venture velocity. big open plenums and open spacers drop booster velocity.
That is another area to improve on a holley carb. If your 750 has straight leg boosters, that is the worst design. down leg booster are an improvement, but the best is replace your boosters with Annular boosters. It makes for the best of idle throttle response.
Thats backwards. Count driveshaft rotations to get 1 full wheel rotation. Been there before. ☺
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
a little update:
so I got my current setup properly tuned and its a night and day difference how the car performs off the line, there is a lot more torque in the bottom end. Now I might just keep my setup as is because it drives pretty good, but if I do switch up it will be the air gap or the weiand 8501.
Will either of these intakes fit underneath a stock L88 hood with a drop base air cleaner with a 1" or 2" carb spacer?
Thanks
so I got my current setup properly tuned and its a night and day difference how the car performs off the line, there is a lot more torque in the bottom end. Now I might just keep my setup as is because it drives pretty good, but if I do switch up it will be the air gap or the weiand 8501.
Will either of these intakes fit underneath a stock L88 hood with a drop base air cleaner with a 1" or 2" carb spacer?
Thanks
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
The 7501 will help signal the carb better down low and give up nothing upstairs as your heads do not flow to the max potential of the intake anyway....and the cam is smallish.....
Carb signal is everything.....and during 99% of intake debates, it is never mentioned.......the ONLY reason you use a dual plane intake is to take advantage of the dual planes ability to split the firing order in half creating more overall vacuum at each primary booster on the carb. Single planes suffer on this because you have one large plenum trying to pull from two boosters at the same time.
Jebby
Carb signal is everything.....and during 99% of intake debates, it is never mentioned.......the ONLY reason you use a dual plane intake is to take advantage of the dual planes ability to split the firing order in half creating more overall vacuum at each primary booster on the carb. Single planes suffer on this because you have one large plenum trying to pull from two boosters at the same time.
Jebby
Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
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From: Vancouver, BC
The 7501 will help signal the carb better down low and give up nothing upstairs as your heads do not flow to the max potential of the intake anyway....and the cam is smallish.....
Carb signal is everything.....and during 99% of intake debates, it is never mentioned.......the ONLY reason you use a dual plane intake is to take advantage of the dual planes ability to split the firing order in half creating more overall vacuum at each primary booster on the carb. Single planes suffer on this because you have one large plenum trying to pull from two boosters at the same time.
Jebby
Carb signal is everything.....and during 99% of intake debates, it is never mentioned.......the ONLY reason you use a dual plane intake is to take advantage of the dual planes ability to split the firing order in half creating more overall vacuum at each primary booster on the carb. Single planes suffer on this because you have one large plenum trying to pull from two boosters at the same time.
Jebby
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Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
Perfect. I should be able to run the air gap with a 1" spacer then. I'm hoping to squeeze out a decent amount of low end power by swapping the Torker with the air gap and getting it tuned. I don't think I will swap out the heads anytime soon or the cam. The adjustments/tuning that have been done currently have been enough to allow me to smoke the 295 rears and then some.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
Perfect. I should be able to run the air gap with a 1" spacer then. I'm hoping to squeeze out a decent amount of low end power by swapping the Torker with the air gap and getting it tuned. I don't think I will swap out the heads anytime soon or the cam. The adjustments/tuning that have been done currently have been enough to allow me to smoke the 295 rears and then some.
An open 1” spacer on an Air-Gap defeats the purpose of having it in the first place and will cost power by negating carb signal.
Jebby
Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
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From: Vancouver, BC
Is there any benefit to adding the 1/2” 4 hole spacer or would you just run it without one?
Dr. Detroit
Joined: Mar 2012
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Likes: 4,025
From: New Braunfels Texas
Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
Update:
So I ended up buying an RPM air gap and a 1/2" 4 hole carb spacer from canton racing products. Now that the intake has been sorted out, I have another question. Is it worth getting the 461 heads ported or should I just buy a set of aluminum heads? I found an engine shop that builds performance motors who quoted me $500 CAD which is like $350 USD to port the 461s. From what I've seen online, a decent set of heads is going to run at a minimum $650 USD for the edelbrock performer up to $1800 for the AFR.
Based on my setup, what would you suggest?
So I ended up buying an RPM air gap and a 1/2" 4 hole carb spacer from canton racing products. Now that the intake has been sorted out, I have another question. Is it worth getting the 461 heads ported or should I just buy a set of aluminum heads? I found an engine shop that builds performance motors who quoted me $500 CAD which is like $350 USD to port the 461s. From what I've seen online, a decent set of heads is going to run at a minimum $650 USD for the edelbrock performer up to $1800 for the AFR.
Based on my setup, what would you suggest?
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
Update:
So I ended up buying an RPM air gap and a 1/2" 4 hole carb spacer from canton racing products. Now that the intake has been sorted out, I have another question. Is it worth getting the 461 heads ported or should I just buy a set of aluminum heads? I found an engine shop that builds performance motors who quoted me $500 CAD which is like $350 USD to port the 461s. From what I've seen online, a decent set of heads is going to run at a minimum $650 USD for the edelbrock performer up to $1800 for the AFR.
Based on my setup, what would you suggest?
So I ended up buying an RPM air gap and a 1/2" 4 hole carb spacer from canton racing products. Now that the intake has been sorted out, I have another question. Is it worth getting the 461 heads ported or should I just buy a set of aluminum heads? I found an engine shop that builds performance motors who quoted me $500 CAD which is like $350 USD to port the 461s. From what I've seen online, a decent set of heads is going to run at a minimum $650 USD for the edelbrock performer up to $1800 for the AFR.
Based on my setup, what would you suggest?
Unless it is a super rare car.....don’t waste time or money on the 461’s. The 66’ in my Avatar had ported 461’s and after a ton of work, flowed what an out of the box Performer RPM head flows.....
The Dart is the only wet flow head out there and is designed to flow beyond just bench numbers....it helps suspend and carry fuel better as well.....
But in reality, pick a head.....I like Dart and have the 200’s on my own car.
Jebby
Thread Starter
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
Bolt a pair of 180 Dart Platinums on it with the corresponding pushrods and rocker arms and hold on....
Unless it is a super rare car.....don’t waste time or money on the 461’s. The 66’ in my Avatar had ported 461’s and after a ton of work, flowed what an out of the box Performer RPM head flows.....
The Dart is the only wet flow head out there and is designed to flow beyond just bench numbers....it helps suspend and carry fuel better as well.....
But in reality, pick a head.....I like Dart and have the 200’s on my own car.
Jebby
Unless it is a super rare car.....don’t waste time or money on the 461’s. The 66’ in my Avatar had ported 461’s and after a ton of work, flowed what an out of the box Performer RPM head flows.....
The Dart is the only wet flow head out there and is designed to flow beyond just bench numbers....it helps suspend and carry fuel better as well.....
But in reality, pick a head.....I like Dart and have the 200’s on my own car.
Jebby
its not a super rare car from what I know, I wasn't able to get a build sheet. How much of a difference did you feel going from the ported 461s to the Dart 200 in your car? Do you have any thoughts on the edelbrock 7501?
Last edited by titanle; Aug 22, 2019 at 12:50 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
Are these the ones you're referring to? https://www.summitracing.com/int/par...1112/overview/
its not a super rare car from what I know, I wasn't able to get a build sheet. How much of a difference did you feel going from the ported 461s to the Dart 200 in your car? Do you have any thoughts on the edelbrock 7501?
its not a super rare car from what I know, I wasn't able to get a build sheet. How much of a difference did you feel going from the ported 461s to the Dart 200 in your car? Do you have any thoughts on the edelbrock 7501?
Yes, those are the heads on Summit.....
The 327 with the 461’s pulled like a train....but it was an L-79 car, so for originality I had the heads done....hardest running stock appearing small block I have ever driven....brutal midrange for a little engine....it ran 13.50’s with 215 BFG’s.....
Jebby
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Jebby, Titanie,
For what its worth, I believe Edelbrock has a soft carb spacer, maybe quarter inch thick, and is a two hole design. Meaning divided left / right just like the 7501 plenum is.
The spacer even has a divider down the middle.
Wouldn't that be better than a four hole spacer, which the Eddy 7501 is not a four hole? Cooler charge for the carb, not too high to clear the hood and being somewhat soft material will have a good seal. I suppose the spacers dividing wall cut be removed with a razor blade.
For what its worth, I believe Edelbrock has a soft carb spacer, maybe quarter inch thick, and is a two hole design. Meaning divided left / right just like the 7501 plenum is.
The spacer even has a divider down the middle.
Wouldn't that be better than a four hole spacer, which the Eddy 7501 is not a four hole? Cooler charge for the carb, not too high to clear the hood and being somewhat soft material will have a good seal. I suppose the spacers dividing wall cut be removed with a razor blade.
Had a 1976 L-82, 4-sp
Joined: Mar 2011
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Contact JB's Power Centre in Alberta for a possible parts source. Good prices and pay only the GST. I would save up your loonies and get AFR heads.