Thread: Engine mod advice needed for more hp.

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Your engine should have 8.5to1 stock not 7.8to1 . With the 305 #601 55 to 58cc heads it should be 9.75to1 . Your stock #624 heads are 76cc . These #601 heads do they have screw in rocker studs ? And your stock rod bolts can not take lots of high RPMs . Maybe you should also rebuild that short block with better pistons and ARP rod bolts . I had a nice running 1978 Z28 . It had a stock 350 short block with a bigger cam and ported heads . It ran mid 13teens before the bolts failed on one of the rods .

Here's some advice on camshaft selection from some of the best in the business. Cam Selection

Originally Posted by camaro_fever68

Here's some advice on camshaft selection from some of the best in the business. Cam Selection

What's funny is they are trying to compare apples to oranges in that thread. One guy starts a thread on street engines with 260cfm flowing street heads, and they are trying to compare a prostock engine which has 4 valves per cylinder requiring a 120LSA. Now I may not completely understand the camshaft, but I know that when dealing with a "small" 2 valve cylinder the LSA needs to be tighter(numerically lower) because there is not adequate low-lift flow. Of course a prostock engine is going to run on a 120LSA or so because they have twice the valve diameter. When it comes to building street engines I think that David Vizard knows what he is talking about. He put it pretty well in this quote "The bottom line is that LCA's are related to how big a cylinder the intake valve has to feed. The bigger the cylinder in relation to the valve, the tighter the LCA needs to be." We are talking about Maximum power here, not streetability.

I'm not trying to start up a firestorm here but "Camking" says, "You tighten up the lobe centers when you have too big of a port, and widen them when the port is too small."
What is your guys opinion on that?
I think there are so many different factors and ways to build a street engine that you cannot say something like that for every situation. These guys are arguing over things that can vary drastically just on how they want the engine to behave. Noone specified on what they were trying to accomplish... max horsepower, broad powerband, or streetability. Anyone know what Camking is talking about when he said that?

Originally Posted by 69elko

What's funny is they are trying to compare apples to oranges in that thread. One guy starts a thread on street engines with 260cfm flowing street heads, and they are trying to compare a prostock engine which has 4 valves per cylinder requiring a 120LSA. Now I may not completely understand the camshaft, but I know that when dealing with a "small" 2 valve cylinder the LSA needs to be tighter(numerically lower) because there is not adequate low-lift flow. Of course a prostock engine is going to run on a 120LSA or so because they have twice the valve diameter. When it comes to building street engines I think that David Vizard knows what he is talking about. He put it pretty well in this quote "The bottom line is that LCA's are related to how big a cylinder the intake valve has to feed. The bigger the cylinder in relation to the valve, the tighter the LCA needs to be." We are talking about Maximum power here, not streetability.

I'm not trying to start up a firestorm here but "Camking" says, "You tighten up the lobe centers when you have too big of a port, and widen them when the port is too small."
What is your guys opinion on that?
I think there are so many different factors and ways to build a street engine that you cannot say something like that for every situation. These guys are arguing over things that can vary drastically just on how they want the engine to behave. Noone specified on what they were trying to accomplish... max horsepower, broad powerband, or streetability. Anyone know what Camking is talking about when he said that?

In a street car I like a wider L/S say 112.
The wider L/S gives you a wider torque/power band in other words the engine will start pulling harder earlier plus this is what you want for the N20.
I have done some dyno testing with L/S.
The wider L/S also makes more cylinder pressure.
The narrow L/S makes the engine seem more "peaky" in other words you "window" is much smaller.
The narrow L/S will make less cylinder pressure in other words it "bleeds" more out the exhaust.
To answer your question.
If the port is to big than it is to big.
If the port is to small then it is to small.
You can move the cam around by advancing it or retarding it to change the power band up or down by a couple hundred rpm's.
You can also tighten or looosen the lash to make the can seem bigger or smaller.
If the head is to large than you can cut back on lift,duration,and valve size.
If the head is to small then you give more lift,duration and a larger valve size.
For a guide line I like to use Flow @28in. of water X 2.06.
A good example would be 270 cfm X 2.06 = 556.
This would be the max. horsepower these heads can support.
This is based on very good VE.
When I sell an engine I always ask about hp goals.
This is when I pick the cylinder heads and the rest follows.
I have said this before about David Vizard he is a good author.
He has a lot of theories some I agee with and some don't work well at all in I.M.O.
One thing you need to ask yourself is how many times in the past year has he had people in the winners circle.
Some of the best engine,head,cam people out there are the ones you never hear about because they don't have time to write a book because they are on the dyno or at the track.

You can build the top end of that engine any way you think best . But what about the stock short block ? How long do you think it will Live ??

Originally Posted by tango

You can build the top end of that engine any way you think best . But what about the stock short block ? How long do you think it will Live ??

I think you mis-understood me.
When I made that statement I was refering to any customers of mine when I build an engine for them.

Originally Posted by erik erikson

In a street car I like a wider L/S say 112.
The wider L/S gives you a wider torque/power band in other words the engine will start pulling harder earlier plus this is what you want for the N20.
I have done some dyno testing with L/S.
The wider L/S also makes more cylinder pressure.
The narrow L/S makes the engine seem more "peaky" in other words you "window" is much smaller.
The narrow L/S will make less cylinder pressure in other words it "bleeds" more out the exhaust.
To answer your question.
If the port is to big than it is to big.
If the port is to small then it is to small.
You can move the cam around by advancing it or retarding it to change the power band up or down by a couple hundred rpm's.
You can also tighten or looosen the lash to make the can seem bigger or smaller.
If the head is to large than you can cut back on lift,duration,and valve size.
If the head is to small then you give more lift,duration and a larger valve size.
For a guide line I like to use Flow @28in. of water X 2.06.
A good example would be 270 cfm X 2.06 = 556.
This would be the max. horsepower these heads can support.
This is based on very good VE.
When I sell an engine I always ask about hp goals.
This is when I pick the cylinder heads and the rest follows.
I have said this before about David Vizard he is a good author.
He has a lot of theories some I agee with and some don't work well at all in I.M.O.
One thing you need to ask yourself is how many times in the past year has he had people in the winners circle.
Some of the best engine,head,cam people out there are the ones you never hear about because they don't have time to write a book because they are on the dyno or at the track.

I see what your saying, to make the heads work that are too big, you tighten up the lobe centers to make the powerband start earlier. That way it makes decent torque and doesn't make all the power up top. Now what I get out of what David Vizard is saying is that when you have an engine with too small of a valve and not enough flow for the application, you tighten the lobe center? Wouldn't that increase overlap and bring in more fuel? That way you get more out of the heads being used? Then again as you increase duration and lift, overlap increases anyways. So what I'm getting at... say you have a 400 with 2.02 camel hump heads. They obviously wouldn't flow enough for the engine to support very high rpm. The cams both being the same duration, approximately 220 intake, lets say 460 lift. Which cam would run better? A cam ground on a 110LSA or a cam ground on a 106LSA? I know the 110 would idle better and be better for the street, but the 106 would come on earlier and maybe match the smaller port heads better? But that is the opposite of what UD Harold and Camking are saying. Maybe they mean something else when they say use wide lobe centers with high velocity ports. Maybe they mean high flow, high velocity ports take wide lobe centers. It gets pretty confusing.

Originally Posted by 69elko

I see what your saying, to make the heads work that are too big, you tighten up the lobe centers to make the powerband start earlier. That way it makes decent torque and doesn't make all the power up top. Now what I get out of what David Vizard is saying is that when you have an engine with too small of a valve and not enough flow for the application, you tighten the lobe center? Wouldn't that increase overlap and bring in more fuel? That way you get more out of the heads being used? Then again as you increase duration and lift, overlap increases anyways. So what I'm getting at... say you have a 400 with 2.02 camel hump heads. They obviously wouldn't flow enough for the engine to support very high rpm. The cams both being the same duration, approximately 220 intake, lets say 460 lift. Which cam would run better? A cam ground on a 110LSA or a cam ground on a 106LSA? I know the 110 would idle better and be better for the street, but the 106 would come on earlier and maybe match the smaller port heads better? But that is the opposite of what UD Harold and Camking are saying. Maybe they mean something else when they say use wide lobe centers with high velocity ports. Maybe they mean high flow, high velocity ports take wide lobe centers. It gets pretty confusing.

No,you want a wider L/S to start the power band earlier.

Well, I'd like to see the dyno numbers on all these different theories... As with many things regarding performance, lots of good theories fall flat on their face when it comes to actually making power!!!! Same thing is true on chassis mods. All the theory and mathematical calculations don't mean much when the car winds up handling like a pig on ice!!!!!

I'm still amazed at the number of people expecting to build big horsepower numbers on a budget, then take it out on the street and just blow the tires off the car!!!!! For the most part, the latest and greatest in high performance engine goodies has very little to do with the overall performance of the car..... The engine is nothing more then one part of the equation for building a performance car...... The entire package and all the components in the car have to be balanced in such a manner that they compliment each other and work good together....

Kind of a rant, I guess. Just tired of seeing all these "killer horsepower" engines installed in cars that couldn't hook up good with 250 horsepower.;....

You're right, but talking about engines is so much funner... most people build the engine and find that the suspension should have been budgeted too.

Well, I think I am gonna go with the 58cc heads..Like I said, I am not looking fo ra race car, just something that has some respect as a driver. I talked to my buddie about our discussion, and he thinks I will be just fine. Suggested I run a comp 280 magnum cam and a 2200-2400 stall converter. Says he has had good luck with this set up for a street car. Check out his web page..He is pretty on the ball. Some of you might have heard of him.. www.spyderprepracingheads.com
He is a local guy, but is nationally known in the racing circut. I stopped down to see him, and filled him in on my bright low budget idea..Racers hate the low budget, but then again, I am not looking to get into the 8's..
I think it will work out fine. Thanks for all the help.

Originally Posted by jchrisd

Well, I think I am gonna go with the 58cc heads..Like I said, I am not looking fo ra race car, just something that has some respect as a driver. I talked to my buddie about our discussion, and he thinks I will be just fine. Suggested I run a comp 280 magnum cam and a 2200-2400 stall converter. Says he has had good luck with this set up for a street car. Check out his web page..He is pretty on the ball. Some of you might have heard of him.. www.spyderprepracingheads.com
He is a local guy, but is nationally known in the racing circut. I stopped down to see him, and filled him in on my bright low budget idea..Racers hate the low budget, but then again, I am not looking to get into the 8's..
I think it will work out fine. Thanks for all the help.

I am surprised he recommend a symetrical cam .
I would think an Isymetrical cam would make more power on the stocker heads.

Interresting you said that.. I was wondering the samething. I also asked him if he thought that that would be too much cam for that engine trans rear set up. I get the impression that he kwen I was after a low budget engine build(and he is a hell of a nice guy) that he just said that because he had god experience with that cam in the past. I did suggest the Voodoo line to him, and he just sort of ignored it and said to stick with the comp cam 280 magnum abd you will be happy for what you are doing..What cam were you thinking of Eric?? Something with the same range, but a dual pattern..

Originally Posted by camaro_fever68

Here's some advice on camshaft selection from some of the best in the business. Cam Selection

I see I am not the only one that thinks David Vizard is an author and paid by the word/page.
The bottom line is if you start with the correct cylinder for the job you don't need to "crutch" anything along.

Originally Posted by jchrisd

Interresting you said that.. I was wondering the samething. I also asked him if he thought that that would be too much cam for that engine trans rear set up. I get the impression that he kwen I was after a low budget engine build(and he is a hell of a nice guy) that he just said that because he had god experience with that cam in the past. I did suggest the Voodoo line to him, and he just sort of ignored it and said to stick with the comp cam 280 magnum abd you will be happy for what you are doing..What cam were you thinking of Eric?? Something with the same range, but a dual pattern..

The Voodoo cams seem to act about one size larger.
If you like the Voodoo cams I would try the cam 69Elko talks about.
I would not go any larger than that in the Voodoo series.
If you like Comp. than I would try the XE268.