Please help - need some speed

[Erik A.]

I need some opinions. I have a 98' HTM SR-24 that I have just purchased. It is powered by a Marine Power 454 with a B&M 174 blower and I believe a 750 carb. I can turn a 26 Bravo 1 at 5000rpm for around the mid 60's. It does not have a chiller on it. I don't have a ton of money to spend since I just purchased the boat but I would like more performance. I know the 174 blower is a little guy but would a chiller and some cam changes let me see a little more speed. The boost is right around 7#s which I have a extra pulley to bump it up to 8 or 9#s. I am a outboard guy so this is new to me. I would like to keep this blower for a little while if at all possible. Any suggestions would be great

[Infomaniac]

I would not spend the money for a chiller that would not work with a big blower.
Save your money and buy the chiller when you can afford a bigger blower.
A cam change and chiller will help but enough to justify the expense?
Also that increase would be just about all I would do to that engine without some engine upgrades as well. Probably a good reason the engine only has that much blower on it.
You might consider selling what you have as a package and add some money to that for a bigger engine and blower.
Just my professional opinion.
[ September 15, 2003, 06:15 PM: Message edited by: Infomaniac ]

[Erik A.]

Thanks for the response Info.

[PHD]

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Im having a problem getting the right rpm. I have a 38 scarab with twin 502 built by Typhoon. I was told 640hp each. They have 3 psi pro chargers. Im running 30 lab four blades. I cant seem to get past 4200-4500 rpm. What rpm should I get at full throttle? I looked into those 5 blade maximus. They look awsome. They tested them and claimed to get almost ten mph increase. Any thoughts on rpm problem?

[gnarley]

Erik, I agree when you have the money then go to a bigger blower & add the chiller. In the mean time you should be able to make that thing pick up some MPH. What ignition does it have? Is the carb boost referenced? How much fuel pressure? What type of flame arrestor do you have & will it flow enough air at the right RPM? Do you have any idea of what the pistons & cam are? What exhaust do you have?
Get the list number off the carb & find out what it really is. A single 750 isn't quite enough IMHO. I run the 830 annular discharge & it seems to keep up & a big ass spark arrestor that will flow enough air to supply the demand of the carb plus the additional 40% of flow that the blower is sucking through the carb. Remember that the carbs flow is based on a naturally aspirated engine @ 0" inches of mercury.
Under boost, the engine could need up to 40 to 50% more fuel and air http://www.holley.com/HiOctn/TechServ/TechInfo/SCTech.html this is from Holley’s site & has some pretty good info.
For a 450 cubic inch engine at 5000 RPM with a maximum boost of 6 pounds. { 651 X 1.408 = 916 CFM } http://www.kuhlsuperchargers.com/tech%20p06.htm also to get a better feel of what to do go to Kuhl’s site & read.
Personally I don’t think your setup is putting out what it is capable of doing & I am sure you can go faster by tweaking & tuning & changing a few parts. My setup isn’t that different than yours & runs solidly in the mid 70’s & I haven’t turned it all the way yet. It is in a 21’ deep V with 21 degree deadrise. Your hull is so much more efficient than mine & with that engine setup right you should be in the 80’s.
If you have any questions just ask.
[ September 16, 2003, 11:21 AM: Message edited by: gnarley ]

[Erik A.]

Thanks Charlie. I will get a list of my parts hopefully after work and get back to you.

[paradigm shift]

Erik you have some good feed back on your motor already. I am a little confused here though. Your numbers just don't add up very well in my opinion not that it's worth much. :D If your numbers are correct you have 26% slip. Pretty high for a cat even at low speeds and not packing any air. Are you sure your RPM and MPH numbers are correct. I know those HTM's will run when you but some HP to them. You may want to check your set up and call HTM also. Good luck and it will be interesting what you find. Keep us posted.
http://www.go-fast.com/Prop_Slip_Calculator.htm

[Erik A.]

Thanks guys for all of the info. I will be going to the lake this Sunday and I will have my GPS with me this time so there is no mistake on my speed. I am also trying to get a list from Marine Power of everything they put in this engine along with size of carb etc. etc. I am used to my Mirage Jaguar that ran 95+ but I know the feel of speed will be different in this boat since I sit so much higher. Anyway thanks again.

[gnarley]

paradigm shift:
If your numbers are correct you have 26% slip. Pretty high for a cat even at low speeds and not packing any air. Are you sure your RPM and MPH numbers are correct. P S, I didn't see what the diameter was? Even with a prop calculator it may be off though Erik said he has a 26, what is the diameter & is the prop in good shape? Is 5K at wide open or have you run it all the way up yet? Erik tell us a little about the prop to. wink Something just doesn't sound right. :confused:

[paradigm shift]

gnarley:
paradigm shift:
If your numbers are correct you have 26% slip. Pretty high for a cat even at low speeds and not packing any air. Are you sure your RPM and MPH numbers are correct. P S, I didn't see what the diameter was? Even with a prop calculator it may be off though Erik said he has a 26, what is the diameter & is the prop in good shape? Is 5K at wide open or have you run it all the way up yet? Erik tell us a little about the prop to. wink Something just doesn't sound
right. :confused: Yea I don't trust prop slip and speed calculators for exact numbers. Never seem to be right on for any given boat for sure even with correct numbers to input. It does give you some reference once you know your boat though. 95 in a Mirage eek! 80 would seem like a walk in the park in an HTM I would think. Not to imply Erik is going that fast now. :)

[Erik A.]

My prop is a 26 Bravo 1. It is in descent shape just a few little dings. My WOT was 5000 rpm with a little positive trim. Is there something else I should be looking for with the prop? Could one of the blades be bent ever so much without me noticing? It has lost its polish look although I don't think that is more than an I sore. Getting someone to talk to me at Marine Power has been a pain to say the least. I have left a message every day this week and still no response. frown

[gnarley]

Erik A.:
Could one of the blades be bent ever so much without me noticing? It has lost its polish look although I don't think that is more than an I sore. Getting someone to talk to me at Marine Power has been a pain to say the least. I have left a message every day this week and still no response. :( Erik if your not sure about the prop have it checked out to be sure what it is including the diameter & pitch. Is the Marine Power 454 stock inside or do you know anything at all about it? What ever you know you should still see what Marine Power says based on the serial number of the engine. If not I'd yank it out & do a tear down to find out what it trully is & unless you KNOW it has forged pistons I'd lay back on the boost & go up to 6 #'s & no more or you might be replacing more parts. What type of ignition does it have?